Report the parse errors of the position test via SAX

The test caught json::parse_error, so it aborted in the ci_test_noexceptions build, where JSON_NOEXCEPTION turns the throw into std::abort(). sax_parse() hands the error position and the exception object to parse_error() without throwing, so the test now records them there and runs in every configuration. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Move the std::vector<std::byte> binary type tests out of unit-regression3
2026-10-13 09:47:12 +00:00 · 2026-10-13 11:22:48 +02:00 · 2026-10-13 09:40:36 +02:00 · 2026-10-13 08:52:49 +02:00 · 2026-10-12 09:33:43 +02:00
40 changed files with 3039 additions and 4832 deletions
@@ -25,7 +25,6 @@ cc_library(
        "include/nlohmann/detail/conversions/from_json.hpp",
        "include/nlohmann/detail/conversions/to_chars.hpp",
        "include/nlohmann/detail/conversions/to_json.hpp",
-        "include/nlohmann/detail/conversions/zmij.hpp",
        "include/nlohmann/detail/exceptions.hpp",
        "include/nlohmann/detail/hash.hpp",
        "include/nlohmann/detail/input/binary_reader.hpp",
@@ -1385,10 +1385,9 @@ THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR I

 - The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2008-2009 [Björn Hoehrmann](https://bjoern.hoehrmann.de/) <bjoern@hoehrmann.de>
 - The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2009 [Florian Loitsch](https://florian.loitsch.com/)
- The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, including the conversion of the digits to text by Xiang JunBo and the SIMD instruction sequence of Dougall Johnson, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
 - The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 - The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0).
- The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
+- The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors

 <img align="right" src="https://git.fsfe.org/reuse/reuse-ci/raw/branch/master/reuse-horizontal.png" alt="REUSE Software">

@@ -59,6 +59,7 @@ Currently, only `remove`, `add`, and `replace` operations are generated.
 - [patch](patch.md) applies a JSON Patch
 - [patch_inplace](patch_inplace.md) applies a JSON Patch in place
 - [merge_patch](merge_patch.md) applies a JSON Merge Patch
+- [merge_diff](merge_diff.md) creates a diff as a JSON Merge Patch

 ## Version history

@@ -62,9 +62,6 @@ Linear.

 ## Notes

-Floating-point numbers are written with the fewest digits that read back as the same value (for `#!cpp double`; see
-[number handling](../../features/types/number_handling.md#number-serialization)).
-
 Binary values are serialized as an object containing two keys:

 - "bytes": an array of bytes as integers
@@ -100,5 +97,3 @@ Binary values are serialized as an object containing two keys:
 - Error handlers added in version 3.4.0.
 - Serialization of binary values added in version 3.8.0.
 - Error handler `keep` added in version 3.13.0.
- Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0; about 0.1% of doubles are
-  written differently, most of them with fewer digits.
@@ -285,6 +285,7 @@ Access to the JSON value
 ### JSON Merge Patch functions

 - [**merge_patch**](merge_patch.md) - applies a JSON Merge Patch
+- [**merge_diff**](merge_diff.md) (_static_) - creates a diff as a JSON Merge Patch

 ## Static functions

@@ -0,0 +1,79 @@
+# <small>nlohmann::basic_json::</small>merge_diff
+
+```cpp
+static basic_json merge_diff(const basic_json& source,
+                             const basic_json& target);
+```
+
+Creates a [JSON Merge Patch](https://tools.ietf.org/html/rfc7396) so that value `source` can be changed into the value
+`target` by calling the [`merge_patch`](merge_patch.md) function. The patch contains only what differs: changed and
+added members with their new values, and removed members with the value `#!json null`. Nested objects are compared
+member by member; any other value that differs, including an array, is replaced as a whole.
+
+For two JSON values `source` and `target`, where `target` contains no object member whose value is `#!json null`, the
+following code always yields `#!cpp true`:
+```cpp
+basic_json patched = source;
+patched.merge_patch(merge_diff(source, target));
+patched == target;
+```
+
+## Parameters
+
+`source` (in)
+:   JSON value to compare from
+
+`target` (in)
+:   JSON value to compare against
+
+## Return value
+
+a JSON Merge Patch to convert the `source` to `target`
+
+## Exception safety
+
+Strong guarantee: `source` and `target` are never modified.
+
+## Complexity
+
+Linear in the total number of values (including nested ones) in `source` and `target`, times the cost of a key-based
+object operation (looking up a key, or adding one to the patch): logarithmic for [`json`](../json.md), and linear for
+[`ordered_json`](../ordered_json.md) (see [`ordered_map` complexity](../ordered_map.md#complexity)). For
+`ordered_json`, diffing two objects with `n` and `m` members therefore takes O((n+m)²).
+
+## Notes
+
+- A merge patch uses `#!json null` to remove a member, so it cannot set a member to `#!json null`. As in RFC 7396, a
+  `#!json null` member of `target` is treated as absent: the patch removes the member from `source` instead of setting
+  it to `#!json null`. A member that is `#!json null` in both `source` and `target` is unchanged and left out of the
+  patch, so `source` keeps it.
+- A merge patch cannot reorder object members, and [`merge_patch`](merge_patch.md) appends added members at the end.
+  For [`ordered_json`](../ordered_json.md), the patched value therefore has the same members as `target`, but not
+  necessarily in the same order, and may compare unequal to it. The patch lists changed and removed members in the
+  order of `source`, followed by added members in the order of `target`.
+
+## Examples
+
+??? example
+
+    The following code shows how a JSON Merge Patch is created as a diff for two JSON values.
+
+    ```cpp
+    --8<-- "examples/merge_diff.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/merge_diff.output"
+    ```
+
+## See also
+
+- [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396)
+- [merge_patch](merge_patch.md) applies a JSON Merge Patch
+- [diff](diff.md) creates a diff as a JSON Patch
+
+## Version history
+
+- Added in version 3.13.0.
@@ -67,6 +67,7 @@ returned by `#!cpp (*this)[key]`); it is read as it was when `merge_patch()` was

 - [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396)
 - [patch](patch.md) apply a JSON patch
+- [merge_diff](merge_diff.md) creates a diff as a JSON Merge Patch

 ## Version history

@@ -23,10 +23,9 @@ type to use.
 ## Template parameters

 `NumberFloatType`
-:   the type to store floating-point numbers. The type must be `#!cpp float`, `#!cpp double`, or
-    `#!cpp long double`. The parser converts `#!cpp float`, `#!cpp double`, and a `#!cpp long double` that is IEEE 754
-    binary64 itself. It converts other `#!cpp long double` formats with `#!cpp std::from_chars` where available, or
-    with `#!cpp std::strtold` otherwise. Serialization falls back to `#!cpp std::snprintf`. The
+:   the type to store floating-point numbers. Parsing and serialization are implemented in terms of
+    `#!cpp std::strtof`/`#!cpp std::strtod`/`#!cpp std::strtold` and `#!cpp std::snprintf`, so the type must be
+    `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
    [binary formats](../../features/binary_formats/index.md) additionally require `#!cpp float` or `#!cpp double`,
    because they have no encoding for `#!cpp long double`. See
    [Template Parameter Requirements](../../features/types/template_parameters.md#numberfloattype).
@@ -0,0 +1,51 @@
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+using namespace nlohmann::literals;
+
+int main()
+{
+    // the source document
+    json source = R"(
+        {
+            "title": "Goodbye!",
+            "author": {
+                "givenName": "John",
+                "familyName": "Doe"
+            },
+            "tags": [
+                "example",
+                "sample"
+            ],
+            "content": "This will be unchanged"
+        }
+    )"_json;
+
+    // the target document
+    json target = R"(
+        {
+            "title": "Hello!",
+            "author": {
+                "givenName": "John"
+            },
+            "tags": [
+                "example"
+            ],
+            "content": "This will be unchanged",
+            "phoneNumber": "+01-123-456-7890"
+        }
+    )"_json;
+
+    // create the patch
+    json patch = json::merge_diff(source, target);
+
+    // roundtrip
+    json patched_source = source;
+    patched_source.merge_patch(patch);
+
+    // output patch and roundtrip result
+    std::cout << std::setw(4) << patch << "\n\n"
+              << std::setw(4) << patched_source << std::endl;
+}
@@ -0,0 +1,22 @@
+{
+    "author": {
+        "familyName": null
+    },
+    "phoneNumber": "+01-123-456-7890",
+    "tags": [
+        "example"
+    ],
+    "title": "Hello!"
+}
+
+{
+    "author": {
+        "givenName": "John"
+    },
+    "content": "This will be unchanged",
+    "phoneNumber": "+01-123-456-7890",
+    "tags": [
+        "example"
+    ],
+    "title": "Hello!"
+}
@@ -9,6 +9,9 @@ syntax that closely mimics the document being modified. Unlike [JSON Patch](json
 express every kind of change (e.g., it cannot reorder array elements or remove a specific array element), but it is
 easier to read and write for object-shaped documents.

+The function [`merge_diff`](../api/basic_json/merge_diff.md) creates a merge patch that changes one JSON value into
+another.
+
 !!! tip "Not a general deep merge"

    A merge patch is not a general deep merge: a `#!json null` value in the patch deletes the key from the target.
@@ -35,4 +38,5 @@ easier to read and write for object-shaped documents.
 - [JSON Patch and Diff](json_patch.md) - a more expressive alternative that describes a sequence of operations
 - [JSON Pointer](json_pointer.md) - the addressing scheme used by JSON Patch
 - Function [`merge_patch`](../api/basic_json/merge_patch.md)
+- Function [`merge_diff`](../api/basic_json/merge_diff.md)
 - Function [`update`](../api/basic_json/update.md) - merge objects, optionally recursively
@@ -82,13 +82,12 @@ flowchart TD

    - Numbers with a decimal digit or scientific notation are always stored as `#!c double`.
    - The number types can be changed, see [Template number types](#template-number-types). 
-    - The library converts integers and floating-point numbers itself, independent of the locale. Floating-point
-      numbers are correctly rounded (to nearest, ties to even). Only a `#!c long double` that is not IEEE 754 binary64
-      (e.g., the 80-bit x87 format) is converted with `#!cpp std::from_chars` where available, or else with
-      [`std::strtold`](https://en.cppreference.com/w/cpp/string/byte/strtof). For that call, the library temporarily
-      replaces the `.` with the decimal point of the current locale (which may be longer than one byte, e.g., in
-      `fa_IR.UTF-8`), so the result does not depend on the locale either. Changing the locale in another thread during
-      parsing is undefined behavior of the C library, though. Before version 3.13.0, the conversion was realized by
+    - Integers are converted by the library's own digit parser. Floating-point numbers are converted with
+      [`std::from_chars`](https://en.cppreference.com/w/cpp/utility/from_chars) if the library is compiled with C++17
+      and the standard library supports it, then with an exact fast path for `#!c double` values with few significant
+      digits, and otherwise with the locale-aware
+      [`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof) (`std::strtof`/`std::strtold` for the
+      other floating-point types). Before version 3.13.0, the conversion was realized by
      [`std::strtoull`](https://en.cppreference.com/w/cpp/string/byte/strtoul),
      [`std::strtoll`](https://en.cppreference.com/w/cpp/string/byte/strtol), and `std::strtod`, respectively.

@@ -101,10 +100,10 @@ flowchart TD
 ### Number limits

 - Any 64-bit signed or unsigned integer can be stored without loss of precision.
- Numbers exceeding the limits of `#!c double` (i.e., numbers whose rounded value is not satisfying
+- Numbers exceeding the limits of `#!c double` (i.e., numbers that after conversion via
+[`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof) are not satisfying
 [`std::isfinite`](https://en.cppreference.com/w/cpp/numeric/math/isfinite) such as `#!c 1E400`) will throw exception
-[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing. Numbers too
-small for `#!c double` (such as `#!c 1E-400`) become zero, with the sign of the number.
+[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing.
 - Floating-point numbers are rounded to the next number representable as `double`. For instance
 `#!c 3.141592653589793238462643383279` is stored as [`0x400921fb54442d18`](https://float.exposed/0x400921fb54442d18).
 This is the same behavior as the code `#!c double x = 3.141592653589793238462643383279;`.
@@ -134,10 +133,9 @@ That is, `-0` is stored as a signed integer, but the serialization does not repr
 ### Number serialization

 - Integer numbers are serialized as is; that is, no scientific notation is used.
- Floating-point numbers are serialized with the fewest digits that read back as the same value (the closest such
-  digits if there are several), in the layout of the `#!c %g` printf modifier: `#!c 1.5`, `#!c 100.0`, `#!c 1e+100`.
-  Doubles are converted with the algorithm of [Żmij](https://github.com/vitaut/zmij), floats with Grisu2, which
-  can write more digits than necessary.
+- Floating-point numbers are serialized as specified by the `#!c %g` printf modifier with 
+  [`std::numeric_limits<double>::max_digits10`](https://en.cppreference.com/w/cpp/types/numeric_limits/max_digits10)
+  significant digits. The rationale is to use the shortest representation while still allowing round-tripping.

 !!! hint "Notes regarding precision of floating-point numbers"

@@ -30,9 +30,9 @@ Requirements are split into two groups:
    diagnosed with dedicated error messages, and violating most of them results in a compiler error somewhere inside
    the library. Four violations are not caught at compile time at all:

-    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and silently misparses numbers
-      stored as a `#!cpp long double` that is not IEEE 754 binary64 (e.g., the 80-bit x87 format), because the lexer
-      hands the buffer to `#!cpp std::strtold`.
+    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and can silently misparse
+      floating-point numbers, because the lexer may hand the buffer to `#!cpp std::strtod`, which reads up to the
+      terminating null character.
    - A stateful [`AllocatorType`](#allocatortype) compiles and silently ignores its state: allocation, deallocation,
      and [`get_allocator()`](../../api/basic_json/get_allocator.md) each use a different default-constructed instance.
    - The two [cross-specialization conversions](#cross-specialization-conversions) below. These abort on an assertion
@@ -353,21 +353,16 @@ using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
 ### Always required

 - A member type `value_type` that is one byte wide and `char`-compatible. The library stores and processes UTF-8
-  encoded `char` data and passes `data()` to functions that take a `#!cpp const char*`, such as `#!cpp std::strtold`
-  (only used to parse a `#!cpp long double` that is not IEEE 754 binary64, see
-  [`NumberFloatType`](#numberfloattype)).
+  encoded `char` data and passes `data()` to functions that take a `#!cpp const char*`, such as `#!cpp std::strtod`.
  `#!cpp std::wstring`, `#!cpp std::u16string`, and `#!cpp std::u32string` are **not** valid choices; see the FAQ on
  [wide string handling](../../home/faq.md#wide-string-handling).
 - Constructors: default, copy, move, from `#!cpp const char*` (which must not be `#!cpp explicit`), from
  `#!cpp (const char*, size_type)`, and from `#!cpp (size_type, char)`; and copy or move assignment.
 - Member functions `size()`, `clear()`, `resize(n, c)`, `data()`, `push_back(char)`, and `operator[]`
  (const and non-const, returning references). `c_str()` and `back()` are **not** required.
- `data()` must return a pointer to a contiguous, **null-terminated** buffer. `#!cpp float`, `#!cpp double`, and a
-  `#!cpp long double` that is IEEE 754 binary64 are converted by the library itself and do not depend on this. For any
-  other `NumberFloatType` (a `#!cpp long double` of another format), the parser falls back to `#!cpp std::strtold` when
-  `#!cpp std::from_chars` is not available or declines the token, and `std::strtold` reads up to the null character. A type whose `data()`
-  is not null-terminated does not fail to compile; with such a `NumberFloatType` it can silently misparse
-  floating-point numbers.
+- `data()` must return a pointer to a contiguous, **null-terminated** buffer -- the parser may hand it to
+  `#!cpp std::strtod`, which reads up to the null character. A type whose `data()` is not null-terminated does not
+  fail to compile; it can silently misparse floating-point numbers.
 - `append(const char*, size_type)`, used by [`dump`](../../api/basic_json/dump.md), and `append(const StringType&)`,
  used by the CBOR reader for indefinite-length strings. The library's internal string concatenation additionally has
  to append a `#!cpp char` and a `#!cpp const char*`; for each it selects between `append(arg)`, `#!cpp operator+=`,
@@ -546,18 +541,16 @@ therefore silently changes parse results rather than raising an error. See

 `NumberFloatType` must be one of `#!cpp float`, `#!cpp double`, or `#!cpp long double`:

- The [parser](../parsing/index.md) converts number literals to `#!cpp float`, `#!cpp double`, and a
-  `#!cpp long double` that is IEEE 754 binary64 itself; other `#!cpp long double` formats are converted with
-  `#!cpp std::from_chars` where available, or with `#!cpp std::strtold`. The library provides overloads for exactly
-  these three types.
+- The [parser](../parsing/index.md) converts number literals with `#!cpp std::from_chars` or, as a fallback, with
+  `#!cpp std::strtof`, `#!cpp std::strtod`, or `#!cpp std::strtold`; the library provides overloads for exactly these
+  three types.
 - [`dump`](../../api/basic_json/dump.md) falls back to `#!cpp std::snprintf` with the `%g` and `%Lg` conversion
  specifiers, for which the library likewise provides only `#!cpp double` and `#!cpp long double` overloads
  (`#!cpp float` is promoted to `#!cpp double`).

-If `#!cpp std::numeric_limits<NumberFloatType>` describes an IEEE 754 binary64 number, `dump` uses the algorithm of
-Żmij, which produces the shortest representation that round-trips. For IEEE 754 binary32 numbers, it uses Grisu2,
-which produces a short representation that round-trips. Otherwise the `snprintf` fallback with `max_digits10` digits is
-used.
+If `#!cpp std::numeric_limits<NumberFloatType>` describes an IEEE 754 binary32 or binary64 number, `dump` uses the
+Grisu2 algorithm, which produces the shortest representation that round-trips. Otherwise the `snprintf` fallback with
+`max_digits10` digits is used.

 ### Required for the binary formats

@@ -569,7 +562,7 @@ binary32 or binary64 field and have no encoding for `#!cpp long double`.

 | Type                     | Support                                                                                                               |
 |--------------------------|-----------------------------------------------------------------------------------------------------------------------|
-| `#!cpp double` (default) | full; shortest round-trip output through Żmij                                                                         |
+| `#!cpp double` (default) | full; short round-trip output through Grisu2                                                                          |
 | `#!cpp float`            | full; short round-trip output through Grisu2                                                                          |
 | `#!cpp long double`      | `dump` and `parse` only; the binary format writers do not compile, as they only handle IEEE 754 binary32 and binary64 |
 | any other type           | not usable                                                                                                            |
@@ -185,7 +185,9 @@ The lexer detects two optional extensions at compile time. Only `iterator_input_
 random-access input of single-byte characters:

 - `supports_seek`, `get_consumed_count()`, and `copy_consumed_range()` let the lexer reconstruct already consumed input
-  for error messages instead of copying every character it reads.
+  for error messages instead of copying every character it reads. With `get_read_count()` and
+  `count_consumed_lines()`, the lexer also derives the read position from the adapter and counts lines only when an
+  error needs them, instead of counting characters and lines on every read.
 - `supports_bulk_scan`, `bulk_data()`, `bulk_remaining()`, and `bulk_skip()` let the lexer scan strings directly in
  contiguous memory, several bytes at a time.

@@ -18,8 +18,6 @@ The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed und

 The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2009 [Florian Loitsch](https://florian.loitsch.com/)

-The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, including the conversion of the digits to text by Xiang JunBo and the SIMD instruction sequence of Dougall Johnson, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
-
 The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).

-The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
+The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors
@@ -182,6 +182,7 @@ nav:
          - 'json_serializer': api/basic_json/json_serializer.md
          - 'max_size': api/basic_json/max_size.md
          - 'meta': api/basic_json/meta.md
+          - 'merge_diff': api/basic_json/merge_diff.md
          - 'merge_patch': api/basic_json/merge_patch.md
          - 'number_float_t': api/basic_json/number_float_t.md
          - 'number_integer_t': api/basic_json/number_integer_t.md
@@ -9,12 +9,11 @@
 #pragma once

 #include <cstdint> // uint64_t
-#include <cstring> // memcpy
-#if defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64)) && (!defined(__SIZEOF_INT128__) || (!defined(__GNUC__) && !defined(__clang__)))
-    #include <intrin0.h> // __umulh, _umul128, _BitScanForward64, _BitScanReverse64
+#if !defined(__SIZEOF_INT128__) && defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+    #include <intrin0.h> // __umulh, _umul128
 #endif

-#include <nlohmann/detail/macro_scope.hpp> // JSON_HEDLEY_ALWAYS_INLINE, NLOHMANN_JSON_NAMESPACE_BEGIN
+#include <nlohmann/detail/abi_macros.hpp>

 // Portable bit-level helpers for the number and string scanners. They use
 // compiler builtins or platform-specific intrinsics where available and plain
@@ -29,10 +28,6 @@ inline int count_leading_zeros(std::uint64_t x) noexcept
 {
 #if defined(__GNUC__) || defined(__clang__)
    return __builtin_clzll(x);
-#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
-    unsigned long index = 0; // NOLINT(runtime/int): the type _BitScan*64 takes
-    _BitScanReverse64(&index, x);
-    return 63 - static_cast<int>(index);
 #else
    int n = 0;
    for (int shift = 32; shift != 0; shift >>= 1)
@@ -47,29 +42,6 @@ inline int count_leading_zeros(std::uint64_t x) noexcept
 #endif
 }

-/// number of trailing zero bits of x (x != 0)
-inline int count_trailing_zeros(std::uint64_t x) noexcept
-{
-#if defined(__GNUC__) || defined(__clang__)
-    return __builtin_ctzll(x);
-#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
-    unsigned long index = 0; // NOLINT(runtime/int): the type _BitScan*64 takes
-    _BitScanForward64(&index, x);
-    return static_cast<int>(index);
-#else
-    int n = 0;
-    for (int shift = 32; shift != 0; shift >>= 1)
-    {
-        if ((x << (64 - shift)) == 0)
-        {
-            n += shift;
-            x >>= shift;
-        }
-    }
-    return n;
-#endif
-}
-
 /// the 128-bit product of two 64-bit numbers
 struct uint128_parts
 {
@@ -103,27 +75,15 @@ inline uint128_parts full_multiplication(std::uint64_t a, std::uint64_t b) noexc
 #endif
 }

