diff --git "a/miniMSVC/VC/Tools/MSVC/14.42.34433/include/xcharconv_ryu.h" "b/miniMSVC/VC/Tools/MSVC/14.42.34433/include/xcharconv_ryu.h" new file mode 100644--- /dev/null +++ "b/miniMSVC/VC/Tools/MSVC/14.42.34433/include/xcharconv_ryu.h" @@ -0,0 +1,2425 @@ +// xcharconv_ryu.h internal header + +// Copyright (c) Microsoft Corporation. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception + + +// Copyright 2018 Ulf Adams +// Copyright (c) Microsoft Corporation. All rights reserved. + +// Boost Software License - Version 1.0 - August 17th, 2003 + +// Permission is hereby granted, free of charge, to any person or organization +// obtaining a copy of the software and accompanying documentation covered by +// this license (the "Software") to use, reproduce, display, distribute, +// execute, and transmit the Software, and to prepare derivative works of the +// Software, and to permit third-parties to whom the Software is furnished to +// do so, all subject to the following: + +// The copyright notices in the Software and this entire statement, including +// the above license grant, this restriction and the following disclaimer, +// must be included in all copies of the Software, in whole or in part, and +// all derivative works of the Software, unless such copies or derivative +// works are solely in the form of machine-executable object code generated by +// a source language processor. + +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT +// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE +// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE, +// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER +// DEALINGS IN THE SOFTWARE. + + +#ifndef _XCHARCONV_RYU_H +#define _XCHARCONV_RYU_H +#include +#if _STL_COMPILER_PREPROCESSOR + +#if !_HAS_CXX17 +#error The contents of are only available with C++17. (Also, you should not include this internal header.) +#endif // !_HAS_CXX17 + +#include +#include +#include +#include +#include +#include + +#if defined(_M_X64) || defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) +#define _HAS_CHARCONV_INTRINSICS 1 +#else // ^^^ intrinsics available / intrinsics unavailable vvv +#define _HAS_CHARCONV_INTRINSICS 0 +#endif // ^^^ intrinsics unavailable ^^^ + +#if _HAS_CHARCONV_INTRINSICS +#if defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) +#include // TRANSITION, VSO-1918426 +#else // ^^^ defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) / defined(_M_X64) vvv +#include _STL_INTRIN_HEADER // for _umul128(), __umulh(), and __shiftright128() +#endif // ^^^ defined(_M_X64) ^^^ +#endif // ^^^ intrinsics available ^^^ + +#pragma pack(push, _CRT_PACKING) +#pragma warning(push, _STL_WARNING_LEVEL) +#pragma warning(disable : _STL_DISABLED_WARNINGS) +_STL_DISABLE_CLANG_WARNINGS +#pragma push_macro("new") +#undef new + +_STD_BEGIN + +// https://github.com/ulfjack/ryu/tree/59661c3/ryu +// (Keep the cgmanifest.json commitHash in sync.) + +// clang-format off + +// vvvvvvvvvv DERIVED FROM common.h vvvvvvvvvv + +_NODISCARD inline uint32_t __decimalLength9(const uint32_t __v) { + // Function precondition: __v is not a 10-digit number. + // (f2s: 9 digits are sufficient for round-tripping.) + // (d2fixed: We print 9-digit blocks.) + _STL_INTERNAL_CHECK(__v < 1000000000); + if (__v >= 100000000) { return 9; } + if (__v >= 10000000) { return 8; } + if (__v >= 1000000) { return 7; } + if (__v >= 100000) { return 6; } + if (__v >= 10000) { return 5; } + if (__v >= 1000) { return 4; } + if (__v >= 100) { return 3; } + if (__v >= 10) { return 2; } + return 1; +} + +// Returns __e == 0 ? 1 : ceil(log_2(5^__e)). +_NODISCARD inline int32_t __pow5bits(const int32_t __e) { + // This approximation works up to the point that the multiplication overflows at __e = 3529. + // If the multiplication were done in 64 bits, it would fail at 5^4004 which is just greater + // than 2^9297. + _STL_INTERNAL_CHECK(__e >= 0); + _STL_INTERNAL_CHECK(__e <= 3528); + return static_cast(((static_cast(__e) * 1217359) >> 19) + 1); +} + +// Returns floor(log_10(2^__e)). +_NODISCARD inline uint32_t __log10Pow2(const int32_t __e) { + // The first value this approximation fails for is 2^1651 which is just greater than 10^297. + _STL_INTERNAL_CHECK(__e >= 0); + _STL_INTERNAL_CHECK(__e <= 1650); + return (static_cast(__e) * 78913) >> 18; +} + +// Returns floor(log_10(5^__e)). +_NODISCARD inline uint32_t __log10Pow5(const int32_t __e) { + // The first value this approximation fails for is 5^2621 which is just greater than 10^1832. + _STL_INTERNAL_CHECK(__e >= 0); + _STL_INTERNAL_CHECK(__e <= 2620); + return (static_cast(__e) * 732923) >> 20; +} + +_NODISCARD inline uint32_t __float_to_bits(const float __f) { + uint32_t __bits = 0; + _CSTD memcpy(&__bits, &__f, sizeof(float)); + return __bits; +} + +_NODISCARD inline uint64_t __double_to_bits(const double __d) { + uint64_t __bits = 0; + _CSTD memcpy(&__bits, &__d, sizeof(double)); + return __bits; +} + +// ^^^^^^^^^^ DERIVED FROM common.h ^^^^^^^^^^ + +// vvvvvvvvvv DERIVED FROM d2s.h vvvvvvvvvv + +inline constexpr int __DOUBLE_MANTISSA_BITS = 52; +inline constexpr int __DOUBLE_BIAS = 1023; + +inline constexpr int __DOUBLE_POW5_INV_BITCOUNT = 122; +inline constexpr int __DOUBLE_POW5_BITCOUNT = 121; + +// ^^^^^^^^^^ DERIVED FROM d2s.h ^^^^^^^^^^ + +// vvvvvvvvvv DERIVED FROM d2s_intrinsics.h vvvvvvvvvv + +#if _HAS_CHARCONV_INTRINSICS + +_NODISCARD inline uint64_t __ryu_umul128(const uint64_t __a, const uint64_t __b, uint64_t* const __productHi) { +#if defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) + *__productHi = __umulh(__a, __b); + return __a * __b; +#else // ^^^ not native X64 / native X64 vvv + return _umul128(__a, __b, __productHi); +#endif // defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) +} + +#else // ^^^ intrinsics available / intrinsics unavailable vvv + +_NODISCARD __forceinline uint64_t __ryu_umul128(const uint64_t __a, const uint64_t __b, uint64_t* const __productHi) { + // TRANSITION, VSO-634761 + // The casts here help MSVC to avoid calls to the __allmul library function. + const uint32_t __aLo = static_cast(__a); + const uint32_t __aHi = static_cast(__a >> 32); + const uint32_t __bLo = static_cast(__b); + const uint32_t __bHi = static_cast(__b >> 32); + + const uint64_t __b00 = static_cast(__aLo) * __bLo; + const uint64_t __b01 = static_cast(__aLo) * __bHi; + const uint64_t __b10 = static_cast(__aHi) * __bLo; + const uint64_t __b11 = static_cast(__aHi) * __bHi; + + const uint32_t __b00Lo = static_cast(__b00); + const uint32_t __b00Hi = static_cast(__b00 >> 32); + + const uint64_t __mid1 = __b10 + __b00Hi; + const uint32_t __mid1Lo = static_cast(__mid1); + const uint32_t __mid1Hi = static_cast(__mid1 >> 32); + + const uint64_t __mid2 = __b01 + __mid1Lo; + const uint32_t __mid2Lo = static_cast(__mid2); + const uint32_t __mid2Hi = static_cast(__mid2 >> 32); + + const uint64_t __pHi = __b11 + __mid1Hi + __mid2Hi; + const uint64_t __pLo = (static_cast(__mid2Lo) << 32) | __b00Lo; + + *__productHi = __pHi; + return __pLo; +} + +#endif // ^^^ intrinsics unavailable ^^^ + +_NODISCARD inline uint64_t __ryu_shiftright128(const uint64_t __lo, const uint64_t __hi, const uint32_t __dist) { + // In the current implementation, the shift value is always < 64. + // If larger shift values are ever required, this function will need to be adjusted. + _STL_INTERNAL_CHECK(__dist < 64); + +#if defined(_M_X64) && !defined(_M_ARM64EC) + return __shiftright128(__lo, __hi, static_cast(__dist)); +#else // ^^^ __shiftright128 intrinsic available / __shiftright128 intrinsic unavailable vvv + if (__dist == 0) { + return __lo; + } + + return (__hi << (64 - __dist)) | (__lo >> __dist); +#endif // ^^^ __shiftright128 intrinsic unavailable ^^^ +} + + +#ifndef _WIN64 + +#if !defined(_M_HYBRID_X86_ARM64) +// Returns the high 64 bits of the 128-bit product of __a and __b. +_NODISCARD inline uint64_t __umulh(const uint64_t __a, const uint64_t __b) { + // Reuse the __ryu_umul128 implementation. + // Optimizers will likely eliminate the instructions used to compute the + // low part of the product. + uint64_t __hi; + (void) __ryu_umul128(__a, __b, &__hi); + return __hi; +} +#endif // ^^^ !defined(_M_HYBRID_X86_ARM64) ^^^ + +// On 32-bit platforms, compilers typically generate calls to library +// functions for 64-bit divisions, even if the divisor is a constant. +// +// TRANSITION, LLVM-37932 +// +// The functions here perform division-by-constant using multiplications +// in the same way as 64-bit compilers would do. +// +// NB: +// The multipliers and shift values are the ones generated by clang x64 +// for expressions like x/5, x/10, etc. + +_NODISCARD inline uint64_t __div5(const uint64_t __x) { + return __umulh(__x, 0xCCCCCCCCCCCCCCCDu) >> 2; +} + +_NODISCARD inline uint64_t __div10(const uint64_t __x) { + return __umulh(__x, 0xCCCCCCCCCCCCCCCDu) >> 3; +} + +_NODISCARD inline uint64_t __div100(const uint64_t __x) { + return __umulh(__x >> 2, 0x28F5C28F5C28F5C3u) >> 2; +} + +_NODISCARD inline uint64_t __div1e8(const uint64_t __x) { + return __umulh(__x, 0xABCC77118461CEFDu) >> 26; +} + +_NODISCARD inline uint64_t __div1e9(const uint64_t __x) { + return __umulh(__x >> 9, 0x44B82FA09B5A53u) >> 11; +} + +_NODISCARD inline uint32_t __mod1e9(const uint64_t __x) { + // Avoid 64-bit math as much as possible. + // Returning static_cast(__x - 1000000000 * __div1e9(__x)) would + // perform 32x64-bit multiplication and 64-bit subtraction. + // __x and 1000000000 * __div1e9(__x) are guaranteed to differ by + // less than 10^9, so their highest 32 bits must be identical, + // so we can truncate both sides to uint32_t before subtracting. + // We can also simplify static_cast(1000000000 * __div1e9(__x)). + // We can truncate before multiplying instead of after, as multiplying + // the highest 32 bits of __div1e9(__x) can't affect the lowest 32 bits. + return static_cast(__x) - 1000000000 * static_cast(__div1e9(__x)); +} + +#else // ^^^ 32-bit / 64-bit vvv + +_NODISCARD inline uint64_t __div5(const uint64_t __x) { + return __x / 5; +} + +_NODISCARD inline uint64_t __div10(const uint64_t __x) { + return __x / 10; +} + +_NODISCARD inline uint64_t __div100(const uint64_t __x) { + return __x / 100; +} + +_NODISCARD inline uint64_t __div1e8(const uint64_t __x) { + return __x / 100000000; +} + +_NODISCARD inline uint64_t __div1e9(const uint64_t __x) { + return __x / 1000000000; +} + +_NODISCARD inline uint32_t __mod1e9(const uint64_t __x) { + return static_cast(__x - 1000000000 * __div1e9(__x)); +} + +#endif // ^^^ 64-bit ^^^ + +_NODISCARD inline uint32_t __pow5Factor(uint64_t __value) { + uint32_t __count = 0; + for (;;) { + _STL_INTERNAL_CHECK(__value != 0); + const uint64_t __q = __div5(__value); + const uint32_t __r = static_cast(__value) - 5 * static_cast(__q); + if (__r != 0) { + break; + } + __value = __q; + ++__count; + } + return __count; +} + +// Returns true if __value is divisible by 5^__p. +_NODISCARD inline bool __multipleOfPowerOf5(const uint64_t __value, const uint32_t __p) { + // I tried a case distinction on __p, but there was no performance difference. + return __pow5Factor(__value) >= __p; +} + +// Returns true if __value is divisible by 2^__p. +_NODISCARD inline bool __multipleOfPowerOf2(const uint64_t __value, const uint32_t __p) { + _STL_INTERNAL_CHECK(__value != 0); + _STL_INTERNAL_CHECK(__p < 64); + // return __builtin_ctzll(__value) >= __p; + return (__value & ((1ull << __p) - 1)) == 0; +} + +// ^^^^^^^^^^ DERIVED FROM d2s_intrinsics.h ^^^^^^^^^^ + +// vvvvvvvvvv DERIVED FROM d2fixed.c vvvvvvvvvv + +inline constexpr int __POW10_ADDITIONAL_BITS = 120; + +#if _HAS_CHARCONV_INTRINSICS +// Returns the low 64 bits of the high 128 bits of the 256-bit product of a and b. +_NODISCARD inline uint64_t __umul256_hi128_lo64( + const uint64_t __aHi, const uint64_t __aLo, const uint64_t __bHi, const uint64_t __bLo) { + uint64_t __b00Hi; + const uint64_t __b00Lo = __ryu_umul128(__aLo, __bLo, &__b00Hi); + uint64_t __b01Hi; + const uint64_t __b01Lo = __ryu_umul128(__aLo, __bHi, &__b01Hi); + uint64_t __b10Hi; + const uint64_t __b10Lo = __ryu_umul128(__aHi, __bLo, &__b10Hi); + uint64_t __b11Hi; + const uint64_t __b11Lo = __ryu_umul128(__aHi, __bHi, &__b11Hi); + (void) __b00Lo; // unused + (void) __b11Hi; // unused + const uint64_t __temp1Lo = __b10Lo + __b00Hi; + const uint64_t __temp1Hi = __b10Hi + (__temp1Lo < __b10Lo); + const uint64_t __temp2Lo = __b01Lo + __temp1Lo; + const uint64_t __temp2Hi = __b01Hi + (__temp2Lo < __b01Lo); + return __b11Lo + __temp1Hi + __temp2Hi; +} + +_NODISCARD inline uint32_t __uint128_mod1e9(const uint64_t __vHi, const uint64_t __vLo) { + // After multiplying, we're going to shift right by 29, then truncate to uint32_t. + // This means that we need only 29 + 32 = 61 bits, so we can truncate to uint64_t before shifting. + const uint64_t __multiplied = __umul256_hi128_lo64(__vHi, __vLo, 0x89705F4136B4A597u, 0x31680A88F8953031u); + + // For uint32_t truncation, see the __mod1e9() comment in d2s_intrinsics.h. + const uint32_t __shifted = static_cast(__multiplied >> 29); + + return static_cast(__vLo) - 1000000000 * __shifted; +} +#endif // ^^^ intrinsics available ^^^ + +_NODISCARD inline uint32_t __mulShift_mod1e9(const uint64_t __m, const uint64_t* const __mul, const int32_t __j) { + uint64_t __high0; // 64 + const uint64_t __low0 = __ryu_umul128(__m, __mul[0], &__high0); // 0 + uint64_t __high1; // 128 + const uint64_t __low1 = __ryu_umul128(__m, __mul[1], &__high1); // 64 + uint64_t __high2; // 192 + const uint64_t __low2 = __ryu_umul128(__m, __mul[2], &__high2); // 128 + const uint64_t __s0low = __low0; // 0 + (void) __s0low; // unused + const uint64_t __s0high = __low1 + __high0; // 64 + const uint32_t __c1 = __s0high < __low1; + const uint64_t __s1low = __low2 + __high1 + __c1; // 128 + const uint32_t __c2 = __s1low < __low2; // __high1 + __c1 can't overflow, so compare against __low2 + const uint64_t __s1high = __high2 + __c2; // 192 + _STL_INTERNAL_CHECK(__j >= 128); + _STL_INTERNAL_CHECK(__j <= 180); +#if _HAS_CHARCONV_INTRINSICS + const uint32_t __dist = static_cast(__j - 128); // __dist: [0, 52] + const uint64_t __shiftedhigh = __s1high >> __dist; + const uint64_t __shiftedlow = __ryu_shiftright128(__s1low, __s1high, __dist); + return __uint128_mod1e9(__shiftedhigh, __shiftedlow); +#else // ^^^ intrinsics available / intrinsics unavailable vvv + if (__j < 160) { // __j: [128, 160) + const uint64_t __r0 = __mod1e9(__s1high); + const uint64_t __r1 = __mod1e9((__r0 << 32) | (__s1low >> 32)); + const uint64_t __r2 = ((__r1 << 32) | (__s1low & 0xffffffff)); + return __mod1e9(__r2 >> (__j - 128)); + } else { // __j: [160, 192) + const uint64_t __r0 = __mod1e9(__s1high); + const uint64_t __r1 = ((__r0 << 32) | (__s1low >> 32)); + return __mod1e9(__r1 >> (__j - 160)); + } +#endif // ^^^ intrinsics unavailable ^^^ +} + +#define _WIDEN(_TYPE, _CHAR) static_cast<_TYPE>(is_same_v<_TYPE, char> ? _CHAR : L##_CHAR) + +template +void __append_n_digits(const uint32_t __olength, uint32_t __digits, _CharT* const __result) { + uint32_t __i = 0; + while (__digits >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = __digits - 10000 * (__digits / 10000); +#else + const uint32_t __c = __digits % 10000; +#endif + __digits /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(__result + __olength - __i - 2, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 4, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + __i += 4; + } + if (__digits >= 100) { + const uint32_t __c = (__digits % 100) << 1; + __digits /= 100; + _CSTD memcpy(__result + __olength - __i - 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + __i += 2; + } + if (__digits >= 10) { + const uint32_t __c = __digits << 1; + _CSTD memcpy(__result + __olength - __i - 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } else { + __result[0] = static_cast<_CharT>(_WIDEN(_CharT, '0') + __digits); + } +} + +inline void __append_d_digits(const uint32_t __olength, uint32_t __digits, char* const __result) { + uint32_t __i = 0; + while (__digits >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = __digits - 10000 * (__digits / 10000); +#else + const uint32_t __c = __digits % 10000; +#endif + __digits /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(__result + __olength + 1 - __i - 2, __DIGIT_TABLE + __c0, 2); + _CSTD memcpy(__result + __olength + 1 - __i - 4, __DIGIT_TABLE + __c1, 2); + __i += 4; + } + if (__digits >= 100) { + const uint32_t __c = (__digits % 100) << 1; + __digits /= 100; + _CSTD memcpy(__result + __olength + 1 - __i - 2, __DIGIT_TABLE + __c, 2); + __i += 2; + } + if (__digits >= 10) { + const uint32_t __c = __digits << 1; + __result[2] = __DIGIT_TABLE[__c + 1]; + __result[1] = '.'; + __result[0] = __DIGIT_TABLE[__c]; + } else { + __result[1] = '.'; + __result[0] = static_cast('0' + __digits); + } +} + +template +void __append_c_digits(const uint32_t __count, uint32_t __digits, _CharT* const __result) { + uint32_t __i = 0; + for (; __i < __count - 1; __i += 2) { + const uint32_t __c = (__digits % 100) << 1; + __digits /= 100; + _CSTD memcpy(__result + __count - __i - 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } + if (__i < __count) { + const _CharT __c = static_cast<_CharT>(_WIDEN(_CharT, '0') + (__digits % 10)); + __result[__count - __i - 1] = __c; + } +} + +template +void __append_nine_digits(uint32_t __digits, _CharT* const __result) { + if (__digits == 0) { + _STD fill_n(__result, 9, _WIDEN(_CharT, '0')); + return; + } + + for (uint32_t __i = 0; __i < 5; __i += 4) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = __digits - 10000 * (__digits / 10000); +#else + const uint32_t __c = __digits % 10000; +#endif + __digits /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(__result + 7 - __i, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + 5 - __i, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + } + __result[0] = static_cast<_CharT>(_WIDEN(_CharT, '0') + __digits); +} + +_NODISCARD inline uint32_t __indexForExponent(const uint32_t __e) { + return (__e + 15) / 16; +} + +_NODISCARD inline uint32_t __pow10BitsForIndex(const uint32_t __idx) { + return 16 * __idx + __POW10_ADDITIONAL_BITS; +} + +_NODISCARD inline uint32_t __lengthForIndex(const uint32_t __idx) { + // +1 for ceil, +16 for mantissa, +8 to round up when dividing by 9 + return (__log10Pow2(16 * static_cast(__idx)) + 1 + 16 + 8) / 9; +} + +template +_NODISCARD pair<_CharT*, errc> __d2fixed_buffered_n(_CharT* _First, _CharT* const _Last, const double __d, + const uint32_t __precision) { + _CharT* const _Original_first = _First; + + const uint64_t __bits = __double_to_bits(__d); + + // Case distinction; exit early for the easy cases. + if (__bits == 0) { + const int32_t _Total_zero_length = 1 // leading zero + + static_cast(__precision != 0) // possible decimal point + + static_cast(__precision); // zeroes after decimal point + + if (_Last - _First < _Total_zero_length) { + return { _Last, errc::value_too_large }; + } + + *_First++ = _WIDEN(_CharT, '0'); + if (__precision > 0) { + *_First++ = _WIDEN(_CharT, '.'); + _STD fill_n(_First, __precision, _WIDEN(_CharT, '0')); + _First += __precision; + } + return { _First, errc{} }; + } + + // Decode __bits into mantissa and exponent. + const uint64_t __ieeeMantissa = __bits & ((1ull << __DOUBLE_MANTISSA_BITS) - 1); + const uint32_t __ieeeExponent = static_cast(__bits >> __DOUBLE_MANTISSA_BITS); + + int32_t __e2; + uint64_t __m2; + if (__ieeeExponent == 0) { + __e2 = 1 - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; + __m2 = __ieeeMantissa; + } else { + __e2 = static_cast(__ieeeExponent) - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; + __m2 = (1ull << __DOUBLE_MANTISSA_BITS) | __ieeeMantissa; + } + + bool __nonzero = false; + if (__e2 >= -52) { + const uint32_t __idx = __e2 < 0 ? 0 : __indexForExponent(static_cast(__e2)); + const uint32_t __p10bits = __pow10BitsForIndex(__idx); + const int32_t __len = static_cast(__lengthForIndex(__idx)); + for (int32_t __i = __len - 1; __i >= 0; --__i) { + const uint32_t __j = __p10bits - __e2; + // Temporary: __j is usually around 128, and by shifting a bit, we push it to 128 or above, which is + // a slightly faster code path in __mulShift_mod1e9. Instead, we can just increase the multipliers. + const uint32_t __digits = __mulShift_mod1e9(__m2 << 8, __POW10_SPLIT[__POW10_OFFSET[__idx] + __i], + static_cast(__j + 8)); + if (__nonzero) { + if (_Last - _First < 9) { + return { _Last, errc::value_too_large }; + } + __append_nine_digits(__digits, _First); + _First += 9; + } else if (__digits != 0) { + const uint32_t __olength = __decimalLength9(__digits); + if (_Last - _First < static_cast(__olength)) { + return { _Last, errc::value_too_large }; + } + __append_n_digits(__olength, __digits, _First); + _First += __olength; + __nonzero = true; + } + } + } + if (!__nonzero) { + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = _WIDEN(_CharT, '0'); + } + if (__precision > 0) { + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = _WIDEN(_CharT, '.'); + } + if (__e2 < 0) { + const int32_t __idx = -__e2 / 16; + const uint32_t __blocks = __precision / 9 + 1; + // 0 = don't round up; 1 = round up unconditionally; 2 = round up if odd. + int __roundUp = 0; + uint32_t __i = 0; + if (__blocks <= __MIN_BLOCK_2[__idx]) { + __i = __blocks; + if (_Last - _First < static_cast(__precision)) { + return { _Last, errc::value_too_large }; + } + _STD fill_n(_First, __precision, _WIDEN(_CharT, '0')); + _First += __precision; + } else if (__i < __MIN_BLOCK_2[__idx]) { + __i = __MIN_BLOCK_2[__idx]; + if (_Last - _First < static_cast(9 * __i)) { + return { _Last, errc::value_too_large }; + } + _STD fill_n(_First, 9 * __i, _WIDEN(_CharT, '0')); + _First += 9 * __i; + } + for (; __i < __blocks; ++__i) { + const int32_t __j = __ADDITIONAL_BITS_2 + (-__e2 - 16 * __idx); + const uint32_t __p = __POW10_OFFSET_2[__idx] + __i - __MIN_BLOCK_2[__idx]; + if (__p >= __POW10_OFFSET_2[__idx + 1]) { + // If the remaining digits are all 0, then we might as well use memset. + // No rounding required in this case. + const uint32_t __fill = __precision - 9 * __i; + if (_Last - _First < static_cast(__fill)) { + return { _Last, errc::value_too_large }; + } + _STD fill_n(_First, __fill, _WIDEN(_CharT, '0')); + _First += __fill; + break; + } + // Temporary: __j is usually around 128, and by shifting a bit, we push it to 128 or above, which is + // a slightly faster code path in __mulShift_mod1e9. Instead, we can just increase the multipliers. + uint32_t __digits = __mulShift_mod1e9(__m2 << 8, __POW10_SPLIT_2[__p], __j + 8); + if (__i < __blocks - 1) { + if (_Last - _First < 9) { + return { _Last, errc::value_too_large }; + } + __append_nine_digits(__digits, _First); + _First += 9; + } else { + const uint32_t __maximum = __precision - 9 * __i; + uint32_t __lastDigit = 0; + for (uint32_t __k = 0; __k < 9 - __maximum; ++__k) { + __lastDigit = __digits % 10; + __digits /= 10; + } + if (__lastDigit != 5) { + __roundUp = __lastDigit > 5; + } else { + // Is m * 10^(additionalDigits + 1) / 2^(-__e2) integer? + const int32_t __requiredTwos = -__e2 - static_cast(__precision) - 1; + const bool __trailingZeros = __requiredTwos <= 0 + || (__requiredTwos < 60 && __multipleOfPowerOf2(__m2, static_cast(__requiredTwos))); + __roundUp = __trailingZeros ? 