--- /dev/null
+// std::to_chars implementation for floating-point types -*- C++ -*-
+
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+// Activate __glibcxx_assert within this file to shake out any bugs.
+#define _GLIBCXX_ASSERTIONS 1
+
+#include <charconv>
+
+#include <bit>
+#include <cfenv>
+#include <cassert>
+#include <cmath>
+#include <cstdio>
+#include <cstring>
+#include <langinfo.h>
+#include <optional>
+#include <string_view>
+#include <type_traits>
+
+// Determine the binary format of 'long double'.
+
+// We support the binary64, float80 (i.e. x86 80-bit extended precision),
+// binary128, and ibm128 formats.
+#define LDK_UNSUPPORTED 0
+#define LDK_BINARY64 1
+#define LDK_FLOAT80 2
+#define LDK_BINARY128 3
+#define LDK_IBM128 4
+
+#if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__
+# define LONG_DOUBLE_KIND LDK_BINARY64
+#elif defined(__SIZEOF_INT128__)
+// The Ryu routines need a 128-bit integer type in order to do shortest
+// formatting of types larger than 64-bit double, so without __int128 we can't
+// support any large long double format. This is the case for e.g. i386.
+# if __LDBL_MANT_DIG__ == 64
+# define LONG_DOUBLE_KIND LDK_FLOAT80
+# elif __LDBL_MANT_DIG__ == 113
+# define LONG_DOUBLE_KIND LDK_BINARY128
+# elif __LDBL_MANT_DIG__ == 106
+# define LONG_DOUBLE_KIND LDK_IBM128
+# endif
+#endif
+#if !defined(LONG_DOUBLE_KIND)
+# define LONG_DOUBLE_KIND LDK_UNSUPPORTED
+#endif
+
+namespace
+{
+ namespace ryu
+ {
+#include "ryu/common.h"
+#include "ryu/digit_table.h"
+#include "ryu/d2s_intrinsics.h"
+#include "ryu/d2s_full_table.h"
+#include "ryu/d2fixed_full_table.h"
+#include "ryu/f2s_intrinsics.h"
+#include "ryu/d2s.c"
+#include "ryu/d2fixed.c"
+#include "ryu/f2s.c"
+
+#ifdef __SIZEOF_INT128__
+ namespace generic128
+ {
+ // Put the generic Ryu bits in their own namespace to avoid name conflicts.
+# include "ryu/generic_128.h"
+# include "ryu/ryu_generic_128.h"
+# include "ryu/generic_128.c"
+ } // namespace generic128
+
+ using generic128::floating_decimal_128;
+ using generic128::generic_binary_to_decimal;
+
+ int
+ to_chars(const floating_decimal_128 v, char* const result)
+ { return generic128::generic_to_chars(v, result); }
+#endif
+ } // namespace ryu
+
+ // A traits class that contains pertinent information about the binary
+ // format of each of the floating-point types we support.
+ template<typename T>
+ struct floating_type_traits
+ { };
+
+ template<>
+ struct floating_type_traits<float>
+ {
+ // We (and Ryu) assume float has the IEEE binary32 format.
+ static_assert(__FLT_MANT_DIG__ == 24);
+ static constexpr int mantissa_bits = 23;
+ static constexpr int exponent_bits = 8;
+ static constexpr bool has_implicit_leading_bit = true;
+ using mantissa_t = uint32_t;
+ using shortest_scientific_t = ryu::floating_decimal_32;
+
+ static constexpr uint64_t pow10_adjustment_tab[]
+ = { 0b0000000000011101011100110101100101101110000000000000000000000000 };
+ };
+
+ template<>
+ struct floating_type_traits<double>
+ {
+ // We (and Ryu) assume double has the IEEE binary64 format.
+ static_assert(__DBL_MANT_DIG__ == 53);
+ static constexpr int mantissa_bits = 52;
+ static constexpr int exponent_bits = 11;
+ static constexpr bool has_implicit_leading_bit = true;
+ using mantissa_t = uint64_t;
+ using shortest_scientific_t = ryu::floating_decimal_64;
+
+ static constexpr uint64_t pow10_adjustment_tab[]
+ = { 0b0000000000000000000000011000110101110111000001100101110000111100,
+ 0b0111100011110101011000011110000000110110010101011000001110011111,
+ 0b0101101100000000011100100100111100110110110100010001010101110000,
+ 0b0011110010111000101111110101100011101100010001010000000101100111,
+ 0b0001010000011001011100100001010000010101101000001101000000000000 };
+ };
+
+#if LONG_DOUBLE_KIND == LDK_BINARY64
+ // When long double is equivalent to double, we just forward the long double
+ // overloads to the double overloads, so we don't need to define a a
+ // floating_type_traits<long double> specialization in this case.