-/// eight bytes as a little-endian word (a single load on little-endian
-/// targets; always inlined, as GCC otherwise calls it in the number loops)
-JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const unsigned char* b) noexcept
+/// eight bytes as a little-endian word (compilers fold this into one load on
+/// little-endian targets)
+inline std::uint64_t read_eight_bytes(const char* p) noexcept
 {
-#if defined(_MSC_VER) || defined(__x86_64__) || defined(__i386__) || (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
-    // the byte order already matches (all MSVC targets are little-endian)
-    std::uint64_t result = 0;
-    std::memcpy(&result, b, sizeof(result));
-    return result;
-#else
+    const auto* b = reinterpret_cast<const unsigned char*>(p); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
    return static_cast<std::uint64_t>(b[0]) | (static_cast<std::uint64_t>(b[1]) << 8u)
           | (static_cast<std::uint64_t>(b[2]) << 16u) | (static_cast<std::uint64_t>(b[3]) << 24u)
           | (static_cast<std::uint64_t>(b[4]) << 32u) | (static_cast<std::uint64_t>(b[5]) << 40u)
           | (static_cast<std::uint64_t>(b[6]) << 48u) | (static_cast<std::uint64_t>(b[7]) << 56u);
-#endif
-}
-
-/// eight bytes as a little-endian word
-JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const char* p) noexcept
-{
-    return read_eight_bytes(reinterpret_cast<const unsigned char*>(p)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
 }

 }  // namespace detail
@@ -4,7 +4,6 @@
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
 // SPDX-FileCopyrightText: 2009 Florian Loitsch <https://florian.loitsch.com/>
-// SPDX-FileCopyrightText: 2025 Victor Zverovich <https://github.com/vitaut/zmij>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT

@@ -12,32 +11,11 @@

 #include <array> // array
 #include <cmath>   // signbit, isfinite
-#include <cstddef> // size_t
 #include <cstdint> // intN_t, uintN_t
 #include <cstring> // memcpy, memmove
 #include <limits> // numeric_limits
 #include <type_traits> // conditional

-#ifdef _MSC_VER
-    #include <cstdlib> // _byteswap_uint64
-#endif
-
-// SSE2 (every x86-64 CPU) and NEON (every 64-bit Arm CPU) convert the 16
-// digits of a double at once
-#if defined(__x86_64__) || (defined(_M_X64) && !defined(_M_ARM64EC))
-    #include <emmintrin.h>
-    #define JSON_DTOA_SSE2 1
-    #define JSON_DTOA_NEON 0
-#elif (defined(__aarch64__) || defined(_M_ARM64)) && !defined(_M_ARM64EC) && !defined(__ARM_BIG_ENDIAN)
-    #include <arm_neon.h>
-    #define JSON_DTOA_SSE2 0
-    #define JSON_DTOA_NEON 1
-#else
-    #define JSON_DTOA_SSE2 0
-    #define JSON_DTOA_NEON 0
-#endif
-
-#include <nlohmann/detail/conversions/zmij.hpp>
 #include <nlohmann/detail/macro_scope.hpp>

 NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -1069,381 +1047,6 @@ inline char* format_buffer(char* buf, int len, int decimal_exponent,
    return append_exponent(buf, n - 1);
 }

-/// eight decimal digits (a value below 10^8) as bytes 0..9, the first digit
-/// in the most significant byte: three steps that divide all lanes at once
-/// by a multiplication (the conversion of Xiang JunBo, as in Zmij)
-inline std::uint64_t eight_digit_bytes(std::uint64_t abcdefgh) noexcept
-{
-    const std::uint64_t abcd_efgh = abcdefgh + (((std::uint64_t{1} << 32u) - 10000u) * ((abcdefgh * (((std::uint64_t{1} << 40u) / 10000u) + 1u)) >> 40u));
-    const std::uint64_t ab_cd_ef_gh = abcd_efgh + (((std::uint64_t{1} << 16u) - 100u) * (((abcd_efgh * (((std::uint64_t{1} << 19u) / 100u) + 1u)) >> 19u) & 0x7F0000007Fu));
-    return ab_cd_ef_gh + (((std::uint64_t{1} << 8u) - 10u) * (((ab_cd_ef_gh * (((std::uint64_t{1} << 10u) / 10u) + 1u)) >> 10u) & 0x000F000F000F000Fu));
-}
-
-/// store the bytes of v, the most significant one first (one byte swap and
-/// one store where the byte order is known: compilers do not reliably merge
-/// the byte stores once this is inlined)
-inline void store_msb_first(char* p, std::uint64_t v) noexcept
-{
-#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-    v = __builtin_bswap64(v);
-    std::memcpy(p, &v, sizeof(v));
-#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-    std::memcpy(p, &v, sizeof(v));
-#elif defined(_MSC_VER) // (little-endian on all its targets)
-    v = _byteswap_uint64(v);
-    std::memcpy(p, &v, sizeof(v));
-#else
-    for (unsigned i = 0; i < 8; ++i)
-    {
-        p[i] = static_cast<char>(v >> (56u - (8u * i)));
-    }
-#endif
-}
-
-/*!
-@brief digits * 10^exp for a double, in the layout of format_buffer()
-
-The layout is that of format_buffer() with min_exp -4 and max_exp 15 (the
-digits10 of double). The digits are converted eight at a time and placed
-with fixed-size moves instead of per-digit loops and moves of the buffer.
-
-@param[in] digits  the digits (not 0, at most 17 digits; trailing zeros allowed)
-@param[in] exp     the decimal exponent of the last digit
-@return a pointer past the text; up to 41 bytes at @a first are written
-        (some beyond the returned end)
-*/
-JSON_HEDLEY_NON_NULL(1)
-JSON_HEDLEY_RETURNS_NON_NULL
-inline char* write_decimal(char* first, std::uint64_t digits, int exp) noexcept
-{
-    JSON_ASSERT(digits != 0 && digits < 100000000000000000u);
-    const std::uint64_t upper = digits / 100000000u;
-    const std::uint64_t b0 = upper / 100000000u; // (one digit: it is its own byte)
-    const std::uint64_t b1 = eight_digit_bytes(upper % 100000000u);
-    const std::uint64_t b2 = eight_digit_bytes(digits % 100000000u);
-    // leading and trailing zero digits: zero bytes, counted without division
-    int leading = 16;
-    int zeros = 16;
-    if (b0 != 0)
-    {
-        leading = count_leading_zeros(b0) / 8;
-    }
-    else if (b1 != 0)
-    {
-        leading = 8 + (count_leading_zeros(b1) / 8);
-    }
-    else
-    {
-        leading += count_leading_zeros(b2) / 8;
-    }
-    if (b2 != 0)
-    {
-        zeros = count_trailing_zeros(b2) / 8;
-    }
-    else if (b1 != 0)
-    {
-        zeros = 8 + (count_trailing_zeros(b1) / 8);
-    }
-    // (else: 16, b0 is the one digit that is not 0)
-    // the digits as text at text + leading, then '0's, so that fixed-size
-    // moves need not check how many digits there are
-    std::array<char, 64> text; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-    store_msb_first(text.data(), b0 + 0x3030303030303030u);
-    store_msb_first(text.data() + 8, b1 + 0x3030303030303030u);
-    store_msb_first(text.data() + 16, b2 + 0x3030303030303030u);
-    std::memset(text.data() + 24, '0', 40);
-    const int k = 24 - leading - zeros; // significant digits
-    const int n = k + exp + zeros;      // position of the decimal point after the first digit
-    const char* const s0 = text.data() + leading;
-
-    if (-4 < n && n <= 15)
-    {
-        // "0.[000]digits" (n <= 0) is the digits after 1 - n leading '0's
-        // with the point after the first; "digits[000].0" (n >= k) and
-        // "dig.its" put the point after n characters
-        const int pad = n <= 0 ? 1 - n : 0;
-        const char* const s = s0 - pad;
-        const int len = k + pad;
-        const int point = n + pad;
-        std::memcpy(first, s, 16);
-        std::memcpy(first + point + 1, s + point, 24);
-        first[point] = '.';
-        return first + (point >= len ? point + 2 : len + 1);
-    }
-
-    // d.igitse+XX, with at least two exponent digits (as append_exponent())
-    std::memcpy(first, s0, 16);
-    std::memcpy(first + 2, s0 + 1, 16);
-    first[1] = '.';
-    char* const end = first + (k == 1 ? 1 : k + 1);
-    const int e = n - 1;
-    const auto ea = e < 0 ? 0u - static_cast<unsigned>(e) : static_cast<unsigned>(e); // (unsigned: no signed overflow to assume)
-    const bool three = ea >= 100;
-    end[0] = 'e';
-    end[1] = e < 0 ? '-' : '+';
-    end[2] = static_cast<char>('0' + (three ? ea / 100 : (ea / 10) % 10));
-    end[3] = static_cast<char>('0' + (three ? (ea / 10) % 10 : ea % 10));
-    end[4] = static_cast<char>('0' + (ea % 10));
-    return end + (three ? 5 : 4);
-}
-
-/*!
-@brief the shortest decimal of a positive double (Zmij), as write_decimal()
-writes it
-
-For a normal double, the shorter candidate has 15 or 16 digits: they are
-converted at once (two halves of eight digits) and followed by the digit
-after them, if there is one, without the multiplication and division by 10
-that counting the digits of one number would take. The fixed layouts move
-the digits after the point by one byte.
-
-@return a pointer past the text; up to 41 bytes at @a first are written
-        (some beyond the returned end)
-*/
-JSON_HEDLEY_NON_NULL(1)
-JSON_HEDLEY_RETURNS_NON_NULL
-inline char* write_shortest(char* first, const zmij::shortest_decimal d) noexcept
-{
-    const std::uint64_t sig = d.integral;
-    if (JSON_HEDLEY_UNLIKELY(sig < 100000000000000u || sig >= 10000000000000000u))
-    {
-        // (subnormals)
-        return d.has_digit ? write_decimal(first, (sig * 10) + d.digit, d.exponent) : write_decimal(first, sig, d.exponent + 1);
-    }
-    const bool sixteen = sig >= 1000000000000000u; // (else 15 digits)
-    const int last = d.has_digit ? d.digit : 0;
-    const std::uint64_t upper = sig / 100000000u;
-#if JSON_DTOA_SSE2
-    // NOLINTBEGIN(portability-simd-intrinsics)
-    // the two halves in the 64-bit lanes, each as abcd * 2^32 + efgh, then as
-    // bytes (as eight_digit_bytes(), one lane each)
-    const __m128i x = _mm_set_epi64x(static_cast<long long>(sig - (upper * 100000000u)), static_cast<long long>(upper)); // NOLINT(runtime/int)
-    const __m128i abcd = _mm_srli_epi64(_mm_mul_epu32(x, _mm_set1_epi64x(109951163)), 40); // 2^40 / 10000 + 1
-    const __m128i abcd_efgh = _mm_add_epi64(x, _mm_mul_epu32(abcd, _mm_set1_epi64x(4294957296))); // 2^32 - 10000
-    // 32-bit lanes in the order of the text: abcd, efgh of both halves
-    const __m128i fours = _mm_shuffle_epi32(abcd_efgh, _MM_SHUFFLE(2, 3, 0, 1));
-    const __m128i ab = _mm_srli_epi16(_mm_mulhi_epu16(fours, _mm_set1_epi32(5243)), 3);
-    const __m128i ab_cd = _mm_or_si128(_mm_slli_epi32(_mm_sub_epi16(fours, _mm_mullo_epi16(ab, _mm_set1_epi32(100))), 16), ab);
-    // 16-bit lanes ab (< 100) -> bytes a, b: 256 * ab - 2559 * (ab / 10)
-    const __m128i bytes = _mm_sub_epi16(_mm_slli_epi16(ab_cd, 8), _mm_mullo_epi16(_mm_set1_epi16(2559), _mm_mulhi_epu16(ab_cd, _mm_set1_epi16(6554))));
-    // the last digit that is not 0 (sig is not 0)
-    const auto nonzero = static_cast<std::uint64_t>(_mm_movemask_epi8(_mm_cmpgt_epi8(bytes, _mm_setzero_si128())));
-    const int digits = 63 - count_leading_zeros(nonzero) + (sixteen ? 1 : 0); // without trailing zeros
-    const __m128i chars = _mm_add_epi8(bytes, _mm_set1_epi8('0'));
-    // the 16 characters from the first digit
-    const __m128i s = sixteen ? chars : _mm_or_si128(_mm_srli_si128(chars, 1), _mm_slli_si128(_mm_cvtsi32_si128('0' + last), 15));
-    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
-    const auto store_16 = [&s](char* p) noexcept
-    {
-        std::memcpy(p, &s, 16);
-    };
-    const char first_digit = static_cast<char>(_mm_cvtsi128_si32(s));
-    // NOLINTEND(portability-simd-intrinsics)
-#elif JSON_DTOA_NEON
-    // as with SSE2: the halves in 32-bit lanes, then abcd, efgh of both
-    const uint32x2_t halves = vcreate_u32(upper | ((sig - (upper * 100000000u)) << 32u));
-    const uint32x2_t abcd = vmovn_u64(vshrq_n_u64(vmull_n_u32(halves, static_cast<std::uint32_t>(((std::uint64_t{1} << 40u) / 10000u) + 1u)), 40));
-    const uint32x2_t efgh = vmls_n_u32(halves, abcd, 10000u);
-    const uint32x4_t fours = vcombine_u32(vzip1_u32(abcd, efgh), vzip2_u32(abcd, efgh));
-    const uint32x4_t ab = vshrq_n_u32(vmulq_n_u32(fours, 5243u), 19);
-    const uint16x8_t ab_cd = vreinterpretq_u16_u32(vorrq_u32(ab, vshlq_n_u32(vmlsq_n_u32(fours, ab, 100u), 16)));
-    const uint16x8_t tens = vshrq_n_u16(vmulq_n_u16(ab_cd, 103u), 10);
-    const uint8x16_t bytes = vreinterpretq_u8_u16(vorrq_u16(tens, vshlq_n_u16(vmlsq_n_u16(ab_cd, tens, 10u), 8)));
-    // the last digit that is not 0 (sig is not 0): a nibble per byte
-    const std::uint64_t nonzero = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(vtstq_u8(bytes, bytes)), 4)), 0);
-    const int digits = ((63 - count_leading_zeros(nonzero)) / 4) + (sixteen ? 1 : 0); // without trailing zeros
-    const uint8x16_t chars = vaddq_u8(bytes, vdupq_n_u8('0'));
-    // the 16 characters from the first digit
-    const uint8x16_t s = sixteen ? chars : vextq_u8(chars, vdupq_n_u8(static_cast<std::uint8_t>('0' + last)), 1);
-    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
-    const auto store_16 = [&s](char* p) noexcept
-    {
-        vst1q_u8(reinterpret_cast<std::uint8_t*>(p), s); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-    };
-    const auto first_digit = static_cast<char>(vgetq_lane_u8(s, 0));
-#else
-    const std::uint64_t hi = eight_digit_bytes(upper);
-    const std::uint64_t lo = eight_digit_bytes(sig - (upper * 100000000u));
-    // trailing zero digits: zero bytes (sig is not 0)
-    const int zeros = lo != 0 ? count_trailing_zeros(lo) / 8 : 8 + (count_trailing_zeros(hi) / 8);
-    const int digits = 15 - zeros + (sixteen ? 1 : 0); // without trailing zeros
-    // the 16 characters from the first digit
-    const std::uint64_t s_hi = (sixteen ? hi : (hi << 8u) | (lo >> 56u)) + 0x3030303030303030u;
-    const std::uint64_t s_lo = (sixteen ? lo : (lo << 8u) | static_cast<std::uint64_t>(last)) + 0x3030303030303030u;
-    const char s16 = static_cast<char>(sixteen ? '0' + last : '0'); // the 17th
-    const auto store_16 = [s_hi, s_lo](char* p) noexcept
-    {
-        store_msb_first(p, s_hi);
-        store_msb_first(p + 8, s_lo);
-    };
-    const auto first_digit = static_cast<char>(s_hi >> 56u);
-#endif
-    const int len = d.has_digit ? 16 + (sixteen ? 1 : 0) : digits; // significant digits
-    const int n = 16 + (sixteen ? 1 : 0) + d.exponent;           // digits before the point
-
-    if (JSON_HEDLEY_LIKELY(n >= 1 && n <= 15))
-    {
-        // "dig.its" and "digits[000].0": the digits after the point move by
-        // one byte ('0's follow the digits)
-#if JSON_DTOA_SSE2
-        // NOLINTBEGIN(portability-simd-intrinsics)
-        // (in the register: reading the digits back from memory right after
-        // storing them waits until the stores are done)
-        const __m128i at = _mm_set1_epi8(static_cast<char>(n));
-        const __m128i index = _mm_setr_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15);
-        const __m128i before = _mm_cmpgt_epi8(at, index);
-        const __m128i after = _mm_cmpgt_epi8(index, at);
-        const __m128i text = _mm_or_si128(_mm_or_si128(_mm_and_si128(s, before), _mm_and_si128(_mm_slli_si128(s, 1), after)),
-                                          _mm_andnot_si128(_mm_or_si128(before, after), _mm_set1_epi8('.')));
-        std::memcpy(first, &text, 16);
-        first[16] = static_cast<char>(_mm_extract_epi16(s, 7) >> 8);
-        first[17] = s16;
-        // NOLINTEND(portability-simd-intrinsics)
-#elif JSON_DTOA_NEON
-        const uint8x16_t index = vcombine_u8(vcreate_u8(0x0706050403020100u), vcreate_u8(0x0F0E0D0C0B0A0908u));
-        const uint8x16_t at = vdupq_n_u8(static_cast<std::uint8_t>(n));
-        const uint8x16_t after_point = vbslq_u8(vcgtq_u8(index, at), vextq_u8(vdupq_n_u8(0), s, 15), vdupq_n_u8('.'));
-        vst1q_u8(reinterpret_cast<std::uint8_t*>(first), vbslq_u8(vcltq_u8(index, at), s, after_point)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-        first[16] = static_cast<char>(vgetq_lane_u8(s, 15));
-        first[17] = s16;
-#else
-        store_16(first);
-        first[16] = s16;
-        std::uint64_t after_point[2]; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::memcpy(after_point, first + n, 16);
-        std::memcpy(first + n + 1, after_point, 16);
-        first[n] = '.';
-#endif
-        return first + (n >= len ? n + 2 : len + 1);
-    }
-    if (n <= 0 && n > -4)
-    {
-        // "0.[000]digits"
-        std::memset(first, '0', 8);
-        first[1] = '.';
-        store_16(first + 2 - n);
-        first[18 - n] = s16;
-        return first + 2 - n + len;
-    }
-    // d.igitse+XX, with at least two exponent digits (as append_exponent())
-    store_16(first + 1);
-    first[17] = s16;
-    first[0] = first_digit;
-    first[1] = '.';
-    char* const end = first + (len == 1 ? 1 : len + 1);
-    const int e = n - 1;
-    const auto ea = e < 0 ? 0u - static_cast<unsigned>(e) : static_cast<unsigned>(e); // (unsigned: no signed overflow to assume)
-    const bool three = ea >= 100;
-    end[0] = 'e';
-    end[1] = e < 0 ? '-' : '+';
-    end[2] = static_cast<char>('0' + (three ? ea / 100 : (ea / 10) % 10));
-    end[3] = static_cast<char>('0' + (three ? (ea / 10) % 10 : ea % 10));
-    end[4] = static_cast<char>('0' + (ea % 10));
-    return end + (three ? 5 : 4);
-}
-
-/*!
-@brief whether FloatType is an IEEE 754 binary64 type (a double, or a long double
-that has the same format, as with MSVC and on Apple's Arm CPUs)
-
-These are the types the conversion of Zmij (see zmij.hpp) is used for; all
-others (binary32, or a format the library does not know) use Grisu2.
-*/
-template<typename FloatType>
-constexpr bool has_binary64_format() noexcept
-{
-    return std::numeric_limits<FloatType>::is_iec559
-           && std::numeric_limits<FloatType>::digits == 53
-           && std::numeric_limits<FloatType>::max_exponent == 1024
-           && sizeof(FloatType) == sizeof(std::uint64_t);
-}
-
-template<typename FloatType>
-struct is_binary64 : std::integral_constant<bool, has_binary64_format<FloatType>()> {};
-
-/// a positive finite float (other than binary64): Grisu2 and format_buffer()
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1, 2)
-JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive_grisu2(char* first, const char* last, FloatType value)
-{
-    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
-    static_cast<void>(last); // (only used in the assertion)
-
-    // Compute v = buffer * 10^decimal_exponent.
-    // The decimal digits are stored in the buffer, which needs to be interpreted
-    // as an unsigned decimal integer.
-    // len is the length of the buffer, i.e., the number of decimal digits.
-    int len = 0;
-    int decimal_exponent = 0;
-    grisu2(first, len, decimal_exponent, value);
-
-    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
-
-    // Format the buffer like printf("%.*g", prec, value)
-    constexpr int kMinExp = -4;
-    // Use digits10 here to increase compatibility with version 2.
-    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
-
-    JSON_ASSERT(last - first >= kMaxExp + 2);
-    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
-    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
-
-    return format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
-}
-
-/// a positive finite binary64 number: the shortest digits (Zmij), laid out by
-/// write_shortest() (through a local buffer if [first, last) is shorter than
-/// the 41 bytes it may write)
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1, 2)
-JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive_zmij(char* first, const char* last, FloatType value)
-{
-    static_assert(is_binary64<FloatType>::value,
-                  "internal error: the conversion of Zmij needs IEEE 754 binary64 numbers");
-    std::uint64_t bits = 0;
-    std::memcpy(&bits, &value, sizeof(bits));
-    const zmij::shortest_decimal d = zmij::to_shortest(bits);
-    if (JSON_HEDLEY_LIKELY(last - first >= 41))
-    {
-        return write_shortest(first, d);
-    }
-    std::array<char, 64> buf; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-    const auto len = static_cast<std::size_t>(write_shortest(buf.data(), d) - buf.data());
-    JSON_ASSERT(last - first >= static_cast<std::ptrdiff_t>(len));
-    std::memcpy(first, buf.data(), len);
-    return first + len;
-}
-
-/// a positive finite binary64 number: Zmij (as a long double has the format of
-/// a double here, its bits are those of the double of the same value)
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1, 2)
-JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive(char* first, const char* last, FloatType value, std::true_type /*is_binary64*/)
-{
-    return write_positive_zmij(first, last, value);
-}
-
-/// a positive finite float of any other format: Grisu2
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1, 2)
-JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive(char* first, const char* last, FloatType value, std::false_type /*is_binary64*/)
-{
-    return write_positive_grisu2(first, last, value);
-}
-
-/// a positive finite float: Zmij for binary64 numbers, Grisu2 otherwise
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1, 2)
-JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive(char* first, const char* last, FloatType value)
-{
-    return write_positive(first, last, value, is_binary64<FloatType> {});
-}
-
 }  // namespace dtoa_impl

 /*!
@@ -1461,6 +1064,7 @@ JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
 char* to_chars(char* first, const char* last, FloatType value)
 {
+    static_cast<void>(last); // maybe unused - fix warning
    JSON_ASSERT(std::isfinite(value));

    // Use signbit(value) instead of (value < 0) since signbit works for -0.
@@ -1486,7 +1090,28 @@ char* to_chars(char* first, const char* last, FloatType value)
    JSON_HEDLEY_DIAGNOSTIC_POP
 #endif