2 : 1; + } + if (__maximum > 0) { + if (_Last - _First < static_cast(__maximum)) { + return { _Last, errc::value_too_large }; + } + __append_c_digits(__maximum, __digits, _First); + _First += __maximum; + } + break; + } + } + if (__roundUp != 0) { + _CharT* _Round = _First; + _CharT* _Dot = _Last; + while (true) { + if (_Round == _Original_first) { + _Round[0] = _WIDEN(_CharT, '1'); + if (_Dot != _Last) { + _Dot[0] = _WIDEN(_CharT, '0'); + _Dot[1] = _WIDEN(_CharT, '.'); + } + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = _WIDEN(_CharT, '0'); + break; + } + --_Round; + const _CharT __c = _Round[0]; + if (__c == _WIDEN(_CharT, '.')) { + _Dot = _Round; + } else if (__c == _WIDEN(_CharT, '9')) { + _Round[0] = _WIDEN(_CharT, '0'); + __roundUp = 1; + } else { + if (__roundUp == 1 || __c % 2 != 0) { + _Round[0] = static_cast<_CharT>(__c + 1); + } + break; + } + } + } + } else { + if (_Last - _First < static_cast(__precision)) { + return { _Last, errc::value_too_large }; + } + _STD fill_n(_First, __precision, _WIDEN(_CharT, '0')); + _First += __precision; + } + return { _First, errc{} }; +} + +_NODISCARD inline to_chars_result __d2exp_buffered_n(char* _First, char* const _Last, const double __d, + uint32_t __precision) { + char* const _Original_first = _First; + + const uint64_t __bits = __double_to_bits(__d); + + // Case distinction; exit early for the easy cases. + if (__bits == 0) { + const int32_t _Total_zero_length = 1 // leading zero + + static_cast(__precision != 0) // possible decimal point + + static_cast(__precision) // zeroes after decimal point + + 4; // "e+00" + if (_Last - _First < _Total_zero_length) { + return { _Last, errc::value_too_large }; + } + *_First++ = '0'; + if (__precision > 0) { + *_First++ = '.'; + _CSTD memset(_First, '0', __precision); + _First += __precision; + } + _CSTD memcpy(_First, "e+00", 4); + _First += 4; + return { _First, errc{} }; + } + + // Decode __bits into mantissa and exponent. + const uint64_t __ieeeMantissa = __bits & ((1ull << __DOUBLE_MANTISSA_BITS) - 1); + const uint32_t __ieeeExponent = static_cast(__bits >> __DOUBLE_MANTISSA_BITS); + + int32_t __e2; + uint64_t __m2; + if (__ieeeExponent == 0) { + __e2 = 1 - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; + __m2 = __ieeeMantissa; + } else { + __e2 = static_cast(__ieeeExponent) - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; + __m2 = (1ull << __DOUBLE_MANTISSA_BITS) | __ieeeMantissa; + } + + const bool __printDecimalPoint = __precision > 0; + ++__precision; + uint32_t __digits = 0; + uint32_t __printedDigits = 0; + uint32_t __availableDigits = 0; + int32_t __exp = 0; + if (__e2 >= -52) { + const uint32_t __idx = __e2 < 0 ? 0 : __indexForExponent(static_cast(__e2)); + const uint32_t __p10bits = __pow10BitsForIndex(__idx); + const int32_t __len = static_cast(__lengthForIndex(__idx)); + for (int32_t __i = __len - 1; __i >= 0; --__i) { + const uint32_t __j = __p10bits - __e2; + // Temporary: __j is usually around 128, and by shifting a bit, we push it to 128 or above, which is + // a slightly faster code path in __mulShift_mod1e9. Instead, we can just increase the multipliers. + __digits = __mulShift_mod1e9(__m2 << 8, __POW10_SPLIT[__POW10_OFFSET[__idx] + __i], + static_cast(__j + 8)); + if (__printedDigits != 0) { + if (__printedDigits + 9 > __precision) { + __availableDigits = 9; + break; + } + if (_Last - _First < 9) { + return { _Last, errc::value_too_large }; + } + __append_nine_digits(__digits, _First); + _First += 9; + __printedDigits += 9; + } else if (__digits != 0) { + __availableDigits = __decimalLength9(__digits); + __exp = __i * 9 + static_cast(__availableDigits) - 1; + if (__availableDigits > __precision) { + break; + } + if (__printDecimalPoint) { + if (_Last - _First < static_cast(__availableDigits + 1)) { + return { _Last, errc::value_too_large }; + } + __append_d_digits(__availableDigits, __digits, _First); + _First += __availableDigits + 1; // +1 for decimal point + } else { + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = static_cast('0' + __digits); + } + __printedDigits = __availableDigits; + __availableDigits = 0; + } + } + } + + if (__e2 < 0 && __availableDigits == 0) { + const int32_t __idx = -__e2 / 16; + for (int32_t __i = __MIN_BLOCK_2[__idx]; __i < 200; ++__i) { + const int32_t __j = __ADDITIONAL_BITS_2 + (-__e2 - 16 * __idx); + const uint32_t __p = __POW10_OFFSET_2[__idx] + static_cast(__i) - __MIN_BLOCK_2[__idx]; + // Temporary: __j is usually around 128, and by shifting a bit, we push it to 128 or above, which is + // a slightly faster code path in __mulShift_mod1e9. Instead, we can just increase the multipliers. + __digits = (__p >= __POW10_OFFSET_2[__idx + 1]) ? 0 : __mulShift_mod1e9(__m2 << 8, __POW10_SPLIT_2[__p], __j + 8); + if (__printedDigits != 0) { + if (__printedDigits + 9 > __precision) { + __availableDigits = 9; + break; + } + if (_Last - _First < 9) { + return { _Last, errc::value_too_large }; + } + __append_nine_digits(__digits, _First); + _First += 9; + __printedDigits += 9; + } else if (__digits != 0) { + __availableDigits = __decimalLength9(__digits); + __exp = -(__i + 1) * 9 + static_cast(__availableDigits) - 1; + if (__availableDigits > __precision) { + break; + } + if (__printDecimalPoint) { + if (_Last - _First < static_cast(__availableDigits + 1)) { + return { _Last, errc::value_too_large }; + } + __append_d_digits(__availableDigits, __digits, _First); + _First += __availableDigits + 1; // +1 for decimal point + } else { + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = static_cast('0' + __digits); + } + __printedDigits = __availableDigits; + __availableDigits = 0; + } + } + } + + const uint32_t __maximum = __precision - __printedDigits; + if (__availableDigits == 0) { + __digits = 0; + } + uint32_t __lastDigit = 0; + if (__availableDigits > __maximum) { + for (uint32_t __k = 0; __k < __availableDigits - __maximum; ++__k) { + __lastDigit = __digits % 10; + __digits /= 10; + } + } + // 0 = don't round up; 1 = round up unconditionally; 2 = round up if odd. + int __roundUp = 0; + if (__lastDigit != 5) { + __roundUp = __lastDigit > 5; + } else { + // Is m * 2^__e2 * 10^(__precision + 1 - __exp) integer? + // __precision was already increased by 1, so we don't need to write + 1 here. + const int32_t __rexp = static_cast(__precision) - __exp; + const int32_t __requiredTwos = -__e2 - __rexp; + bool __trailingZeros = __requiredTwos <= 0 + || (__requiredTwos < 60 && __multipleOfPowerOf2(__m2, static_cast(__requiredTwos))); + if (__rexp < 0) { + const int32_t __requiredFives = -__rexp; + __trailingZeros = __trailingZeros && __multipleOfPowerOf5(__m2, static_cast(__requiredFives)); + } + __roundUp = __trailingZeros ? 2 : 1; + } + if (__printedDigits != 0) { + if (_Last - _First < static_cast(__maximum)) { + return { _Last, errc::value_too_large }; + } + if (__digits == 0) { + _CSTD memset(_First, '0', __maximum); + } else { + __append_c_digits(__maximum, __digits, _First); + } + _First += __maximum; + } else { + if (__printDecimalPoint) { + if (_Last - _First < static_cast(__maximum + 1)) { + return { _Last, errc::value_too_large }; + } + __append_d_digits(__maximum, __digits, _First); + _First += __maximum + 1; // +1 for decimal point + } else { + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + *_First++ = static_cast('0' + __digits); + } + } + if (__roundUp != 0) { + char* _Round = _First; + while (true) { + if (_Round == _Original_first) { + _Round[0] = '1'; + ++__exp; + break; + } + --_Round; + const char __c = _Round[0]; + if (__c == '.') { + // Keep going. + } else if (__c == '9') { + _Round[0] = '0'; + __roundUp = 1; + } else { + if (__roundUp == 1 || __c % 2 != 0) { + _Round[0] = static_cast(__c + 1); + } + break; + } + } + } + + char _Sign_character; + + if (__exp < 0) { + _Sign_character = '-'; + __exp = -__exp; + } else { + _Sign_character = '+'; + } + + const int _Exponent_part_length = __exp >= 100 + ? 5 // "e+NNN" + : 4; // "e+NN" + + if (_Last - _First < _Exponent_part_length) { + return { _Last, errc::value_too_large }; + } + + *_First++ = 'e'; + *_First++ = _Sign_character; + + if (__exp >= 100) { + const int32_t __c = __exp % 10; + _CSTD memcpy(_First, __DIGIT_TABLE + 2 * (__exp / 10), 2); + _First[2] = static_cast('0' + __c); + _First += 3; + } else { + _CSTD memcpy(_First, __DIGIT_TABLE + 2 * __exp, 2); + _First += 2; + } + + return { _First, errc{} }; +} + +// ^^^^^^^^^^ DERIVED FROM d2fixed.c ^^^^^^^^^^ + +// vvvvvvvvvv DERIVED FROM f2s.c vvvvvvvvvv + +inline constexpr int __FLOAT_MANTISSA_BITS = 23; +inline constexpr int __FLOAT_BIAS = 127; + +// This table is generated by PrintFloatLookupTable. +inline constexpr int __FLOAT_POW5_INV_BITCOUNT = 59; +inline constexpr uint64_t __FLOAT_POW5_INV_SPLIT[31] = { + 576460752303423489u, 461168601842738791u, 368934881474191033u, 295147905179352826u, + 472236648286964522u, 377789318629571618u, 302231454903657294u, 483570327845851670u, + 386856262276681336u, 309485009821345069u, 495176015714152110u, 396140812571321688u, + 316912650057057351u, 507060240091291761u, 405648192073033409u, 324518553658426727u, + 519229685853482763u, 415383748682786211u, 332306998946228969u, 531691198313966350u, + 425352958651173080u, 340282366920938464u, 544451787073501542u, 435561429658801234u, + 348449143727040987u, 557518629963265579u, 446014903970612463u, 356811923176489971u, + 570899077082383953u, 456719261665907162u, 365375409332725730u +}; +inline constexpr int __FLOAT_POW5_BITCOUNT = 61; +inline constexpr uint64_t __FLOAT_POW5_SPLIT[47] = { + 1152921504606846976u, 1441151880758558720u, 1801439850948198400u, 2251799813685248000u, + 1407374883553280000u, 1759218604441600000u, 2199023255552000000u, 1374389534720000000u, + 1717986918400000000u, 2147483648000000000u, 1342177280000000000u, 1677721600000000000u, + 2097152000000000000u, 1310720000000000000u, 1638400000000000000u, 2048000000000000000u, + 1280000000000000000u, 1600000000000000000u, 2000000000000000000u, 1250000000000000000u, + 1562500000000000000u, 1953125000000000000u, 1220703125000000000u, 1525878906250000000u, + 1907348632812500000u, 1192092895507812500u, 1490116119384765625u, 1862645149230957031u, + 1164153218269348144u, 1455191522836685180u, 1818989403545856475u, 2273736754432320594u, + 1421085471520200371u, 1776356839400250464u, 2220446049250313080u, 1387778780781445675u, + 1734723475976807094u, 2168404344971008868u, 1355252715606880542u, 1694065894508600678u, + 2117582368135750847u, 1323488980084844279u, 1654361225106055349u, 2067951531382569187u, + 1292469707114105741u, 1615587133892632177u, 2019483917365790221u +}; + +_NODISCARD inline uint32_t __pow5Factor(uint32_t __value) { + uint32_t __count = 0; + for (;;) { + _STL_INTERNAL_CHECK(__value != 0); + const uint32_t __q = __value / 5; + const uint32_t __r = __value % 5; + if (__r != 0) { + break; + } + __value = __q; + ++__count; + } + return __count; +} + +// Returns