+#elif LONG_DOUBLE_KIND == LDK_FLOAT80
+ template<>
+ struct floating_type_traits<long double>
+ {
+ static constexpr int mantissa_bits = 64;
+ static constexpr int exponent_bits = 15;
+ static constexpr bool has_implicit_leading_bit = false;
+ using mantissa_t = uint64_t;
+ using shortest_scientific_t = ryu::floating_decimal_128;
+
+ static constexpr uint64_t pow10_adjustment_tab[]
+ = { 0b0000000000000000000000000000110101011111110100010100110000011101,
+ 0b1001100101001111010011011111101000101111110001011001011101110000,
+ 0b0000101111111011110010001000001010111101011110111111010100011001,
+ 0b0011100000011111001101101011111001111100100010000101001111101001,
+ 0b0100100100000000100111010010101110011000110001101101110011001010,
+ 0b0111100111100010100000010011000010010110101111110101000011110100,
+ 0b1010100111100010011110000011011101101100010110000110101010101010,
+ 0b0000001111001111000000101100111011011000101000110011101100110010,
+ 0b0111000011100100101101010100001101111110101111001000010011111111,
+ 0b0010111000100110100100100010101100111010110001101010010111001000,
+ 0b0000100000010110000011001001000111000001111010100101101000001111,
+ 0b0010101011101000111100001011000010011101000101010010010000101111,
+ 0b1011111011101101110010101011010001111000101000101101011001100011,
+ 0b1010111011011011110111110011001010000010011001110100101101000101,
+ 0b0011000001110110011010010000011100100011001011001100001101010110,
+ 0b0100011111011000111111101000011110000010111110101001000000001001,
+ 0b1110000001110001001101101110011000100000001010000111100010111010,
+ 0b1110001001010011101000111000001000010100110000010110100011110000,
+ 0b0000011010110000110001111000011111000011001101001101001001000110,
+ 0b1010010111001000101001100101010110100100100010010010000101000010,
+ 0b1011001110000111100010100110000011100011111001110111001100000101,
+ 0b0110101001001000010110001000010001010101110101100001111100011001,
+ 0b1111100011110101011110011010101001010010100011000010110001101001,
+ 0b0100000100001000111101011100010011011111011001000000001100011000,
+ 0b1110111111000111100101110111110000000011001110011100011011011001,
+ 0b1100001100100000010001100011011000111011110000110011010101000011,
+ 0b1111111011100111011101001111111000010000001111010111110010000100,
+ 0b1110111001111110101111000101000000001010001110011010001000111010,
+ 0b1000010001011000101111111010110011111101110101101001111000111010,
+ 0b0100000111101001000111011001101000001010111011101001101111000100,
+ 0b0000011100110001000111011100111100110001101111111010110111100000,
+ 0b0000011101011100100110010011110101010100010011110010010111010000,
+ 0b0011011001100111110101111100001001101110101101001110110011110110,
+ 0b1011000101000001110100111001100100111100110011110000000001101000,
+ 0b1011100011110100001001110101010110111001000000001011101001011110,
+ 0b1111001010010010100000010110101010101011101000101000000000001100,
+ 0b1000001111100100111001110101100001010011111111000001000011110000,
+ 0b0001011101001000010000101101111000001110101100110011001100110111,
+ 0b1110011100000010101011011111001010111101111110100000011100000011,
+ 0b1001110110011100101010011110100010110001001110110000101011100110,
+ 0b1001101000100011100111010000011011100001000000110101100100001001,
+ 0b1010111000101000101101010111000010001100001010100011111100000100,
+ 0b0111101000100011000101101011111011100010001101110111001111001011,
+ 0b1110100111010110001110110110000000010110100011110000010001111100,
+ 0b1100010100011010001011001000111001010101011110100101011001000000,
+ 0b0000110001111001100110010110111010101101001101000000000010010101,
+ 0b0001110111101000001111101010110010010000111110111100000111110100,
+ 0b0111110111001001111000110001101101001010101110110101111110000100,
+ 0b0000111110111010101111100010111010011100010110011011011001000001,
+ 0b1010010100100100101110111111111000101100000010111111101101000110,
+ 0b1000100111111101100011001101000110001000000100010101010100001101,
+ 0b1100101010101000111100101100001000110001110010100000000010110101,
+ 0b1010000100111101100100101010010110100010000000110101101110000100,
+ 0b1011111011110001110000100100000000001010111010001101100000100100,
+ 0b0111101101100011001110011100000001000101101101111000100111011111,
+ 0b0100111010010011011001010011110100001100111010010101111111100011,
+ 0b0010001001011000111000001100110111110111110010100011000110110110,
+ 0b0101010110000000010000100000110100111011111101000100000111010010,
+ 0b0110000011011101000001010100110101101110011100110101000000001001,
+ 0b1101100110100000011000001111000100100100110001100110101010101100,
+ 0b0010100101010110010010001010101000011111111111001011001010001111,