-    return dtoa_impl::write_positive(first, last, value);
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
+
+    // Compute v = buffer * 10^decimal_exponent.
+    // The decimal digits are stored in the buffer, which needs to be interpreted
+    // as an unsigned decimal integer.
+    // len is the length of the buffer, i.e., the number of decimal digits.
+    int len = 0;
+    int decimal_exponent = 0;
+    dtoa_impl::grisu2(first, len, decimal_exponent, value);
+
+    JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
+
+    // Format the buffer like printf("%.*g", prec, value)
+    constexpr int kMinExp = -4;
+    // Use digits10 here to increase compatibility with version 2.
+    constexpr int kMaxExp = std::numeric_limits<FloatType>::digits10;
+
+    JSON_ASSERT(last - first >= kMaxExp + 2);
+    JSON_ASSERT(last - first >= 2 + (-kMinExp - 1) + std::numeric_limits<FloatType>::max_digits10);
+    JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10 + 6);
+
+    return dtoa_impl::format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
 }

 }  // namespace detail
@@ -1,219 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2025 Victor Zverovich <https://github.com/vitaut/zmij>
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-#pragma once
-
-#include <array> // array
-#include <cstddef> // size_t
-#include <cstdint> // uint32_t, uint64_t
-
-#include <nlohmann/detail/abi_macros.hpp>
-#include <nlohmann/detail/bit_ops.hpp>
-#include <nlohmann/detail/input/pow5_table.hpp>
-#include <nlohmann/detail/macro_scope.hpp>
-
-NLOHMANN_JSON_NAMESPACE_BEGIN
-namespace detail
-{
-
-/*!
-@brief the shortest decimal representation of a double
-
-A C++11 port of the conversion of Zmij by Victor Zverovich
-(https://github.com/vitaut/zmij, MIT license): the shortest decimal in the
-rounding interval of a double, the closest one if there are several. Zmij
-credits Xiang JunBo (producing the shorter candidate without a division) and
-Dougall Johnson (the compressed powers of ten). The powers of ten are taken
-from the table for number parsing (pow5_table.hpp) where it holds them, and
-computed from the compressed tables of Zmij beyond it.
-*/
-namespace zmij
-{
-
-/// the compressed powers of ten of Zmij
-inline const std::array<std::uint64_t, 28>& pow10_minor() noexcept
-{
-    static const std::array<std::uint64_t, 28> table =
-    {
-        {
-            0x8000000000000000u, 0xa000000000000000u, 0xc800000000000000u, 0xfa00000000000000u, 0x9c40000000000000u,
-            0xc350000000000000u, 0xf424000000000000u, 0x9896800000000000u, 0xbebc200000000000u, 0xee6b280000000000u,
-            0x9502f90000000000u, 0xba43b74000000000u, 0xe8d4a51000000000u, 0x9184e72a00000000u, 0xb5e620f480000000u,
-            0xe35fa931a0000000u, 0x8e1bc9bf04000000u, 0xb1a2bc2ec5000000u, 0xde0b6b3a76400000u, 0x8ac7230489e80000u,
-            0xad78ebc5ac620000u, 0xd8d726b7177a8000u, 0x878678326eac9000u, 0xa968163f0a57b400u, 0xd3c21bcecceda100u,
-            0x84595161401484a0u, 0xa56fa5b99019a5c8u, 0xcecb8f27f4200f3au
-        }
-    };
-    return table;
-}
-
-/// (high, low) pairs
-inline const std::array<std::uint64_t, 50>& pow10_major() noexcept
-{
-    static const std::array<std::uint64_t, 50> table =
-    {
-        {
-            0xaddcb9e83c6b1793u, 0xdf4abe242a1bbf3eu, 0xaf8e5410288e1b6fu, 0x07ecf0ae5ee44ddau, 0xb1442798f49ffb4au, 0x99cd11cfdf41779du,
-            0xb2fe3f0b8599ef07u, 0x861fa7e6dcb4aa15u, 0xb4bca50b065abe63u, 0x0fed077a756b53aau, 0xb67f6455292cbf08u, 0x1a3bc84c17b1d543u,
-            0xb84687c269ef3bfbu, 0x3d5d514f40eea742u, 0xba121a4650e4ddebu, 0x92f34d62616ce413u, 0xbbe226efb628afeau, 0x890489f70a55368cu,
-            0xbdb6b8e905cb600fu, 0x5400e987bbc1c921u, 0xbf8fdb78849a5f96u, 0xde98520472bdd034u, 0xc16d9a0095928a27u, 0x75b7053c0f178294u,
-            0xc350000000000000u, 0x0000000000000000u, 0xc5371912364ce305u, 0x6c28000000000000u, 0xc722f0ef9d80aad6u, 0x424d3ad2b7b97ef6u,
-            0xc913936dd571c84cu, 0x03bc3a19cd1e38eau, 0xcb090c8001ab551cu, 0x5cadf5bfd3072cc6u, 0xcd036837130890a1u, 0x36dba887c37a8c10u,
-            0xcf02b2c21207ef2eu, 0x94f967e45e03f4bcu, 0xd106f86e69d785c7u, 0xe13336d701beba52u, 0xd31045a8341ca07cu, 0x1ede48111209a051u,
-            0xd51ea6fa85785631u, 0x552a74227f3ea566u, 0xd732290fbacaf133u, 0xa97c177947ad4096u, 0xd94ad8b1c7380874u, 0x18375281ae7822bdu,
-            0xdb68c2ca82ed2a05u, 0xa67398db9f6820e1u
-        }
-    };
-    return table;
-}
-
-/// one bit per power: whether the computed value is one unit too large
-inline const std::array<std::uint32_t, 21>& pow10_fixups() noexcept
-{
-    static const std::array<std::uint32_t, 21> table =
-    {
-        {
-            0x8d8fc810u, 0x06100293u, 0x19000000u, 0x00100000u, 0x00000908u, 0x00000000u, 0x04e00300u, 0x3807e0b2u, 0x3d83d793u, 0x0006f5ccu,
-            0x00000000u, 0xffff0000u, 0x8076337du, 0x4ff45ba0u, 0x09405033u, 0x034376d9u, 0x09000000u, 0x4e100501u, 0x076d14dcu, 0xf964f45eu,
-            0x0000003du
-        }
-    };
-    return table;
-}
-
-/// the 128-bit significand of 10^k, rounded down, for k in [-307, 341]
-/// (compute_pow10 of Zmij)
-inline uint128_parts compute_pow10(int k) noexcept
-{
-    const auto i = static_cast<unsigned>(k + 307);
-    const std::uint64_t m = pow10_minor()[(i + 24) % 28];
-    const std::size_t j = 2 * static_cast<std::size_t>((i + 24) / 28);
-    const std::uint64_t h_hi = pow10_major()[j];
-    const std::uint64_t h_lo = pow10_major()[j + 1];
-    const std::uint64_t h1 = full_multiplication(h_lo, m).high;
-    const std::uint64_t c0 = h_lo * m;
-    const std::uint64_t c1 = h1 + (h_hi * m);
-    const std::uint64_t c2 = (c1 < h1 ? 1u : 0u) + full_multiplication(h_hi, m).high;
-    uint128_parts r{};
-    if ((c2 >> 63u) != 0)
-    {
-        r.high = c2;
-        r.low = c1;
-    }
-    else
-    {
-        r.high = (c2 << 1u) | (c1 >> 63u);
-        r.low = (c1 << 1u) | (c0 >> 63u);
-    }
-    r.low -= (pow10_fixups()[i >> 5u] >> (i & 31u)) & 1u;
-    return r;
-}
-
-/// The 128-bit significand of 10^k, rounded down, for k in [-342, 341].
-/// Up to 10^308, the table for number parsing holds the same significands
-/// (those of 5^k), except for k in [-27, -1], where it holds them one unit
-/// larger (as the Eisel-Lemire algorithm needs them).
-inline uint128_parts pow10(int k) noexcept
-{
-    if (k > pow5_128_largest_power)
-    {
-        return compute_pow10(k); // (only for the smallest doubles)
-    }
-    const auto i = 2 * static_cast<std::size_t>(k - pow5_128_smallest_power);
-    uint128_parts r{pow5_128()[i + 1], pow5_128()[i]};
-    const std::uint64_t adjust = static_cast<unsigned>(k + 27) < 27u ? 1u : 0u;
-    r.high -= r.low < adjust ? 1u : 0u;
-    r.low -= adjust;
-    return r;
-}
-
-/// (x_hi * 2^64 + x_lo) * y >> 64, as 128 bits
-inline uint128_parts umul192_hi128(std::uint64_t x_hi, std::uint64_t x_lo, std::uint64_t y) noexcept
-{
-    const uint128_parts p = full_multiplication(x_hi, y);
-    uint128_parts r{};
-    r.low = p.low + full_multiplication(x_lo, y).high;
-    r.high = p.high + (r.low < p.low ? 1u : 0u);
-    return r;
-}
-
-/// (x * y + c) >> 64
-inline std::uint64_t umul128_add_hi64(std::uint64_t x, std::uint64_t y, std::uint64_t c) noexcept
-{
-    const uint128_parts p = full_multiplication(x, y);
-    return p.high + (p.low + c < p.low ? 1u : 0u);
-}
-
-/// the result of Zmij: the shorter candidate and, if that is outside the
-/// rounding interval, the digit after it (16 bytes: returned in registers)
-struct shortest_decimal
-{
-    std::uint64_t integral;  ///< the shorter candidate (15 or 16 digits for normal doubles)
-    int exponent;            ///< the decimal exponent of the digit after it
-    unsigned char digit;     ///< the digit after it (if has_digit)
-    bool has_digit;          ///< whether the shortest decimal is integral * 10 + digit
-};
-
-/// The shortest decimal in the rounding interval of a positive finite double
-/// given by its bits, the closest one if there are several (to_decimal of
-/// Zmij, which keeps the last digit apart: the 15 or 16 digits before it can be
-/// converted without a multiplication by 10 first). Always inlined: GCC
-/// otherwise calls it, and its result goes through memory.
-JSON_HEDLEY_ALWAYS_INLINE shortest_decimal to_shortest(std::uint64_t bits) noexcept
-{
-    constexpr int extra_shift = 9;
-    const auto raw_exp = static_cast<int>((bits >> 52u) & 0x7FFu);
-    std::uint64_t bin_sig = bits & ((std::uint64_t{1} << 52u) - 1);
-    // a power of two has a narrower interval below (except the smallest normal)
-    const bool regular = bin_sig != 0 || raw_exp <= 1;
-    const int bin_exp = (raw_exp == 0 ? 1 : raw_exp) - 1075;
-    if (raw_exp != 0)
-    {
-        bin_sig |= std::uint64_t{1} << 52u;
-    }
-    // floor(log10(2^bin_exp)), or floor(log10(3/4 * 2^bin_exp)) for the irregular case
-    const int dec_exp = ((bin_exp * 315653) - (regular ? 0 : 131072)) >> 20;
-    // scaled by 10^(-dec_exp - 1): the integral part is the shorter candidate
-    const int shift = bin_exp + ((-(dec_exp + 1) * 217707) >> 16) + 1 + extra_shift;
-    const uint128_parts p10 = pow10(-dec_exp - 1);
-    const uint128_parts p = umul192_hi128(p10.high, p10.low, bin_sig << static_cast<unsigned>(shift));
-    std::uint64_t integral = p.high >> static_cast<unsigned>(extra_shift);
-    const std::uint64_t fractional = (p.high << static_cast<unsigned>(64 - extra_shift)) | (p.low >> static_cast<unsigned>(extra_shift));
-    std::uint64_t digit = 0;
-    bool round_up = false;
-    bool round_down = false;
-    if (JSON_HEDLEY_LIKELY(regular))
-    {
-        const std::uint64_t half_ulp = (p10.high >> static_cast<unsigned>(extra_shift + 1 - shift)) + (1 - (bin_sig & 1u));
-        round_up = fractional + half_ulp < fractional;
-        round_down = half_ulp > fractional;
-        // the last digit of the longer candidate, rounded to nearest
-        digit = umul128_add_hi64(fractional, 10, (std::uint64_t{1} << 63u) + 6);
-        if (fractional == (std::uint64_t{1} << 62u))
-        {
-            digit = 2; // 2.5 rounds to 2
-        }
-    }
-    else
-    {
-        const std::uint64_t half_ulp = p10.high >> static_cast<unsigned>(extra_shift + 1 - shift);
-        round_up = half_ulp > ~std::uint64_t{0} - fractional;
-        round_down = (half_ulp >> 1u) > fractional;
-        digit = umul128_add_hi64(fractional, 10, (std::uint64_t{1} << 63u) - 1);
-        const std::uint64_t lowest = umul128_add_hi64(fractional - (half_ulp >> 1u), 10, ~std::uint64_t{0});
-        digit = digit < lowest ? lowest : digit;
-    }
-    integral += round_up ? 1u : 0u;
-    // if the shorter candidate is outside the rounding interval: one digit more
-    return shortest_decimal{integral, dec_exp, static_cast<unsigned char>(digit), !round_up && !round_down};
-}
-
-}  // namespace zmij
-}  // namespace detail
-NLOHMANN_JSON_NAMESPACE_END
@@ -8,12 +8,12 @@

 #pragma once

-#include <algorithm> // min
+#include <algorithm> // count, find, min
 #include <array> // array
 #include <cstddef> // size_t
 #include <cstdint> // uint32_t
 #include <cstring> // strlen
-#include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
+#include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next, reverse_iterator
 #include <streambuf> // streambuf
 #include <string> // string, char_traits
 #include <type_traits> // enable_if, is_base_of, is_pointer, is_integral, remove_pointer
@@ -297,6 +297,7 @@ class iterator_input_adapter
            return result;
        }

+        ++eof_reads;
        return char_traits<char_type>::eof();
    }

@@ -306,6 +307,26 @@ class iterator_input_adapter
        return static_cast<std::size_t>(std::distance(begin, current));
    }

+    // number of get_character() calls so far, including those that returned
+    // EOF; the lexer derives its position from it (see lexer::lazy_position)
+    std::size_t get_read_count() const
+    {
+        return get_consumed_count() + eof_reads;
+    }
+
+    // number of newlines in the consumed range [0, last_index); @a line_start
+    // is set to the index after the last of them (0 if there is none); only
+    // valid when supports_seek
+    std::size_t count_consumed_lines(std::size_t last_index, std::size_t& line_start) const
+    {
+        const auto to = std::next(begin, static_cast<typename std::iterator_traits<IteratorType>::difference_type>(last_index));
+        const auto newline = char_traits<char_type>::to_char_type('\n');
+        using reverse_it = std::reverse_iterator<IteratorType>;
+        const auto last_newline = std::find(reverse_it(to), reverse_it(begin), newline);
+        line_start = static_cast<std::size_t>(std::distance(begin, last_newline.base()));
+        return static_cast<std::size_t>(std::count(begin, last_newline.base(), newline));
+    }
+
    // append the already-consumed characters in the half-open range
    // [first_index, last_index) to @a out; only valid when supports_seek
    template<typename ContainerType>
@@ -422,6 +443,8 @@ class iterator_input_adapter
    IteratorType begin;
    IteratorType current;
    SentinelType end;
+    /// number of get_character() calls that returned EOF
+    std::size_t eof_reads = 0;

    template<typename BaseInputAdapter, size_t T>
    friend struct wide_string_input_helper;
@@ -217,7 +217,7 @@ struct diagnostic_positions
        {
            // Lexer has read the first character of the container, so
            // subtract 1 from the position to get the correct start position.
-            v.start_position = lexer->get_position() - 1;
+            v.start_position = lexer->get_chars_read_total() - 1;
        }
    }

@@ -231,7 +231,7 @@ struct diagnostic_positions
        if (lexer)
        {
            // Lexer's position is past the closing brace or bracket, so set that as the end position.
-            v.end_position = lexer->get_position();
+            v.end_position = lexer->get_chars_read_total();
        }
    }

@@ -247,7 +247,7 @@ struct diagnostic_positions
            // Lexer has read past the current field value, so set the end position to the current position.
            // The start position will be set below based on the length of the string representation
            // of the value.
-            v.end_position = lexer->get_position();
+            v.end_position = lexer->get_chars_read_total();

            switch (v.type())
            {
@@ -186,6 +186,15 @@ class lexer : public lexer_base<BasicJsonType>
    static constexpr bool lazy_token_string =
        input_adapter_supports_seek<InputAdapterType>(is_detected<detect_supports_seek, InputAdapterType> {});

+    /// whether the read position is derived from the input adapter on demand
+    /// instead of being counted on every scanned character. Seekable adapters
+    /// know how much input they consumed and can revisit it, so
+    /// chars_read_total is the adapter's read count (minus a pending unget),
+    /// and line and column are recomputed from the consumed input only when
+    /// get_position() is called (errors). Counting per character kept two
+    /// increments and a newline check in the hot path of every get().
+    static constexpr bool lazy_position = lazy_token_string;
+
    /// whether a simulated unget can be passed on to the input adapter, which
    /// then leaves the character in the input; see
    /// input_adapter_supports_lookahead
@@ -195,7 +204,9 @@ class lexer : public lexer_base<BasicJsonType>
    /// whether string scanning may bulk-consume runs of ordinary characters
    /// directly from a contiguous input buffer (SWAR fast path). This requires
    /// the token to be reconstructible lazily (lazy_token_string), so bypassing
-    /// the per-character capture in get() cannot lose error diagnostics.
+    /// the per-character capture in get() cannot lose error diagnostics. It
+    /// also implies lazy_position, so the bulk paths need not advance the
+    /// position counters.
    static constexpr bool bulk_scan =
        lazy_token_string
        && input_adapter_supports_bulk_scan<InputAdapterType>(is_detected<detect_supports_bulk_scan, InputAdapterType> {});
@@ -221,44 +232,6 @@ class lexer : public lexer_base<BasicJsonType>
    // scan functions
    /////////////////////

-    /// contiguous input: try to decode the 4 hex digits following `\\u`
-    /// directly from the input buffer via hex_codepoint(), instead of 4 calls
-    /// to get(). On success, advances the adapter and the position counters
-    /// exactly as those 4 get() calls would (a hex digit is never '\n', so
-    /// only the flat counters move) and leaves @a current holding the last of
-    /// the 4 digits, just as the last such get() would; the codepoint is
-    /// written to @a out. Makes no state change and returns false - for a
-    /// pending unget, fewer than 4 remaining bytes, or any of the 4 bytes not
-    /// being a hex digit - so the caller falls back unchanged to the
-    /// per-character loop, which then reports the same diagnostic (stopping
-    /// at the first invalid digit) as before this optimization.
-    bool get_codepoint_bulk(std::true_type /*bulk*/, int& out)
-    {
-        if (next_unget || ia.bulk_remaining() < 4)
-        {
-            return false;
-        }
-        const char_type* const raw = ia.bulk_data();
-        const int codepoint = hex_codepoint(reinterpret_cast<const unsigned char*>(raw));
-        if (codepoint < 0)
-        {
-            return false;
-        }
-        ia.bulk_skip(4);
-        // a hex digit is never a newline, so only the flat counters advance
-        position.chars_read_total += 4;
-        position.chars_read_current_line += 4;
-        current = char_traits<char_type>::to_int_type(raw[3]);
-        out = codepoint;
-        return true;
-    }
-
-    /// streaming input: no bulk fast path
-    bool get_codepoint_bulk(std::false_type /*bulk*/, int& /*out*/) const noexcept
-    {
-        return false;
-    }
-
    /*!
    @brief get codepoint from 4 hex characters following `\\u`

@@ -278,14 +251,6 @@ class lexer : public lexer_base<BasicJsonType>
    {
        // this function only makes sense after reading `\u`
        JSON_ASSERT(current == 'u');
-
-        // contiguous input: decode all 4 hex digits directly from the buffer
-        int fast_codepoint = 0;
-        if (get_codepoint_bulk(std::integral_constant<bool, bulk_scan> {}, fast_codepoint))
-        {
-            return fast_codepoint;
-        }
-
        int codepoint = 0;

        const auto factors = { 12u, 8u, 4u, 0u };
@@ -377,10 +342,6 @@ class lexer : public lexer_base<BasicJsonType>
        }
        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), pos);
        ia.bulk_skip(pos);
-        // the run contains no newline (all bytes < 0x20 are treated as special),
-        // so only the flat character counters advance
-        position.chars_read_total += pos;
-        position.chars_read_current_line += pos;
    }

    /// streaming input: no bulk fast path
@@ -1090,11 +1051,9 @@ class lexer : public lexer_base<BasicJsonType>
            token_type::parse_error otherwise

    @note The scanner is independent of the current locale: token_buffer
-          always holds `.`. The conversion of float and double does not use
-          the locale either. Only the std::strtold fallback of
-          convert_number() for long double formats other than binary64
-          depends on it, and it looks up the decimal point right before
-          converting (see detail::convert_float_locale_aware()).
+          always holds `.`. Only the std::strtod fallback of convert_number()
+          depends on the locale, and it looks up the decimal point right
+          before converting (see detail::convert_float_locale_aware()).
    */
    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
    {
@@ -1107,7 +1066,7 @@ class lexer : public lexer_base<BasicJsonType>

        // offset just past the last mantissa byte in token_buffer (i.e. the
        // index of 'e'/'E', or the whole token when there is no exponent).
-        // convert_number() uses it to split the token; npos means
+        // convert_number() uses it to count significant digits; npos means
        // "not seen an exponent yet" and is resolved at scan_number_done
        std::size_t mantissa_end = std::string::npos;

@@ -1437,8 +1396,8 @@ scan_number_done:
    @param[in] mantissa_end  offset just past the last mantissa byte in
                             token_buffer (the index of 'e'/'E', or
                             token_buffer.size() when there is no exponent);
-                             with decimal_point_position, it locates the parts
-                             of a float token without scanning it again
+                             used to skip Clinger's fast path when it cannot
+                             possibly succeed - see detail::mantissa_fits_clinger()
    */
    token_type convert_number(token_type number_type, std::size_t mantissa_end)
    {
@@ -1492,11 +1451,10 @@ scan_number_done:
        }

        // this code is reached if we parse a floating-point number or if an
-        // integer conversion above overflowed. float and double (and long
-        // double where it is binary64) are converted by the library itself,
-        // correctly rounded and independent of the locale; other long double
-        // formats use std::from_chars when available, otherwise the
-        // locale-aware strtold.
+        // integer conversion above overflowed. Prefer std::from_chars
+        // (Eisel-Lemire, locale-independent, correctly rounded) when available;
+        // otherwise the exact Clinger fast path (double only); otherwise the
+        // locale-aware strtof/strtod/strtold.
        if (convert_float_fast(num_begin, num_end, decimal_point_position, mantissa_end, value_float))
        {
            return token_type::value_float;
@@ -1616,8 +1574,6 @@ scan_number_done:
            if (JSON_HEDLEY_LIKELY(integer_result != token_type::uninitialized))
            {
                ia.bulk_skip(len - 1);
-                position.chars_read_total += (len - 1);
-                position.chars_read_current_line += (len - 1);
                return integer_result;
            }
            // The value does not fit an integer, so this token converts as a
@@ -1634,8 +1590,6 @@ scan_number_done:
        decimal_point_position = dot_index;

        ia.bulk_skip(len - 1);
-        position.chars_read_total += (len - 1);
-        position.chars_read_current_line += (len - 1);

        return convert_number(number_type, mantissa_end);
    }
@@ -1686,7 +1640,7 @@ scan_number_done:

 #if JSON_DIAGNOSTIC_POSITIONS
        // the first character of the token has already been read, hence the -1
-        token_start_position = position.chars_read_total - 1;
+        token_start_position = get_chars_read_total() - 1;
 #endif

        note_token_start(std::integral_constant<bool, lazy_token_string> {});
@@ -1739,6 +1693,15 @@ scan_number_done:
    /// per-character position counters (line-count-on-'\n' bookkeeping is
    /// handled afterwards, in track_after_read(), once `current` is known)
    void advance_position() noexcept
+    {
+        advance_position_impl(std::integral_constant<bool, lazy_position> {});
+    }
+
+    /// seekable adapter: the position is derived from the adapter on demand
+    void advance_position_impl(std::true_type /*lazy*/) const noexcept {}
+
+    /// streaming adapter: count the character
+    void advance_position_impl(std::false_type /*lazy*/) noexcept
    {
        ++position.chars_read_total;
        ++position.chars_read_current_line;
@@ -1752,7 +1715,16 @@ scan_number_done:
        // seekable adapters reconstruct the token lazily on error (see
        // get_token_string), so the eager per-character copy is skipped
        capture_char(std::integral_constant<bool, lazy_token_string> {});
+        track_newline(std::integral_constant<bool, lazy_position> {});
+        return current;
+    }

+    /// seekable adapter: lines are counted on demand in get_position()
+    void track_newline(std::true_type /*lazy*/) const noexcept {}
+
+    /// streaming adapter: start a new line after reading a newline
+    void track_newline(std::false_type /*lazy*/) noexcept
+    {
        if (current == '\n')
        {
            ++position.lines_read;
@@ -1761,8 +1733,6 @@ scan_number_done:
            chars_read_before_newline = position.chars_read_current_line;
            position.chars_read_current_line = 0;
        }
-
-        return current;
    }

    /*!
@@ -1806,12 +1776,22 @@ scan_number_done:
    We implement unget by setting variable next_unget to true. The input is not
    changed - we just simulate ungetting by modifying chars_read_total,
    chars_read_current_line, and token_string. The next call to get() will
-    behave as if the unget character is read again.
+    behave as if the unget character is read again. With lazy_position, the
+    pending next_unget is all get_chars_read_total() needs.
    */
    void unget()
    {
        next_unget = true;
+        unget_position(std::integral_constant<bool, lazy_position> {});
+        uncapture_char(std::integral_constant<bool, lazy_token_string> {});
+    }

+    /// seekable adapter: get_chars_read_total() accounts for next_unget
+    void unget_position(std::true_type /*lazy*/) const noexcept {}
+
+    /// streaming adapter: step the counters back over the ungotten character
+    void unget_position(std::false_type /*lazy*/) noexcept
+    {
        --position.chars_read_total;

        // in case we "unget" a newline, we have to also decrement the lines_read
@@ -1834,8 +1814,6 @@ scan_number_done:
        {
            --position.chars_read_current_line;
        }
-
-        uncapture_char(std::integral_constant<bool, lazy_token_string> {});
    }

    /// adapter without lookahead: nothing to do (see release_lookahead)
@@ -1906,10 +1884,21 @@ scan_number_done:
    // diagnostics
    /////////////////////

-    /// return position of last read token
-    constexpr position_t get_position() const noexcept
+    /*!
+    @brief return the number of characters read so far
+
+    Unlike get_position(), this is O(1) for all adapters, so it may be called
+    for every value (JSON_DIAGNOSTIC_POSITIONS).
+    */
+    std::size_t get_chars_read_total() const noexcept
    {
-        return position;
+        return get_chars_read_total_impl(std::integral_constant<bool, lazy_position> {});
+    }
+
+    /// return position of last read token
+    position_t get_position() const
+    {
+        return get_position_impl(std::integral_constant<bool, lazy_position> {});
    }

    /*!
@@ -1946,6 +1935,43 @@ scan_number_done:
    }
 #endif

+  private:
+    /// seekable adapter: every get() either read from the adapter (including
+    /// reads at EOF, which get() counts as characters as well) or replayed an
+    /// ungotten character, so the count is the adapter's read count minus a
+    /// still pending unget
+    std::size_t get_chars_read_total_impl(std::true_type /*lazy*/) const noexcept
+    {
+        return ia.get_read_count() - (next_unget ? 1u : 0u);
+    }
+
+    /// streaming adapter: the counter is maintained by get() and unget()
+    std::size_t get_chars_read_total_impl(std::false_type /*lazy*/) const noexcept
+    {
+        return position.chars_read_total;
+    }
+
+    /// seekable adapter: count the lines in the consumed input; O(input read
+    /// so far), but only called on errors
+    position_t get_position_impl(std::true_type /*lazy*/) const
+    {
+        position_t result;
+        result.chars_read_total = get_chars_read_total();
+        // reads at EOF count as characters but are not part of the input
+        const std::size_t consumed = (std::min)(result.chars_read_total, ia.get_consumed_count());
+        std::size_t line_start = 0;
+        result.lines_read = ia.count_consumed_lines(consumed, line_start);
+        result.chars_read_current_line = result.chars_read_total - line_start;
+        return result;
+    }
+
+    /// streaming adapter: the position is maintained by get() and unget()
+    position_t get_position_impl(std::false_type /*lazy*/) const noexcept
+    {
+        return position;
+    }
+
+  public:
    /// seekable adapter: rebuild the last read token from the input on demand
    const std::vector<char_type>& collect_token_chars(std::vector<char_type>& out, std::true_type /*lazy*/) const
    {
@@ -2061,7 +2087,7 @@ scan_number_done:
    token_type scan()
    {
        // initially, skip the BOM
-        if (position.chars_read_total == 0 && !skip_bom())
+        if (get_chars_read_total() == 0 && !skip_bom())
        {
            error_message = "invalid BOM; must be 0xEF 0xBB 0xBF if given";
            return token_type::parse_error;
@@ -2088,7 +2114,7 @@ scan_number_done:
    token_type scan_expecting(token_type expected_type)
    {
        JSON_ASSERT(expected_type == token_type::name_separator || expected_type == token_type::value_separator);
-        JSON_ASSERT(position.chars_read_total > 0);
+        JSON_ASSERT(get_chars_read_total() > 0);
        const char_int_type expected_char = static_cast<unsigned char>((expected_type == token_type::name_separator) ? ':' : ',');
        skip_whitespace();
        if (JSON_HEDLEY_LIKELY(current == expected_char))
@@ -370,7 +370,7 @@ class parser
                    }
                    case token_type::end_of_input:
                    {
-                        if (JSON_HEDLEY_UNLIKELY(m_lexer.get_position().chars_read_total == 1))
+                        if (JSON_HEDLEY_UNLIKELY(m_lexer.get_chars_read_total() == 1))
                        {
                            return syntax_error(*sax, "attempting to parse an empty input; check that your input string or stream contains the expected JSON");
                        }
@@ -520,8 +520,10 @@ class parser
    {
        // MSVC 2015 reports C4100 (unreferenced parameter) when SAX::parse_error is static
        static_cast<void>(sax);
-        return sax.parse_error(m_lexer.get_position(), m_lexer.get_token_string(),
-                               parse_error::create(exception_id::syntax_error, m_lexer.get_position(), message, nullptr));
+        // computing the position is O(input read so far) for seekable input
+        const position_t position = m_lexer.get_position();
+        return sax.parse_error(position, m_lexer.get_token_string(),
+                               parse_error::create(exception_id::syntax_error, position, message, nullptr));
    }

    std::string exception_message(const token_type expected, const std::string& context)
@@ -22,10 +22,6 @@ namespace detail
 constexpr std::int64_t pow5_128_smallest_power = -342;
 constexpr std::int64_t pow5_128_largest_power = 308;

-// every entry of pow5_128() holds two 64-bit halves of 5^q, one per covered power of 5
-static_assert((pow5_128_largest_power - pow5_128_smallest_power + 1) * 2 == 1302,
-              "pow5_128_smallest_power/pow5_128_largest_power must match the size of the pow5_128() table");
-
 /*!
@brief 128-bit approximations of 5^q for q in [-342, 308]

@@ -8,12 +8,10 @@

 #pragma once

-#include <array> // array
 #include <cstddef> // size_t
-#include <cstdint> // uint64_t, uint8_t
+#include <cstdint> // uint64_t
 #include <cstring> // memcpy

-#include <nlohmann/detail/bit_ops.hpp>
 #include <nlohmann/detail/macro_scope.hpp>

 // Optional SIMD backend for bulk UTF-8 validation. This is an opt-in external
@@ -71,12 +69,18 @@ inline std::size_t find_string_special(const unsigned char* data, std::size_t n)
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        const std::uint64_t special = swar_string_special(read_eight_bytes(data + i));
-        if (special != 0)
+        std::uint64_t word = 0;
+        std::memcpy(&word, data + i, sizeof(word));
+        if (swar_string_special(word) != 0)
        {
-            // the lowest flagged byte is the first special one: the borrows of
-            // the subtractions can only flag bytes above a true hit
-            return i + (static_cast<std::size_t>(count_trailing_zeros(special)) / 8);
+            // a special byte is in this word; locate it (endian-agnostic)
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                if (is_string_special(data[i + j]))
+                {
+                    return i + j;
+                }
+            }
        }
    }
    for (; i < n; ++i)
@@ -110,7 +114,8 @@ inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        const std::uint64_t v = read_eight_bytes(data + i);
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
        const std::uint64_t d = v ^ 0x7F7F7F7F7F7F7F7Full; // DEL  (0x7F)
@@ -121,9 +126,7 @@ inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_
                                   | (v & high);               // >= 0x80
        if (stop != 0)
        {
-            // the lowest flagged byte is the first one to stop at (see
-            // find_string_special())
-            return i + (static_cast<std::size_t>(count_trailing_zeros(stop)) / 8);
+            break;
        }
    }
    for (; i < n; ++i)
@@ -250,18 +253,12 @@ inline std::size_t scalar_string_bulk_run(const unsigned char* data, std::size_t
        {
            break; // end of buffer, or a quote/escape/control byte
        }
-        // a run of multi-byte sequences (e.g. CJK text) is validated sequence
-        // by sequence without searching for the next special byte in between
-        do
+        const std::size_t seq = validate_one_utf8(data + pos, n - pos);
+        if (seq == 0)
        {
-            const std::size_t seq = validate_one_utf8(data + pos, n - pos);
-            if (seq == 0)
-            {
-                return pos; // ill-formed or truncated: let the byte path diagnose it
-            }
-            pos += seq;
+            break; // ill-formed or truncated: let the byte path diagnose it
        }
-        while (pos < n && data[pos] >= 0x80u);
+        pos += seq;
    }
    return pos;
 }
@@ -276,7 +273,8 @@ inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t
    std::size_t i = 0;
    for (; i + 8 <= n; i += 8)
    {
-        const std::uint64_t v = read_eight_bytes(data + i);
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
        const std::uint64_t q = v ^ 0x2222222222222222ull;
        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull;
        const std::uint64_t hit = ((q - ones) & ~q & high)
@@ -284,8 +282,14 @@ inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t
                                  | ((v - 0x2020202020202020ull) & ~v & high);
        if (hit != 0)
        {
-            // the lowest flagged byte is the first delimiter (see find_string_special())
-            return i + (static_cast<std::size_t>(count_trailing_zeros(hit)) / 8);
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                const unsigned char c = data[i + j];
+                if (c == '\"' || c == '\\' || c < 0x20u)
+                {
+                    return i + j;
+                }
+            }
        }
    }
    for (; i < n; ++i)
@@ -316,50 +320,5 @@ inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noe
    return scalar_string_bulk_run(data, n);
 }

-// Decode the 4 hex digits at [data, data+4) - the digits following a `\u`
-// escape - into a codepoint 0x0000..0xFFFF via one table lookup per byte
-// (after yyjson's read_hex_u16), or return -1 if any of the 4 bytes is not a
-// hex digit ('0'..'9', 'A'..'F', 'a'..'f'). The caller must already have
-// checked that 4 bytes are available; used by lexer::get_codepoint()'s
-// contiguous fast path. On -1 it falls back to the byte-at-a-time loop, which
-// stops at the first invalid digit, so the reported error and position are
-// unaffected by this fast path.
-inline int hex_codepoint(const unsigned char* data) noexcept
-{
-    static const std::array<std::uint8_t, 256> hex_digit_table = // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
-    {
-        {
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 00..0F
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 10..1F
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 20..2F
-            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 30..3F ('0'..'9')
-            0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 40..4F ('A'..'F')
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 50..5F
-            0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 60..6F ('a'..'f')
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 70..7F
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 80..8F
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 90..9F
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // A0..AF
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // B0..BF
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // C0..CF
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // D0..DF
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // E0..EF
-            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF  // F0..FF
-        }
-    };
-
-    const std::uint8_t d0 = hex_digit_table[data[0]];
-    const std::uint8_t d1 = hex_digit_table[data[1]];
-    const std::uint8_t d2 = hex_digit_table[data[2]];
-    const std::uint8_t d3 = hex_digit_table[data[3]];
-    // every valid digit is <= 0xF; the combined OR only exceeds it if at
-    // least one of the four bytes was not a hex digit (looked up as 0xFF)
-    if ((d0 | d1 | d2 | d3) > 0x0F)
-    {
-        return -1;
-    }
-    return (d0 << 12) | (d1 << 8) | (d2 << 4) | d3;
-}
-
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
@@ -21,8 +21,6 @@
 #undef JSON_NO_UNIQUE_ADDRESS
 #undef JSON_DISABLE_ENUM_SERIALIZATION
 #undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
-#undef JSON_DTOA_SSE2
-#undef JSON_DTOA_NEON

 #ifndef JSON_TEST_KEEP_MACROS
    #undef JSON_CATCH
@@ -1366,9 +1366,8 @@ class serializer
    /*!
    @brief dump an integer

-    Dump a given integer, appending it to @ref write_buffer (directly: copying
-    the digits from another buffer right after writing them waits until the
-    stores are done).
+    Dump a given integer, appending it to @ref write_buffer. Works internally with
+    @a number_buffer.

    @param[in] x  integer number (signed or unsigned) to dump
    @tparam NumberType either @a number_integer_t or @a number_unsigned_t
@@ -1403,57 +1402,33 @@ class serializer
            return;
        }

-        // use a pointer to fill the buffer (room for as much as number_buffer holds)
-        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + number_buffer.size() > write_buffer.size()))
-        {
-            flush();
-        }
-        auto* buffer_ptr = write_buffer.data() + write_buffer_pos;
+        // use a pointer to fill the buffer
+        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto)

        number_unsigned_t abs_value;

-        // one byte for the minus sign
-        unsigned int n_chars = 0;
+        unsigned int n_chars{};

        if (is_negative_number(x))
        {
            *buffer_ptr = '-';
            abs_value = remove_sign(static_cast<number_integer_t>(x));
-            n_chars = 1;
+
+            // account one more byte for the minus sign
+            n_chars = 1 + count_digits(abs_value);
        }
        else
        {
            abs_value = static_cast<number_unsigned_t>(x);
+            n_chars = count_digits(abs_value);
        }

-        // up to 16 digits: eight at a time (as the digits of floats), written
-        // without leading zeros
-        if (abs_value < 10000000000000000u)
-        {
-            const std::uint64_t value = abs_value;
-            const std::uint64_t upper = value / 100000000u;
-            const std::uint64_t first = dtoa_impl::eight_digit_bytes(upper != 0 ? upper : value);
-            const auto leading = static_cast<unsigned>(count_leading_zeros(first) / 8); // (first is not 0)
-            char* const p = buffer_ptr + n_chars;
-            dtoa_impl::store_msb_first(p, (first << (8 * leading)) + 0x3030303030303030u);
-            n_chars += 8 - leading;
-            if (upper != 0)
-            {
-                dtoa_impl::store_msb_first(p + 8 - leading, dtoa_impl::eight_digit_bytes(value - (upper * 100000000u)) + 0x3030303030303030u);
-                n_chars += 8;
-            }
-            write_buffer_pos += n_chars;
-            return;
-        }
-
-        n_chars += count_digits(abs_value);
-
        // spare 1 byte for '\0'
        JSON_ASSERT(n_chars < number_buffer.size() - 1);

        // jump to the end to generate the string from backward,
        // so we later avoid reversing the result
-        buffer_ptr += n_chars;
+        buffer_ptr += static_cast<typename decltype(number_buffer)::difference_type>(n_chars);

        // Fast int2ascii implementation inspired by "Fastware" talk by Andrei Alexandrescu
        // See: https://www.youtube.com/watch?v=o4-CwDo2zpg
@@ -1476,13 +1451,14 @@ class serializer
            *(--buffer_ptr) = static_cast<char>('0' + abs_value);
        }

-        write_buffer_pos += n_chars;
+        put_buffer(number_buffer, n_chars);
    }

    /*!
    @brief dump a floating-point number

-    Dump a given floating-point number, appending it to @ref write_buffer.
+    Dump a given floating-point number, appending it to @ref write_buffer. Works internally
+    with @a number_buffer.

    @param[in] x  floating-point number to dump
    */
@@ -1509,15 +1485,10 @@ class serializer

    void dump_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
    {
-        // directly into the write buffer: copying the text from number_buffer
-        // right after to_chars() wrote it waits until its stores are done
-        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + number_buffer.size() > write_buffer.size()))
-        {
-            flush();
-        }
-        auto* begin = write_buffer.data() + write_buffer_pos;
+        auto* begin = number_buffer.data();
        auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
-        write_buffer_pos += static_cast<std::size_t>(end - begin);
+
+        put_buffer(number_buffer, static_cast<std::size_t>(end - begin));
    }

    JSON_HEDLEY_NON_NULL(1)
@@ -7449,6 +7449,176 @@ public:
    }

  public:
+    /// @brief creates a diff as a JSON Merge Patch
+    /// @sa https://json.nlohmann.me/api/basic_json/merge_diff/
+    JSON_HEDLEY_WARN_UNUSED_RESULT
+    static basic_json merge_diff(const basic_json& source, const basic_json& target)
+    {
+        // unless both are objects, the patch is the target itself
+        if (!source.is_object() || !target.is_object())
+        {
+            return target;
+        }
+
+        return merge_diff_recursively(source, target, 0);
+    }
+
+  private:
+    /// @brief two objects @ref merge_diff_iteratively is diffing
+    struct merge_diff_frame
+    {
+        merge_diff_frame(const basic_json* source_, const basic_json* target_)
+            : source(source_), target(target_), member(source_->cbegin()), patch(value_t::object)
+        {}
+
+        // declared for GCC's -Weffc++, as in diff_frame
+        merge_diff_frame(const merge_diff_frame&) = default;
+        merge_diff_frame(merge_diff_frame&&) = default;
+        merge_diff_frame& operator=(const merge_diff_frame&) = default;
+        merge_diff_frame& operator=(merge_diff_frame&&) = default;
+        ~merge_diff_frame() = default;
+
+        /// the objects being diffed
+        const basic_json* source;
+        const basic_json* target;
+        /// the member of source being diffed; advanced once it is done
+        const_iterator member;
+        /// the patch for the members of source diffed so far
+        basic_json patch;
+    };
+
+    /// @brief add the members of object @a target that @a source does not
+    ///        have to the merge patch @a result
+    static void merge_diff_added_members(basic_json& result, const basic_json& source, const basic_json& target)
+    {
+        for (auto it = target.begin(); it != target.end(); ++it)
+        {
+            auto itf = source.find(it.key());
+            if (itf == source.end())
+            {
+                result[it.key()] = it.value();
+            }
+        }
+    }
+
+    /*!
+    @brief @ref merge_diff of two objects at nesting level @a depth
+
+    Diffing two nested objects calls this function again, once per nesting
+    level, so values nested deeply enough would exhaust the call stack and
+    terminate the process. The descent is bounded here: once @ref
+    detail::recursion_depth_limit levels have been entered, @ref
+    merge_diff_iteratively diffs what is left without the call stack.
+    */
+    static basic_json merge_diff_recursively(const basic_json& source, const basic_json& target, const std::size_t depth)
+    {
+        JSON_ASSERT(source.is_object() && target.is_object());
+
+        if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
+        {
+            return merge_diff_iteratively(source, target);
+        }
+
+        basic_json result(value_t::object);
+
+        for (auto it = source.begin(); it != source.end(); ++it)
+        {
+            auto itf = target.find(it.key());
+            if (itf != target.end())
+            {
+                if (it.value().is_object() && itf.value().is_object())
+                {
+                    auto diff = merge_diff_recursively(it.value(), itf.value(), depth + 1);
+                    if (!diff.empty())
+                    {
+                        result[it.key()] = std::move(diff);
+                    }
+                }
+                else if (it.value() != itf.value())
+                {
+                    result[it.key()] = itf.value();
+                }
+            }
+            else
+            {
+                result[it.key()] = value_t::null;
+            }
+        }
+
+        merge_diff_added_members(result, source, target);
+        return result;
+    }
+
+    /*!
+    @brief @ref merge_diff of two objects without the call stack
+
+    Produces the same patch as @ref merge_diff_recursively, keeping the objects
+    being diffed on an explicit stack instead of descending into them. Two
+    nested objects are still diffed completely before the next member, so the
+    patch has its members in the same order as in the recursive version. Only
+    reached for objects nested more deeply than @ref
+    detail::recursion_depth_limit.
+    */
+    static basic_json merge_diff_iteratively(const basic_json& source, const basic_json& target)
+    {
+        // the patch of source and target, set once their frame is popped
+        basic_json result;
+        std::vector<merge_diff_frame> stack;
+        stack.emplace_back(&source, &target);
+        while (!stack.empty())
+        {
+            // the frame's members are copied out and it is changed through
+            // stack.back(): pushing a frame for nested objects or popping
+            // this one would invalidate a reference to it
+            const basic_json* const s = stack.back().source;
+            const basic_json* const t = stack.back().target;
+            const const_iterator it = stack.back().member;
+
+            if (it != s->cend())
+            {
+                const const_iterator itf = t->find(it.key());
+                if (itf != t->cend())
+                {
+                    if (it.value().is_object() && itf.value().is_object())
+                    {
+                        // member is advanced once their patch is under its key
+                        stack.emplace_back(&it.value(), &itf.value());
+                        continue;
+                    }
+                    if (it.value() != itf.value())
+                    {
+                        stack.back().patch[it.key()] = itf.value();
+                    }
+                }
+                else
+                {
+                    stack.back().patch[it.key()] = value_t::null;
+                }
+                ++stack.back().member;
+                continue;
+            }
+
+            merge_diff_added_members(stack.back().patch, *s, *t);
+
+            // these objects are done: continue with the ones they are in
+            basic_json patch = std::move(stack.back().patch);
+            stack.pop_back();
+            if (stack.empty())
+            {
+                result = std::move(patch);
+            }
+            else
+            {
+                if (!patch.empty())
+                {
+                    stack.back().patch[stack.back().member.key()] = std::move(patch);
+                }
+                ++stack.back().member;
+            }
+        }
+        return result;
+    }
+
    /// @}
 };