true if __value is divisible by 5^__p. +_NODISCARD inline bool __multipleOfPowerOf5(const uint32_t __value, const uint32_t __p) { + return __pow5Factor(__value) >= __p; +} + +// Returns true if __value is divisible by 2^__p. +_NODISCARD inline bool __multipleOfPowerOf2(const uint32_t __value, const uint32_t __p) { + _STL_INTERNAL_CHECK(__value != 0); + _STL_INTERNAL_CHECK(__p < 32); + // return __builtin_ctz(__value) >= __p; + return (__value & ((1u << __p) - 1)) == 0; +} + +_NODISCARD inline uint32_t __mulShift(const uint32_t __m, const uint64_t __factor, const int32_t __shift) { + _STL_INTERNAL_CHECK(__shift > 32); + + // The casts here help MSVC to avoid calls to the __allmul library + // function. + const uint32_t __factorLo = static_cast(__factor); + const uint32_t __factorHi = static_cast(__factor >> 32); + const uint64_t __bits0 = static_cast(__m) * __factorLo; + const uint64_t __bits1 = static_cast(__m) * __factorHi; + +#ifndef _WIN64 + // On 32-bit platforms we can avoid a 64-bit shift-right since we only + // need the upper 32 bits of the result and the shift value is > 32. + const uint32_t __bits0Hi = static_cast(__bits0 >> 32); + uint32_t __bits1Lo = static_cast(__bits1); + uint32_t __bits1Hi = static_cast(__bits1 >> 32); + __bits1Lo += __bits0Hi; + __bits1Hi += (__bits1Lo < __bits0Hi); + const int32_t __s = __shift - 32; + return (__bits1Hi << (32 - __s)) | (__bits1Lo >> __s); +#else // ^^^ 32-bit / 64-bit vvv + const uint64_t __sum = (__bits0 >> 32) + __bits1; + const uint64_t __shiftedSum = __sum >> (__shift - 32); + _STL_INTERNAL_CHECK(__shiftedSum <= UINT32_MAX); + return static_cast(__shiftedSum); +#endif // ^^^ 64-bit ^^^ +} + +_NODISCARD inline uint32_t __mulPow5InvDivPow2(const uint32_t __m, const uint32_t __q, const int32_t __j) { + return __mulShift(__m, __FLOAT_POW5_INV_SPLIT[__q], __j); +} + +_NODISCARD inline uint32_t __mulPow5divPow2(const uint32_t __m, const uint32_t __i, const int32_t __j) { + return __mulShift(__m, __FLOAT_POW5_SPLIT[__i], __j); +} + +// A floating decimal representing m * 10^e. +struct __floating_decimal_32 { + uint32_t __mantissa; + int32_t __exponent; +}; + +_NODISCARD inline __floating_decimal_32 __f2d(const uint32_t __ieeeMantissa, const uint32_t __ieeeExponent) { + int32_t __e2; + uint32_t __m2; + if (__ieeeExponent == 0) { + // We subtract 2 so that the bounds computation has 2 additional bits. + __e2 = 1 - __FLOAT_BIAS - __FLOAT_MANTISSA_BITS - 2; + __m2 = __ieeeMantissa; + } else { + __e2 = static_cast(__ieeeExponent) - __FLOAT_BIAS - __FLOAT_MANTISSA_BITS - 2; + __m2 = (1u << __FLOAT_MANTISSA_BITS) | __ieeeMantissa; + } + const bool __even = (__m2 & 1) == 0; + const bool __acceptBounds = __even; + + // Step 2: Determine the interval of valid decimal representations. + const uint32_t __mv = 4 * __m2; + const uint32_t __mp = 4 * __m2 + 2; + // Implicit bool -> int conversion. True is 1, false is 0. + const uint32_t __mmShift = __ieeeMantissa != 0 || __ieeeExponent <= 1; + const uint32_t __mm = 4 * __m2 - 1 - __mmShift; + + // Step 3: Convert to a decimal power base using 64-bit arithmetic. + uint32_t __vr, __vp, __vm; + int32_t __e10; + bool __vmIsTrailingZeros = false; + bool __vrIsTrailingZeros = false; + uint8_t __lastRemovedDigit = 0; + if (__e2 >= 0) { + const uint32_t __q = __log10Pow2(__e2); + __e10 = static_cast(__q); + const int32_t __k = __FLOAT_POW5_INV_BITCOUNT + __pow5bits(static_cast(__q)) - 1; + const int32_t __i = -__e2 + static_cast(__q) + __k; + __vr = __mulPow5InvDivPow2(__mv, __q, __i); + __vp = __mulPow5InvDivPow2(__mp, __q, __i); + __vm = __mulPow5InvDivPow2(__mm, __q, __i); + if (__q != 0 && (__vp - 1) / 10 <= __vm / 10) { + // We need to know one removed digit even if we are not going to loop below. We could use + // __q = X - 1 above, except that would require 33 bits for the result, and we've found that + // 32-bit arithmetic is faster even on 64-bit machines. + const int32_t __l = __FLOAT_POW5_INV_BITCOUNT + __pow5bits(static_cast(__q - 1)) - 1; + __lastRemovedDigit = static_cast(__mulPow5InvDivPow2(__mv, __q - 1, + -__e2 + static_cast(__q) - 1 + __l) % 10); + } + if (__q <= 9) { + // The largest power of 5 that fits in 24 bits is 5^10, but __q <= 9 seems to be safe as well. + // Only one of __mp, __mv, and __mm can be a multiple of 5, if any. + if (__mv % 5 == 0) { + __vrIsTrailingZeros = __multipleOfPowerOf5(__mv, __q); + } else if (__acceptBounds) { + __vmIsTrailingZeros = __multipleOfPowerOf5(__mm, __q); + } else { + __vp -= __multipleOfPowerOf5(__mp, __q); + } + } + } else { + const uint32_t __q = __log10Pow5(-__e2); + __e10 = static_cast(__q) + __e2; + const int32_t __i = -__e2 - static_cast(__q); + const int32_t __k = __pow5bits(__i) - __FLOAT_POW5_BITCOUNT; + int32_t __j = static_cast(__q) - __k; + __vr = __mulPow5divPow2(__mv, static_cast(__i), __j); + __vp = __mulPow5divPow2(__mp, static_cast(__i), __j); + __vm = __mulPow5divPow2(__mm, static_cast(__i), __j); + if (__q != 0 && (__vp - 1) / 10 <= __vm / 10) { + __j = static_cast(__q) - 1 - (__pow5bits(__i + 1) - __FLOAT_POW5_BITCOUNT); + __lastRemovedDigit = static_cast(__mulPow5divPow2(__mv, static_cast(__i + 1), __j) % 10); + } + if (__q <= 1) { + // {__vr,__vp,__vm} is trailing zeros if {__mv,__mp,__mm} has at least __q trailing 0 bits. + // __mv = 4 * __m2, so it always has at least two trailing 0 bits. + __vrIsTrailingZeros = true; + if (__acceptBounds) { + // __mm = __mv - 1 - __mmShift, so it has 1 trailing 0 bit iff __mmShift == 1. + __vmIsTrailingZeros = __mmShift == 1; + } else { + // __mp = __mv + 2, so it always has at least one trailing 0 bit. + --__vp; + } + } else if (__q < 31) { // TRANSITION(ulfjack): Use a tighter bound here. + __vrIsTrailingZeros = __multipleOfPowerOf2(__mv, __q - 1); + } + } + + // Step 4: Find the shortest decimal representation in the interval of valid representations. + int32_t __removed = 0; + uint32_t _Output; + if (__vmIsTrailingZeros || __vrIsTrailingZeros) { + // General case, which happens rarely (~4.0%). + while (__vp / 10 > __vm / 10) { +#ifdef __clang__ // TRANSITION, LLVM-23106 + __vmIsTrailingZeros &= __vm - (__vm / 10) * 10 == 0; +#else + __vmIsTrailingZeros &= __vm % 10 == 0; +#endif + __vrIsTrailingZeros &= __lastRemovedDigit == 0; + __lastRemovedDigit = static_cast(__vr % 10); + __vr /= 10; + __vp /= 10; + __vm /= 10; + ++__removed; + } + if (__vmIsTrailingZeros) { + while (__vm % 10 == 0) { + __vrIsTrailingZeros &= __lastRemovedDigit == 0; + __lastRemovedDigit = static_cast(__vr % 10); + __vr /= 10; + __vp /= 10; + __vm /= 10; + ++__removed; + } + } + if (__vrIsTrailingZeros && __lastRemovedDigit == 5 && __vr % 2 == 0) { + // Round even if the exact number is .....50..0. + __lastRemovedDigit = 4; + } + // We need to take __vr + 1 if __vr is outside bounds or we need to round up. + _Output = __vr + ((__vr == __vm && (!__acceptBounds || !__vmIsTrailingZeros)) || __lastRemovedDigit >= 5); + } else { + // Specialized for the common case (~96.0%). Percentages below are relative to this. + // Loop iterations below (approximately): + // 0: 13.6%, 1: 70.7%, 2: 14.1%, 3: 1.39%, 4: 0.14%, 5+: 0.01% + while (__vp / 10 > __vm / 10) { + __lastRemovedDigit = static_cast(__vr % 10); + __vr /= 10; + __vp /= 10; + __vm /= 10; + ++__removed; + } + // We need to take __vr + 1 if __vr is outside bounds or we need to round up. + _Output = __vr + (__vr == __vm || __lastRemovedDigit >= 5); + } + const int32_t __exp = __e10 + __removed; + + __floating_decimal_32 __fd; + __fd.__exponent = __exp; + __fd.__mantissa = _Output; + return __fd; +} + +template +_NODISCARD pair<_CharT*, errc> _Large_integer_to_chars(_CharT* const _First, _CharT* const _Last, + const uint32_t _Mantissa2, const int32_t _Exponent2) { + + // Print the integer _Mantissa2 * 2^_Exponent2 exactly. + + // For nonzero integers, _Exponent2 >= -23. (The minimum value occurs when _Mantissa2 * 2^_Exponent2 is 1. + // In that case, _Mantissa2 is the implicit 1 bit followed by 23 zeros, so _Exponent2 is -23 to shift away + // the zeros.) The dense range of exactly representable integers has negative or zero exponents + // (as positive exponents make the range non-dense). For that dense range, Ryu will always be used: + // every digit is necessary to uniquely identify the value, so Ryu must print them all. + + // Positive exponents are the non-dense range of exactly representable integers. + // This contains all of the values for which Ryu can't be used (and a few Ryu-friendly values). + + // Performance note: Long division appears to be faster than losslessly widening float to double and calling + // __d2fixed_buffered_n(). If __f2fixed_buffered_n() is implemented, it might be faster than long division. + + _STL_INTERNAL_CHECK(_Exponent2 > 0); + _STL_INTERNAL_CHECK(_Exponent2 <= 104); // because __ieeeExponent <= 254 + + // Manually represent _Mantissa2 * 2^_Exponent2 as a large integer. _Mantissa2 is always 24 bits + // (due to the implicit bit), while _Exponent2 indicates a shift of at most 104 bits. + // 24 + 104 equals 128 equals 4 * 32, so we need exactly 4 32-bit elements. + // We use a little-endian representation, visualized like this: + + // << left shift << + // most significant + // _Data[3] _Data[2] _Data[1] _Data[0] + // least significant + // >> right shift >> + + constexpr uint32_t _Data_size = 4; + uint32_t _Data[_Data_size]{}; + + // _Maxidx is the index of the most significant nonzero element. + uint32_t _Maxidx = ((24 + static_cast(_Exponent2) + 31) / 32) - 1; + _STL_INTERNAL_CHECK(_Maxidx < _Data_size); + + const uint32_t _Bit_shift = static_cast(_Exponent2) % 32; + if (_Bit_shift <= 8) { // _Mantissa2's 24 bits don't cross an element boundary + _Data[_Maxidx] = _Mantissa2 << _Bit_shift; + } else { // _Mantissa2's 24 bits cross an element boundary + _Data[_Maxidx - 1] = _Mantissa2 << _Bit_shift; + _Data[_Maxidx] = _Mantissa2 >> (32 - _Bit_shift); + } + + // If Ryu hasn't determined the total output length, we need to buffer the digits generated from right to left + // by long division. The largest possible float is: 340'282346638'528859811'704183484'516925440 + uint32_t _Blocks[4]; + int32_t _Filled_blocks = 0; + // From left to right, we're going to print: + // _Data[0] will be [1, 10] digits. + // Then if _Filled_blocks > 0: + // _Blocks[_Filled_blocks - 1], ..., _Blocks[0] will be 0-filled 9-digit blocks. + + if (_Maxidx != 0) { // If the integer is actually large, perform long division. + // Otherwise, skip to printing _Data[0]. + for (;;) { + // Loop invariant: _Maxidx != 0 (i.e. the integer is actually large) + + const uint32_t _Most_significant_elem = _Data[_Maxidx]; + const uint32_t _Initial_remainder = _Most_significant_elem % 1000000000; + const uint32_t _Initial_quotient = _Most_significant_elem / 1000000000; + _Data[_Maxidx] = _Initial_quotient; + uint64_t _Remainder = _Initial_remainder; + + // Process less significant elements. + uint32_t _Idx = _Maxidx; + do { + --_Idx; // Initially, _Remainder is at most 10^9 - 1. + + // Now, _Remainder is at most (10^9 - 1) * 2^32 + 2^32 - 1, simplified to 10^9 * 2^32 - 1. + _Remainder = (_Remainder << 32) | _Data[_Idx]; + + // floor((10^9 * 2^32 - 1) / 10^9) == 2^32 - 1, so uint32_t _Quotient is lossless. + const uint32_t _Quotient = static_cast(__div1e9(_Remainder)); + + // _Remainder is at most 10^9 - 1 again. + // For uint32_t truncation, see the __mod1e9() comment in d2s_intrinsics.h. + _Remainder = static_cast(_Remainder) - 1000000000u * _Quotient; + + _Data[_Idx] = _Quotient; + } while (_Idx != 0); + + // Store a 0-filled 9-digit block. + _Blocks[_Filled_blocks++] = static_cast(_Remainder); + + if (_Initial_quotient == 0) { // Is the large integer shrinking? + --_Maxidx; // log2(10^9) is 29.9, so we can't shrink by more than one element. + if (_Maxidx == 0) { + break; // We've finished long division. Now we need to print _Data[0]. + } + } + } + } + + _STL_INTERNAL_CHECK(_Data[0] != 0); + for (uint32_t _Idx = 1; _Idx < _Data_size; ++_Idx) { + _STL_INTERNAL_CHECK(_Data[_Idx] == 0); + } + + const uint32_t _Data_olength = _Data[0] >= 1000000000 ? 