+ 0b0111001010001111001100111001010101001000110101000011110000001000,
+ 0b0110010011001001001111110001010010001011010010001101110110110011,
+ 0b0110010100111011000100111000001001101011111001110010111110111111,
+ 0b0101110111001001101100110100101001110010101110011001101110001000,
+ 0b0100110101010111011010001100010111100011010011111001010100111000,
+ 0b0111000110110111011110100100010111000110000110110110110001111110,
+ 0b1000101101010100100100111110100011110110110010011001110011110101,
+ 0b1001101110101001010100111101101011000101000010110101101111110000,
+ 0b0100100101001011011001001011000010001101001010010001010110101000,
+ 0b0010100001001011100110101000010110000111000111000011100101011011,
+ 0b0110111000011001111101101011111010001000000010101000101010011110,
+ 0b1000110110100001111011000001111100001001000000010110010100100100,
+ 0b1001110100011111100111101011010000010101011100101000010010100110,
+ 0b0001010110101110100010101010001110110110100011101010001001111100,
+ 0b1010100101101100000010110011100110100010010000100100001110000100,
+ 0b0001000000010000001010000010100110000001110100111001110111101101,
+ 0b1100000000000000000000000000000000000000000000000000000000000000 };
+ };
+#elif LONG_DOUBLE_KIND == LDK_BINARY128
+ template<>
+ struct floating_type_traits<long double>
+ {
+ static constexpr int mantissa_bits = 112;
+ static constexpr int exponent_bits = 15;
+ static constexpr bool has_implicit_leading_bit = true;
+ using mantissa_t = unsigned __int128;
+ using shortest_scientific_t = ryu::floating_decimal_128;
+
+ static constexpr uint64_t pow10_adjustment_tab[]
+ = { 0b0000000000000000000000000000000000000000000000000100000010000000,
+ 0b1011001111110100000100010101101110011100100110000110010110011000,
+ 0b1010100010001101111111000000001101010010100010010000111011110111,
+ 0b1011111001110001111000011111000010110111000111110100101010100101,
+ 0b0110100110011110011011000011000010011001110001001001010011100011,
+ 0b0000011111110010101111101011101010000110011111100111001110100111,
+ 0b0100010101010110000010111011110100000010011001001010001110111101,
+ 0b1101110111000010001101100000110100000111001001101011000101011011,
+ 0b0100111011101101010000001101011000101100101110010010110000101011,
+ 0b0100000110111000000110101000010011101000110100010110000011101101,
+ 0b1011001101001000100001010001100100001111011101010101110001010110,
+ 0b1000000001000000101001110010110010001111101101010101001100000110,
+ 0b0101110110100110000110000001001010111110001110010000111111010011,
+ 0b1010001111100111000100011100100100111100100101000001011001000111,
+ 0b1010011000011100110101100111001011100101111111100001110100000100,
+ 0b1100011100100010100000110001001010000000100000001001010111011101,
+ 0b0101110000100011001111101101000000100110000010010111010001111010,
+ 0b0100111100011010110111101000100110000111001001101100000001111100,
+ 0b1100100100111110101011000100000101011010110111000111110100110101,
+ 0b0110010000010111010100110011000000111010000010111011010110000100,
+ 0b0101001001010010110111010111000101011100000111100111000001110010,
+ 0b1101111111001011101010110001000111011010111101001011010110100100,
+ 0b0001000100110000011111101011001101110010110110010000000011100100,
+ 0b0001000000000101001001001000000000011000100011001110101001001110,
+ 0b0010010010001000111010011011100001000110011011011110110100111000,
+ 0b0000100110101100000111100010100100011100110111011100001111001100,
+ 0b1011111010001110001100000011110111111111100000001011111111101100,
+ 0b0000011100001111010101110000100110111100101101110111101001000001,
+ 0b1100010001110110111100001001001101101000011100000010110101001011,
+ 0b0100101001101011111001011110101101100011011111011100101010101111,
+ 0b0001101001111001110000101101101100001011010001011110011101000010,
+ 0b1111000000101001101111011010110011101110100001011011001011100010,
+ 0b0101001010111101101100001111100010010110001101001000001101100100,
+ 0b0101100101011110001100101011111000111001111001001001101101100001,
+ 0b1111001101010010100100011011000110110010001111000111010001001101,
+ 0b0001110010011000000001000110110111011000011100001000011001110111,
+ 0b0100001011011011011011110011101100100101111111101100101000001110,
+ 0b0101011110111101010111100111101111000101111111111110100011011010,
+ 0b1110101010001001110100000010110111010111111010111110100110010110,
+ 0b1010001111100001001100101000110100001100011100110010000011010111,
+ 0b1111111101101111000100111100000101011000001110011011101010111001,
+ 0b1111101100001110100101111101011001000100000101110000110010100011,
+ 0b1001010110110101101101000101010001010000101011011111010011010000,