@@ -1,599 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-#pragma once
-
-#include <array> // array
-#include <cstdint> // uint32_t, uint64_t
-
-// Number tokens that are hard to round correctly, with the IEEE-754 binary64
-// and binary32 bits of their correctly rounded values (ties to even; infinity
-// for an overflow, a signed zero for an underflow).
-//
-// For doubles and floats around 0, the smallest normal number, 1, 2^24, 2^53,
-// 0.1, and the largest finite number, and for random ones, the exact midpoint
-// m to the next number gives: m, m with one unit more and less in the last
-// digit, m with "01" and "0...01" appended, m with trailing zeros, and m cut
-// after 17 to 30 digits (rounded down and up, so that the rounding is decided
-// after the 19th digit), in fixed and exponent notation, 30% of them negative.
-// Tokens longer than 80 characters are left out, except for four of 700 digits
-// and more. Zeros, underflow, overflow, huge exponents, and integers beyond 64
-// bits complete the set. Of the 508 tokens, 134 (as double) and 150 (as
-// float) need the exact comparison with the midpoint (detail::digit_comparison()).
-//
-// The expected bits were computed with exact rational arithmetic in Python
-// (fractions.Fraction) and cross-checked with Python's float(); strtod_l and
-// strtof_l of Apple's libc and of glibc agree. Generated by
-// compact_hard_cases.py 5 (with hard_cases.py), see the pull request that
-// added this file.
-
-namespace float_hard_cases
-{
-
-struct hard_case
-{
-    const char* token;
-    std::uint64_t bits64;
-    std::uint32_t bits32;
-};
-
-inline const std::array<hard_case, 508>& cases()
-{
-    static const std::array<hard_case, 508> table =
-    {
-        {
-            {"-2.4703282292062327e-324", 0x8000000000000000u, 0x80000000u},
-            {"24703282292062328e-340", 0x0000000000000001u, 0x00000000u},
-            {"247032822920623272e-341", 0x0000000000000000u, 0x00000000u},
-            {"-0.2470328229206232721e-323", 0x8000000000000001u, 0x80000000u},
-            {"-0.24703282292062327208e-323", 0x8000000000000000u, 0x80000000u},
-            {"-2.4703282292062327209e-324", 0x8000000000000001u, 0x80000000u},
-            {"2.47032822920623272088e-324", 0x0000000000000000u, 0x00000000u},
-            {"247032822920623272089e-344", 0x0000000000000001u, 0x00000000u},
-            {"-247032822920623272088284396434e-353", 0x8000000000000000u, 0x80000000u},
-            {"0.247032822920623272088284396435e-323", 0x0000000000000001u, 0x00000000u},
-            {"-74109846876186981e-340", 0x8000000000000001u, 0x80000000u},
-            {"0.74109846876186982e-323", 0x0000000000000002u, 0x00000000u},
-            {"-0.7410984687618698162e-323", 0x8000000000000001u, 0x80000000u},
-            {"-7.410984687618698163e-324", 0x8000000000000002u, 0x80000000u},
-            {"7.4109846876186981626e-324", 0x0000000000000001u, 0x00000000u},
-            {"-74109846876186981627e-343", 0x8000000000000002u, 0x80000000u},
-            {"-741098468761869816264e-344", 0x8000000000000001u, 0x80000000u},
-            {"0.741098468761869816265e-323", 0x0000000000000002u, 0x00000000u},
-            {"0.741098468761869816264853189302e-323", 0x0000000000000001u, 0x00000000u},
-            {"-7.41098468761869816264853189303e-324", 0x8000000000000002u, 0x80000000u},
-            {"0.22250738585072006e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"2.2250738585072007e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"2.225073858507200641e-308", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"-2225073858507200642e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"22250738585072006419e-327", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"0.2225073858507200642e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"0.222507385850720064199e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"2.225073858507200642e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.22507385850720064199176395546e-308", 0x800FFFFFFFFFFFFEu, 0x80000000u},
-            {"222507385850720064199176395547e-337", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.2250738585072011e-308", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"-22250738585072012e-324", 0x8010000000000000u, 0x80000000u},
-            {"-2225073858507201136e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"0.2225073858507201137e-307", 0x0010000000000000u, 0x00000000u},
-            {"0.2225073858507201136e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.2250738585072011361e-308", 0x8010000000000000u, 0x80000000u},
-            {"2.22507385850720113605e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"222507385850720113606e-328", 0x0010000000000000u, 0x00000000u},
-            {"22250738585072011360574097967e-336", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"0.222507385850720113605740979671e-307", 0x0010000000000000u, 0x00000000u},
-            {"22250738585072016e-324", 0x0010000000000000u, 0x00000000u},
-            {"0.22250738585072017e-307", 0x0010000000000001u, 0x00000000u},
-            {"0.222507385850720163e-307", 0x0010000000000000u, 0x00000000u},
-            {"2.225073858507201631e-308", 0x0010000000000001u, 0x00000000u},
-            {"-2.2250738585072016301e-308", 0x8010000000000000u, 0x80000000u},
-            {"22250738585072016302e-327", 0x0010000000000001u, 0x00000000u},
-            {"-222507385850720163012e-328", 0x8010000000000000u, 0x80000000u},
-            {"0.222507385850720163013e-307", 0x0010000000000001u, 0x00000000u},
-            {"0.222507385850720163012305563795e-307", 0x0010000000000000u, 0x00000000u},
-            {"-2.22507385850720163012305563796e-308", 0x8010000000000001u, 0x80000000u},
-            {"0.17976931348623156E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"1.7976931348623157e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"1.797693134862315608e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"-1797693134862315609e290", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"-17976931348623156083e289", 0xFFEFFFFFFFFFFFFEu, 0xFF800000u},
-            {"-0.17976931348623156084E+309", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"0.179769313486231560835E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"-1.79769313486231560836e308", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"1.79769313486231560835325876058e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"179769313486231560835325876059e279", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"1.7976931348623158e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"17976931348623159e292", 0x7FF0000000000000u, 0x7F800000u},
-            {"1797693134862315807e290", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"0.1797693134862315808E+309", 0x7FF0000000000000u, 0x7F800000u},
-            {"0.17976931348623158079E+309", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"-1.797693134862315808e308", 0xFFF0000000000000u, 0xFF800000u},
-            {"1.79769313486231580793e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"179769313486231580794e288", 0x7FF0000000000000u, 0x7F800000u},
-            {"179769313486231580793728971405e279", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"-0.179769313486231580793728971406E+309", 0xFFF0000000000000u, 0xFF800000u},
-            {"100000000000000011102230246251565404236316680908203125e-53", 0x3FF0000000000000u, 0x3F800000u},
-            {"-1.00000000000000011102230246251565404236316680908203126", 0xBFF0000000000001u, 0xBF800000u},
-            {"1.00000000000000011102230246251565404236316680908203124e0", 0x3FF0000000000000u, 0x3F800000u},
-            {"10000000000000001110223024625156540423631668090820312501e-55", 0x3FF0000000000001u, 0x3F800000u},
-            {"1.00000000000000011102230246251565404236316680908203125000000000000000000001", 0x3FF0000000000001u, 0x3F800000u},
-            {"10000000000000001e-16", 0x3FF0000000000000u, 0x3F800000u},
-            {"1.0000000000000002", 0x3FF0000000000001u, 0x3F800000u},
-            {"1.000000000000000111", 0x3FF0000000000000u, 0x3F800000u},
-            {"1.000000000000000112e0", 0x3FF0000000000001u, 0x3F800000u},
-            {"1.000000000000000111e0", 0x3FF0000000000000u, 0x3F800000u},
-            {"-10000000000000001111e-19", 0xBFF0000000000001u, 0xBF800000u},
-            {"-100000000000000011102e-20", 0xBFF0000000000000u, 0xBF800000u},
-            {"-1.00000000000000011103", 0xBFF0000000000001u, 0xBF800000u},
-            {"1.00000000000000011102230246251", 0x3FF0000000000000u, 0x3F800000u},
-            {"1.00000000000000011102230246252e0", 0x3FF0000000000001u, 0x3F800000u},
-            {"-0.999999999999999944488848768742172978818416595458984375", 0xBFF0000000000000u, 0xBF800000u},
-            {"-9.99999999999999944488848768742172978818416595458984376e-1", 0xBFF0000000000000u, 0xBF800000u},
-            {"999999999999999944488848768742172978818416595458984374e-54", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
-            {"0.99999999999999994448884876874217297881841659545898437501", 0x3FF0000000000000u, 0x3F800000u},
-            {"9.99999999999999944488848768742172978818416595458984375000000000000000000001e-1", 0x3FF0000000000000u, 0x3F800000u},
-            {"-0.99999999999999994", 0xBFEFFFFFFFFFFFFFu, 0xBF800000u},
-            {"9.9999999999999995e-1", 0x3FF0000000000000u, 0x3F800000u},
-            {"9.999999999999999444e-1", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
-            {"9999999999999999445e-19", 0x3FF0000000000000u, 0x3F800000u},
-            {"99999999999999994448e-20", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
-            {"-0.99999999999999994449", 0xBFF0000000000000u, 0xBF800000u},
-            {"0.999999999999999944488", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
-            {"-9.99999999999999944489e-1", 0xBFF0000000000000u, 0xBF800000u},
-            {"9.99999999999999944488848768742e-1", 0x3FEFFFFFFFFFFFFFu, 0x3F800000u},
-            {"999999999999999944488848768743e-30", 0x3FF0000000000000u, 0x3F800000u},
-            {"-9.007199254740993e15", 0xC340000000000000u, 0xDA000000u},
-            {"9007199254740994e0", 0x4340000000000001u, 0x5A000000u},
-            {"9007199254740992", 0x4340000000000000u, 0x5A000000u},
-            {"9.00719925474099301e15", 0x4340000000000001u, 0x5A000000u},
-            {"9007199254740993000000000000000000001e-21", 0x4340000000000001u, 0x5A000000u},
-            {"-9007199254740993.000000000000000000000000000000", 0xC340000000000000u, 0xDA000000u},
-            {"90071992547409915e-1", 0x4340000000000000u, 0x5A000000u},
-            {"-9007199254740991.6", 0xC340000000000000u, 0xDA000000u},
-            {"9.0071992547409914e15", 0x433FFFFFFFFFFFFFu, 0x5A000000u},
-            {"-9007199254740991501e-3", 0xC340000000000000u, 0xDA000000u},
-            {"9007199254740991.5000000000000000000001", 0x4340000000000000u, 0x5A000000u},
-            {"9.0071992547409915000000000000000000000000000000e15", 0x4340000000000000u, 0x5A000000u},
-            {"0.100000000000000012490009027033011079765856266021728515625", 0x3FB999999999999Au, 0x3DCCCCCDu},
-            {"1.00000000000000012490009027033011079765856266021728515626e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"100000000000000012490009027033011079765856266021728515624e-57", 0x3FB999999999999Au, 0x3DCCCCCDu},
-            {"0.10000000000000001249000902703301107976585626602172851562501", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"0.10000000000000001", 0x3FB999999999999Au, 0x3DCCCCCDu},
-            {"1.0000000000000002e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"-1.000000000000000124e-1", 0xBFB999999999999Au, 0xBDCCCCCDu},
-            {"1000000000000000125e-19", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"-10000000000000001249e-20", 0xBFB999999999999Au, 0xBDCCCCCDu},
-            {"0.1000000000000000125", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"0.10000000000000001249", 0x3FB999999999999Au, 0x3DCCCCCDu},
-            {"1.00000000000000012491e-1", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"1.00000000000000012490009027033e-1", 0x3FB999999999999Au, 0x3DCCCCCDu},
-            {"100000000000000012490009027034e-30", 0x3FB999999999999Bu, 0x3DCCCCCDu},
-            {"2.45134755833537796875e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"-245134755833537796876e-6", 0xC2EBDE5C4164D83Au, 0xD75EF2E2u},
-            {"-245134755833537.796874", 0xC2EBDE5C4164D839u, 0xD75EF2E2u},
-            {"2.4513475583353779687501e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"245134755833537796875000000000000000000001e-27", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"245134755833537.796875000000000000000000000000000000", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"2.4513475583353779e14", 0x42EBDE5C4164D839u, 0x575EF2E2u},
-            {"2451347558335378e-1", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"2451347558335377968e-4", 0x42EBDE5C4164D839u, 0x575EF2E2u},
-            {"245134755833537.7969", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
-            {"245134755833537.79687", 0x42EBDE5C4164D839u, 0x575EF2E2u},
-            {"2.4513475583353779688e14", 0x42EBDE5C4164D83Au, 0x575EF2E2u},
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-            {"-1000000052154064178466796874e-28", 0xBFB99999B0000000u, 0xBDCCCCCDu},
-            {"0.100000005215406417846679687501", 0x3FB99999B0000000u, 0x3DCCCCCEu},
-            {"1.000000052154064178466796875000000000000000000001e-1", 0x3FB99999B0000000u, 0x3DCCCCCEu},
-            {"-1000000052154064178466796875000000000000000000000000000000e-58", 0xBFB99999B0000000u, 0xBDCCCCCEu},
-            {"-0.10000000521540641", 0xBFB99999AFFFFFFFu, 0xBDCCCCCDu},
-            {"-1.0000000521540642e-1", 0xBFB99999B0000000u, 0xBDCCCCCEu},
-            {"1.000000052154064178e-1", 0x3FB99999B0000000u, 0x3DCCCCCDu},
-            {"-1000000052154064179e-19", 0xBFB99999B0000000u, 0xBDCCCCCEu},
-            {"10000000521540641784e-20", 0x3FB99999B0000000u, 0x3DCCCCCDu},
-            {"0.10000000521540641785", 0x3FB99999B0000000u, 0x3DCCCCCEu},
-            {"0.100000005215406417846", 0x3FB99999B0000000u, 0x3DCCCCCDu},
-            {"1.00000005215406417847e-1", 0x3FB99999B0000000u, 0x3DCCCCCEu},
-            {"5.429001220703125e3", 0x40B5350050000000u, 0x45A9A802u},
-            {"-5429001220703126e-12", 0xC0B5350050000001u, 0xC5A9A803u},
-            {"-5429.001220703124", 0xC0B535004FFFFFFFu, 0xC5A9A802u},
-            {"5.42900122070312501e3", 0x40B5350050000000u, 0x45A9A803u},
-            {"5429001220703125000000000000000000001e-33", 0x40B5350050000000u, 0x45A9A803u},
-            {"-5429.001220703125000000000000000000000000000000", 0xC0B5350050000000u, 0xC5A9A802u},
-            {"503719056e0", 0x41BE062490000000u, 0x4DF03124u},
-            {"503719057", 0x41BE062491000000u, 0x4DF03125u},
-            {"5.03719055e8", 0x41BE06248F000000u, 0x4DF03124u},
-            {"50371905601e-2", 0x41BE062490028F5Cu, 0x4DF03125u},
-            {"503719056.000000000000000000001", 0x41BE062490000000u, 0x4DF03125u},
-            {"5.03719056000000000000000000000000000000e8", 0x41BE062490000000u, 0x4DF03124u},
-            {"-92331620", 0xC196037990000000u, 0xCCB01BCCu},
-            {"9.233163e7", 0x41960379B8000000u, 0x4CB01BCEu},
-            {"9233161e1", 0x4196037968000000u, 0x4CB01BCBu},
-            {"92331620.1", 0x4196037990666666u, 0x4CB01BCDu},
-            {"9.233162000000000000000000001e7", 0x4196037990000000u, 0x4CB01BCDu},
-            {"9233162000000000000000000000000000000e-29", 0x4196037990000000u, 0x4CB01BCCu},
-            {"3.002458625e6", 0x4146E82D50000000u, 0x4A37416Au},
-            {"3002458626e-3", 0x4146E82D5020C49Cu, 0x4A37416Bu},
-            {"3002458.624", 0x4146E82D4FDF3B64u, 0x4A37416Au},
-            {"-3.00245862501e6", 0xC146E82D500053E3u, 0xCA37416Bu},
-            {"3002458625000000000000000000001e-24", 0x4146E82D50000000u, 0x4A37416Bu},
-            {"3002458.625000000000000000000000000000000", 0x4146E82D50000000u, 0x4A37416Au},
-            {"-1095485584696182596504479582065262592e1", 0xC7A07BA830000000u, 0xFD03DD42u},
-            {"10954855846961825965044795820652625930", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"1.095485584696182596504479582065262591e37", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"109548558469618259650447958206526259201e-1", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"-10954855846961825965044795820652625920.00000000000000000001", 0xC7A07BA830000000u, 0xFD03DD42u},
-            {"1.095485584696182596504479582065262592000000000000000000000000000000e37", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"10954855846961825e21", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"10954855846961826000000000000000000000", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"10954855846961825960000000000000000000", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"1.095485584696182597e37", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"1.0954855846961825965e37", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"-10954855846961825966e18", 0xC7A07BA830000000u, 0xFD03DD42u},
-            {"10954855846961825965e18", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"10954855846961825965100000000000000000", 0x47A07BA830000000u, 0x7D03DD42u},
-            {"10954855846961825965044795820600000000", 0x47A07BA830000000u, 0x7D03DD41u},
-            {"-1.09548558469618259650447958207e37", 0xC7A07BA830000000u, 0xFD03DD42u},
-            {"1.6449216019182103706535606608388384863861375606575165875256061553955078126e-21", 0x3B9F125A50000000u, 0x1CF892D3u},
-            {"-16449216019182103706535606608388384863861375606575165875256061553955078124e-94", 0xBB9F125A50000000u, 0x9CF892D2u},
-            {"-0.0000000000000000000016449216019182103", 0xBB9F125A50000000u, 0x9CF892D2u},
-            {"-1.6449216019182104e-21", 0xBB9F125A50000000u, 0x9CF892D3u},
-            {"-1.64492160191821037e-21", 0xBB9F125A50000000u, 0x9CF892D2u},
-            {"-1644921601918210371e-39", 0xBB9F125A50000000u, 0x9CF892D3u},
-            {"-16449216019182103706e-40", 0xBB9F125A50000000u, 0x9CF892D2u},
-            {"0.0000000000000000000016449216019182103707", 0x3B9F125A50000000u, 0x1CF892D3u},
-            {"0.00000000000000000000164492160191821037065", 0x3B9F125A50000000u, 0x1CF892D2u},
-            {"1.64492160191821037066e-21", 0x3B9F125A50000000u, 0x1CF892D3u},
-            {"1.64492160191821037065356066083e-21", 0x3B9F125A50000000u, 0x1CF892D2u},
-            {"164492160191821037065356066084e-50", 0x3B9F125A50000000u, 0x1CF892D3u},
-            {"6.565061509609222412109375e-1", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"6565061509609222412109376e-25", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"0.6565061509609222412109374", 0x3FE5021930000000u, 0x3F2810C9u},
-            {"6.56506150960922241210937501e-1", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"6565061509609222412109375000000000000000000001e-46", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"-0.6565061509609222412109375000000000000000000000000000000", 0xBFE5021930000000u, 0xBF2810CAu},
-            {"6.5650615096092224e-1", 0x3FE5021930000000u, 0x3F2810C9u},
-            {"-65650615096092225e-17", 0xBFE5021930000000u, 0xBF2810CAu},
-            {"6565061509609222412e-19", 0x3FE5021930000000u, 0x3F2810C9u},
-            {"0.6565061509609222413", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"0.65650615096092224121", 0x3FE5021930000000u, 0x3F2810C9u},
-            {"6.5650615096092224122e-1", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"-6.5650615096092224121e-1", 0xBFE5021930000000u, 0xBF2810C9u},
-            {"656506150960922241211e-21", 0x3FE5021930000000u, 0x3F2810CAu},
-            {"18014627239033005156980393746124491372029297053813934326171875e-77", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"0.00000000000000018014627239033005156980393746124491372029297053813934326171876", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"-1.8014627239033005156980393746124491372029297053813934326171874e-16", 0xBCA9F63970000000u, 0xA54FB1CBu},
-            {"1801462723903300515698039374612449137202929705381393432617187501e-79", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"18014627239033005e-32", 0x3CA9F63970000000u, 0x254FB1CBu},
-            {"0.00000000000000018014627239033006", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"0.0000000000000001801462723903300515", 0x3CA9F63970000000u, 0x254FB1CBu},
-            {"-1.801462723903300516e-16", 0xBCA9F63970000000u, 0xA54FB1CCu},
-            {"-1.8014627239033005156e-16", 0xBCA9F63970000000u, 0xA54FB1CBu},
-            {"18014627239033005157e-35", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"180146272390330051569e-36", 0x3CA9F63970000000u, 0x254FB1CBu},
-            {"-0.00000000000000018014627239033005157", 0xBCA9F63970000000u, 0xA54FB1CCu},
-            {"0.000000000000000180146272390330051569803937461", 0x3CA9F63970000000u, 0x254FB1CBu},
-            {"1.80146272390330051569803937462e-16", 0x3CA9F63970000000u, 0x254FB1CCu},
-            {"0.05534819327294826507568359375", 0x3FAC569930000000u, 0x3D62B4CAu},
-            {"-5.534819327294826507568359376e-2", 0xBFAC569930000000u, 0xBD62B4CAu},
-            {"5534819327294826507568359374e-29", 0x3FAC569930000000u, 0x3D62B4C9u},
-            {"-0.0553481932729482650756835937501", 0xBFAC569930000000u, 0xBD62B4CAu},
-            {"5.534819327294826507568359375000000000000000000001e-2", 0x3FAC569930000000u, 0x3D62B4CAu},
-            {"5534819327294826507568359375000000000000000000000000000000e-59", 0x3FAC569930000000u, 0x3D62B4CAu},
-            {"0.055348193272948265", 0x3FAC569930000000u, 0x3D62B4C9u},
-            {"5.5348193272948266e-2", 0x3FAC569930000000u, 0x3D62B4CAu},
-            {"5.534819327294826507e-2", 0x3FAC569930000000u, 0x3D62B4C9u},
-            {"5534819327294826508e-20", 0x3FAC569930000000u, 0x3D62B4CAu},
-            {"55348193272948265075e-21", 0x3FAC569930000000u, 0x3D62B4C9u},
-            {"-0.055348193272948265076", 0xBFAC569930000000u, 0xBD62B4CAu},
-            {"0.0553481932729482650756", 0x3FAC569930000000u, 0x3D62B4C9u},
-            {"-5.53481932729482650757e-2", 0xBFAC569930000000u, 0xBD62B4CAu},
-            {"5.179692133247783258005389047985340416e36", 0x478F2C9450000000u, 0x7C7964A2u},
-            {"5179692133247783258005389047985340417e0", 0x478F2C9450000000u, 0x7C7964A3u},
-            {"5179692133247783258005389047985340415", 0x478F2C9450000000u, 0x7C7964A2u},
-            {"-5.17969213324778325800538904798534041601e36", 0xC78F2C9450000000u, 0xFC7964A3u},
-            {"-5179692133247783258005389047985340416000000000000000000001e-21", 0xC78F2C9450000000u, 0xFC7964A3u},
-            {"-5179692133247783258005389047985340416.000000000000000000000000000000", 0xC78F2C9450000000u, 0xFC7964A2u},
-            {"5.1796921332477832e36", 0x478F2C9450000000u, 0x7C7964A2u},
-            {"51796921332477833e20", 0x478F2C9450000000u, 0x7C7964A3u},
-            {"-5179692133247783258e18", 0xC78F2C9450000000u, 0xFC7964A2u},
-            {"5179692133247783259000000000000000000", 0x478F2C9450000000u, 0x7C7964A3u},
-            {"5179692133247783258000000000000000000", 0x478F2C9450000000u, 0x7C7964A2u},
-            {"5.1796921332477832581e36", 0x478F2C9450000000u, 0x7C7964A3u},
-            {"-5.179692133247783258e36", 0xC78F2C9450000000u, 0xFC7964A2u},
-            {"-517969213324778325801e16", 0xC78F2C9450000000u, 0xFC7964A3u},
-            {"517969213324778325800538904798e7", 0x478F2C9450000000u, 0x7C7964A2u},
-            {"5179692133247783258005389047990000000", 0x478F2C9450000000u, 0x7C7964A3u},
-            {
-                "0.22250738585072011360574097967091319759348195463516456480234261097248222220210769455165295239081350"
-                "8791414915891303962110687008643869459464552765720740782062174337998814106326732925355228688137214901"
-                "2981122451451889849057222307285255133155755015914397476397983411801999323962548289017107081850690630"
-                "6666559949382757725720157630626906633326475653000092458883164330377797918696120494973903778297049050"
-                "5108060994073026293712895895000358379996720725430436028407889577179615094551674824347103070260914462"
-                "1572289880258182545180325707018860872113128079512233426288368622321503775666622503982534335974568884"
-                "4239002654981983854879482922068947216898310996983658468140228542433306603398508864458040010349339704"
-                "2756718644338377048603786162277173854562306587467901408672332763671875e-307", 0x0010000000000000u, 0x00000000u
-            },
-            {
-                "2.22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508"
-                "7914149158913039621106870086438694594645527657207407820621743379988141063267329253552286881372149012"
-                "9811224514518898490572223072852551331557550159143974763979834118019993239625482890171070818506906306"
-                "6665599493827577257201576306269066333264756530000924588831643303777979186961204949739037782970490505"
-                "1080609940730262937128958950003583799967207254304360284078895771796150945516748243471030702609144621"
-                "5722898802581825451803257070188608721131280795122334262883686223215037756666225039825343359745688844"
-                "2390026549819838548794829220689472168983109969836584681402285424333066033985088644580400103493397042"
-                "756718644338377048603786162277173854562306587467901408672332763671875000000000000000000001e-308", 0x0010000000000000u, 0x00000000u
-            },
-            {
-                "0.11754942807573642917278829910357665133228589927589904276829631184250030649651730385585324256680905"
-                "8189392089843750000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "00000000000000000000000000000000000000000000000000000000000000000e-37", 0x380FFFFFE0000000u, 0x00800000u
-            },
-            {
-                "1175494280757364291727882991035766513322858992758990427682963118425003064965173038558532425668090581"
-                "8939208984375000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "00000000000001e-751", 0x380FFFFFE0000000u, 0x00800000u
-            },
-            {"0", 0x0000000000000000u, 0x00000000u},
-            {"-0", 0x8000000000000000u, 0x80000000u},
-            {"0.0", 0x0000000000000000u, 0x00000000u},
-            {"-0.0", 0x8000000000000000u, 0x80000000u},
-            {"0e999999999999999999999", 0x0000000000000000u, 0x00000000u},
-            {"-0.000e-99999", 0x8000000000000000u, 0x80000000u},
-            {"1e-400", 0x0000000000000000u, 0x00000000u},
-            {"-1e-400", 0x8000000000000000u, 0x80000000u},
-            {"1e400", 0x7FF0000000000000u, 0x7F800000u},
-            {"-1e400", 0xFFF0000000000000u, 0xFF800000u},
-            {"1e-50", 0x358DEE7A4AD4B81Fu, 0x00000000u},
-            {"-1e-50", 0xB58DEE7A4AD4B81Fu, 0x80000000u},
-            {"1e39", 0x48078287F49C4A1Du, 0x7F800000u},
-            {"-1e39", 0xC8078287F49C4A1Du, 0xFF800000u},
-            {"1e99999999999999999999999999", 0x7FF0000000000000u, 0x7F800000u},
-            {"1e-99999999999999999999999999", 0x0000000000000000u, 0x00000000u},
-            {"1e0000000000000000000000000000000000000000308", 0x7FE1CCF385EBC8A0u, 0x7F800000u},
-            {"123456789012345678901234567890e-30", 0x3FBF9ADD3746F65Fu, 0x3DFCD6EAu},
-            {"18446744073709551615", 0x43F0000000000000u, 0x5F800000u},
-            {"18446744073709551616", 0x43F0000000000000u, 0x5F800000u},
-            {"-9223372036854775808", 0xC3E0000000000000u, 0xDF000000u},
-            {"-9223372036854775809", 0xC3E0000000000000u, 0xDF000000u},
-        }
-    };
-    return table;
-}
-
-} // namespace float_hard_cases
@@ -38,7 +38,7 @@ TEST_CASE("Binary Formats")
        const auto ubjson_2_size = json::to_ubjson(j, true).size();
        const auto ubjson_3_size = json::to_ubjson(j, true, true).size();