10 : __decimalLength9(_Data[0]); + const uint32_t _Total_fixed_length = _Data_olength + 9 * _Filled_blocks; + + if (_Last - _First < static_cast(_Total_fixed_length)) { + return { _Last, errc::value_too_large }; + } + + _CharT* _Result = _First; + + // Print _Data[0]. While it's up to 10 digits, + // which is more than Ryu generates, the code below can handle this. + __append_n_digits(_Data_olength, _Data[0], _Result); + _Result += _Data_olength; + + // Print 0-filled 9-digit blocks. + for (int32_t _Idx = _Filled_blocks - 1; _Idx >= 0; --_Idx) { + __append_nine_digits(_Blocks[_Idx], _Result); + _Result += 9; + } + + return { _Result, errc{} }; +} + +template +_NODISCARD pair<_CharT*, errc> __to_chars(_CharT* const _First, _CharT* const _Last, const __floating_decimal_32 __v, + chars_format _Fmt, const uint32_t __ieeeMantissa, const uint32_t __ieeeExponent) { + // Step 5: Print the decimal representation. + uint32_t _Output = __v.__mantissa; + const int32_t _Ryu_exponent = __v.__exponent; + const uint32_t __olength = __decimalLength9(_Output); + int32_t _Scientific_exponent = _Ryu_exponent + static_cast(__olength) - 1; + + if (_Fmt == chars_format{}) { + int32_t _Lower; + int32_t _Upper; + + if (__olength == 1) { + // Value | Fixed | Scientific + // 1e-3 | "0.001" | "1e-03" + // 1e4 | "10000" | "1e+04" + _Lower = -3; + _Upper = 4; + } else { + // Value | Fixed | Scientific + // 1234e-7 | "0.0001234" | "1.234e-04" + // 1234e5 | "123400000" | "1.234e+08" + _Lower = -static_cast(__olength + 3); + _Upper = 5; + } + + if (_Lower <= _Ryu_exponent && _Ryu_exponent <= _Upper) { + _Fmt = chars_format::fixed; + } else { + _Fmt = chars_format::scientific; + } + } else if (_Fmt == chars_format::general) { + // C11 7.21.6.1 "The fprintf function"/8: + // "Let P equal [...] 6 if the precision is omitted [...]. + // Then, if a conversion with style E would have an exponent of X: + // - if P > X >= -4, the conversion is with style f [...]. + // - otherwise, the conversion is with style e [...]." + if (-4 <= _Scientific_exponent && _Scientific_exponent < 6) { + _Fmt = chars_format::fixed; + } else { + _Fmt = chars_format::scientific; + } + } + + if (_Fmt == chars_format::fixed) { + // Example: _Output == 1729, __olength == 4 + + // _Ryu_exponent | Printed | _Whole_digits | _Total_fixed_length | Notes + // --------------|----------|---------------|----------------------|--------------------------------------- + // 2 | 172900 | 6 | _Whole_digits | Ryu can't be used for printing + // 1 | 17290 | 5 | (sometimes adjusted) | when the trimmed digits are nonzero. + // --------------|----------|---------------|----------------------|--------------------------------------- + // 0 | 1729 | 4 | _Whole_digits | Unified length cases. + // --------------|----------|---------------|----------------------|--------------------------------------- + // -1 | 172.9 | 3 | __olength + 1 | This case can't happen for + // -2 | 17.29 | 2 | | __olength == 1, but no additional + // -3 | 1.729 | 1 | | code is needed to avoid it. + // --------------|----------|---------------|----------------------|--------------------------------------- + // -4 | 0.1729 | 0 | 2 - _Ryu_exponent | C11 7.21.6.1 "The fprintf function"/8: + // -5 | 0.01729 | -1 | | "If a decimal-point character appears, + // -6 | 0.001729 | -2 | | at least one digit appears before it." + + const int32_t _Whole_digits = static_cast(__olength) + _Ryu_exponent; + + uint32_t _Total_fixed_length; + if (_Ryu_exponent >= 0) { // cases "172900" and "1729" + _Total_fixed_length = static_cast(_Whole_digits); + if (_Output == 1) { + // Rounding can affect the number of digits. + // For example, 1e11f is exactly "99999997952" which is 11 digits instead of 12. + // We can use a lookup table to detect this and adjust the total length. + static constexpr uint8_t _Adjustment[39] = { + 0,0,0,0,0,0,0,0,0,0,0,1,1,1,0,1,0,1,1,1,0,0,1,1,0,1,0,1,1,0,0,1,0,1,1,0,1,1,1 }; + _Total_fixed_length -= _Adjustment[_Ryu_exponent]; + // _Whole_digits doesn't need to be adjusted because these cases won't refer to it later. + } + } else if (_Whole_digits > 0) { // case "17.29" + _Total_fixed_length = __olength + 1; + } else { // case "0.001729" + _Total_fixed_length = static_cast(2 - _Ryu_exponent); + } + + if (_Last - _First < static_cast(_Total_fixed_length)) { + return { _Last, errc::value_too_large }; + } + + _CharT* _Mid; + if (_Ryu_exponent > 0) { // case "172900" + bool _Can_use_ryu; + + if (_Ryu_exponent > 10) { // 10^10 is the largest power of 10 that's exactly representable as a float. + _Can_use_ryu = false; + } else { + // Ryu generated X: __v.__mantissa * 10^_Ryu_exponent + // __v.__mantissa == 2^_Trailing_zero_bits * (__v.__mantissa >> _Trailing_zero_bits) + // 10^_Ryu_exponent == 2^_Ryu_exponent * 5^_Ryu_exponent + + // _Trailing_zero_bits is [0, 29] (aside: because 2^29 is the largest power of 2 + // with 9 decimal digits, which is float's round-trip limit.) + // _Ryu_exponent is [1, 10]. + // Normalization adds [2, 23] (aside: at least 2 because the pre-normalized mantissa is at least 5). + // This adds up to [3, 62], which is well below float's maximum binary exponent 127. + + // Therefore, we just need to consider (__v.__mantissa >> _Trailing_zero_bits) * 5^_Ryu_exponent. + + // If that product would exceed 24 bits, then X can't be exactly represented as a float. + // (That's not a problem for round-tripping, because X is close enough to the original float, + // but X isn't mathematically equal to the original float.) This requires a high-precision fallback. + + // If the product is 24 bits or smaller, then X can be exactly represented as a float (and we don't + // need to re-synthesize it; the original float must have been X, because Ryu wouldn't produce the + // same output for two different floats X and Y). This allows Ryu's output to be used (zero-filled). + + // (2^24 - 1) / 5^0 (for indexing), (2^24 - 1) / 5^1, ..., (2^24 - 1) / 5^10 + static constexpr uint32_t _Max_shifted_mantissa[11] = { + 16777215, 3355443, 671088, 134217, 26843, 5368, 1073, 214, 42, 8, 1 }; + + unsigned long _Trailing_zero_bits; + (void) _BitScanForward(&_Trailing_zero_bits, __v.__mantissa); // __v.__mantissa is guaranteed nonzero + const uint32_t _Shifted_mantissa = __v.__mantissa >> _Trailing_zero_bits; + _Can_use_ryu = _Shifted_mantissa <= _Max_shifted_mantissa[_Ryu_exponent]; + } + + if (!_Can_use_ryu) { + const uint32_t _Mantissa2 = __ieeeMantissa | (1u << __FLOAT_MANTISSA_BITS); // restore implicit bit + const int32_t _Exponent2 = static_cast(__ieeeExponent) + - __FLOAT_BIAS - __FLOAT_MANTISSA_BITS; // bias and normalization + + // Performance note: We've already called Ryu, so this will redundantly perform buffering and bounds checking. + return _Large_integer_to_chars(_First, _Last, _Mantissa2, _Exponent2); + } + + // _Can_use_ryu + // Print the decimal digits, left-aligned within [_First, _First + _Total_fixed_length). + _Mid = _First + __olength; + } else { // cases "1729", "17.29", and "0.001729" + // Print the decimal digits, right-aligned within [_First, _First + _Total_fixed_length). + _Mid = _First + _Total_fixed_length; + } + + while (_Output >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = _Output - 10000 * (_Output / 10000); +#else + const uint32_t __c = _Output % 10000; +#endif + _Output /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + } + if (_Output >= 100) { + const uint32_t __c = (_Output % 100) << 1; + _Output /= 100; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } + if (_Output >= 10) { + const uint32_t __c = _Output << 1; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } else { + *--_Mid = static_cast<_CharT>(_WIDEN(_CharT, '0') + _Output); + } + + if (_Ryu_exponent > 0) { // case "172900" with _Can_use_ryu + // Performance note: it might be more efficient to do this immediately after setting _Mid. + _STD fill_n(_First + __olength, _Ryu_exponent, _WIDEN(_CharT, '0')); + } else if (_Ryu_exponent == 0) { // case "1729" + // Done! + } else if (_Whole_digits > 0) { // case "17.29" + // Performance note: moving digits might not be optimal. + _CSTD memmove(_First, _First + 1, static_cast(_Whole_digits) * sizeof(_CharT)); + _First[_Whole_digits] = _WIDEN(_CharT, '.'); + } else { // case "0.001729" + // Performance note: a larger memset() followed by overwriting '.' might be more efficient. + _First[0] = _WIDEN(_CharT, '0'); + _First[1] = _WIDEN(_CharT, '.'); + _STD fill_n(_First + 2, -_Whole_digits, _WIDEN(_CharT, '0')); + } + + return { _First + _Total_fixed_length, errc{} }; + } + + const uint32_t _Total_scientific_length = + __olength + (__olength > 1) + 4; // digits + possible decimal point + scientific exponent + if (_Last - _First < static_cast(_Total_scientific_length)) { + return { _Last, errc::value_too_large }; + } + _CharT* const __result = _First; + + // Print the decimal digits. + uint32_t __i = 0; + while (_Output >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = _Output - 10000 * (_Output / 10000); +#else + const uint32_t __c = _Output % 10000; +#endif + _Output /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(__result + __olength - __i - 1, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 3, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + __i += 4; + } + if (_Output >= 100) { + const uint32_t __c = (_Output % 100) << 1; + _Output /= 100; + _CSTD memcpy(__result + __olength - __i - 1, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + __i += 2; + } + if (_Output >= 10) { + const uint32_t __c = _Output << 1; + // We can't use memcpy here: the decimal dot goes between these two digits. + __result[2] = __DIGIT_TABLE<_CharT>[__c + 1]; + __result[0] = __DIGIT_TABLE<_CharT>[__c]; + } else { + __result[0] = static_cast<_CharT>(_WIDEN(_CharT, '0') + _Output); + } + + // Print decimal point if needed. + uint32_t __index; + if (__olength > 1) { + __result[1] = _WIDEN(_CharT, '.'); + __index = __olength + 1; + } else { + __index = 1; + } + + // Print the exponent. + __result[__index++] = _WIDEN(_CharT, 'e'); + if (_Scientific_exponent < 0) { + __result[__index++] = _WIDEN(_CharT, '-'); + _Scientific_exponent = -_Scientific_exponent; + } else { + __result[__index++] = _WIDEN(_CharT, '+'); + } + + _CSTD memcpy(__result + __index, __DIGIT_TABLE<_CharT> + 2 * _Scientific_exponent, 2 * sizeof(_CharT)); + __index += 2; + + return { _First + _Total_scientific_length, errc{} }; +} + +_NODISCARD inline to_chars_result _Convert_to_chars_result(const pair& _Pair) { + return {_Pair.first, _Pair.second}; +} + +template +_NODISCARD pair<_CharT*, errc> __f2s_buffered_n(_CharT* const _First, _CharT* const _Last, const float __f, + const chars_format _Fmt) { + + // Step 1: Decode the floating-point number, and unify normalized