+ 0b0111001110110011101001100111000001000100001010110000010000001101,
+ 0b0101111100111110100111011001111001111011011110010111010011101010,
+ 0b1110111000000001100100111001100100110001011011001110101111110111,
+ 0b0001010001001101010111101010011111000011110001101101011001111111,
+ 0b0101000011100011010010001101100001011101011010100110101100100010,
+ 0b0001000101011000100101111100110110000101101101111000110001001011,
+ 0b0101100101001011011000010101000000010100011100101101000010011111,
+ 0b1000010010001011101001011010100010111011110100110011011000100111,
+ 0b1000011011100001010111010111010011101100100010010010100100101001,
+ 0b1001001001010111110101000010111010000000101111010100001010010010,
+ 0b0011011110110010010101111011000001000000000011011111000011111011,
+ 0b1011000110100011001110000001000100000001011100010111010010011110,
+ 0b0111101110110101110111110000011000000100011100011000101101101110,
+ 0b1001100101111011011100011110101011001111100111101010101010110111,
+ 0b1100110010010001100011001111010000000100011101001111011101001111,
+ 0b1000111001111010100101000010000100000001001100101010001011001101,
+ 0b0011101011110000110010100101010100110010100001000010101011111101,
+ 0b1100000000000110000010101011000000011101000110011111100010111111,
+ 0b0010100110000011011100010110111100010110101100110011101110001101,
+ 0b0010111101010011111000111001111100110111111100100011110001101110,
+ 0b1001110111001001101001001001011000010100110001000000100011010110,
+ 0b0011110101100111011011111100001000011001010100111100100101111010,
+ 0b0010001101000011000010100101110000010101101000100110000100001010,
+ 0b0010000010100110010101100101110011101111000111111111001001100001,
+ 0b0100111111011011011011100111111011000010011101101111011111110110,
+ 0b1111111111010110101011101000100101110100001110001001101011100111,
+ 0b1011111101000101110000111100100010111010100001010000010010110010,
+ 0b1111010101001011101011101010000100110110001110111100100110111111,
+ 0b1011001101000001001101000010101010010110010001100001011100011010,
+ 0b0101001011011101010001110100010000010001111100100100100001001101,
+ 0b0010100000111001100011000101100101000001111100111001101000000010,
+ 0b1011001111010101011001000100100110100100110111110100000110111000,
+ 0b0101011111010011100011010010111101110010100001111111100010001001,
+ 0b0010111011101100100000000000001111111010011101100111100001001101,
+ 0b1101000000000000000000000000000000000000000000000000000000000000 };
+ };
+#elif LONG_DOUBLE_KIND == LDK_IBM128
+ template<>
+ struct floating_type_traits<long double>
+ {
+ static constexpr int mantissa_bits = 105;
+ static constexpr int exponent_bits = 11;
+ static constexpr bool has_implicit_leading_bit = true;
+ using mantissa_t = unsigned __int128;
+ using shortest_scientific_t = ryu::floating_decimal_128;
+
+ static constexpr uint64_t pow10_adjustment_tab[]
+ = { 0b0000000000000000000000000000000000000000000000001000000100000000,
+ 0b0000000000000000000100000000000000000000001000000000000000000010,
+ 0b0000100000000000000000001001000000000000000001100100000000000000,
+ 0b0011000000000000000000000000000001110000010000000000000000000000,
+ 0b0000100000000000001000000000000000000000000000100000000000000000 };
+ };
+#endif
+
+ // An IEEE-style decomposition of a floating-point value of type T.
+ template<typename T>
+ struct ieee_t
+ {
+ typename floating_type_traits<T>::mantissa_t mantissa;
+ uint32_t biased_exponent;
+ bool sign;
+ };
+
+ // Decompose the floating-point value into its IEEE components.
+ template<typename T>
+ ieee_t<T>
+ get_ieee_repr(const T value)
+ {
+ constexpr int mantissa_bits = floating_type_traits<T>::mantissa_bits;
+ constexpr int exponent_bits = floating_type_traits<T>::exponent_bits;
+ constexpr int total_bits = mantissa_bits + exponent_bits + 1;
+
+ constexpr auto get_uint_t = [] {
+ if constexpr (total_bits <= 32)
+ return uint32_t{};
+ else if constexpr (total_bits <= 64)
+ return uint64_t{};
+#ifdef __SIZEOF_INT128__
+ else if constexpr (total_bits <= 128)
+ return (unsigned __int128){};
+#endif
+ };
+ using uint_t = decltype(get_uint_t());
+ uint_t value_bits = 0;
+ memcpy(&value_bits, &value, sizeof(value));
+
+ ieee_t<T> ieee_repr;
+ ieee_repr.mantissa = value_bits & ((uint_t{1} << mantissa_bits) - 1u);
+ ieee_repr.biased_exponent
+ = (value_bits >> mantissa_bits) & ((uint_t{1} << exponent_bits) - 1u);
+ ieee_repr.sign = (value_bits >> (mantissa_bits + exponent_bits)) & 1;
+ return ieee_repr;
+ }
+
+#if LONG_DOUBLE_KIND == LDK_IBM128
+ template<>
+ ieee_t<long double>
+ get_ieee_repr(const long double value)
+ {
+ // The layout of __ibm128 isn't compatible with the standard IEEE format.
