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json/include/nlohmann/detail/view/simd.hpp
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Niels Lohmann dd7686a269 json_view: faster reading, indexing and C-stream parsing (#5888) 
* Read C streams into a json_document in blocks

json_document::parse(FILE*) (and read(), accept(), parse_copy()) went through the
library's file input adapter and appended the text character by character
with fgetc. Read it with fread in blocks instead, like the std::istream
overload already does.

Parsing citm_catalog.json (1.7 MB) from a FILE*:
  Apple M1: 80.6 M -> 8.4 M instructions, 4.8 ms -> 0.55 ms (parse of the same text from a std::string: 8.7 M)
  Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 47.0 M -> 13.7 M / 45.8 M -> 14.2 M
The parsed documents and the error cases are identical (checked over the test corpus
and 30 mutants of each file). A null FILE* is handled as before (by the library's adapter).

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Index arrays without subtrees directly

operator[](idx), at(idx) and back() skipped the elements of an array one
after the other, whatever they were. In an array none of whose elements is
an array or object (numbers, strings, booleans, null) the elements are
adjacent nodes, which the array node's own sizes tell: its subtree has
exactly one node more than it has elements. Such an element is now the
node idx after the array node; any other array is walked as before.

Reading r[i] for every i of an array of 3000 integers:
  Apple M1: 28.8 M instructions, 3.1 ms -> 0.1 M instructions, 4 us
  Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 84.1 M -> 3.1 M / 75.0 M -> 3.0 M
Arrays that contain arrays are unchanged.

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Skip the bounds checks of number and string tokens in NUL-terminated input

For a NUL-terminated input (std::string, C string, string literal), the
parser reads the terminator instead of comparing p with the end, via
cursor::cur(). Number and string scanning still tested `p != e` before each
look at the next byte (after the integer digits for '.', for 'e', after
the exponent sign and digits, and after a string for its closing quote),
although the terminator can never be one of those characters. They now use
cur(), which is the plain load for NUL-terminated input and the bounds check
for ptr+len input, as before.

Parsing, Apple M1 instructions per parse: twitter 3.126 M -> 3.089 M (-1.2 %),
citm_catalog 8.70 M -> 8.58 M (-1.3 %), jeopardy 306.1 M -> 302.5 M (-1.2 %), signed
integers 281 M -> 266 M (-5.4 %), canada and floats -0.1 % / -0.9 %.
Linux x86-64 Ir, GCC 13 / Clang 18: twitter -0.5 % / -0.0 %, signed integers +0.2 % / -0.7 %.

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Make the index text of items() on arrays lazy

basic_json_view::items() on an array formatted every element's index with
std::to_string when the item was made, whether or not the loop asks for the
key. The item now keeps the position and makes the text on the first key()
call. Objects are not affected.

Iterating over the items of an array of 3000 numbers and reading only the values:
  Apple M1: 25.5 us -> 4.6 us (0.45 M -> ~0 net instructions)
  Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 14.9 M -> 4.1 M / 15.3 M -> 4.6 M
Reading key() costs what it did (24.5 us).

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Make the default of value() with a C string only if the member is missing

basic_json_view::value(key, "text") and value(pointer, "text") built a
std::string from the default first and passed it on, so a call allocated
for the default even when the member exists, and copied it again when it
does not. They now look the member up and make the result directly: from the
member if there is one, else from the C string. Behavior, including the
exceptions, is the same.

Two calls (member found, member missing) with a 40 character default, Apple M1:
  1.6 K -> 0.7 K instructions
  Linux x86-64 Ir (500 rounds), GCC 13 / Clang 18: 2.46 M -> 2.22 M / 2.40 M -> 2.15 M

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Materialize scalars directly and keep the stack of small subtrees local

basic_json_view::materialize() (and get<BasicJsonType>()) always set up the
SAX handler that parse() uses and a std::vector for the open containers,
sized from the document's deepest nesting. For a scalar, which is most of what
is materialized one value at a time, neither is needed: the value is made
directly (the same constructors the handler ends up calling). For arrays and
objects the stack of open containers is now a local array for the first 16
levels, and the vector is only used for deeper documents.