-        CHECK(json_size == 2090234);
+        CHECK(json_size == 2090303);
        CHECK(bjdata_1_size == 1112030);
        CHECK(bjdata_2_size == 1224148);
        CHECK(bjdata_3_size == 1224148);
@@ -51,16 +51,16 @@ TEST_CASE("Binary Formats")
        CHECK(ubjson_3_size == 1169069);

        CHECK((100.0 * double(json_size) / double(json_size)) == Approx(100.0));
-        CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(53.201));
-        CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(58.565));
-        CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(58.565));
-        CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(50.511));
-        CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(85.853));
-        CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(50.499));
-        CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(50.528));
-        CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(53.201));
-        CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(58.565));
-        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(55.930));
+        CHECK((100.0 * double(bjdata_1_size) / double(json_size)) == Approx(53.199));
+        CHECK((100.0 * double(bjdata_2_size) / double(json_size)) == Approx(58.563));
+        CHECK((100.0 * double(bjdata_3_size) / double(json_size)) == Approx(58.563));
+        CHECK((100.0 * double(bon8_size) / double(json_size)) == Approx(50.509));
+        CHECK((100.0 * double(bson_size) / double(json_size)) == Approx(85.849));
+        CHECK((100.0 * double(cbor_size) / double(json_size)) == Approx(50.497));
+        CHECK((100.0 * double(msgpack_size) / double(json_size)) == Approx(50.526));
+        CHECK((100.0 * double(ubjson_1_size) / double(json_size)) == Approx(53.199));
+        CHECK((100.0 * double(ubjson_2_size) / double(json_size)) == Approx(58.563));
+        CHECK((100.0 * double(ubjson_3_size) / double(json_size)) == Approx(55.928));
    }

    SECTION("twitter.json")
@@ -13,20 +13,16 @@
 using nlohmann::json;

 #include <array> // array
+#include <cfloat> // FLT_EVAL_METHOD
 #include <cstdint> // uint32_t, uint64_t
-#include <cstdio> // snprintf
 #include <cstdlib> // strtod
 #include <cstring> // memcpy
 #include <limits> // numeric_limits
-#include <map> // map
-#include <random> // mt19937
 #include <sstream> // stringstream
 #include <string> // string
 #include <utility> // pair
 #include <vector> // vector

-#include "float_hard_cases.hpp"
-
 namespace
 {
 // shortcut to scan a string literal
@@ -262,7 +258,7 @@ TEST_CASE("lexer number fast path")
            "123456789012345678901234567890",  // huge -> float
            "0.30000000000000004", "2.2250738585072014e-308", "1e308",
            // high-precision / wide-exponent values that exercise the
-            // Eisel-Lemire path beyond the Clinger subset
+            // std::from_chars (Eisel-Lemire) path beyond the Clinger subset
            "1.7976931348623157e308", "1.2345678901234567e-250",
            "9007199254740993", "5e-324", "1e-320"
        };
@@ -284,18 +280,20 @@ TEST_CASE("lexer number fast path")
        }
    }

-    SECTION("significant digits around Clinger's fast path")
+    SECTION("significant-digit gate for the Clinger fast path")
    {
-        // Clinger's fast path needs a significand of at most 2^53, which
-        // tokens with 17 or more significant digits exceed. The conversion
-        // splits the token at the positions the scanners recorded, so leading
-        // zeros must not count as digits - "0.1234567890123456" has 16
-        // significant digits, not 17 - and both scanners must agree.
+        // Clinger's fast path needs a significand below 2^53, so it cannot
+        // succeed once the mantissa has 17 or more significant digits (the
+        // significand would be at least 10^16). The lexer skips the attempt
+        // there. That is only allowed to save work: every value must still come
+        // out bit-exactly, and both scanners must agree. In particular the gate
+        // must not fire for tokens whose leading zeros merely look like extra
+        // digits - "0.1234567890123456" has 16 significant digits, not 17.
        const std::vector<std::string> numbers =
        {
            "1234567890123456",                  // 16 significant digits
-            "12345678901234567",                 // 17
-            "123456789012345678",                // 18
+            "12345678901234567",                 // 17 -> attempt skipped
+            "123456789012345678",                // 18 -> attempt skipped
            "0.1234567890123456",                // 16: the leading "0" is not significant
            "0.12345678901234567",               // 17
            "0.00000000000000001",               // 1, in a long token
@@ -666,323 +664,46 @@ TEST_CASE("lexer string fast path")
    }
 }

-TEST_CASE("lexer escape fast path")
+TEST_CASE("parse_float_fast declines what it cannot convert exactly")
 {
-    // json::accept() never throws, so this section stays covered without
-    // exceptions; it pins which of the cases below are valid/invalid and
-    // checks the contiguous and streaming paths agree on that classification.
-    SECTION("accept() parity")
+    // The lexer only hands well-formed numbers to parse_float_fast, so the
+    // malformed ones below can only be passed to it directly. Declining is
+    // always safe: the caller then falls back to a slower, exact conversion.
+    const auto fast = [](const std::string & s, double & out)
    {
-        const std::vector<std::pair<std::string, bool>> cases =
-        {
-            {"\\u0041", true}, {"\\u00e4", true}, {"\\u00E4", true},
-            {"\\uD83D\\uDE00", true},
-            {"\\u12", false}, {"\\u12G4", false}, {"\\uXYZW", false},
-            {"\\uD800", false}, {"\\uD800A", false}, {"\\uD800\\u0041", false},
-            {"\\uDC00", false}, {"\\u", false}
-        };
-
-        for (const auto& c : cases)
-        {
-            for (const std::size_t offset :
-                    {
-                        std::size_t{0}, std::size_t{9}
-                    })
-            {
-                const std::string doc = "[\"" + std::string(offset, 'a') + c.first + "\"]";
-                CAPTURE(doc)
-                CHECK(json::accept(doc) == c.second);
-                std::stringstream ss(doc);
-                CHECK(json::accept(ss) == c.second);
-            }
-        }
-    }
-
-#if !defined(JSON_NOEXCEPTION)
-    // the full outcome of parsing @a doc: the parsed value, or the exact
-    // error message, so a mismatch in either is caught
-    const auto outcome = [](const std::string & doc, bool streaming) -> std::string
-    {
-        try
-        {
-            if (streaming)
-            {
-                std::stringstream ss(doc);
-                const json j = json::parse(ss);
-                return j.dump();
-            }
-            const json j = json::parse(doc);
-            return j.dump();
-        }
-        catch (const json::exception& e)
-        {
-            return {e.what()};
-        }
+        return nlohmann::detail::parse_float_fast(s.data(), s.data() + s.size(), out);
    };
+    double out = 0;

-    SECTION("contiguous vs streaming parity")
-    {
-        const std::vector<std::string> escapes =
-        {
-            "\\u0041",             // "A"
-            "\\u00e4",             // "ä" (lowercase hex)
-            "\\u00E4",             // "ä" (uppercase hex)
-            "\\uD83D\\uDE00",      // valid surrogate pair (an emoji)
-            "\\u12",               // truncated: only 2 hex digits before the closing quote
-            "\\u12G4",             // invalid hex digit at the 3rd position
-            "\\uXYZW",             // all 4 bytes invalid
-            "\\uD800",             // lone high surrogate, string ends right after
-            "\\uD800A",            // high surrogate not followed by another \u escape
-            "\\uD800\\u0041",      // high surrogate followed by \u, but not a low surrogate
-            "\\uDC00",             // lone low surrogate
-            "\\u",                 // '\u' with nothing after (closing quote right away)
-        };
-
-        // once at the start of the string and once past the first 8-byte SWAR
-        // word of the outer string_bulk_run, so the escape is reached both
-        // right after the opening quote and mid-run
-        for (const auto& escape : escapes)
-        {
-            for (const std::size_t offset :
-                    {
-                        std::size_t{0}, std::size_t{9}
-                    })
-            {
-                const std::string doc = "[\"" + std::string(offset, 'a') + escape + "\"]";
-                CAPTURE(doc)
-                CHECK(outcome(doc, false) == outcome(doc, true));
-            }
-
-            // the escape is the last thing before end of input: no closing
-            // quote at all
-            const std::string truncated_doc = "[\"" + escape;
-            CAPTURE(truncated_doc)
-            CHECK(outcome(truncated_doc, false) == outcome(truncated_doc, true));
-        }
-    }
-
-    SECTION("truncated \\u escape at every distance from the end of input")
-    {
-        // ia.bulk_remaining() must correctly report fewer than 4 bytes for
-        // every possible count of trailing hex-looking bytes (0, 1, 2, or 3)
-        // before end of input, so the fast path declines and the byte path
-        // alone reports the "must be followed by 4 hex digits" error, at the
-        // same position, in every case
-        for (const std::string& tail :
-                {
-                    std::string{}, std::string("1"), std::string("12"), std::string("123")
-                })
-        {
-            const std::string doc = "[\"\\u" + tail;
-            CAPTURE(doc)
-            CHECK(outcome(doc, false) == outcome(doc, true));
-            CHECK(outcome(doc, false).find("must be followed by 4 hex digits") != std::string::npos);
-        }
-    }
-
-    SECTION("invalid hex digit at every position of the 4")
-    {
-        // the fast path must decline for *any* invalid byte among the 4, not
-        // just the first, and the byte path must then stop at exactly that
-        // position - same as it always has
-        for (std::size_t bad_pos = 0; bad_pos < 4; ++bad_pos)
-        {
-            std::string digits = "1234";
-            digits[bad_pos] = 'g'; // not a hex digit
-            const std::string doc = "[\"\\u" + digits + "\"]";
-            CAPTURE(doc)
-            CHECK(outcome(doc, false) == outcome(doc, true));
-            CHECK(outcome(doc, false).find("must be followed by 4 hex digits") != std::string::npos);
-        }
-    }
-
-    SECTION("random escapes")
-    {
-        // A seeded PRNG builds the 4 bytes following `\u` from a mix of hex
-        // digits and non-hex bytes, at varying distances from the start of
-        // the string, to compare the two scanners on many more shapes than
-        // are practical to enumerate by hand.
-        std::mt19937 gen(7654321); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
-        const std::string hex_alphabet = "0123456789AaBbCcDdEeFf";
-        std::uniform_int_distribution<std::size_t> pick_hex(0, hex_alphabet.size() - 1);
-        std::uniform_int_distribution<int> pick_byte(1, 255); // never NUL
-        std::uniform_int_distribution<int> pick_is_hex(0, 4); // 4-in-5 chance of a hex digit
-        std::uniform_int_distribution<std::size_t> pick_offset(0, 12);
-
-        std::vector<std::string> mismatches;
-        for (int iter = 0; iter < 3000; ++iter)
-        {
-            std::string digits;
-            for (int i = 0; i < 4; ++i)
-            {
-                if (pick_is_hex(gen) != 0)
-                {
-                    digits += hex_alphabet[pick_hex(gen)];
-                }
-                else
-                {
-                    char c = static_cast<char>(pick_byte(gen));
-                    if (c == '"' || c == '\\')
-                    {
-                        // keep the string well-formed apart from the escape
-                        // itself, so any mismatch is attributable to the \u
-                        // handling and not to an unrelated quote/escape
-                        c = 'z';
-                    }
-                    digits += c;
-                }
-            }
-            const std::string doc = "[\"" + std::string(pick_offset(gen), 'a') + "\\u" + digits + "\"]";
-            if (outcome(doc, false) != outcome(doc, true))
-            {
-                mismatches.push_back(doc);
-            }
-        }
-        CAPTURE(mismatches)
-        CHECK(mismatches.empty());
-    }
+#if defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD != 0
+    // without true double precision, the fast path declines everything
+    CHECK_FALSE(fast("1.5", out));
+#else
+    CHECK(fast("1.5", out));
+    CHECK(out == 1.5);
+    CHECK(fast("+2.5e1", out));
+    CHECK(out == 25.0);
+    CHECK(fast("-25E-1", out));
+    CHECK(out == -2.5);
+    CHECK(fast("1e", out));
+    CHECK(out == 1.0);
 #endif
-}

-namespace
-{
-// the index of the decimal point (or npos) and of the end of the mantissa of a
-// number token, which the lexer records while scanning it
-std::pair<std::size_t, std::size_t> float_token_layout(const std::string& s)
-{
-    std::size_t dot = std::string::npos;
-    std::size_t mantissa_end = s.size();
-    for (std::size_t i = 0; i < s.size(); ++i)
-    {
-        if (s[i] == '.')
-        {
-            dot = i;
-        }
-        else if (s[i] == 'e' || s[i] == 'E')
-        {
-            mantissa_end = i;
-            break;
-        }
-    }
-    return {dot, mantissa_end};
-}
+    // not a number
+    CHECK_FALSE(fast("", out));
+    CHECK_FALSE(fast("-", out));
+    CHECK_FALSE(fast(".", out));
+    CHECK_FALSE(fast("1.2.3", out));
+    CHECK_FALSE(fast("1x", out));
+    CHECK_FALSE(fast("1e+", out));
+    CHECK_FALSE(fast("1e1x", out));

-template<typename FloatType>
-FloatType parse_native(const std::string& s)
-{
-    const auto layout = float_token_layout(s);
-    return nlohmann::detail::parse_float_native<FloatType>(s.data(), s.data() + s.size(), layout.first, layout.second);
-}
-
-std::uint64_t bits_of(double d)
-{
-    std::uint64_t b = 0;
-    std::memcpy(&b, &d, sizeof(b));
-    return b;
-}
-
-std::uint32_t bits_of(float f)
-{
-    std::uint32_t b = 0;
-    std::memcpy(&b, &f, sizeof(b));
-    return b;
-}
-
-std::uint64_t native_bits64(const std::string& s)
-{
-    return bits_of(parse_native<double>(s));
-}
-
-std::uint32_t native_bits32(const std::string& s)
-{
-    return bits_of(parse_native<float>(s));
-}
-} // namespace
-
-TEST_CASE("parse_float_native rounds correctly")
-{
-    SECTION("double")
-    {
-        CHECK(native_bits64("1.5") == 0x3FF8000000000000u);
-        CHECK(native_bits64("0.1") == 0x3FB999999999999Au);
-        CHECK(native_bits64("-0.0") == 0x8000000000000000u);
-        CHECK(native_bits64("0e999999999999999999999") == 0u);
-        // 2^53 + 1 is exactly between two doubles: ties to even, unless more digits follow
-        CHECK(native_bits64("9007199254740993") == 0x4340000000000000u);
-        CHECK(native_bits64("9007199254740993.0000000000000000001") == 0x4340000000000001u);
-        CHECK(native_bits64("9007199254740992.9999999999999999999") == 0x4340000000000000u);
-        // 1 + 2^-53 exactly (a tie), and one unit in the 55th digit around it
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203125") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203126") == 0x3FF0000000000001u);
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203124") == 0x3FF0000000000000u);
-        // subnormal and overflow boundaries
-        CHECK(native_bits64("2.4703282292062327e-324") == 0u);
-        CHECK(native_bits64("2.4703282292062328e-324") == 1u);
-        CHECK(native_bits64("2.2250738585072011e-308") == 0x000FFFFFFFFFFFFFu);
-        CHECK(native_bits64("2.2250738585072012e-308") == 0x0010000000000000u);
-        CHECK(native_bits64("1.7976931348623157e308") == 0x7FEFFFFFFFFFFFFFu);
-        CHECK(native_bits64("1.7976931348623159e308") == 0x7FF0000000000000u);
-        CHECK(native_bits64("-1e400") == 0xFFF0000000000000u);
-        CHECK(native_bits64("-1e-400") == 0x8000000000000000u);
-        // exponents and zeros far beyond the range cancel out
-        CHECK(native_bits64("0." + std::string(1000, '0') + "1e1001") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1" + std::string(1000, '0') + "e-1000") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1e-99999999999999999999999") == 0u);
-        CHECK(native_bits64("1E+99999999999999999999999") == 0x7FF0000000000000u);
-        // more digits than any midpoint has (769): only whether a nonzero digit follows matters
-        const std::string tie = "1.00000000000000011102230246251565404236316680908203125";
-        CHECK(native_bits64(tie + std::string(800, '0')) == 0x3FF0000000000000u);
-        CHECK(native_bits64(tie + std::string(800, '0') + "1") == 0x3FF0000000000001u);
-    }
-
-    SECTION("float")
-    {
-        CHECK(native_bits32("1.5") == 0x3FC00000u);
-        CHECK(native_bits32("0.1") == 0x3DCCCCCDu);
-        CHECK(native_bits32("-0.0") == 0x80000000u);
-        // 2^24 + 1 is exactly between two floats
-        CHECK(native_bits32("16777217") == 0x4B800000u);
-        CHECK(native_bits32("16777217.000000000000000000001") == 0x4B800001u);
-        CHECK(native_bits32("16777218.999999999999999999999") == 0x4B800001u);
-        CHECK(native_bits32("16777219") == 0x4B800002u);
-        // subnormal and overflow boundaries
-        CHECK(native_bits32("3.4028235677973366e38") == 0x7F7FFFFFu);
-        CHECK(native_bits32("3.4028235677973367e38") == 0x7F800000u);
-        CHECK(native_bits32("7.006492321624085e-46") == 0u);
-        CHECK(native_bits32("7.006492321624086e-46") == 1u);
-        CHECK(native_bits32("1.1754942e-38") == 0x007FFFFFu);
-        CHECK(native_bits32("-1.17549435e-38") == 0x80800000u);
-        CHECK(native_bits32("1e39") == 0x7F800000u);
-        CHECK(native_bits32("-1e-50") == 0x80000000u);
-        // not rounded through double: its double would round to another float
-        CHECK(native_bits32("1.00000005960464477539062500000000001") == 0x3F800001u);
-        CHECK(native_bits32("9007199254740993") == 0x5A000000u);
-    }
-
-    SECTION("the conversion shared with other parsers")
-    {
-        // convert_float() gives the lexer's results, for every type
-        const std::vector<std::string> tokens =
-        {
-            "0", "-0.0", "1.5", "0.1", "1e-400", "-2.5E+3", "123456789012345678901234567890",
-            "9007199254740993.0000000000000000001", "4.9406564584124654e-324"
-        };
-        using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
-        using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
-        for (const auto& t : tokens)
-        {
-            CAPTURE(t)
-            const auto layout = float_token_layout(t);
-            const char* const first = t.data();
-            const char* const last = first + t.size();
-            const auto d = nlohmann::detail::convert_float<double>(first, last, layout.first, layout.second);
-            const auto f = nlohmann::detail::convert_float<float>(first, last, layout.first, layout.second);
-            const auto ld = nlohmann::detail::convert_float<long double>(first, last, layout.first, layout.second);
-            CHECK(bits_of(d) == bits_of(json::parse(t).get<double>()));
-            CHECK(bits_of(f) == bits_of(float_json::parse(t).get<float>()));
-            CHECK(ld == long_double_json::parse(t).get<long double>());
-        }
-    }
+    // numbers that are not represented exactly on the fast path
+    CHECK_FALSE(fast("12345678901234567890", out));
+    CHECK_FALSE(fast("1e10000", out));
+    CHECK_FALSE(fast("9007199254740993", out));
+    CHECK_FALSE(fast("1e23", out));
+    CHECK_FALSE(fast("1e-23", out));
 }

 namespace
@@ -1086,6 +807,40 @@ std::size_t big_bit_length(const big_uint& a)
    }
    return n;
 }
+
+std::uint64_t bits_of(double d)
+{
+    std::uint64_t b = 0;
+    std::memcpy(&b, &d, sizeof(b));
+    return b;
+}
+
+bool eisel_lemire(const std::string& s, double& out)
+{
+    return nlohmann::detail::parse_float_eisel_lemire(s.data(), s.data() + s.size(), out);
+}
+
+// significant digits of a token, without trailing zeros
+std::size_t significant_digits(const std::string& s)
+{
+    std::string digits;
+    for (const char c : s)
+    {
+        if (c == 'e' || c == 'E')
+        {
+            break;
+        }
+        if (c >= '0' && c <= '9' && !(digits.empty() && c == '0'))
+        {
+            digits += c;
+        }
+    }
+    while (!digits.empty() && digits.back() == '0')
+    {
+        digits.pop_back();
+    }
+    return digits.size();
+}
 } // namespace