+ // So we transform it into an IEEE-compatible format, suitable for
+ // consumption by the generic Ryu API, with an 11-bit exponent and 105-bit
+ // mantissa (plus an implicit leading bit). We use the exponent and sign
+ // of the high part, and we merge the mantissa of the high part with the
+ // mantissa (and the implicit leading bit) of the low part.
+ using uint_t = unsigned __int128;
+ uint_t value_bits = 0;
+ memcpy(&value_bits, &value, sizeof(value_bits));
+
+ const uint64_t value_hi = value_bits;
+ const uint64_t value_lo = value_bits >> 64;
+
+ uint64_t mantissa_hi = value_hi & ((1ull << 52) - 1);
+ unsigned exponent_hi = (value_hi >> 52) & ((1ull << 11) - 1);
+ const int sign_hi = (value_hi >> 63) & 1;
+
+ uint64_t mantissa_lo = value_lo & ((1ull << 52) - 1);
+ const unsigned exponent_lo = (value_lo >> 52) & ((1ull << 11) - 1);
+ const int sign_lo = (value_lo >> 63) & 1;
+
+ {
+ // The following code for adjusting the low-part mantissa to combine
+ // it with the high-part mantissa is taken from the glibc source file
+ // sysdeps/ieee754/ldbl-128ibm/printf_fphex.c.
+ mantissa_lo <<= 7;
+ if (exponent_lo != 0)
+ mantissa_lo |= (1ull << (52 + 7));
+ else
+ mantissa_lo <<= 1;
+
+ const int ediff = exponent_hi - exponent_lo - 53;
+ if (ediff > 63)
+ mantissa_lo = 0;
+ else if (ediff > 0)
+ mantissa_lo >>= ediff;
+ else if (ediff < 0)
+ mantissa_lo <<= -ediff;
+
+ if (sign_lo != sign_hi && mantissa_lo != 0)
+ {
+ mantissa_lo = (1ull << 60) - mantissa_lo;
+ if (mantissa_hi == 0)
+ {
+ mantissa_hi = 0xffffffffffffeLL | (mantissa_lo >> 59);
+ mantissa_lo = 0xfffffffffffffffLL & (mantissa_lo << 1);
+ exponent_hi--;
+ }
+ else
+ mantissa_hi--;
+ }
+ }
+
+ ieee_t<long double> ieee_repr;
+ ieee_repr.mantissa = ((uint_t{mantissa_hi} << 64)
+ | (uint_t{mantissa_lo} << 4)) >> 11;
+ ieee_repr.biased_exponent = exponent_hi;
+ ieee_repr.sign = sign_hi;
+ return ieee_repr;
+ }
+#endif
+
+ // Invoke Ryu to obtain the shortest scientific form for the given
+ // floating-point number.
+ template<typename T>
+ typename floating_type_traits<T>::shortest_scientific_t
+ floating_to_shortest_scientific(const T value)
+ {
+ if constexpr (std::is_same_v<T, float>)
+ return ryu::floating_to_fd32(value);
+ else if constexpr (std::is_same_v<T, double>)
+ return ryu::floating_to_fd64(value);
+#ifdef __SIZEOF_INT128__
+ else if constexpr (std::is_same_v<T, long double>)
+ {
+ constexpr int mantissa_bits
+ = floating_type_traits<T>::mantissa_bits;
+ constexpr int exponent_bits
+ = floating_type_traits<T>::exponent_bits;
+ constexpr bool has_implicit_leading_bit
+ = floating_type_traits<T>::has_implicit_leading_bit;
+
+ const auto [mantissa, exponent, sign] = get_ieee_repr(value);
+ return ryu::generic_binary_to_decimal(mantissa, exponent, sign,
+ mantissa_bits, exponent_bits,
+ !has_implicit_leading_bit);
+ }
+#endif
+ }
+
+ // This subroutine returns true if the shortest scientific form fd is a
+ // positive power of 10, and the floating-point number that has this shortest
+ // scientific form is smaller than this power of 10.
+ //
+ // For instance, the exactly-representable 64-bit number
+ // 99999999999999991611392.0 has the shortest scientific form 1e23, so its
+ // exact value is smaller than its shortest scientific form.
+ //
+ // For these powers of 10 the length of the fixed form is one digit less
+ // than what the scientific exponent suggests.
+ //
+ // This subroutine inspects a lookup table to detect when fd is such a
+ // "rounded up" power of 10.
