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6
Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 Niels Lohmann
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3e031b06a5 |
Use standard library helpers where available, with C++11 fallbacks (#5876)
* Use standard library helpers where available, with C++11 fallbacks Add detail helpers that call the standard library function when the library provides it (checked with the __cpp_lib_* feature-test macros, so no new ABI-tag macros) and a C++11 implementation otherwise: - detail::clamp (std::clamp): by value, so that static constexpr members need no out-of-line definition before C++17; used in json_view's dump() buffer sizing, where step() can now be a static constexpr member. - detail::bit_cast (std::bit_cast): replaces dtoa_impl::reinterpret_bits and the memcpy bit copies in the number parser, to_chars, the json_view serializer, and binary_writer::to_char_type. - detail::byteswap (std::byteswap): one implementation instead of the binary writer's own byte_swap() overloads and the bswap chain in to_chars' store_msb_first(). - count_leading_zeros/count_trailing_zeros: two 32-bit _BitScanReverse/ _BitScanForward calls for MSVC x86/ARM32 instead of the loop, and std::countl_zero/countr_zero for compilers without builtins. - conjunction, disjunction, negation, bool_constant, and uncvref_t map to their std counterparts in C++17/C++20. Builtins and intrinsics stay ahead of the <bit> functions, as MSVC's std::countl_zero checks for LZCNT at run time unless AVX2 is enabled. The generated code is unchanged with Clang (C++11/20/23, arm64 and x86-64) and GCC 16 for parsing, dumping, and the binary formats. The binary reader keeps its own byte_swap() and the writer its memcpy calls: the smaller code from detail::byteswap/std::bit_cast there made GCC 16 inline get_number()/write_number() differently, which slowed reading by 10-18 % and writing by about 1 %. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Name the target byte order once (JSON_LITTLE_ENDIAN_TARGET, JSON_BIG_ENDIAN_TARGET) to_chars.hpp and bit_ops.hpp repeated the long __BYTE_ORDER__/_MSC_VER conditions; macro_scope.hpp now defines them once (undefined again in macro_unscope.hpp). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Explain why the serializer growth bound is not a clamp Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me> |
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Niels Lohmann
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91a7a94cc6 |
Write doubles with the shortest digits (Żmij), digits in registers (#5634)
* Write doubles with the shortest digits (Żmij), digits in registers Write doubles with the conversion of Zmij by Victor Zverovich (MIT), ported to C++11 (detail/conversions/zmij.hpp). It finds the shortest decimal that reads back as the same double, and the closest one if there are several. Grisu2, used until now, is fast but not always shortest: it sometimes writes a 17th digit where 16 suffice, or a last digit that is not the closest. The layout is unchanged (1.5, 100.0, 1e+100, -0.0); float keeps Grisu2. Digits are converted eight at a time with the BCD conversion of Xiang JunBo, as in Zmij, and written with one byte swap per eight digits and fixed-size moves instead of per-digit loops. Leading and trailing zeros are counted from those bytes. to_chars() uses a local buffer when the caller's is shorter than the 41 bytes this may write. The powers of ten come from the number-parsing table, adjusted where it holds values rounded up, and extended with Zmij's compressed tables beyond 10^308. write_shortest() converts its 16 digits in one vector register (SSE2 on x86-64, NEON on 64-bit Arm, both baseline) and inserts the decimal point inside the register, avoiding a store-forwarding stall that cost about 25% of the time to write a double. dump() writes floats and integers straight into the serializer's write buffer instead of copying them from a member buffer, and small integers eight digits at a time. read_eight_bytes() and parse_eight_digits() are marked always-inline, which GCC had been calling out of line in the number-parsing loops. Of one million random doubles, about 0.14% are now written with different digits, always to a value that still reads back as the same double. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Fix CI findings in the Zmij writer and its tests - bit_ops.hpp: include macro_scope.hpp (JSON_HEDLEY_ALWAYS_INLINE); fixes IWYU - to_chars.hpp: C4100 for the unused parameter in release builds, clang-tidy sign comparison, cpplint runtime/int, GCC -Wstrict-overflow (unsigned abs) - unit-to_chars.cpp: parse with the library instead of strtod (MinGW's strtod rounds some 16/17 digit inputs wrongly); no floating-point std::to_chars with icpc Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Select the Zmij conversion by a trait, not by the double overload The non-template overloads for double asserted binary64 doubles wherever json.hpp was included, so the library no longer compiled where double is not IEEE 754 binary64 (AVR, -fshort-double). A trait now picks Zmij for any binary64 type, including a long double of that format (MSVC, Apple Arm), and Grisu2 for the others. Remove the unused write_short_decimal, powers_of_ten_16, zmij::decimal, zmij::to_decimal, and shortest_digits(double). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Credit Zmij's authors in to_chars.hpp, the README, and the license page Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Silence MSVC C4127 for a platform-constant check in the to_chars test Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Regenerate the amalgamated headers Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me> |
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Niels Lohmann
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5b4c8f9b00 |
Speed up the lexer: own float parser, string scan, and \u table (#5738)