and subnormal cases. + const uint32_t __bits = __float_to_bits(__f); + + // Case distinction; exit early for the easy cases. + if (__bits == 0) { + if (_Fmt == chars_format::scientific) { + if (_Last - _First < 5) { + return { _Last, errc::value_too_large }; + } + + if constexpr (is_same_v<_CharT, char>) { + _CSTD memcpy(_First, "0e+00", 5); + } else { + _CSTD memcpy(_First, L"0e+00", 5 * sizeof(wchar_t)); + } + + return { _First + 5, errc{} }; + } + + // Print "0" for chars_format::fixed, chars_format::general, and chars_format{}. + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + + *_First = _WIDEN(_CharT, '0'); + + return { _First + 1, errc{} }; + } + + // Decode __bits into mantissa and exponent. + const uint32_t __ieeeMantissa = __bits & ((1u << __FLOAT_MANTISSA_BITS) - 1); + const uint32_t __ieeeExponent = __bits >> __FLOAT_MANTISSA_BITS; + + // When _Fmt == chars_format::fixed and the floating-point number is a large integer, + // it's faster to skip Ryu and immediately print the integer exactly. + if (_Fmt == chars_format::fixed) { + const uint32_t _Mantissa2 = __ieeeMantissa | (1u << __FLOAT_MANTISSA_BITS); // restore implicit bit + const int32_t _Exponent2 = static_cast(__ieeeExponent) + - __FLOAT_BIAS - __FLOAT_MANTISSA_BITS; // bias and normalization + + // Normal values are equal to _Mantissa2 * 2^_Exponent2. + // (Subnormals are different, but they'll be rejected by the _Exponent2 test here, so they can be ignored.) + + if (_Exponent2 > 0) { + return _Large_integer_to_chars(_First, _Last, _Mantissa2, _Exponent2); + } + } + + const __floating_decimal_32 __v = __f2d(__ieeeMantissa, __ieeeExponent); + return __to_chars(_First, _Last, __v, _Fmt, __ieeeMantissa, __ieeeExponent); +} + +// ^^^^^^^^^^ DERIVED FROM f2s.c ^^^^^^^^^^ + +// vvvvvvvvvv DERIVED FROM d2s.c vvvvvvvvvv + +// We need a 64x128-bit multiplication and a subsequent 128-bit shift. +// Multiplication: +// The 64-bit factor is variable and passed in, the 128-bit factor comes +// from a lookup table. We know that the 64-bit factor only has 55 +// significant bits (i.e., the 9 topmost bits are zeros). The 128-bit +// factor only has 124 significant bits (i.e., the 4 topmost bits are +// zeros). +// Shift: +// In principle, the multiplication result requires 55 + 124 = 179 bits to +// represent. However, we then shift this value to the right by __j, which is +// at least __j >= 115, so the result is guaranteed to fit into 179 - 115 = 64 +// bits. This means that we only need the topmost 64 significant bits of +// the 64x128-bit multiplication. +// +// There are several ways to do this: +// 1. Best case: the compiler exposes a 128-bit type. +// We perform two 64x64-bit multiplications, add the higher 64 bits of the +// lower result to the higher result, and shift by __j - 64 bits. +// +// We explicitly cast from 64-bit to 128-bit, so the compiler can tell +// that these are only 64-bit inputs, and can map these to the best +// possible sequence of assembly instructions. +// x64 machines happen to have matching assembly instructions for +// 64x64-bit multiplications and 128-bit shifts. +// +// 2. Second best case: the compiler exposes intrinsics for the x64 assembly +// instructions mentioned in 1. +// +// 3. We only have 64x64 bit instructions that return the lower 64 bits of +// the result, i.e., we have to use plain C. +// Our inputs are less than the full width, so we have three options: +// a. Ignore this fact and just implement the intrinsics manually. +// b. Split both into 31-bit pieces, which guarantees no internal overflow, +// but requires extra work upfront (unless we change the lookup table). +// c. Split only the first factor into 31-bit pieces, which also guarantees +// no internal overflow, but requires extra work since the intermediate +// results are not perfectly aligned. +#if _HAS_CHARCONV_INTRINSICS + +_NODISCARD inline uint64_t __mulShift(const uint64_t __m, const uint64_t* const __mul, const int32_t __j) { + // __m is maximum 55 bits + uint64_t __high1; // 128 + const uint64_t __low1 = __ryu_umul128(__m, __mul[1], &__high1); // 64 + uint64_t __high0; // 64 + (void) __ryu_umul128(__m, __mul[0], &__high0); // 0 + const uint64_t __sum = __high0 + __low1; + if (__sum < __high0) { + ++__high1; // overflow into __high1 + } + return __ryu_shiftright128(__sum, __high1, static_cast(__j - 64)); +} + +_NODISCARD inline uint64_t __mulShiftAll(const uint64_t __m, const uint64_t* const __mul, const int32_t __j, + uint64_t* const __vp, uint64_t* const __vm, const uint32_t __mmShift) { + *__vp = __mulShift(4 * __m + 2, __mul, __j); + *__vm = __mulShift(4 * __m - 1 - __mmShift, __mul, __j); + return __mulShift(4 * __m, __mul, __j); +} + +#else // ^^^ intrinsics available / intrinsics unavailable vvv + +_NODISCARD __forceinline uint64_t __mulShiftAll(uint64_t __m, const uint64_t* const __mul, const int32_t __j, + uint64_t* const __vp, uint64_t* const __vm, const uint32_t __mmShift) { // TRANSITION, VSO-634761 + __m <<= 1; + // __m is maximum 55 bits + uint64_t __tmp; + const uint64_t __lo = __ryu_umul128(__m, __mul[0], &__tmp); + uint64_t __hi; + const uint64_t __mid = __tmp + __ryu_umul128(__m, __mul[1], &__hi); + __hi += __mid < __tmp; // overflow into __hi + + const uint64_t __lo2 = __lo + __mul[0]; + const uint64_t __mid2 = __mid + __mul[1] + (__lo2 < __lo); + const uint64_t __hi2 = __hi + (__mid2 < __mid); + *__vp = __ryu_shiftright128(__mid2, __hi2, static_cast(__j - 64 - 1)); + + if (__mmShift == 1) { + const uint64_t __lo3 = __lo - __mul[0]; + const uint64_t __mid3 = __mid - __mul[1] - (__lo3 > __lo); + const uint64_t __hi3 = __hi - (__mid3 > __mid); + *__vm = __ryu_shiftright128(__mid3, __hi3, static_cast(__j - 64 - 1)); + } else { + const uint64_t __lo3 = __lo + __lo; + const uint64_t __mid3 = __mid + __mid + (__lo3 < __lo); + const uint64_t __hi3 = __hi + __hi + (__mid3 < __mid); + const uint64_t __lo4 = __lo3 - __mul[0]; + const uint64_t __mid4 = __mid3 - __mul[1] - (__lo4 > __lo3); + const uint64_t __hi4 = __hi3 - (__mid4 > __mid3); + *__vm = __ryu_shiftright128(__mid4, __hi4, static_cast(__j - 64)); + } + + return __ryu_shiftright128(__mid, __hi, static_cast(__j - 64 - 1)); +} + +#endif // ^^^ intrinsics unavailable ^^^ + +_NODISCARD inline uint32_t __decimalLength17(const uint64_t __v) { + // This is slightly faster than a loop. + // The average output length is 16.38 digits, so we check high-to-low. + // Function precondition: __v is not an 18, 19, or 20-digit number. + // (17 digits are sufficient for round-tripping.) + _STL_INTERNAL_CHECK(__v < 100000000000000000u); + if (__v >= 10000000000000000u) { return 17; } + if (__v >= 1000000000000000u) { return 16; } + if (__v >= 100000000000000u) { return 15; } + if (__v >= 10000000000000u) { return 14; } + if (__v >= 1000000000000u) { return 13; } + if (__v >= 100000000000u) { return 12; } + if (__v >= 10000000000u) { return 11; } + if (__v >= 1000000000u) { return 10; } + if (__v >= 100000000u) { return 9; } + if (__v >= 10000000u) { return 8; } + if (__v >= 1000000u) { return 7; } + if (__v >= 100000u) { return 6; } + if (__v >= 10000u) { return 5; } + if (__v >= 1000u) { return 4; } + if (__v >= 100u) { return 3; } + if (__v >= 10u) { return 2; } + return 1; +} + +// A floating decimal representing m * 10^e. +struct __floating_decimal_64 { + uint64_t __mantissa; + int32_t __exponent; +}; + +_NODISCARD inline __floating_decimal_64 __d2d(const uint64_t __ieeeMantissa, const uint32_t __ieeeExponent) { + int32_t __e2; + uint64_t __m2; + if (__ieeeExponent == 0) { + // We subtract 2 so that the bounds computation has 2 additional bits. + __e2 = 1 - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS - 2; + __m2 = __ieeeMantissa; + } else { + __e2 = static_cast(__ieeeExponent) - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS - 2; + __m2 = (1ull << __DOUBLE_MANTISSA_BITS) | __ieeeMantissa; + } + const bool __even = (__m2 & 1) == 0; + const bool __acceptBounds = __even; + + // Step 2: Determine the interval of valid decimal representations. + const uint64_t __mv = 4 * __m2; + // Implicit bool -> int conversion. True is 1, false is 0. + const uint32_t __mmShift = __ieeeMantissa != 0 || __ieeeExponent <= 1; + // We would compute __mp and __mm like this: + // uint64_t __mp = 4 * __m2 + 2; + // uint64_t __mm = __mv - 1 - __mmShift; + + // Step 3: Convert to a decimal power base using 128-bit arithmetic. + uint64_t __vr, __vp, __vm; + int32_t __e10; + bool __vmIsTrailingZeros = false; + bool __vrIsTrailingZeros = false; + if (__e2 >= 0) { + // I tried special-casing __q == 0, but there was no effect on performance. + // This expression is slightly faster than max(0, __log10Pow2(__e2) - 1). + const uint32_t __q = __log10Pow2(__e2) - (__e2 > 3); + __e10 = static_cast(__q); + const int32_t __k = __DOUBLE_POW5_INV_BITCOUNT + __pow5bits(static_cast(__q)) - 1; + const int32_t __i = -__e2 + static_cast(__q) + __k; + __vr = __mulShiftAll(__m2, __DOUBLE_POW5_INV_SPLIT[__q], __i, &__vp, &__vm, __mmShift); + if (__q <= 21) { + // This should use __q <= 22, but I think 21 is also safe. Smaller values + // may still be safe, but it's more difficult to reason about them. + // Only one of __mp, __mv, and __mm can be a multiple of 5, if any. + const uint32_t __mvMod5 = static_cast(__mv) - 5 * static_cast(__div5(__mv)); + if (__mvMod5 == 0) { + __vrIsTrailingZeros = __multipleOfPowerOf5(__mv, __q); + } else if (__acceptBounds) { + // Same as min(__e2 + (~__mm & 1), __pow5Factor(__mm)) >= __q + // <=> __e2 + (~__mm & 1) >= __q && __pow5Factor(__mm) >= __q + // <=> true && __pow5Factor(__mm) >= __q, since __e2 >= __q. + __vmIsTrailingZeros = __multipleOfPowerOf5(__mv - 1 - __mmShift, __q); + } else { + // Same as min(__e2 + 1, __pow5Factor(__mp)) >= __q. + __vp -= __multipleOfPowerOf5(__mv + 2, __q); + } + } + } else { + // This expression is slightly faster than max(0, __log10Pow5(-__e2) - 1). + const uint32_t __q = __log10Pow5(-__e2) - (-__e2 > 1); + __e10 = static_cast(__q) + __e2; + const int32_t __i = -__e2 - static_cast(__q); + const int32_t __k = __pow5bits(__i) - __DOUBLE_POW5_BITCOUNT; + const int32_t __j = static_cast(__q) - __k; + __vr = __mulShiftAll(__m2, __DOUBLE_POW5_SPLIT[__i], __j, &__vp, &__vm, __mmShift); + if (__q <= 1) { + // {__vr,__vp,__vm} is trailing zeros if {__mv,__mp,__mm} has at least __q trailing 0 bits. + // __mv = 4 * __m2, so it always has at least two trailing 0 bits. + __vrIsTrailingZeros = true; + if (__acceptBounds) { + // __mm = __mv - 1 - __mmShift, so it has 1 trailing 0 bit iff __mmShift == 1. + __vmIsTrailingZeros = __mmShift == 1; + } else { + // __mp = __mv + 2, so it always has at least one trailing 0 bit. + --__vp; + } + } else if (__q < 63) { // TRANSITION(ulfjack): Use a tighter bound here. + // We need to compute min(ntz(__mv), __pow5Factor(__mv) - __e2) >= __q - 1 + // <=> ntz(__mv) >= __q - 1 && __pow5Factor(__mv) - __e2 >= __q - 1 + // <=> ntz(__mv) >= __q - 1 (__e2 is negative and -__e2 >= __q) + // <=> (__mv & ((1 << (__q - 1)) - 1)) == 0 + // We also need to make sure that the left shift does not overflow. + __vrIsTrailingZeros = __multipleOfPowerOf2(__mv, __q - 1); + } + } + + // Step 4: Find the shortest decimal representation in the interval of valid representations. + int32_t __removed = 0; + uint8_t __lastRemovedDigit = 0; + uint64_t _Output; + // On average, we remove ~2 digits. + if (__vmIsTrailingZeros || __vrIsTrailingZeros) { + // General case, which happens rarely (~0.7%). + for (;;) { + const uint64_t __vpDiv10 = __div10(__vp); + const uint64_t __vmDiv10 = __div10(__vm); + if (__vpDiv10 <= __vmDiv10) { + break; + } + const uint32_t __vmMod10 = static_cast(__vm) - 10 * static_cast(__vmDiv10); + const uint64_t __vrDiv10 = __div10(__vr); + const uint32_t __vrMod10 = static_cast(__vr) - 10 * static_cast(__vrDiv10); + __vmIsTrailingZeros &= __vmMod10 == 0; + __vrIsTrailingZeros &= __lastRemovedDigit == 0; + __lastRemovedDigit = static_cast(__vrMod10); + __vr = __vrDiv10; + __vp = __vpDiv10; + __vm = __vmDiv10; + ++__removed; + } + if (__vmIsTrailingZeros) { + for (;;) { + const uint64_t __vmDiv10 = __div10(__vm); + const uint32_t __vmMod10 = static_cast(__vm) - 10 * static_cast(__vmDiv10); + if (__vmMod10 != 0) { + break; + } + const uint64_t __vpDiv10 = __div10(__vp); + const uint64_t __vrDiv10 = __div10(__vr); + const uint32_t __vrMod10 = static_cast(__vr) - 10 * static_cast(__vrDiv10); + __vrIsTrailingZeros &= __lastRemovedDigit == 0; + __lastRemovedDigit = static_cast(__vrMod10); + __vr = __vrDiv10; + __vp = __vpDiv10; + __vm = __vmDiv10; + ++__removed; + } + } + if (__vrIsTrailingZeros && __lastRemovedDigit == 5 && __vr % 2 == 0) { + // Round even if the exact number is .....50..0. + __lastRemovedDigit = 4; + } + // We need to take __vr + 1 if __vr is outside bounds or we need to round up. + _Output = __vr + ((__vr == __vm && (!