+ template<typename T>
+ bool
+ is_rounded_up_pow10_p(const typename
+ floating_type_traits<T>::shortest_scientific_t fd)
+ {
+ if (fd.exponent < 0 || fd.mantissa != 1) [[likely]]
+ return false;
+
+ constexpr auto& pow10_adjustment_tab
+ = floating_type_traits<T>::pow10_adjustment_tab;
+ __glibcxx_assert(fd.exponent/64 < (int)std::size(pow10_adjustment_tab));
+ return (pow10_adjustment_tab[fd.exponent/64]
+ & (1ull << (63 - fd.exponent%64)));
+ }
+
+ int
+ get_mantissa_length(const ryu::floating_decimal_32 fd)
+ { return ryu::decimalLength9(fd.mantissa); }
+
+ int
+ get_mantissa_length(const ryu::floating_decimal_64 fd)
+ { return ryu::decimalLength17(fd.mantissa); }
+
+#ifdef __SIZEOF_INT128__
+ int
+ get_mantissa_length(const ryu::floating_decimal_128 fd)
+ { return ryu::generic128::decimalLength(fd.mantissa); }
+#endif
+} // anon namespace
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+// This subroutine of __floating_to_chars_* handles writing nan, inf and 0 in
+// all formatting modes.
+template<typename T>
+ static optional<to_chars_result>
+ __handle_special_value(char* first, char* const last, const T value,
+ const chars_format fmt, const int precision)
+ {
+ __glibcxx_assert(precision >= 0);
+
+ string_view str;
+ switch (__builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL,
+ FP_ZERO, value))
+ {
+ case FP_INFINITE:
+ str = "-inf";
+ break;
+
+ case FP_NAN:
+ str = "-nan";
+ break;
+
+ case FP_ZERO:
+ break;
+
+ default:
+ case FP_SUBNORMAL:
+ case FP_NORMAL: [[likely]]
+ return nullopt;
+ }
+
+ if (!str.empty())
+ {
+ // We're formatting +-inf or +-nan.
+ if (!__builtin_signbit(value))
+ str.remove_prefix(strlen("-"));
+
+ if (last - first < (int)str.length())
+ return {{last, errc::value_too_large}};
+
+ memcpy(first, &str[0], str.length());
+ first += str.length();
+ return {{first, errc{}}};
+ }
+
+ // We're formatting 0.
+ __glibcxx_assert(value == 0);
+ const auto orig_first = first;
+ const bool sign = __builtin_signbit(value);
+ int expected_output_length;
+ switch (fmt)
+ {
+ case chars_format::fixed:
+ case chars_format::scientific:
+ case chars_format::hex:
+ expected_output_length = sign + 1;
+ if (precision)
+ expected_output_length += strlen(".") + precision;
+ if (fmt == chars_format::scientific)
+ expected_output_length += strlen("e+00");
+ else if (fmt == chars_format::hex)
+ expected_output_length += strlen("p+0");
+ if (last - first < expected_output_length)
+ return {{last, errc::value_too_large}};
+
+ if (sign)
+ *first++ = '-';
+ *first++ = '0';
+ if (precision)
+ {
+ *first++ = '.';
+ memset(first, '0', precision);
+ first += precision;
+ }
+ if (fmt == chars_format::scientific)
+ {
+ memcpy(first, "e+00", 4);
+ first += 4;
+ }
+ else if (fmt == chars_format::hex)
+ {
+ memcpy(first, "p+0", 3);
+ first += 3;
+ }
+ break;
+
+ case chars_format::general:
+ default: // case chars_format{}:
+ expected_output_length = sign + 1;
+ if (last - first < expected_output_length)
+ return {{last, errc::value_too_large}};
+
+ if (sign)
+ *first++ = '-';
+ *first++ = '0';
+ break;
+ }
+ __glibcxx_assert(first - orig_first == expected_output_length);
+ return {{first, errc{}}};
+ }
+
+// This subroutine of the floating-point to_chars overloads performs
+// hexadecimal formatting.
+template<typename T>
+ static to_chars_result
+ __floating_to_chars_hex(char* first, char* const last, const T value,
+ const optional<int> precision)
+ {
+ if (precision.has_value() && precision.value() < 0) [[unlikely]]
+ // A negative precision argument is treated as if it were omitted.
+ return __floating_to_chars_hex(first, last, value, nullopt);
+
+ __glibcxx_requires_valid_range(first, last);
+
+ constexpr int mantissa_bits = floating_type_traits<T>::mantissa_bits;
+ constexpr bool has_implicit_leading_bit
+ = floating_type_traits<T>::has_implicit_leading_bit;
+ constexpr int exponent_bits = floating_type_traits<T>::exponent_bits;
+ constexpr int exponent_bias = (1u << (exponent_bits - 1)) - 1;
+ using mantissa_t = typename floating_type_traits<T>::mantissa_t;
+ constexpr int mantissa_t_width = sizeof(mantissa_t) * __CHAR_BIT__;
+
+ if (auto result = __handle_special_value(first, last, value,
+ chars_format::hex,
+ precision.value_or(0)))
+ return *result;
+
+ // Extract the sign, mantissa and exponent from the value.