* Speed up the lexer: own float parser, string scan, and \u table Give the library its own correctly rounded float converter for binary32 and binary64 (IEEE 754), and speed up the lexer's string and escape scanning. The converter splits a number token into sign, significand, and decimal exponent, then tries Clinger's fast path, then a templated Eisel-Lemire step, and falls back to an exact big-integer digit comparison for tokens with more than 19 significant digits whose two candidate values round differently. This replaces std::from_chars and strtod/strtof for both formats, so parsed values no longer depend on the C/C++ library or the current locale. The strtold fallback kept for other long double formats (x87, binary128) now also copies a multi-byte decimal point correctly, fixing #5660. eisel_lemire() and decimal_to_float() are always inlined so callers keep the whole conversion in their hot loop. The string-scanning kernels in string_scan.hpp find a stop byte with the trailing-zero count of the SWAR mask instead of a byte loop, and scalar_string_bulk_run() validates a run of multi-byte UTF-8 sequences one after another instead of re-searching after each one. get_codepoint() decodes a contiguous \uXXXX escape with one table lookup per byte instead of four range-checked get() calls; the streaming path and all error positions are unchanged. Adds 508 generated hard float-parsing cases with expected binary32 and binary64 bits, and kernel-comparison tests for the string scans and the escape table against byte-by-byte references. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Fix CI warnings in own float parser - pow5_table.hpp: pow5_128_largest_power was unused in this branch's own code (GCC -Werror=unused-const-variable); tie it to the table size with a static_assert instead of removing it, since a later branch in the stack (json-view/23-zmij) uses it. - number_parse.hpp: rename the local variable `copy` to `buffer` to satisfy cpplint's build/include_what_you_use check. - unit-class_lexer.cpp: extend the NOLINT list on the seeded mt19937 with bugprone-random-generator-seed, and parenthesize `8 * sizeof(Bits) - 1` for clang-tidy. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Load string scan words with memcpy and use MSVC bit-scan intrinsics Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Reword float conversion notes for the string type and number_float_t docs Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Fix clang-tidy 22 findings in unit-class_lexer.cpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Mark the unsigned long of the MSVC bit scans for cpplint Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Regenerate the amalgamated headers Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Drop the position updates in the bulk \u path, which #5809 made unused Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Address review: std::any_of in has_nonzero_digit, comment punctuation Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Use data() instead of c_str() in the multi-byte decimal point path Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me> |
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Niels Lohmann
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aa9620fb15 |
Skip the indentation after a newline 8 bytes at a time (#5810)
Pretty-printed JSON indents every line with a run of spaces, which skip_whitespace() read one character at a time. For contiguous input (bulk_scan) the lexer now skips the spaces after a newline 8 bytes at a time directly in the input buffer, including the leading spaces of the last, partial word. This bypasses get(), which is safe because bulk_scan implies the lazy position from the previous commit: nothing is counted per character. Compared to lazy positions alone, pretty-printed input (twitter, citm_catalog with indent 2 and 4) parses up to 13% faster and accept() gets up to 30% faster (GCC 13 and clang 18 on x86-64, Apple clang 21 on arm64). Minified input is unchanged within noise. Signed-off-by: Niels Lohmann <mail@nlohmann.me> |
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 Suyog Verma
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a269794db7 |
Use MSVC intrinsics for full multiplication (#5782)
* Use MSVC intrinsics for full multiplication Signed-off-by: Suyog Verma <suyogverma0057@gmail.com> * Fix formatting in unit-class_lexer Signed-off-by: Suyog Verma <suyogverma0057@gmail.com> * Address review feedback Signed-off-by: Suyog Verma <suyogverma0057@gmail.com> --------- Signed-off-by: Suyog Verma <suyogverma0057@gmail.com> |
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Niels Lohmann
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d268eaa693 |
Convert floats with Eisel-Lemire when std::from_chars is unavailable (#5617)
* Convert floats with Eisel-Lemire when std::from_chars is unavailable Float tokens that Clinger's fast path cannot convert (e.g. the 17-digit coordinates of canada.json) went to strtod unless std::from_chars was available. It is not used in C++11/14, and not with libc++, which does not define __cpp_lib_to_chars. The Eisel-Lemire algorithm (after fast_float's compute_float) now converts them with integer arithmetic, correctly rounded for any token with at most 19 significant digits. Longer tokens are truncated; the result is used if w and w + 1 round alike, else strtod decides as before. Overflow still yields infinity (out_of_range.406). The table of powers of five (fast_float's) lives in pow5_table.hpp; a unit test recomputes every entry with big-integer arithmetic. Further tests: known values generated with Python (whose float() is correctly rounded), 200,000 round trips through to_chars, and the 128-bit multiplication and leading-zero count against big-integer references (both with and without a 128-bit type). Checked against strtod on 6.5 million tokens, among them 60,000 exact halfway cases: no difference. json::parse on canada.json: -8.6% (C++11), -7.6% (C++17, Apple clang); other files unchanged. Compile time of a TU including json.hpp: +0.7%. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Fix CI: unused parse result and find() == npos in the Eisel-Lemire tests GCC (-Werror=unused-result) rejected CHECK_THROWS_WITH_AS(json::parse(...)) because parse() is [[nodiscard]]; assign the result to a dummy json as the other tests do. clang-tidy flagged longer.find('.') == npos with abseil-string-find-str-contains; store the position in a variable first. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me> |