Materializing five scalars of a small document, Apple M1: 3.6 K -> 0.9 K instructions
  Linux x86-64 Ir (500 rounds), GCC 13 / Clang 18: 2.96 M -> 2.37 M / 2.90 M -> 2.29 M

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Copy the text between escapes while scanning it

A string that contains an escape is decoded by builder::slow_string(). After
each escape it scanned the next run of plain bytes (8 or 16 byte-by-byte
steps, then a vector loop), and then copied that run to the decode arena in a
second pass. The run is now copied 16 bytes at a time while it is scanned
(one vector load, a store of the same 16 bytes, and the mask of the bytes
that end the run), and the write position lives in a local variable, not in
the builder, since a store of a character may alias the builder's members and
made the compiler reload it after every escape. A run that ends at a quote
needs no scan, and non-ASCII text goes through the UTF-8 check as before;
the portable code is unchanged.

Parsing, Apple M1 instructions: jeopardy.json 304.0 M -> 293.8 M (-3.4 %), 3000 strings with
escapes 1.72 M -> 1.54 M (-10 %), twitter -0.6 %.
Linux x86-64 Ir, GCC 13 / Clang 18: escaped strings -7.6 % / -11.4 %, twitter 0.0 % / 0.0 %.
Documents and error messages are identical on 900 k random strings of escapes, UTF-8 and control
characters (also under ASan), and on mutants of the test corpus.

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Hash the last bytes of a key of a large object without a loop

key_hash() mixed a key eight bytes at a time and then packed the remaining
0-7 bytes one by one, in a loop. The last word of a key of eight or more
bytes is now read as the last eight bytes of the key (overlapping the word
before), and a key of 2-7 bytes as two overlapping words of four or two
bytes. A product only moves bits upwards, and the slot is taken from the low
bits: the high bits of the last word are folded down before the
multiplication, since keys that differ only in their last characters ("user_17",
"user_18") would otherwise share slots. The hash is not stored, so its values
may change.

Looking up every key of an object of 1000 random keys, Apple M1 instructions per 1000 lookups:
  keys of 5 bytes 175 K -> 93 K, hex strings of 8 bytes 177 K -> 168 K, keys of 12 bytes 196 K -> 186 K
Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 5-byte keys -4.7 % / -8.8 %, 12-byte keys -3.3 % / -7.4 %.
Building the tables while parsing such objects is cheaper as well (5-byte keys: 13.3 us -> 10.1 us).

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Compare short keys of a large object without a call of memcmp

find_indexed() compared the key of a member the table points to with
memcmp, a library call for any length. Up to 16 bytes, the bytes are now
compared as two overlapping words (the first and the last 8, 4, or 2 bytes),
as find_member() already does for the objects without a table; longer keys
still use memcmp.

Looking up every key of an object of 1000 random keys, Apple M1 instructions per 1000 lookups
(with the previous commit): keys of 5 bytes 93 K -> 72 K, hex strings of 8 bytes 168 K -> 148 K,
keys of 12 bytes 186 K -> 170 K, keys of 24 bytes 198 K -> 193 K (unchanged, memcmp).
Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 5-byte keys -7.2 % / -7.3 %, 12-byte keys -5.9 % / -6.6 %.

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Read an unedited editable document like a read-only one

Views of a json_editable_document followed edits at every step: the
lookup, the element access, back(), dump() and materialize() were built
for nodes that can be moved or linked, though no edit changes the index until
the first one (every edit creates the edit state before it touches a node).
Until then these now take the read-only code: one check of the document's
edit state per call, not per member or per node. After the first edit
nothing changes. Views that were made earlier keep working, as the check is
made when they are used.

Unedited editable document, Apple M1: dump() of twitter.json 1.40 M -> 1.22 M instructions (-12.6 %);
lookups unchanged. Linux x86-64 Ir, GCC 13 / Clang 18: dump -1.7 % / -1.0 %, lookups -0.1 % / 0.0 %.
Walking with iterators is unchanged, and so is dump() after an edit.

Belongs to the PR "json_view: read-side speedups".

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Format the numbered test keys of json_view's index with a stream

The keys were made with snprintf() and a format from a list, which
Flawfinder reports as an error (CWE-134, a format string that is not a
literal). A stream now formats them; the 30000 keys of the test are the
same as before.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Put the key number of the json_view index test in parentheses

astyle formatted i * step after << as a pointer declaration (i* step),
which failed the amalgamation check.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix the compiler and lint findings of json_view's read side and tests

- find() and contains() dispatch on Editable for the member lookup; for
  documents that cannot be edited both branches were the same call
  (GCC -Wduplicated-branches)
- json_view.hpp includes <cstdio> for the FILE overload (cpplint)
- the arena check macro of the builder is on one line (cpplint read it
  as an if body without braces)
- tests: no nested conditional (also MSVC C4018), no useless cast,
  parentheses around mixed operators, raw string literals, += instead
  of temporary concatenations, and NOLINT for the fixed seeds and a
  find() != npos, as elsewhere in the tests

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Grow the decode arena through a function and store its position back on every return

slow_string() kept its write position in locals and grew the arena through
the macro NLOHMANN_VIEW_ENSURE. The macro is now the always-inline member
arena_ensure() (a lambda is not inlined at every call site by clang, which
then keeps the position in memory: +11 % instructions on escape-heavy
strings), and a guard stores the position back into m_arena_write on every
return instead of by hand on the successful one. Instruction counts are
unchanged (clang) or 1 % lower (GCC).