+ const auto [ieee_mantissa, biased_exponent, sign] = get_ieee_repr(value);
+ const bool is_normal_number = (biased_exponent != 0);
+
+ // Calculate the unbiased exponent.
+ const int32_t unbiased_exponent = (is_normal_number
+ ? biased_exponent - exponent_bias
+ : 1 - exponent_bias);
+
+ // Shift the mantissa so that its bitwidth is a multiple of 4.
+ constexpr unsigned rounded_mantissa_bits = (mantissa_bits + 3) / 4 * 4;
+ static_assert(mantissa_t_width >= rounded_mantissa_bits);
+ mantissa_t effective_mantissa
+ = ieee_mantissa << (rounded_mantissa_bits - mantissa_bits);
+ if (is_normal_number)
+ {
+ if constexpr (has_implicit_leading_bit)
+ // Restore the mantissa's implicit leading bit.
+ effective_mantissa |= mantissa_t{1} << rounded_mantissa_bits;
+ else
+ // The explicit mantissa bit should already be set.
+ __glibcxx_assert(effective_mantissa & (mantissa_t{1} << (mantissa_bits
+ - 1u)));
+ }
+
+ // Compute the shortest precision needed to print this value exactly,
+ // disregarding trailing zeros.
+ constexpr int full_hex_precision = (has_implicit_leading_bit
+ ? (mantissa_bits + 3) / 4
+ // With an explicit leading bit, we
+ // use the four leading nibbles as the
+ // hexit before the decimal point.
+ : (mantissa_bits - 4 + 3) / 4);
+ const int trailing_zeros = __countr_zero(effective_mantissa) / 4;
+ const int shortest_full_precision = full_hex_precision - trailing_zeros;
+ __glibcxx_assert(shortest_full_precision >= 0);
+
+ int written_exponent = unbiased_exponent;
+ const int effective_precision = precision.value_or(shortest_full_precision);
+ if (effective_precision < shortest_full_precision)
+ {
+ // When limiting the precision, we need to determine how to round the
+ // least significant printed hexit. The following branchless
+ // bit-level-parallel technique computes whether to round up the
+ // mantissa bit at index N (according to round-to-nearest rules) when
+ // dropping N bits of precision, for each index N in the bit vector.
+ // This technique is borrowed from the MSVC implementation.
+ using bitvec = mantissa_t;
+ const bitvec round_bit = effective_mantissa << 1;
+ const bitvec has_tail_bits = round_bit - 1;
+ const bitvec lsb_bit = effective_mantissa;
+ const bitvec should_round = round_bit & (has_tail_bits | lsb_bit);
+
+ const int dropped_bits = 4*(full_hex_precision - effective_precision);
+ // Mask out the dropped nibbles.
+ effective_mantissa >>= dropped_bits;
+ effective_mantissa <<= dropped_bits;
+ if (should_round & (mantissa_t{1} << dropped_bits))
+ {
+ // Round up the least significant nibble.
+ effective_mantissa += mantissa_t{1} << dropped_bits;
+ // Check and adjust for overflow of the leading nibble. When the
+ // type has an implicit leading bit, then the leading nibble
+ // before rounding is either 0 or 1, so it can't overflow.
+ if constexpr (!has_implicit_leading_bit)
+ {
+ // The only supported floating-point type with explicit
+ // leading mantissa bit is LDK_FLOAT80, i.e. x86 80-bit
+ // extended precision, and so we hardcode the below overflow
+ // check+adjustment for this type.
+ static_assert(mantissa_t_width == 64
+ && rounded_mantissa_bits == 64);
+ if (effective_mantissa == 0)
+ {
+ // We rounded up the least significant nibble and the
+ // mantissa overflowed, e.g f.fcp+10 with precision=1
+ // became 10.0p+10. Absorb this extra hexit into the
+ // exponent to obtain 1.0p+14.
+ effective_mantissa
+ = mantissa_t{1} << (rounded_mantissa_bits - 4);
+ written_exponent += 4;
+ }
+ }
+ }
+ }
+
+ // Compute the leading hexit and mask it out from the mantissa.
+ char leading_hexit;
+ if constexpr (has_implicit_leading_bit)
+ {
+ const unsigned nibble = effective_mantissa >> rounded_mantissa_bits;
+ __glibcxx_assert(nibble <= 2);
+ leading_hexit = '0' + nibble;
+ effective_mantissa &= ~(mantissa_t{0b11} << rounded_mantissa_bits);
+ }
+ else
+ {
+ const unsigned nibble = effective_mantissa >> (rounded_mantissa_bits-4);
+ __glibcxx_assert(nibble < 16);
+ leading_hexit = "0123456789abcdef"[nibble];
+ effective_mantissa &= ~(mantissa_t{0b1111} << (rounded_mantissa_bits-4));
+ written_exponent -= 3;
+ }
+
+ // Now before we start writing the string, determine the total length of
+ // the output string and perform a single bounds check.