__acceptBounds || !__vmIsTrailingZeros)) || __lastRemovedDigit >= 5); + } else { + // Specialized for the common case (~99.3%). Percentages below are relative to this. + bool __roundUp = false; + const uint64_t __vpDiv100 = __div100(__vp); + const uint64_t __vmDiv100 = __div100(__vm); + if (__vpDiv100 > __vmDiv100) { // Optimization: remove two digits at a time (~86.2%). + const uint64_t __vrDiv100 = __div100(__vr); + const uint32_t __vrMod100 = static_cast(__vr) - 100 * static_cast(__vrDiv100); + __roundUp = __vrMod100 >= 50; + __vr = __vrDiv100; + __vp = __vpDiv100; + __vm = __vmDiv100; + __removed += 2; + } + // Loop iterations below (approximately), without optimization above: + // 0: 0.03%, 1: 13.8%, 2: 70.6%, 3: 14.0%, 4: 1.40%, 5: 0.14%, 6+: 0.02% + // Loop iterations below (approximately), with optimization above: + // 0: 70.6%, 1: 27.8%, 2: 1.40%, 3: 0.14%, 4+: 0.02% + for (;;) { + const uint64_t __vpDiv10 = __div10(__vp); + const uint64_t __vmDiv10 = __div10(__vm); + if (__vpDiv10 <= __vmDiv10) { + break; + } + const uint64_t __vrDiv10 = __div10(__vr); + const uint32_t __vrMod10 = static_cast(__vr) - 10 * static_cast(__vrDiv10); + __roundUp = __vrMod10 >= 5; + __vr = __vrDiv10; + __vp = __vpDiv10; + __vm = __vmDiv10; + ++__removed; + } + // We need to take __vr + 1 if __vr is outside bounds or we need to round up. + _Output = __vr + (__vr == __vm || __roundUp); + } + const int32_t __exp = __e10 + __removed; + + __floating_decimal_64 __fd; + __fd.__exponent = __exp; + __fd.__mantissa = _Output; + return __fd; +} + +template +_NODISCARD pair<_CharT*, errc> __to_chars(_CharT* const _First, _CharT* const _Last, const __floating_decimal_64 __v, + chars_format _Fmt, const double __f) { + // Step 5: Print the decimal representation. + uint64_t _Output = __v.__mantissa; + const int32_t _Ryu_exponent = __v.__exponent; + const uint32_t __olength = __decimalLength17(_Output); + int32_t _Scientific_exponent = _Ryu_exponent + static_cast(__olength) - 1; + + if (_Fmt == chars_format{}) { + int32_t _Lower; + int32_t _Upper; + + if (__olength == 1) { + // Value | Fixed | Scientific + // 1e-3 | "0.001" | "1e-03" + // 1e4 | "10000" | "1e+04" + _Lower = -3; + _Upper = 4; + } else { + // Value | Fixed | Scientific + // 1234e-7 | "0.0001234" | "1.234e-04" + // 1234e5 | "123400000" | "1.234e+08" + _Lower = -static_cast(__olength + 3); + _Upper = 5; + } + + if (_Lower <= _Ryu_exponent && _Ryu_exponent <= _Upper) { + _Fmt = chars_format::fixed; + } else { + _Fmt = chars_format::scientific; + } + } else if (_Fmt == chars_format::general) { + // C11 7.21.6.1 "The fprintf function"/8: + // "Let P equal [...] 6 if the precision is omitted [...]. + // Then, if a conversion with style E would have an exponent of X: + // - if P > X >= -4, the conversion is with style f [...]. + // - otherwise, the conversion is with style e [...]." + if (-4 <= _Scientific_exponent && _Scientific_exponent < 6) { + _Fmt = chars_format::fixed; + } else { + _Fmt = chars_format::scientific; + } + } + + if (_Fmt == chars_format::fixed) { + // Example: _Output == 1729, __olength == 4 + + // _Ryu_exponent | Printed | _Whole_digits | _Total_fixed_length | Notes + // --------------|----------|---------------|----------------------|--------------------------------------- + // 2 | 172900 | 6 | _Whole_digits | Ryu can't be used for printing + // 1 | 17290 | 5 | (sometimes adjusted) | when the trimmed digits are nonzero. + // --------------|----------|---------------|----------------------|--------------------------------------- + // 0 | 1729 | 4 | _Whole_digits | Unified length cases. + // --------------|----------|---------------|----------------------|--------------------------------------- + // -1 | 172.9 | 3 | __olength + 1 | This case can't happen for + // -2 | 17.29 | 2 | | __olength == 1, but no additional + // -3 | 1.729 | 1 | | code is needed to avoid it. + // --------------|----------|---------------|----------------------|--------------------------------------- + // -4 | 0.1729 | 0 | 2 - _Ryu_exponent | C11 7.21.6.1 "The fprintf function"/8: + // -5 | 0.01729 | -1 | | "If a decimal-point character appears, + // -6 | 0.001729 | -2 | | at least one digit appears before it." + + const int32_t _Whole_digits = static_cast(__olength) + _Ryu_exponent; + + uint32_t _Total_fixed_length; + if (_Ryu_exponent >= 0) { // cases "172900" and "1729" + _Total_fixed_length = static_cast(_Whole_digits); + if (_Output == 1) { + // Rounding can affect the number of digits. + // For example, 1e23 is exactly "99999999999999991611392" which is 23 digits instead of 24. + // We can use a lookup table to detect this and adjust the total length. + static constexpr uint8_t _Adjustment[309] = { + 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,1,1,0,1,0,1,1,1,0,1,1,1,0,0,0,0,0, + 1,1,0,0,1,0,1,1,1,0,0,0,0,1,1,1,1,0,0,0,1,1,1,1,0,0,0,1,1,1,1,0,1,0,1,0,1,1,0,0,0,0,1,1,1, + 1,0,0,0,0,0,0,0,1,1,0,1,1,0,0,1,0,1,0,1,0,1,1,0,0,0,0,0,1,1,1,0,0,1,1,1,1,1,0,1,0,1,1,0,1, + 1,0,0,0,0,0,0,0,0,0,1,1,1,0,0,1,0,0,1,0,0,1,1,1,1,0,0,1,1,0,1,1,0,1,1,0,1,0,0,0,1,0,0,0,1, + 0,1,0,1,0,1,1,1,0,0,0,0,0,0,1,1,1,1,0,0,1,0,1,1,1,0,0,0,1,0,1,1,1,1,1,1,0,1,0,1,1,0,0,0,1, + 1,1,0,1,1,0,0,0,1,0,0,0,1,0,1,0,0,0,0,0,0,0,1,0,1,1,0,0,1,1,1,0,0,0,1,0,1,0,0,0,0,0,1,1,0, + 0,1,0,1,1,1,0,0,1,0,0,0,0,1,0,1,0,0,0,0,0,1,0,1,0,1,1,0,1,0,0,0,0,0,1,1,0,1,0 }; + _Total_fixed_length -= _Adjustment[_Ryu_exponent]; + // _Whole_digits doesn't need to be adjusted because these cases won't refer to it later. + } + } else if (_Whole_digits > 0) { // case "17.29" + _Total_fixed_length = __olength + 1; + } else { // case "0.001729" + _Total_fixed_length = static_cast(2 - _Ryu_exponent); + } + + if (_Last - _First < static_cast(_Total_fixed_length)) { + return { _Last, errc::value_too_large }; + } + + _CharT* _Mid; + if (_Ryu_exponent > 0) { // case "172900" + bool _Can_use_ryu; + + if (_Ryu_exponent > 22) { // 10^22 is the largest power of 10 that's exactly representable as a double. + _Can_use_ryu = false; + } else { + // Ryu generated X: __v.__mantissa * 10^_Ryu_exponent + // __v.__mantissa == 2^_Trailing_zero_bits * (__v.__mantissa >> _Trailing_zero_bits) + // 10^_Ryu_exponent == 2^_Ryu_exponent * 5^_Ryu_exponent + + // _Trailing_zero_bits is [0, 56] (aside: because 2^56 is the largest power of 2 + // with 17 decimal digits, which is double's round-trip limit.) + // _Ryu_exponent is [1, 22]. + // Normalization adds [2, 52] (aside: at least 2 because the pre-normalized mantissa is at least 5). + // This adds up to [3, 130], which is well below double's maximum binary exponent 1023. + + // Therefore, we just need to consider (__v.__mantissa >> _Trailing_zero_bits) * 5^_Ryu_exponent. + + // If that product would exceed 53 bits, then X can't be exactly represented as a double. + // (That's not a problem for round-tripping, because X is close enough to the original double, + // but X isn't mathematically equal to the original double.) This requires a high-precision fallback. + + // If the product is 53 bits or smaller, then X can be exactly represented as a double (and we don't + // need to re-synthesize it; the original double must have been X, because Ryu wouldn't produce the + // same output for two different doubles X and Y). This allows Ryu's output to be used (zero-filled). + + // (2^53 - 1) / 5^0 (for indexing), (2^53 - 1) / 5^1, ..., (2^53 - 1) / 5^22 + static constexpr uint64_t _Max_shifted_mantissa[23] = { + 9007199254740991u, 1801439850948198u, 360287970189639u, 72057594037927u, 14411518807585u, + 2882303761517u, 576460752303u, 115292150460u, 23058430092u, 4611686018u, 922337203u, 184467440u, + 36893488u, 7378697u, 1475739u, 295147u, 59029u, 11805u, 2361u, 472u, 94u, 18u, 3u }; + + unsigned long _Trailing_zero_bits; +#ifdef _WIN64 + (void) _BitScanForward64(&_Trailing_zero_bits, __v.__mantissa); // __v.__mantissa is guaranteed nonzero +#else // ^^^ 64-bit / 32-bit vvv + const uint32_t _Low_mantissa = static_cast(__v.__mantissa); + if (_Low_mantissa != 0) { + (void) _BitScanForward(&_Trailing_zero_bits, _Low_mantissa); + } else { + const uint32_t _High_mantissa = static_cast(__v.__mantissa >> 32); // nonzero here + (void) _BitScanForward(&_Trailing_zero_bits, _High_mantissa); + _Trailing_zero_bits += 32; + } +#endif // ^^^ 32-bit ^^^ + const uint64_t _Shifted_mantissa = __v.__mantissa >> _Trailing_zero_bits; + _Can_use_ryu = _Shifted_mantissa <= _Max_shifted_mantissa[_Ryu_exponent]; + } + + if (!