Also word the complexity of back() as that of at().

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-24 07:41:06 +02:00

373 lines
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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-FileCopyrightText: 2018-2025 The simdjson authors <https://github.com/simdjson/simdjson>
// SPDX-License-Identifier: MIT
#pragma once
#include <array> // array
#include <atomic> // atomic
#include <cstddef> // size_t
#include <cstdint> // uint8_t, uint64_t
#include <nlohmann/json.hpp>
#include <nlohmann/detail/view/macro_scope.hpp>
// Vector code for long runs of string bytes. NEON (AArch64) and SSE2 (x86-64)
// belong to the baseline instruction sets and are used by default. The vector
// UTF-8 check needs NEON or SSSE3. SSSE3 is not part of x86-64, and the code
// must not depend on the flags of a translation unit (two translation units
// with different flags would have different definitions of the same inline
// functions): the check is compiled for SSSE3 with a function attribute and
// used where the CPU has SSSE3 (all x86-64 CPUs since about 2011), else the
// portable check. JSON_VIEW_USE_SSSE3 skips the CPU check (for code compiled
// for SSSE3 anyway); JSON_VIEW_NO_SIMD selects the portable code.
// NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE (set by the GCC module interface, where GCC
// ignores the target attribute and then rejects the SSSE3 intrinsics) keeps the
// check portable without disabling the SSE2 code.
#if !defined(JSON_VIEW_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
#include <arm_neon.h>
#define NLOHMANN_VIEW_NEON 1
#else
#define NLOHMANN_VIEW_NEON 0
#endif
// (x86 only: other targets can define __SSE2__ as well, e.g., WebAssembly with -msse2, but have no <cpuid.h>)
#if !defined(JSON_VIEW_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
#include <emmintrin.h>
#define NLOHMANN_VIEW_SSE2 1
#else
#define NLOHMANN_VIEW_SSE2 0
#endif
#if NLOHMANN_VIEW_SSE2 && defined(JSON_VIEW_USE_SSSE3)
#include <tmmintrin.h>
#define NLOHMANN_VIEW_SSSE3 1 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#else
#define NLOHMANN_VIEW_SSSE3 0 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#endif
#if NLOHMANN_VIEW_SSE2 && !NLOHMANN_VIEW_SSSE3 && !defined(NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE) && ((defined(__clang__) && __clang_major__ >= 4) || (defined(__GNUC__) && !defined(__clang__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9))))
// (GCC before 4.9 has no SSSE3 intrinsics without -mssse3)
// <cpuid.h> of GCC before 11 has no include guard, and json.hpp and
// json_view.hpp both include it
#ifndef NLOHMANN_JSON_CPUID_INCLUDED
#define NLOHMANN_JSON_CPUID_INCLUDED
#include <cpuid.h>
#endif
#include <tmmintrin.h>
#define NLOHMANN_VIEW_SSSE3_DISPATCH 1 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#define NLOHMANN_VIEW_SSSE3_TARGET __attribute__((target("ssse3")))
#elif NLOHMANN_VIEW_SSE2 && !NLOHMANN_VIEW_SSSE3 && defined(_MSC_VER)
// (MSVC compiles intrinsics of any instruction set)
#include <intrin.h>
#include <tmmintrin.h>
#define NLOHMANN_VIEW_SSSE3_DISPATCH 1 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#define NLOHMANN_VIEW_SSSE3_TARGET
#else
#define NLOHMANN_VIEW_SSSE3_DISPATCH 0 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
#define NLOHMANN_VIEW_SSSE3_TARGET
#endif
#define NLOHMANN_VIEW_VECTOR (NLOHMANN_VIEW_NEON || NLOHMANN_VIEW_SSE2)
#define NLOHMANN_VIEW_VECTOR_UTF8 (NLOHMANN_VIEW_NEON || NLOHMANN_VIEW_SSSE3 || NLOHMANN_VIEW_SSSE3_DISPATCH)
NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
namespace view
{
#if NLOHMANN_VIEW_VECTOR
/*!
@brief the first byte of a string run that is a quote, a backslash, a control
