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adressing comments by @jwakely

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This commit is contained in:
Daniel Lemire 2026-06-06 13:13:49 -04:00
parent b72e07132c
commit 520fded4a3
2 changed files with 26 additions and 7 deletions
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26
include/fast_float/float_common.h
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@ -203,15 +203,27 @@ using parse_options = parse_options_t<char>;
// the hot frame and hurt ILP on some targets). Used at the call site as // the hot frame and hurt ILP on some targets). Used at the call site as
// if fastfloat_unlikely(cond) { ... } // if fastfloat_unlikely(cond) { ... }
// (the macro supplies the parentheses). It expands to the standard [[unlikely]] // (the macro supplies the parentheses). It expands to the standard [[unlikely]]
// attribute in C++20 or newer, otherwise to __builtin_expect on GCC/Clang, or // attribute when supported, otherwise to __builtin_expect on GCC/Clang, or
// to a no-op elsewhere (e.g. pre-C++20 MSVC, which has no equivalent hint). // to a no-op elsewhere (e.g. pre-C++20 MSVC, which has no equivalent hint).
// The [[unlikely]] branch is gated on the language version, not just on #ifdef __has_cpp_attribute
// __has_cpp_attribute: GCC and Clang report the attribute as available even #if __has_cpp_attribute(unlikely) >= 201803L
// under -std=c++17, where using it would trip -Wc++20-extensions/-Werror. #define FASTFLOAT_USE_UNLIKELY_ATTR 1
#if (__cplusplus >= 202002L || \ #endif
(defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)) && \ #endif
defined(__has_cpp_attribute) && __has_cpp_attribute(unlikely) >= 201803L
#ifdef FASTFLOAT_USE_UNLIKELY_ATTR
// We have to disable -Wc++20-extensions for the [[unlikely]] attribute
// See comment for @jwakely at
// https://github.com/fastfloat/fast_float/pull/387#discussion_r3366943539
// This is unfortunate.
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wc++20-extensions"
#endif
#define fastfloat_unlikely(x) (x) [[unlikely]] #define fastfloat_unlikely(x) (x) [[unlikely]]
#ifdef __clang__
#pragma clang diagnostic pop
#endif
#elif defined(__GNUC__) || defined(__clang__) #elif defined(__GNUC__) || defined(__clang__)
#define fastfloat_unlikely(x) (__builtin_expect(!!(x), 0)) #define fastfloat_unlikely(x) (__builtin_expect(!!(x), 0))
#else #else

7
include/fast_float/parse_number.h
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@ -351,6 +351,10 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
// Slow path A (rare): > 19 significant digits. The no-span parse left the // Slow path A (rare): > 19 significant digits. The no-span parse left the
// mantissa un-truncated and skipped the span-based recompute; the cold helper // mantissa un-truncated and skipped the span-based recompute; the cold helper
// re-parses with spans and runs the full algorithm. // re-parses with spans and runs the full algorithm.
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wc++20-extensions"
#endif
if fastfloat_unlikely (pns.too_many_digits) { if fastfloat_unlikely (pns.too_many_digits) {
return parse_number_slow_path<T, UC>(first, last, value, options, bjf); return parse_number_slow_path<T, UC>(first, last, value, options, bjf);
} }
@ -371,6 +375,9 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
if fastfloat_unlikely (am.power2 < 0) { if fastfloat_unlikely (am.power2 < 0) {
return parse_number_slow_path<T, UC>(first, last, value, options, bjf); return parse_number_slow_path<T, UC>(first, last, value, options, bjf);
} }
#ifdef __clang__
#pragma clang diagnostic pop
#endif
to_float(pns.negative, am, value); to_float(pns.negative, am, value);
// Test for over/underflow. // Test for over/underflow.
if ((pns.mantissa != 0 && am.mantissa == 0 && am.power2 == 0) || if ((pns.mantissa != 0 && am.mantissa == 0 && am.power2 == 0) ||