 TEST_CASE("Eisel-Lemire float conversion")
@@ -1513,33 +1268,26 @@ TEST_CASE("Eisel-Lemire float conversion")
        for (const auto& c : known)
        {
            CAPTURE(c.first)
-            CHECK(native_bits64(c.first) == c.second);
+            double out = 0;
+            if (eisel_lemire(c.first, out))
+            {
+                CHECK(bits_of(out) == c.second);
+            }
+            else
+            {
+                // only tokens with more than 19 significant digits are left to
+                // strtod: those whose value lies too close to a tie
+                CHECK(significant_digits(c.first) > 19);
+            }
        }
    }

-    SECTION("binary32")
-    {
-        using binary32 = nlohmann::detail::ieee_binary_format<24>;
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 1) == 0x3F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 1) == 0x3DCCCCCDu);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 15) == 0x3FC00000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777217) == 0x4B800000u); // tie, to even
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777219) == 0x4B800002u); // tie, to even
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-45, 1) == 0x00000001u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 7) == 0x00000000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 8) == 0x00000001u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-65, 9999999999999999999u) == 0x00000000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823466385288598u) == 0x7F7FFFFFu);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823669209384635u) == 0x7F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(39, 1) == 0x7F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-5, 0) == 0x00000000u);
-    }
-
    SECTION("round trip")
    {
-        // every double written by to_chars and read back, and its 17-digit
-        // form with trailing digits that make the token longer than 19 digits
+        // every double written by to_chars and read back, also with trailing
+        // digits that make the token longer than 19 digits
        std::uint64_t state = 5295;
+        std::size_t declined = 0;
        for (int i = 0; i < 200000; ++i)
        {
            state ^= state << 13u;
@@ -1561,51 +1309,30 @@ TEST_CASE("Eisel-Lemire float conversion")
            const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), d);
            const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
            CAPTURE(token)
-            CHECK(native_bits64(token) == b);
+            double out = 0;
+            REQUIRE(eisel_lemire(token, out));
+            CHECK(bits_of(out) == b);

-            // insert digits before the exponent of the 17-digit form: that
-            // form lies strictly inside the rounding interval of the double
-            // (the shortest one may lie on its boundary), and the digits move
-            // it by far less than the distance to the boundary, so the value
-            // must not change
-            std::array<char, 64> digits17{};
-            static_cast<void>(std::snprintf(digits17.data(), digits17.size(), "%.17g", d)); // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-            std::string longer = digits17.data();
+            // insert digits before the exponent: the value moves by far less
+            // than the distance to the rounding boundary, so it must not change
+            std::string longer = token;
            const std::size_t e = longer.find('e');
            const std::size_t dot = longer.find('.');
            const std::string extra = dot == std::string::npos ? ".000000000000000000001" : "000000000000000000001";
            longer.insert(e == std::string::npos ? longer.size() : e, extra);
            CAPTURE(longer)
-            CHECK(native_bits64(longer) == b);
-        }
-    }
-
-    SECTION("round trip, binary32")
-    {
-        std::uint32_t state = 5295;
-        for (int i = 0; i < 100000; ++i)
-        {
-            state ^= state << 13u;
-            state ^= state >> 17u;
-            state ^= state << 5u;
-            std::uint32_t b = state;
-            if ((b & 0x7F800000u) == 0x7F800000u)
+            if (eisel_lemire(longer, out))
            {
-                continue; // infinity or NaN
+                CHECK(bits_of(out) == b);
            }
-            if (i % 4 == 0)
+            else
            {
-                b &= 0x807FFFFFu; // subnormals
+                // w and w + 1 round differently: only when the value is very
+                // close to a rounding boundary
+                ++declined;
            }
-            float f = 0;
-            std::memcpy(&f, &b, sizeof(f));
-
-            std::array<char, 64> buffer{};
-            const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), f);
-            const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
-            CAPTURE(token)
-            CHECK(native_bits32(token) == b);
        }
+        CHECK(declined < 1000); // 107 of the 200,000
    }

    SECTION("used by the lexer")
@@ -1619,184 +1346,3 @@ TEST_CASE("Eisel-Lemire float conversion")
                             "[json.exception.out_of_range.406] number overflow parsing '1.7976931348623159e308'", json::out_of_range&);
    }
 }
-
-namespace
-{
-using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
-
-// the bits of the float that parse() gives for a token, via both scanners;
-// the value must be the same for both
-template<typename Json, typename Bits>
-void check_parse(const std::string& token, Bits expected, Bits infinity)
-{
-    std::stringstream stream(token);
-    if ((expected & ~(Bits{1} << ((8 * sizeof(Bits)) - 1))) == infinity)
-    {
-        Json _;
-        CHECK_THROWS_WITH_AS(_ = Json::parse(token), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
-        CHECK_THROWS_WITH_AS(_ = Json::parse(stream), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
-        return;
-    }
-    const Json contiguous = Json::parse(token);
-    const Json streamed = Json::parse(stream);
-    if (contiguous.is_number_float()) // not an integer that fits
-    {
-        CHECK(bits_of(contiguous.template get<typename Json::number_float_t>()) == expected);
-        CHECK(bits_of(streamed.template get<typename Json::number_float_t>()) == expected);
-    }
-    else
-    {
-        CHECK(streamed.is_number_integer());
-    }
-}
-} // namespace
-
-TEST_CASE("float conversion of hard cases")
-{
-    // see float_hard_cases.hpp
-    for (const auto& c : float_hard_cases::cases())
-    {
-        const std::string token = c.token;
-        CAPTURE(token)
-        CHECK(native_bits64(token) == c.bits64);
-        CHECK(native_bits32(token) == c.bits32);
-        check_parse<json>(token, c.bits64, std::uint64_t{0x7FF0000000000000u});
-        check_parse<float_json>(token, c.bits32, std::uint32_t{0x7F800000u});
-    }
-}
-
-TEST_CASE("float overflow and underflow in the parser")
-{
-    SECTION("double")
-    {
-        check_parse<json>("1.7976931348623157e308", std::uint64_t{0x7FEFFFFFFFFFFFFFu}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1.7976931348623159e308", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-1e309", std::uint64_t{0xFFF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1" + std::string(400, '0'), std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1e99999999999999999999", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        // an underflow gives a zero with the sign of the token
-        check_parse<json>("1e-400", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-1e-400", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-2.4703282292062327e-324", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("0." + std::string(400, '0') + "1", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
-    }
-
-    SECTION("float")
-    {
-        check_parse<float_json>("3.4028234e38", std::uint32_t{0x7F7FFFFFu}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("3.4028236e38", std::uint32_t{0x7F800000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-1e39", std::uint32_t{0xFF800000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("1e-46", std::uint32_t{0}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-1e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-7.006492321624085e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-7.006492321624086e-46", std::uint32_t{0x80000001u}, std::uint32_t{0x7F800000u});
-    }
-}
-
-TEST_CASE("string scanning kernels")
-{
-    // the word-at-a-time kernels must stop exactly where a byte-by-byte scan
-    // stops, for any content, length, and alignment
-    const auto reference_special = [](const unsigned char* data, std::size_t n)
-    {
-        std::size_t i = 0;
-        while (i < n && !nlohmann::detail::is_string_special(data[i]))
-        {
-            ++i;
-        }
-        return i;
-    };
-    const auto reference_copyable = [](const unsigned char* data, std::size_t n)
-    {
-        std::size_t i = 0;
-        while (i < n && nlohmann::detail::is_ascii_copyable(data[i]))
-        {
-            ++i;
-        }
-        return i;
-    };
-    const auto reference_bulk_run = [](const unsigned char* data, std::size_t n)
-    {
-        std::size_t i = 0;
-        while (i < n)
-        {
-            if (data[i] < 0x80u)
-            {
-                if (nlohmann::detail::is_string_special(data[i]))
-                {
-                    break;
-                }
-                ++i;
-                continue;
-            }
-            const std::size_t seq = nlohmann::detail::validate_one_utf8(data + i, n - i);
-            if (seq == 0)
-            {
-                break;
-            }
-            i += seq;
-        }
-        return i;
-    };
-
-    // pieces: ordinary ASCII, stops, DEL, well-formed sequences of every
-    // length, and ill-formed or truncated ones
-    const std::vector<std::string> pieces =
-    {
-        "a", "Z", " ", "~", "0123456789", "\"", "\\", std::string(1, '\0'), "\n", "\x1F", "\x7F",
-        "\xC3\xA4", "\xE2\x82\xAC", "\xE6\x97\xA5\xE6\x9C\xAC", "\xF0\x9F\x98\x80", "\xED\x9F\xBF",
-        "\x80", "\xC0\x80", "\xC3", "\xE2\x82", "\xED\xA0\x80", "\xF4\x90\x80\x80", "\xFF",
-    };
-    std::uint64_t state = 5295;
-    const auto next = [&state]()
-    {
-        state ^= state << 13u;
-        state ^= state >> 7u;
-        state ^= state << 17u;
-        return state;
-    };
-    // the upper half as a 32-bit value: converts to std::size_t implicitly on
-    // every platform (a cast of std::uint64_t is useless where both are the
-    // same type, and required where std::size_t is 32 bits wide)
-    const auto next_small = [&next]()
-    {
-        return static_cast<std::uint32_t>(next() >> 32u);
-    };
-    for (int round = 0; round < 100000; ++round)
-    {
-        // mostly ordinary text, so that runs span several words
-        std::string text(next_small() % 8u, '.');
-        const std::size_t count = next_small() % 12u;
-        for (std::size_t k = 0; k < count; ++k)
-        {
-            const std::size_t p = (next() % 4 == 0) ? next_small() % pieces.size() : 0;
-            text += pieces[p];
-            text += std::string(next_small() % 10u, 'x');
-        }
-        const auto* data = reinterpret_cast<const unsigned char*>(text.data()); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-        for (std::size_t offset = 0; offset < 3 && offset <= text.size(); ++offset)
-        {
-            const std::size_t n = text.size() - offset;
-            CAPTURE(text)
-            CAPTURE(offset)
-            CHECK(nlohmann::detail::find_string_special(data + offset, n) == reference_special(data + offset, n));
-            CHECK(nlohmann::detail::find_ascii_copyable_run(data + offset, n) == reference_copyable(data + offset, n));
-            CHECK(nlohmann::detail::scalar_string_bulk_run(data + offset, n) == reference_bulk_run(data + offset, n));
-        }
-    }
-
-    // the trailing-zero count, whichever implementation the compiler gets
-    for (int k = 0; k < 64; ++k)
-    {
-        const std::uint64_t bit = std::uint64_t{1} << k;
-        CHECK(nlohmann::detail::count_trailing_zeros(bit) == k);
-        CHECK(nlohmann::detail::count_trailing_zeros(bit | (bit << 1u) | 0x8000000000000000u) == k);
-    }
-
-    // eight bytes as a little-endian word, at any alignment
-    const std::array<unsigned char, 16> bytes = {{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF}};
-    CHECK(nlohmann::detail::read_eight_bytes(bytes.data()) == 0x0807060504030201u);
-    CHECK(nlohmann::detail::read_eight_bytes(bytes.data() + 1) == 0x0908070605040302u);
-    CHECK(nlohmann::detail::read_eight_bytes(bytes.data() + 8) == 0xFF0F0E0D0C0B0A09u);
-    CHECK(nlohmann::detail::read_eight_bytes(reinterpret_cast<const char*>(bytes.data()) + 3) == 0x0B0A090807060504u);
-}
@@ -8,6 +8,13 @@

 #include "doctest_compatibility.h"

+// capture whether JSON_DISABLE_ENUM_SERIALIZATION was enabled on the command
+// line before including json.hpp, which #undefs it; std::byte is an enum, so
+// converting std::vector<std::byte> needs enum serialization
+#if defined(JSON_DISABLE_ENUM_SERIALIZATION) && (JSON_DISABLE_ENUM_SERIALIZATION == 1)
+    #define SKIP_TESTS_FOR_ENUM_SERIALIZATION
+#endif
+
 #include <nlohmann/json.hpp>

 #include <cstdint>
@@ -85,3 +92,53 @@ TEST_CASE("binary type whose value type is not std::uint8_t")
    }
 #endif
 }
+
+#ifdef JSON_HAS_CPP_17
+// moved from unit-regression3.cpp, so that file does not instantiate a second
+// basic_json specialization (MinGW section limit, see windows.yml)
+TEST_CASE("std::vector<std::byte> as binary type")
+{
+    SECTION("issue #4804: from_cbor incompatible with std::vector<std::byte> as binary_t")
+    {
+        const std::vector<std::uint8_t> data = {0x80};
+        const auto decoded = byte_binary_json::from_cbor(data);
+        CHECK((decoded == byte_binary_json::array()));
+    }
+
+#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
+    SECTION("discussion #4209 - custom BinaryType direct assignment and round-tripping")
+    {
+        // Test that assigning a custom BinaryType directly creates a binary value, not an array
+        const std::vector<std::byte> original{std::byte{1}, std::byte{2}, std::byte{3}};
+        const byte_binary_json j = original;
+        CHECK(j.is_binary());
+        CHECK(!j.is_array());
+
+        // Test round-tripping: extracting the binary value back as the custom container type
+        const auto extracted = j.get<std::vector<std::byte>>();
+        CHECK(extracted == original);
+
+        // Test that the default json alias behavior is unchanged: std::vector<uint8_t> -> array
+        const nlohmann::json default_json = std::vector<std::uint8_t> {1, 2, 3};
+        CHECK(default_json.is_array());
+        CHECK(!default_json.is_binary());
+    }
+
+    SECTION("discussion #4209 - custom BinaryType extraction from parsed array")
+    {
+        // Test that extracting a custom BinaryType from a parsed JSON array still works
+        // (not just from a binary-typed node)
+        const auto j = byte_binary_json::parse("[1,2,3]");
+        CHECK(j.is_array());
+        CHECK(!j.is_binary());
+
+        // Extracting as custom BinaryType should work from arrays
+        const auto extracted = j.get<std::vector<std::byte>>();
+        CHECK(extracted.size() == 3);
+        CHECK(extracted[0] == std::byte{1});
+        CHECK(extracted[1] == std::byte{2});
+        CHECK(extracted[2] == std::byte{3});
+    }
+#endif
+}
+#endif
@@ -35,6 +35,7 @@ using nlohmann::json;
 #include <sstream>
 #include <string>
 #include <valarray>
+#include <vector>

 #include "sax_event_loggers.hpp"

@@ -1250,3 +1251,66 @@ TEST_CASE_TEMPLATE("deserialization of different character types (UTF-32)", T, c
    CHECK(json::sax_parse(v, &l));
    CHECK(l.events.size() == 1);
 }
+
+namespace
+{
+// records the position and message of a parse error; reporting the error via
+// SAX does not throw, so the test also runs with JSON_NOEXCEPTION
+struct SaxErrorRecorder : public SaxEventLogger
+{
+    bool parse_error(std::size_t position, const std::string& /*last_token*/, const json::exception& ex) override
+    {
+        error = std::to_string(position) + " " + ex.what();
+        return false;
+    }
+
+    std::string error {}; // NOLINT(readability-redundant-member-init)
+};
+} // namespace
+
+TEST_CASE("parse error positions are the same for contiguous and stream input")
+{
+    // contiguous input derives the position from the input on error, stream
+    // input counts it while reading (see lexer::lazy_position); the cases
+    // cover newlines before the error, ungetting a newline after a number,
+    // newlines inside a string, a comment, and reads at the end of input
+    struct test_case
+    {
+        std::string input;
+        std::size_t byte;
+        std::string message;
+    };
+    const std::vector<test_case> cases =
+    {
+        {"[\n  1,\n  2\n", 12, "[json.exception.parse_error.101] parse error at line 4, column 1: syntax error while parsing array - unexpected end of input; expected ']'"},
+        {"[1\n,2,\n]", 8, "[json.exception.parse_error.101] parse error at line 3, column 1: syntax error while parsing value - unexpected ']'; expected '[', '{', or a literal"},
+        {"[1\n x]", 5, "[json.exception.parse_error.101] parse error at line 2, column 2: syntax error while parsing array - invalid literal; last read: '1<U+000A> x'; expected ']'"},
+        {"1\n2", 3, "[json.exception.parse_error.101] parse error at line 2, column 1: syntax error while parsing value - unexpected number literal; expected end of input"},
+        {
+            "{\"a\":\n\"b\nc\"}", 9, R"([json.exception.parse_error.101] parse error at line 3, column 0: syntax error while parsing value - invalid string: control character U+000A (LF) must be escaped to \u000A or \n; last read: '"b<U+000A>')"
+        },
+        {"/* a\n b */\n x", 13, "[json.exception.parse_error.101] parse error at line 3, column 2: syntax error while parsing value - invalid literal; last read: '/* a<U+000A> b */<U+000A> x'"},
+        {"\n\n", 3, "[json.exception.parse_error.101] parse error at line 3, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal"},
+        {"[\"a\",\n 1e\n]", 10, "[json.exception.parse_error.101] parse error at line 3, column 0: syntax error while parsing value - invalid number; expected '+', '-', or digit after exponent; last read: '1e<U+000A>'"},
+        {"[tru\n]", 5, "[json.exception.parse_error.101] parse error at line 2, column 0: syntax error while parsing value - invalid literal; last read: '[tru<U+000A>'"},
+    };
+
+    for (const auto& c : cases)
+    {
+        CAPTURE(c.input)
+        const std::string expected = std::to_string(c.byte) + " " + c.message;
+
+        SaxErrorRecorder string_sax;
+        CHECK_FALSE(json::sax_parse(c.input, &string_sax, json::input_format_t::json, true, true));
+        CHECK(string_sax.error == expected);
+
+        SaxErrorRecorder pointer_sax;
+        CHECK_FALSE(json::sax_parse(c.input.data(), c.input.data() + c.input.size(), &pointer_sax, json::input_format_t::json, true, true));
+        CHECK(pointer_sax.error == expected);
+
+        std::istringstream is(c.input);
+        SaxErrorRecorder stream_sax;
+        CHECK_FALSE(json::sax_parse(is, &stream_sax, json::input_format_t::json, true, true));
+        CHECK(stream_sax.error == expected);
+    }
+}
@@ -567,9 +567,9 @@ TEST_CASE("Regression tests for extended diagnostics")
    }
 }

-TEST_CASE("Better diagnostics past the descent bound of update() and merge_patch()")
+TEST_CASE("Better diagnostics past the descent bound of update(), merge_patch() and merge_diff()")
 {
-    // Both merge objects nested more than detail::recursion_depth_limit()
+    // All three handle objects nested more than detail::recursion_depth_limit()
    // (128) levels deep without recursing; the values they add or replace
    // there must still know their parents.
    // The values are built rather than parsed, so that the expected messages
@@ -615,4 +615,19 @@ TEST_CASE("Better diagnostics past the descent bound of update() and merge_patch
        CHECK_THROWS_WITH_AS(p->at("x").at(0), expected_x.c_str(), json::type_error);
        CHECK_THROWS_WITH_AS(p->at("y").at(0), expected_y.c_str(), json::type_error);
    }
+
+    SECTION("merge_diff()")
+    {
+        // target and patch differ only in their innermost members, so the
+        // diff of the two is nested as deeply: {"a": ... {"x": null, "y": 2}}
+        const json diff = json::merge_diff(target, patch); // NOLINT(readability-suspicious-call-argument)
+
+        const json* p = &diff;
+        for (std::size_t i = 0; i < depth; ++i)
+        {
+            p = &p->at("a");
+        }
+        CHECK(p->at("x").is_null());
+        CHECK_THROWS_WITH_AS(p->at("y").at(0), expected_y.c_str(), json::type_error);
+    }
 }
@@ -260,11 +260,10 @@ struct LocaleSwitchingSax final: public nlohmann::json_sax<json>