character, or not ASCII, 16 bytes per step
Stops at such a byte, or where fewer than 16 bytes are left (the caller tells
the two apart). A signed compare with 0x20 finds control characters and
non-ASCII bytes at once.
*/
NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* vector_plain_run(const unsigned char* p, const unsigned char* e) noexcept
{
while (e - p >= 16)
{
#if NLOHMANN_VIEW_NEON
const uint8x16_t in = vld1q_u8(p);
const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))),
vcltq_s8(vreinterpretq_s8_u8(in), vdupq_n_s8(0x20)));
// one nibble per byte (the usual NEON replacement of x86's movemask, see
// D. Kutenin, "Porting x86 vector bitmask optimizations to Arm NEON", 2022)
const std::uint64_t bits = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(special), 4)), 0);
if (bits != 0)
{
return p + (count_trailing_zeros(bits) >> 2u);
}
#else
const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
_mm_cmplt_epi8(in, _mm_set1_epi8(0x20)));
const auto bits = static_cast<std::uint64_t>(static_cast<unsigned>(_mm_movemask_epi8(special)));
if (bits != 0)
{
return p + count_trailing_zeros(bits);
}
#endif
p += 16;
}
return p;
}
/*!
@brief copy 16 bytes from p to w, and find the first quote, backslash,
control character, or non-ASCII byte among them
The bytes are copied whether or not they are all plain (the caller has room
for 16 bytes and keeps only the plain ones).
@return the offset of that byte, or 16 if there is none
*/
NLOHMANN_VIEW_ALWAYS_INLINE unsigned copy_plain_run16(const unsigned char* p, char* w) noexcept
{
#if NLOHMANN_VIEW_NEON
const uint8x16_t in = vld1q_u8(p);
vst1q_u8(reinterpret_cast<std::uint8_t*>(w), in); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))),
vcltq_s8(vreinterpretq_s8_u8(in), vdupq_n_s8(0x20)));
const std::uint64_t bits = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(special), 4)), 0);
return bits != 0 ? static_cast<unsigned>(count_trailing_zeros(bits) >> 2u) : 16u;
#else
const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
_mm_storeu_si128(static_cast<__m128i*>(static_cast<void*>(w)), in); // NOLINT(bugprone-casting-through-void)
const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
_mm_cmplt_epi8(in, _mm_set1_epi8(0x20)));
const auto bits = static_cast<std::uint64_t>(static_cast<unsigned>(_mm_movemask_epi8(special)));
return bits != 0 ? static_cast<unsigned>(count_trailing_zeros(bits)) : 16u;
#endif
}
#endif
#if NLOHMANN_VIEW_SSSE3_DISPATCH
/// whether the CPU has SSSE3 (CPUID leaf 1, ECX bit 9)
inline bool cpu_ssse3() noexcept
{
#if defined(_MSC_VER) && !defined(__clang__)
std::array<int, 4> regs {{}};
__cpuid(regs.data(), 1);
return (static_cast<unsigned>(regs[2]) & (1u << 9u)) != 0;
#else
unsigned eax = 0;
unsigned ebx = 0;
unsigned ecx = 0;
unsigned edx = 0;
return __get_cpuid(1, &eax, &ebx, &ecx, &edx) != 0 && (ecx & (1u << 9u)) != 0;
#endif
}
/// whether the CPU has SSSE3, asked once: the answer is kept in an atomic
/// that is initialized at compile time, so that neither a guard of a local
/// static nor a global constructor is needed (threads that ask at the same
/// time all store the same answer)
NLOHMANN_VIEW_ALWAYS_INLINE bool cpu_has_ssse3() noexcept
{
static std::atomic<int> known{0}; // 0: not asked yet, 1: no, 2: yes
int state = known.load(std::memory_order_relaxed);
if (NLOHMANN_VIEW_UNLIKELY(state == 0))
{
state = cpu_ssse3() ? 2 : 1;
known.store(state, std::memory_order_relaxed);
}
return state == 2;
}
#endif
#if NLOHMANN_VIEW_VECTOR_UTF8
/// Tables of the UTF-8 check of J. Keiser and D. Lemire, "Validating UTF-8 In
/// Less Than One Instruction Per Byte" (2021), as in simdjson ("lookup4"): each
/// maps a nibble (high and low nibble of the previous byte, high nibble of the