_Can_use_ryu) { + // Print the integer exactly. + // Performance note: This will redundantly perform bounds checking. + // Performance note: This will redundantly decompose the IEEE representation. + return __d2fixed_buffered_n(_First, _Last, __f, 0); + } + + // _Can_use_ryu + // Print the decimal digits, left-aligned within [_First, _First + _Total_fixed_length). + _Mid = _First + __olength; + } else { // cases "1729", "17.29", and "0.001729" + // Print the decimal digits, right-aligned within [_First, _First + _Total_fixed_length). + _Mid = _First + _Total_fixed_length; + } + + // We prefer 32-bit operations, even on 64-bit platforms. + // We have at most 17 digits, and uint32_t can store 9 digits. + // If _Output doesn't fit into uint32_t, we cut off 8 digits, + // so the rest will fit into uint32_t. + if ((_Output >> 32) != 0) { + // Expensive 64-bit division. + const uint64_t __q = __div1e8(_Output); + uint32_t __output2 = static_cast(_Output - 100000000 * __q); + _Output = __q; + + const uint32_t __c = __output2 % 10000; + __output2 /= 10000; + const uint32_t __d = __output2 % 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + const uint32_t __d0 = (__d % 100) << 1; + const uint32_t __d1 = (__d / 100) << 1; + + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __d0, 2 * sizeof(_CharT)); + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __d1, 2 * sizeof(_CharT)); + } + uint32_t __output2 = static_cast(_Output); + while (__output2 >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = __output2 - 10000 * (__output2 / 10000); +#else + const uint32_t __c = __output2 % 10000; +#endif + __output2 /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + } + if (__output2 >= 100) { + const uint32_t __c = (__output2 % 100) << 1; + __output2 /= 100; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } + if (__output2 >= 10) { + const uint32_t __c = __output2 << 1; + _CSTD memcpy(_Mid -= 2, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + } else { + *--_Mid = static_cast<_CharT>(_WIDEN(_CharT, '0') + __output2); + } + + if (_Ryu_exponent > 0) { // case "172900" with _Can_use_ryu + // Performance note: it might be more efficient to do this immediately after setting _Mid. + _STD fill_n(_First + __olength, _Ryu_exponent, _WIDEN(_CharT, '0')); + } else if (_Ryu_exponent == 0) { // case "1729" + // Done! + } else if (_Whole_digits > 0) { // case "17.29" + // Performance note: moving digits might not be optimal. + _CSTD memmove(_First, _First + 1, static_cast(_Whole_digits) * sizeof(_CharT)); + _First[_Whole_digits] = _WIDEN(_CharT, '.'); + } else { // case "0.001729" + // Performance note: a larger memset() followed by overwriting '.' might be more efficient. + _First[0] = _WIDEN(_CharT, '0'); + _First[1] = _WIDEN(_CharT, '.'); + _STD fill_n(_First + 2, -_Whole_digits, _WIDEN(_CharT, '0')); + } + + return { _First + _Total_fixed_length, errc{} }; + } + + const uint32_t _Total_scientific_length = __olength + (__olength > 1) // digits + possible decimal point + + (-100 < _Scientific_exponent && _Scientific_exponent < 100 ? 4 : 5); // + scientific exponent + if (_Last - _First < static_cast(_Total_scientific_length)) { + return { _Last, errc::value_too_large }; + } + _CharT* const __result = _First; + + // Print the decimal digits. + uint32_t __i = 0; + // We prefer 32-bit operations, even on 64-bit platforms. + // We have at most 17 digits, and uint32_t can store 9 digits. + // If _Output doesn't fit into uint32_t, we cut off 8 digits, + // so the rest will fit into uint32_t. + if ((_Output >> 32) != 0) { + // Expensive 64-bit division. + const uint64_t __q = __div1e8(_Output); + uint32_t __output2 = static_cast(_Output) - 100000000 * static_cast(__q); + _Output = __q; + + const uint32_t __c = __output2 % 10000; + __output2 /= 10000; + const uint32_t __d = __output2 % 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + const uint32_t __d0 = (__d % 100) << 1; + const uint32_t __d1 = (__d / 100) << 1; + _CSTD memcpy(__result + __olength - __i - 1, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 3, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 5, __DIGIT_TABLE<_CharT> + __d0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 7, __DIGIT_TABLE<_CharT> + __d1, 2 * sizeof(_CharT)); + __i += 8; + } + uint32_t __output2 = static_cast(_Output); + while (__output2 >= 10000) { +#ifdef __clang__ // TRANSITION, LLVM-38217 + const uint32_t __c = __output2 - 10000 * (__output2 / 10000); +#else + const uint32_t __c = __output2 % 10000; +#endif + __output2 /= 10000; + const uint32_t __c0 = (__c % 100) << 1; + const uint32_t __c1 = (__c / 100) << 1; + _CSTD memcpy(__result + __olength - __i - 1, __DIGIT_TABLE<_CharT> + __c0, 2 * sizeof(_CharT)); + _CSTD memcpy(__result + __olength - __i - 3, __DIGIT_TABLE<_CharT> + __c1, 2 * sizeof(_CharT)); + __i += 4; + } + if (__output2 >= 100) { + const uint32_t __c = (__output2 % 100) << 1; + __output2 /= 100; + _CSTD memcpy(__result + __olength - __i - 1, __DIGIT_TABLE<_CharT> + __c, 2 * sizeof(_CharT)); + __i += 2; + } + if (__output2 >= 10) { + const uint32_t __c = __output2 << 1; + // We can't use memcpy here: the decimal dot goes between these two digits. + __result[2] = __DIGIT_TABLE<_CharT>[__c + 1]; + __result[0] = __DIGIT_TABLE<_CharT>[__c]; + } else { + __result[0] = static_cast<_CharT>(_WIDEN(_CharT, '0') + __output2); + } + + // Print decimal point if needed. + uint32_t __index; + if (__olength > 1) { + __result[1] = _WIDEN(_CharT, '.'); + __index = __olength + 1; + } else { + __index = 1; + } + + // Print the exponent. + __result[__index++] = _WIDEN(_CharT, 'e'); + if (_Scientific_exponent < 0) { + __result[__index++] = _WIDEN(_CharT, '-'); + _Scientific_exponent = -_Scientific_exponent; + } else { + __result[__index++] = _WIDEN(_CharT, '+'); + } + + if (_Scientific_exponent >= 100) { + const int32_t __c = _Scientific_exponent % 10; + _CSTD memcpy(__result + __index, __DIGIT_TABLE<_CharT> + 2 * (_Scientific_exponent / 10), 2 * sizeof(_CharT)); + __result[__index + 2] = static_cast<_CharT>(_WIDEN(_CharT, '0') + __c); + __index += 3; + } else { + _CSTD memcpy(__result + __index, __DIGIT_TABLE<_CharT> + 2 * _Scientific_exponent, 2 * sizeof(_CharT)); + __index += 2; + } + + return { _First + _Total_scientific_length, errc{} }; +} + +_NODISCARD inline bool __d2d_small_int(const uint64_t __ieeeMantissa, const uint32_t __ieeeExponent, + __floating_decimal_64* const __v) { + const uint64_t __m2 = (1ull << __DOUBLE_MANTISSA_BITS) | __ieeeMantissa; + const int32_t __e2 = static_cast(__ieeeExponent) - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; + + if (__e2 > 0) { + // f = __m2 * 2^__e2 >= 2^53 is an integer. + // Ignore this case for now. + return false; + } + + if (__e2 < -52) { + // f < 1. + return false; + } + + // Since 2^52 <= __m2 < 2^53 and 0 <= -__e2 <= 52: 1 <= f = __m2 / 2^-__e2 < 2^53. + // Test if the lower -__e2 bits of the significand are 0, i.e. whether the fraction is 0. + const uint64_t __mask = (1ull << -__e2) - 1; + const uint64_t __fraction = __m2 & __mask; + if (__fraction != 0) { + return false; + } + + // f is an integer in the range [1, 2^53). + // Note: __mantissa might contain trailing (decimal) 0's. + // Note: since 2^53 < 10^16, there is no need to adjust __decimalLength17(). + __v->__mantissa = __m2 >> -__e2; + __v->__exponent = 0; + return true; +} + +template +_NODISCARD pair<_CharT*, errc> __d2s_buffered_n(_CharT* const _First, _CharT* const _Last, const double __f, + const chars_format _Fmt) { + + // Step 1: Decode the floating-point number, and unify normalized and subnormal cases. + const uint64_t __bits = __double_to_bits(__f); + + // Case distinction; exit early for the easy cases. + if (__bits == 0) { + if (_Fmt == chars_format::scientific) { + if (_Last - _First < 5) { + return { _Last, errc::value_too_large }; + } + + if constexpr (is_same_v<_CharT, char>) { + _CSTD memcpy(_First, "0e+00", 5); + } else { + _CSTD memcpy(_First, L"0e+00", 5 * sizeof(wchar_t)); + } + + return { _First + 5, errc{} }; + } + + // Print "0" for chars_format::fixed, chars_format::general, and chars_format{}. + if (_First == _Last) { + return { _Last, errc::value_too_large }; + } + + *_First = _WIDEN(_CharT, '0'); + + return { _First + 1, errc{} }; + } + + // Decode __bits into mantissa and exponent. + const uint64_t __ieeeMantissa = __bits & ((1ull << __DOUBLE_MANTISSA_BITS) - 1); + const uint32_t __ieeeExponent = static_cast(__bits >> __DOUBLE_MANTISSA_BITS); + + if (_Fmt == chars_format::fixed) { + // const uint64_t _Mantissa2 = __ieeeMantissa | (1ull << __DOUBLE_MANTISSA_BITS); // restore implicit bit + const int32_t _Exponent2 = static_cast(__ieeeExponent) + - __DOUBLE_BIAS - __DOUBLE_MANTISSA_BITS; // bias and normalization + + // Normal values are equal to _Mantissa2 * 2^_Exponent2. + // (Subnormals are different, but they'll be rejected by the _Exponent2 test here, so they can be ignored.) + + // For nonzero integers, _Exponent2 >= -52. (The minimum value occurs when _Mantissa2 * 2^_Exponent2 is 1. + // In that case, _Mantissa2 is the implicit 1 bit followed by 52 zeros, so _Exponent2 is -52 to shift away + // the zeros.) The dense range of exactly representable integers has negative or zero exponents + // (as positive exponents make the range non-dense). For that dense range, Ryu will always be used: + // every digit is necessary to uniquely identify the value, so Ryu must print them all. + + // Positive exponents are the non-dense range of exactly representable integers. This contains all of the values + // for which Ryu can't be used (and a few Ryu-friendly values). We can save time by detecting positive + // exponents here and skipping Ryu. Calling __d2fixed_buffered_n() with precision 0 is valid for all integers + // (so it's okay if we call it with a Ryu-friendly value). + if (_Exponent2 > 0) { + return __d2fixed_buffered_n(_First, _Last, __f, 0); + } + } + + __floating_decimal_64 __v; + const bool __isSmallInt = __d2d_small_int(__ieeeMantissa, __ieeeExponent, &__v); + if (__isSmallInt) { + // For small integers in the range [1, 2^53), __v.__mantissa might contain trailing (decimal) zeros. + // For scientific notation we need to move these zeros into the exponent. + // (This is not needed for fixed-point notation, so it might be beneficial to trim + // trailing zeros in __to_chars only if needed - once fixed-point notation output is implemented.) + for (;;) { + const uint64_t __q = __div10(__v.__mantissa); + const uint32_t __r = static_cast(__v.__mantissa) - 10 * static_cast(__q); + if (__r != 0) { + break; + } + __v.__mantissa = __q; + ++__v.__exponent; + } + } else { + __v = __d2d(__ieeeMantissa, __ieeeExponent); + } + + return __to_chars(_First, _Last, __v, _Fmt, __f); +} + +// ^^^^^^^^^^ DERIVED FROM d2s.c ^^^^^^^^^^ + +// clang-format on + +template +_NODISCARD to_chars_result _Floating_to_chars_ryu( + char* const _First, char* const _Last, const _Floating _Value, const chars_format _Fmt) noexcept { + if constexpr (is_same_v<_Floating, float>) { + return _Convert_to_chars_result(__f2s_buffered_n(_First, _Last, _Value, _Fmt)); + } else { + return _Convert_to_chars_result(__d2s_buffered_n(_First, _Last, _Value, _Fmt)); + } +} + +template +_NODISCARD to_chars_result _Floating_to_chars_scientific_precision( + char* const _First, char* const _Last, const _Floating _Value, int _Precision) noexcept { + + // C11 7.21.6.1 "The fprintf function"/5: + // "A negative precision argument is taken as if the precision were omitted." + // /8: "e,E [...] if the precision is missing, it is taken as 6" + + if (_Precision < 0) { + _Precision = 6; + } else if (_Precision < 1'000'000'000) { + // _Precision is ok. + } else { + // Avoid integer overflow. + // (This defensive check is slightly nonconformant; it can be carefully improved in the future.) + return {_Last, errc::value_too_large}; + } + + return __d2exp_buffered_n(_First, _Last, _Value, static_cast(_Precision)); +} + +template +_NODISCARD to_chars_result _Floating_to_chars_fixed_precision( + char* const _First, char* const _Last, const _Floating _Value, int _Precision) noexcept { + + // C11 7.21.6.1 "The fprintf function"/5: + // "A negative precision argument is taken as if the precision were omitted." + // /8: "f,F [...] If the precision is missing, it is taken as 6" + + if (_Precision < 0) { + _Precision = 6; + } else if (_Precision < 1'000'000'000) { + // _Precision is ok. + } else { + // Avoid integer overflow. + // (This defensive check is slightly nonconformant; it can be carefully improved in the future.) + return {_Last, errc::value_too_large}; + } + + return _Convert_to_chars_result(__d2fixed_buffered_n(_First, _Last, _Value, static_cast(_Precision))); +} + +_STD_END + +#undef _HAS_CHARCONV_INTRINSICS +#undef _WIDEN + +#pragma pop_macro("new") +_STL_RESTORE_CLANG_WARNINGS +#pragma warning(pop) +#pragma pack(pop) + +#endif // _STL_COMPILER_PREPROCESSOR +#endif // _XCHARCONV_RYU_H