 TEST_CASE("locale changes between lexer construction and number conversion (#5198)")
 {
-    // float and double are converted without the locale. A long double that
-    // is not binary64 can take the strtold fallback, which honors the locale
-    // that is current at conversion time. The numbers are chosen so that it
-    // does: too many significant digits for Clinger's fast path, an underflow
-    // that std::from_chars rejects, and a plain value.
+    // The numbers are chosen so that the conversion also takes the strtod
+    // fallback, which honors the locale that is current at conversion time:
+    // too many significant digits for Clinger's fast path, an underflow that
+    // std::from_chars rejects, and a plain value.
    const std::vector<std::string> numbers = {"3.14159265358979323846", "1.5e-400", "12.34", "-0.000123456789012345678"};
    std::string text = "[";
    for (const auto& n : numbers)
@@ -328,8 +327,7 @@ TEST_CASE("locale changes between lexer construction and number conversion (#519
            }
        }

-        // a long double goes through std::strtold unless it is binary64 or
-        // std::from_chars supports it
+        // a long double goes through std::strtold unless std::from_chars supports it
        {
            bool switched = false;
            const auto cb = [&](int /*depth*/, long_double_json::parse_event_t event, long_double_json& /*parsed*/) noexcept
@@ -355,15 +353,8 @@ TEST_CASE("locale with a multi-byte decimal point")
 {
    // Some locales use a decimal point that is not a single character, e.g.
    // U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
-    // substituted in place for '.', so the strtold fallback (only for long
-    // double formats other than binary64) converts a copy of the token with
-    // the whole decimal point instead (#5660). The values must be those of the
-    // "C" locale.
-    using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
-    const char* const long_double_numbers = "[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]";
-    REQUIRE(std::setlocale(LC_NUMERIC, "C") != nullptr);
-    const long_double_json expected_long_double = long_double_json::parse(long_double_numbers);
-
+    // substituted in place for '.', so the strtod fallback stops early. The
+    // conversion must still terminate rather than retry forever.
    const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
    bool tested = false;
    for (const char* name : names)
@@ -381,20 +372,12 @@ TEST_CASE("locale with a multi-byte decimal point")
        tested = true;

        // too many significant digits for Clinger's fast path, and an underflow
-        // that std::from_chars rejects: double does not depend on the locale
+        // that std::from_chars rejects: both reach the strtod fallback
        json j;
        CHECK_NOTHROW(j = json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
        CHECK(j.is_array());
-        CHECK(j[0] == 3.14159265358979323846);
-        CHECK(j[1] == 0.0);
-        CHECK(j[2] == -0.000123456789012345678);
        CHECK(json::accept("3.14159265358979323846"));

-        // a long double that reaches the strtold fallback is not truncated
-        long_double_json ld;
-        CHECK_NOTHROW(ld = long_double_json::parse(long_double_numbers));
-        CHECK(ld == expected_long_double);
-
        // a value the locale-independent paths convert is not affected
        CHECK(json::parse("12.5") == 12.5);
    }
@@ -58,11 +58,6 @@ using ordered_json = nlohmann::ordered_json;
        #include <optional>
    #elif __has_include(<experimental/optional>)
    #endif
-
-    /////////////////////////////////////////////////////////////////////
-    // for #4804
-    /////////////////////////////////////////////////////////////////////
-    using json_4804 = nlohmann::json::with_binary_t<std::vector<std::byte>>;
 #endif

 #ifdef JSON_HAS_CPP_20
@@ -458,49 +453,6 @@ TEST_CASE("regression tests 3")
 #endif

 #ifdef JSON_HAS_CPP_17
-    SECTION("issue #4804: from_cbor incompatible with std::vector<std::byte> as binary_t")
-    {
-        const std::vector<std::uint8_t> data = {0x80};
-        const auto decoded = json_4804::from_cbor(data);
-        CHECK((decoded == json_4804::array()));
-    }
-
-#ifndef SKIP_TESTS_FOR_ENUM_SERIALIZATION
-    SECTION("discussion #4209 - custom BinaryType direct assignment and round-tripping")
-    {
-        // Test that assigning a custom BinaryType directly creates a binary value, not an array
-        const std::vector<std::byte> original{std::byte{1}, std::byte{2}, std::byte{3}};
-        const json_4804 j = original;
-        CHECK(j.is_binary());
-        CHECK(!j.is_array());
-
-        // Test round-tripping: extracting the binary value back as the custom container type
-        const auto extracted = j.get<std::vector<std::byte>>();
-        CHECK(extracted == original);
-
-        // Test that the default json alias behavior is unchanged: std::vector<uint8_t> -> array
-        const json default_json = std::vector<std::uint8_t> {1, 2, 3};
-        CHECK(default_json.is_array());
-        CHECK(!default_json.is_binary());
-    }
-
-    SECTION("discussion #4209 - custom BinaryType extraction from parsed array")
-    {
-        // Test that extracting a custom BinaryType from a parsed JSON array still works
-        // (not just from a binary-typed node)
-        const auto j = json_4804::parse("[1,2,3]");
-        CHECK(j.is_array());
-        CHECK(!j.is_binary());
-
-        // Extracting as custom BinaryType should work from arrays
-        const auto extracted = j.get<std::vector<std::byte>>();
-        CHECK(extracted.size() == 3);
-        CHECK(extracted[0] == std::byte{1});
-        CHECK(extracted[1] == std::byte{2});
-        CHECK(extracted[2] == std::byte{3});
-    }
-#endif
-
    SECTION("issue #5046 - implicit conversion of return json to std::optional no longer implicit")
    {
        const json jval{};
@@ -15,24 +15,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::detail::dtoa_impl::reinterpret_bits;

-#include <algorithm>
-#include <array>
-#include <cmath>
-#include <cstdint>
-#include <cstdio>
-#include <cstdlib>
-#include <iomanip>
-#include <limits>
-#include <locale>
-#include <random>
-#include <sstream>
-#include <string>
-#include <utility>
-#include <vector>
-#if defined(JSON_HAS_CPP_17)
-    #include <charconv>
-#endif
-
 namespace
 {
 float make_float(uint32_t sign_bit, uint32_t biased_exponent, uint32_t significand)
@@ -468,7 +450,7 @@ TEST_CASE("formatting")
        check_double(  1.2345e+18,   "1.2345e+18"             ); //  1.2345e+18                1.2345e+18                1.2345e18
        check_double(  1.2345e+19,   "1.2345e+19"             ); //  1.2345e+19                1.2345e+19                1.2345e19
        check_double(  1.2345e+20,   "1.2345e+20"             ); //  1.2345e+20                1.2345e+20                1.2345e20
-        check_double(  1.2345e+21,   "1.2345e+21"             ); //  1.2345e+21                1.2344999999999999e+21    1.2345e21
+        check_double(  1.2345e+21,   "1.2344999999999999e+21" ); //  1.2345e+21                1.2344999999999999e+21    1.2345e21
        check_double(  1.2345e+22,   "1.2345e+22"             ); //  1.2345e+22                1.2345e+22                1.2345e22
    }

@@ -532,327 +514,3 @@ TEST_CASE("formatting")
        check_integer(1000000000000000000LL, "1000000000000000000");
    }
 }
-
-namespace
-{
-// a small unsigned big integer (32-bit limbs, least significant first), to
-// recompute the powers of ten of the shortest double conversion
-using big = std::vector<std::uint32_t>;
-
-void big_mul_small(big& x, std::uint32_t m)
-{
-    std::uint64_t carry = 0;
-    for (auto& limb : x)
-    {
-        const std::uint64_t v = (static_cast<std::uint64_t>(limb) * m) + carry;
-        limb = static_cast<std::uint32_t>(v);
-        carry = v >> 32u;
-    }
-    if (carry != 0)
-    {
-        x.push_back(static_cast<std::uint32_t>(carry));
-    }
-}
-
-void big_div_small(big& x, std::uint32_t d)
-{
-    std::uint64_t rest = 0;
-    for (std::size_t i = x.size(); i-- > 0;)
-    {
-        const std::uint64_t v = (rest << 32u) | x[i];
-        x[i] = static_cast<std::uint32_t>(v / d);
-        rest = v % d;
-    }
-    while (!x.empty() && x.back() == 0)
-    {
-        x.pop_back();
-    }
-}
-
-std::size_t big_bit_length(const big& x)
-{
-    std::size_t n = 32 * x.size();
-    for (std::uint32_t top = x.back(); (top & 0x80000000u) == 0; top <<= 1u)
-    {
-        --n;
-    }
-    return n;
-}
-
-bool big_bit(const big& x, std::size_t i)
-{
-    return ((x[i / 32] >> (i % 32)) & 1u) != 0;
-}
-
-/// the 128 most significant bits of x (floor), shifted left if x has fewer bits
-std::pair<std::uint64_t, std::uint64_t> big_top128(const big& x)
-{
-    const std::size_t n = big_bit_length(x);
-    std::uint64_t high = 0;
-    std::uint64_t low = 0;
-    for (std::size_t k = 0; k < 128; ++k)
-    {
-        const bool bit = k < n && big_bit(x, n - 1 - k);
-        if (k < 64)
-        {
-            high = (high << 1u) | (bit ? 1u : 0u);
-        }
-        else
-        {
-            low = (low << 1u) | (bit ? 1u : 0u);
-        }
-    }
-    return {high, low};
-}
-
-/// the digits (without trailing zeros) and the decimal exponent of a
-/// representation "[-]d[.ddd][e[+-]x]"
-std::pair<std::string, int> digits_and_exponent(const std::string& s)
-{
-    std::string digits;
-    int point = -1;
-    int exponent = 0;
-    for (std::size_t i = 0; i < s.size(); ++i)
-    {
-        const char c = s[i];
-        if (c >= '0' && c <= '9')
-        {
-            digits += c;
-        }
-        else if (c == '.')
-        {
-            point = static_cast<int>(digits.size());
-        }
-        else if (c == 'e' || c == 'E')
-        {
-            exponent = std::stoi(s.substr(i + 1));
-            break;
-        }
-    }
-    int e = exponent + (point < 0 ? static_cast<int>(digits.size()) : point) - static_cast<int>(digits.size());
-    const std::size_t first = digits.find_first_not_of('0');
-    digits = first == std::string::npos ? "0" : digits.substr(first);
-    while (digits.size() > 1 && digits.back() == '0')
-    {
-        digits.pop_back();
-        ++e;
-    }
-    return {digits, e};
-}
-
-/// the correctly rounded double of a decimal text
-/// (not std::strtod: the C runtimes of some platforms, e.g. MinGW's, round
-/// some 16 and 17 digit inputs wrongly)
-double parse_double(const std::string& text)
-{
-    const nlohmann::json j = nlohmann::json::parse(text, nullptr, false);
-    // (a discarded value: out of range, as strtod's HUGE_VAL)
-    return j.is_discarded() ? std::numeric_limits<double>::infinity() : j.get<double>();
-}
-
-/// whether the decimal digits * 10^e reads back as v
-bool reads_back(const std::string& digits, int e, double v)
-{
-    const std::string text = digits + "e" + std::to_string(e);
-    // (compared bit for bit: v is positive and finite, and -Wfloat-equal)
-    return reinterpret_bits<std::uint64_t>(parse_double(text)) == reinterpret_bits<std::uint64_t>(v);
-}
-
-/// Check the representation of a positive finite double: it reads back as
-/// the same value, and no representation with fewer digits does.
-void check_shortest(double v)
-{
-    std::array<char, 33> buf{};
-    char* end = nlohmann::detail::to_chars(buf.data(), buf.data() + 32, v);
-    const std::string text(buf.data(), end);
-    CAPTURE(text)
-    CHECK(parse_double(text) == v);
-    // the layout is that of format_buffer() for the digits of Zmij
-    const auto sd = nlohmann::detail::zmij::to_shortest(reinterpret_bits<std::uint64_t>(v));
-    const std::uint64_t significand = sd.has_digit ? (sd.integral * 10) + sd.digit : sd.integral;
-    int exponent = sd.has_digit ? sd.exponent : sd.exponent + 1;
-    std::string significand_digits = std::to_string(significand);
-    while (significand_digits.size() > 1 && significand_digits.back() == '0')
-    {
-        significand_digits.pop_back();
-        ++exponent;
-    }
-    std::array<char, 64> reference{};
-    std::copy(significand_digits.begin(), significand_digits.end(), reference.begin());
-    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), static_cast<int>(significand_digits.size()), exponent, -4, 15);
-    CHECK(text == std::string(reference.data(), static_cast<std::size_t>(reference_end - reference.data())));
-    // and write_positive() is what to_chars() calls
-    std::array<char, 64> positive{};
-    const char* const positive_end = nlohmann::detail::dtoa_impl::write_positive(positive.data(), positive.data() + positive.size(), v);
-    CHECK(text == std::string(positive.data(), static_cast<std::size_t>(positive_end - positive.data())));
-    const auto de = digits_and_exponent(text);
-    const std::string& digits = de.first;
-    if (digits.size() > 1)
-    {
-        // the decimals of one digit fewer next to the value
-        // (a stream rather than snprintf("%.*e"), whose output GCC cannot bound)
-        std::ostringstream shorter;
-        shorter.imbue(std::locale::classic());
-        shorter << std::scientific << std::setprecision(static_cast<int>(digits.size()) - 2) << v;
-        const auto near = digits_and_exponent(shorter.str());
-        // as an integer with digits.size() - 1 digits
-        std::string m = near.first;
-        int e = near.second;
-        while (m.size() < digits.size() - 1)
-        {
-            m += '0';
-            --e;
-        }
-        const std::uint64_t mid = std::stoull(m);
-        for (const std::uint64_t candidate :
-                {
-                    mid - 1, mid, mid + 1
-                })
-        {
-            CAPTURE(candidate)
-            CHECK(!reads_back(std::to_string(candidate), e, v));
-        }
-    }
-    // (icpc with libstdc++ 11 defines __cpp_lib_to_chars, but has no floating-point std::to_chars)
-#if defined(JSON_HAS_CPP_17) && defined(__cpp_lib_to_chars) && !defined(__INTEL_COMPILER)
-    // the closest of the shortest representations, as std::to_chars finds it
-    std::array<char, 64> std_text{};
-    const auto r = std::to_chars(std_text.data(), std_text.data() + std_text.size(), v, std::chars_format::scientific);
-    CHECK(digits_and_exponent(std::string(std_text.data(), r.ptr)) == de);
-#endif
-}
-} // namespace
-
-TEST_CASE("shortest digits of doubles")
-{
-    SECTION("powers of ten")
-    {
-        // the 128-bit significands of 10^k, rounded down, recomputed
-        for (int k = -342; k <= 341; ++k)
-        {
-            CAPTURE(k)
-            big x{1};
-            if (k >= 0)
-            {
-                for (int i = 0; i < k; ++i)
-                {
-                    big_mul_small(x, 10);
-                }
-            }
-            else
-            {
-                // floor(2^b / 10^-k) for a b that leaves more than 128 bits
-                const int b = 128 + 64 + (4 * -k);
-                x.assign(static_cast<std::size_t>(b / 32) + 1, 0);
-                x.back() = 1u << (b % 32);
-                for (int i = 0; i < -k; ++i)
-                {
-                    big_div_small(x, 10);
-                }
-            }
-            const auto expected = big_top128(x);
-            const auto actual = nlohmann::detail::zmij::pow10(k);
-            CHECK(actual.high == expected.first);
-            CHECK(actual.low == expected.second);
-        }
-    }
-
-    SECTION("boundary values")
-    {
-        for (const double v :
-                {
-                    std::numeric_limits<double>::min(), std::numeric_limits<double>::max(), std::numeric_limits<double>::denorm_min(),
-                    std::nextafter(std::numeric_limits<double>::min(), 0.0), 1.0, 2.0, 0.1, 0.3, 1e21, 1e22, 1e23, 5e-324, 9007199254740993.0,
-                    1.2345e+21, 2.2250738585072014e-308, 1.7976931348623157e308, 4.9406564584124654e-324, 123456789012345680.0
-                })
-        {
-            check_shortest(v);
-        }
-        // all powers of two (their rounding interval is narrower below)
-        for (int e = -1074; e <= 1023; ++e)
-        {
-            check_shortest(std::ldexp(1.0, e));
-        }
-        // powers of ten and their neighbors
-        for (int e = -323; e <= 308; ++e)
-        {
-            const double p = std::strtod(("1e" + std::to_string(e)).c_str(), nullptr);
-            check_shortest(p);
-            check_shortest(std::nextafter(p, 0.0));
-            check_shortest(std::nextafter(p, std::numeric_limits<double>::infinity()));
-        }
-    }
-
-    SECTION("random doubles")
-    {
-        std::mt19937_64 rng(5295); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
-        for (int i = 0; i < 100000; ++i)
-        {
-            const std::uint64_t bits = rng() & 0x7FFFFFFFFFFFFFFFu;
-            const auto v = reinterpret_bits<double>(bits);
-            if (std::isfinite(v) && bits != 0)
-            {
-                check_shortest(v);
-            }
-        }
-    }
-}
-
-TEST_CASE("choice of the conversion")
-{
-    using nlohmann::detail::dtoa_impl::is_binary64;
-
-    SECTION("by the format of the type")
-    {
-        // Zmij needs binary64 numbers; everything else uses Grisu2
-        static_assert(!is_binary64<float>::value, "float is not binary64");
-        static_assert(is_binary64<double>::value == (std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53),
-                      "double is binary64 where it is IEEE 754 with 53 digits");
-        static_assert(!is_binary64<int>::value, "integers are not binary64");
-        static_assert(is_binary64<long double>::value == (std::numeric_limits<long double>::is_iec559 && std::numeric_limits<long double>::digits == 53 && sizeof(long double) == 8),
-                      "long double is binary64 where it has the format of a double");
-        CHECK(!is_binary64<float>::value);
-        CHECK(is_binary64<double>::value);
-    }
-
-    SECTION("float: Grisu2, double: Zmij")
-    {
-        // 5.3165205877497296e+16 is one of the doubles for which Grisu2 does not find the shortest digits
-        constexpr double value = 5.3165205877497296e+16;
-        std::array<char, 64> buf{};
-        const char* const last = buf.data() + buf.size();
-
-        char* end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, value);
-        CHECK(std::string(buf.data(), end) == "5.31652058774973e+16");
-        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, value);
-        CHECK(std::string(buf.data(), end) == "5.3165205877497296e+16");
-
-        constexpr float f = 1.1754944e-38f;
-        end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, f);
-        const std::string dispatched(buf.data(), end);
-        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, f);
-        CHECK(dispatched == std::string(buf.data(), end));
-    }
-
-    SECTION("long double with the format of a double: Zmij")
-    {
-        // (on platforms where long double is wider, Grisu2 does not apply either: the snprintf fallback does)
-        // (constant on a given platform)
-        DOCTEST_MSVC_SUPPRESS_WARNING_PUSH
-        DOCTEST_MSVC_SUPPRESS_WARNING(4127)
-        if (std::numeric_limits<long double>::digits == 53 && std::numeric_limits<long double>::is_iec559)
-        {
-            using long_double_json = nlohmann::json::with_float_t<long double>;
-            for (const double d :
-                    {
-                        5.3165205877497296e+16, 1.0, 0.1, 123456.789, 2.2250738585072014e-308, 1.7976931348623157e+308, -5.3165205877497296e+16
-                    })
-            {
-                CAPTURE(d)
-                CHECK(long_double_json(static_cast<long double>(d)).dump() == nlohmann::json(d).dump());
-            }
-            CHECK(long_double_json(5.3165205877497296e+16L).dump() == "5.31652058774973e+16");
-        }
-        DOCTEST_MSVC_SUPPRESS_WARNING_POP
-    }
-}
Author	SHA1	Message	Date
Niels Lohmann	1d4dfc3af0	Report the parse errors of the position test via SAX The test caught json::parse_error, so it aborted in the ci_test_noexceptions build, where JSON_NOEXCEPTION turns the throw into std::abort(). sax_parse() hands the error position and the exception object to parse_error() without throwing, so the test now records them there and runs in every configuration. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-10-13 11:22:48 +02:00
Niels Lohmann	db3d98de07	Move the std::vector<std::byte> binary type tests out of unit-regression3 The #4804/#4209 tests instantiated a second basic_json specialization (with_binary_t<std::vector<std::byte>>), including its parser and CBOR reader. With clang 18, the C++20 object of unit-regression3.cpp had 32656 COFF sections on develop; the lazy position helpers pushed it to 32975, past what the MinGW linker of the Windows clang jobs handles ("relocation truncated to fit: IMAGE_REL_AMD64_REL32 against .rdata"). unit-custom-binary-type.cpp already instantiates the same type, so the tests move there; unit-regression3.cpp drops to 27616 sections. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-10-13 09:40:36 +02:00
Niels Lohmann	3dbed2a0cb	Derive the lexer position lazily for seekable input The lexer counted the read position on every character: two increments and a newline check per get(), all on members kept in memory. For seekable input (pointers, strings, other random-access byte ranges) the position can be derived instead: chars_read_total is the adapter's read count (including reads at EOF) minus a pending unget, and line and column are recomputed from the consumed input only when get_position() is called, i.e. on parse errors. JSON_DIAGNOSTIC_POSITIONS uses the new O(1) get_chars_read_total(). Stream, file, wide-string and user-defined adapters keep the eager counters. Parsing pretty-printed input gets 8-12% faster and accept() 12-27% (canada, citm_catalog, twitter; clang 21 arm64 and GCC 13 x86-64). Error messages, byte offsets, SAX positions and diagnostic positions are unchanged (differential comparison against develop on 548k inputs). Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-10-13 08:52:49 +02:00
satelliteprogrammer	40a62947d3	support JSON Merge Patch (RFC 7396) diff creation (#4965 ) * support JSON Merge Patch (RFC 7396) diff creation The JSON merge patch document format describes the set of modifications to a resource's content, that more closely mimics the syntax of the resource being modified. However, and in contrast to JSON Patch (RFC 6902), a JSON Merge Patch cannot express certain modifications, e.g., changing an array element at a specific index, or setting a specific object value to null. The null value in a JSON Merge Patch is used to remove the key from the object. The diff algorithm is not part of the RFC 7396, but it was tested against all examples provided, plus additional cases on how null values are handled. Signed-off-by: Luís Murta <luis@murta.dev> * improve algorithm efficiency Signed-off-by: Luís Murta <luis@murta.dev> * fix inconsistent nulls and empty arrays Also add CHECKs for the patch, documentation and run `make amalgamate`. Signed-off-by: Luís Murta <luis@murta.dev> * documentation cleanups Signed-off-by: Luís Murta <luis@murta.dev> * add an iterative fallback to merge_diff Bound the recursion depth like diff() and merge_patch(), and test values nested past the bound. Signed-off-by: Luís Murta <luis@murta.dev> * address the remaining review comments Signed-off-by: Luís Murta <luis@murta.dev> * move multi-line raw strings out of CHECK macros GCC 4.8/5, ICPC and NVHPC mis-tokenize multi-line raw string literals inside macro arguments, breaking the build or the parsed JSON. Signed-off-by: Luís Murta <luis@murta.dev> --------- Signed-off-by: Luís Murta <luis@murta.dev>	2026-10-12 09:33:43 +02:00