/// current byte) to the errors it allows; a byte pair is ill-formed if all
/// three have an error bit in common.
template<typename Dummy = void>
struct utf8_lookup4
{
static constexpr std::uint8_t too_short = 1u << 0u, too_long = 1u << 1u, overlong_3 = 1u << 2u, too_large = 1u << 3u;
static constexpr std::uint8_t surrogate = 1u << 4u, overlong_2 = 1u << 5u, too_large_1000 = 1u << 6u, overlong_4 = 1u << 6u;
static constexpr std::uint8_t two_conts = 1u << 7u, carry = too_short | too_long | two_conts;
static const std::array<std::uint8_t, 16> byte_1_high;
static const std::array<std::uint8_t, 16> byte_1_low;
static const std::array<std::uint8_t, 16> byte_2_high;
};
template<typename Dummy>
const std::array<std::uint8_t, 16> utf8_lookup4<Dummy>::byte_1_high =
{
{
too_long, too_long, too_long, too_long, too_long, too_long, too_long, too_long,
two_conts, two_conts, two_conts, two_conts,
too_short | overlong_2, too_short, too_short | overlong_3 | surrogate, too_short | too_large | too_large_1000 | overlong_4
}
};
template<typename Dummy>
const std::array<std::uint8_t, 16> utf8_lookup4<Dummy>::byte_1_low =
{
{
carry | overlong_3 | overlong_2 | overlong_4, carry | overlong_2, carry, carry,
carry | too_large, carry | too_large | too_large_1000, carry | too_large | too_large_1000, carry | too_large | too_large_1000,
carry | too_large | too_large_1000, carry | too_large | too_large_1000, carry | too_large | too_large_1000, carry | too_large | too_large_1000,
carry | too_large | too_large_1000, carry | too_large | too_large_1000 | surrogate, carry | too_large | too_large_1000, carry | too_large | too_large_1000
}
};
template<typename Dummy>
const std::array<std::uint8_t, 16> utf8_lookup4<Dummy>::byte_2_high =
{
{
too_short, too_short, too_short, too_short, too_short, too_short, too_short, too_short,
static_cast<std::uint8_t>(too_long | overlong_2 | two_conts | overlong_3 | too_large_1000 | overlong_4),
static_cast<std::uint8_t>(too_long | overlong_2 | two_conts | overlong_3 | too_large),
static_cast<std::uint8_t>(too_long | overlong_2 | two_conts | surrogate | too_large),
static_cast<std::uint8_t>(too_long | overlong_2 | two_conts | surrogate | too_large),
too_short, too_short, too_short, too_short
}
};
/// the end of scan_string_vector from block, where the vector loop stopped
/// (ill-formed UTF-8, or fewer than 16 bytes left): one byte or sequence at a
/// time, from the start of a sequence that crosses into the block
inline const unsigned char* scan_string_finish(const unsigned char* p, const unsigned char* block, const unsigned char* e, const std::uint8_t* plain) noexcept
{
for (int i = 1; i <= 3 && block - i >= p; ++i)
{
const unsigned char c = block[-i];
if (c < 0x80)
{
break;
}
if (c >= 0xC0)
{
const int len = 2 + static_cast<int>(c >= 0xE0) + static_cast<int>(c >= 0xF0);
if (len > i)
{
block -= i;
}
break;
}
}
for (p = block; p != e;)
{
if (*p < 0x80)
{
if (plain[*p] == 0)
{
return p;
}
++p;
continue;
}
const std::size_t n = validate_one_utf8(p, static_cast<std::size_t>(e - p));
if (n == 0)
{
return p;
}
p += n;
}
return p;
}
/*!
@brief the rest of a string from p (a character boundary), 16 bytes per step
The first quote, backslash, or control character is found with vector
compares, and the UTF-8 check covers the bytes up to it. Returns where the
string scan stops, like scan_string_run: before ill-formed UTF-8 and for the
last bytes of the input, the bytes are checked one sequence at a time. Out of
line, so that no constants of the check occupy registers in the parse loop.
On x86-64, it is compiled for SSSE3 (see cpu_has_ssse3()).
*/
NLOHMANN_VIEW_SSSE3_TARGET NLOHMANN_VIEW_NOINLINE inline const unsigned char* scan_string_vector(const unsigned char* p, const unsigned char* e, const std::uint8_t* plain) noexcept
{
using lookup = utf8_lookup4<>;
const unsigned char* block = p;
#if NLOHMANN_VIEW_NEON
const uint8x16_t t1h = vld1q_u8(lookup::byte_1_high.data());
const uint8x16_t t1l = vld1q_u8(lookup::byte_1_low.data());
const uint8x16_t t2h = vld1q_u8(lookup::byte_2_high.data());
uint8x16_t prev = vdupq_n_u8(0);
while (e - block >= 16)
{
const uint8x16_t in = vld1q_u8(block);
const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))), vcltq_u8(in, vdupq_n_u8(0x20)));
const uint8x16_t prev1 = vextq_u8(prev, in, 15);
const uint8x16_t sc = vandq_u8(vandq_u8(vqtbl1q_u8(t1h, vshrq_n_u8(prev1, 4)), vqtbl1q_u8(t1l, vandq_u8(prev1, vdupq_n_u8(0x0F)))), vqtbl1q_u8(t2h, vshrq_n_u8(in, 4)));
const uint8x16_t must23 = vorrq_u8(vqsubq_u8(vextq_u8(prev, in, 14), vdupq_n_u8(0xE0 - 0x80)), vqsubq_u8(vextq_u8(prev, in, 13), vdupq_n_u8(0xF0 - 0x80)));
const uint8x16_t err = veorq_u8(vandq_u8(must23, vdupq_n_u8(0x80)), sc);
const std::uint64_t special_bits = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(special), 4)), 0);
const std::uint64_t err_bits = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(vtstq_u8(err, err)), 4)), 0);
if (special_bits != 0)
{
// errors up to the special byte count (an incomplete sequence
// before a quote shows at the quote); the bytes after it do not
const unsigned k = static_cast<unsigned>(count_trailing_zeros(special_bits)) >> 2u;
const std::uint64_t upto = k == 15 ? ~std::uint64_t{0} :
(std::uint64_t{1} << (4u * (k + 1u))) - 1u;
if ((err_bits & upto) == 0)
{
return block + k;
}
break;
}
if (err_bits != 0)
{
break;
}
prev = in;
block += 16;
}
#else
// the same with SSSE3 (pshufb for the table lookups; nibbles from 16-bit
// shifts, as there are no byte shifts)
const __m128i t1h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_high.data()))); // NOLINT(bugprone-casting-through-void)
const __m128i t1l = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_low.data()))); // NOLINT(bugprone-casting-through-void)
const __m128i t2h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_2_high.data()))); // NOLINT(bugprone-casting-through-void)
const __m128i nibble = _mm_set1_epi8(0x0F);
const __m128i zero = _mm_setzero_si128();
__m128i prev = zero;
while (e - block >= 16)
{
const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(block))); // NOLINT(bugprone-casting-through-void)
const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
_mm_cmpeq_epi8(_mm_subs_epu8(in, _mm_set1_epi8(0x1F)), zero)); // in < 0x20
const __m128i prev1 = _mm_alignr_epi8(in, prev, 15);
const __m128i sc = _mm_and_si128(_mm_and_si128(_mm_shuffle_epi8(t1h, _mm_and_si128(_mm_srli_epi16(prev1, 4), nibble)),
_mm_shuffle_epi8(t1l, _mm_and_si128(prev1, nibble))),
_mm_shuffle_epi8(t2h, _mm_and_si128(_mm_srli_epi16(in, 4), nibble)));
const __m128i must23 = _mm_or_si128(_mm_subs_epu8(_mm_alignr_epi8(in, prev, 14), _mm_set1_epi8(0xE0 - 0x80)),
_mm_subs_epu8(_mm_alignr_epi8(in, prev, 13), _mm_set1_epi8(0xF0 - 0x80)));
const __m128i err = _mm_xor_si128(_mm_and_si128(must23, _mm_set1_epi8(static_cast<char>(-128))), sc);
const auto special_bits = static_cast<unsigned>(_mm_movemask_epi8(special));
const auto err_bits = ~static_cast<unsigned>(_mm_movemask_epi8(_mm_cmpeq_epi8(err, zero))) & 0xFFFFu;
if (special_bits != 0)
{
const auto k = static_cast<unsigned>(count_trailing_zeros(static_cast<std::uint64_t>(special_bits)));
if ((err_bits & ((2u << k) - 1u)) == 0)
{
return block + k;
}
break;
}
if (err_bits != 0)
{
break;
}
prev = in;
block += 16;
}
#endif
return scan_string_finish(p, block, e, plain);
}
#endif
} // namespace view
} // namespace detail
NLOHMANN_JSON_NAMESPACE_END
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