+ int expected_output_length = sign + 1;
+ if (effective_precision != 0)
+ expected_output_length += strlen(".") + effective_precision;
+ const int abs_written_exponent = abs(written_exponent);
+ expected_output_length += (abs_written_exponent >= 10000 ? strlen("p+ddddd")
+ : abs_written_exponent >= 1000 ? strlen("p+dddd")
+ : abs_written_exponent >= 100 ? strlen("p+ddd")
+ : abs_written_exponent >= 10 ? strlen("p+dd")
+ : strlen("p+d"));
+ if (last - first < expected_output_length)
+ return {last, errc::value_too_large};
+
+ const auto saved_first = first;
+ // Write the negative sign and the leading hexit.
+ if (sign)
+ *first++ = '-';
+ *first++ = leading_hexit;
+
+ if (effective_precision > 0)
+ {
+ *first++ = '.';
+ int written_hexits = 0;
+ // Extract and mask out the leading nibble after the decimal point,
+ // write its corresponding hexit, and repeat until the mantissa is
+ // empty.
+ int nibble_offset = rounded_mantissa_bits;
+ if constexpr (!has_implicit_leading_bit)
+ // We already printed the entire leading hexit.
+ nibble_offset -= 4;
+ while (effective_mantissa != 0)
+ {
+ nibble_offset -= 4;
+ const unsigned nibble = effective_mantissa >> nibble_offset;
+ __glibcxx_assert(nibble < 16);
+ *first++ = "0123456789abcdef"[nibble];
+ ++written_hexits;
+ effective_mantissa &= ~(mantissa_t{0b1111} << nibble_offset);
+ }
+ __glibcxx_assert(nibble_offset >= 0);
+ __glibcxx_assert(written_hexits <= effective_precision);
+ // Since the mantissa is now empty, every hexit hereafter must be '0'.
+ if (int remaining_hexits = effective_precision - written_hexits)
+ {
+ memset(first, '0', remaining_hexits);
+ first += remaining_hexits;
+ }
+ }
+
+ // Finally, write the exponent.
+ *first++ = 'p';
+ if (written_exponent >= 0)
+ *first++ = '+';
+ const to_chars_result result = to_chars(first, last, written_exponent);
+ __glibcxx_assert(result.ec == errc{}
+ && result.ptr == saved_first + expected_output_length);
+ return result;
+ }
+
+template<typename T>
+ static to_chars_result
+ __floating_to_chars_shortest(char* first, char* const last, const T value,
+ chars_format fmt)
+ {
+ if (fmt == chars_format::hex)
+ return __floating_to_chars_hex(first, last, value, nullopt);
+
+ __glibcxx_assert(fmt == chars_format::fixed
+ || fmt == chars_format::scientific
+ || fmt == chars_format::general
+ || fmt == chars_format{});
+ __glibcxx_requires_valid_range(first, last);
+
+ if (auto result = __handle_special_value(first, last, value, fmt, 0))
+ return *result;
+
+ const auto fd = floating_to_shortest_scientific(value);
+ const int mantissa_length = get_mantissa_length(fd);
+ const int scientific_exponent = fd.exponent + mantissa_length - 1;
+
+ if (fmt == chars_format::general)
+ {
+ // Resolve the 'general' formatting mode as per the specification of
+ // the 'g' printf output specifier. Since there is no precision
+ // argument, the default precision of the 'g' specifier, 6, applies.
+ if (scientific_exponent >= -4 && scientific_exponent < 6)
+ fmt = chars_format::fixed;
+ else
+ fmt = chars_format::scientific;
+ }
+ else if (fmt == chars_format{})
+ {
+ // The 'plain' formatting mode resolves to 'scientific' if it yields
+ // the shorter string, and resolves to 'fixed' otherwise. The
+ // following lower and upper bounds on the exponent characterize when
+ // to prefer 'fixed' over 'scientific'.
+ int lower_bound = -(mantissa_length + 3);
+ int upper_bound = 5;
+ if (mantissa_length == 1)
+ // The decimal point in scientific notation will be omitted in this
+ // case; tighten the bounds appropriately.
+ ++lower_bound, --upper_bound;
+
+ if (fd.exponent >= lower_bound && fd.exponent <= upper_bound)
+ fmt = chars_format::fixed;
+ else
+ fmt = chars_format::scientific;
+ }
+
+ if (fmt == chars_format::scientific)
+ {
+ // Calculate the total length of the output string, perform a bounds
+ // check, and then defer to Ryu's to_chars subroutine.
+ int expected_output_length = fd.sign + mantissa_length;
+ if (mantissa_length > 1)
+ expected_output_length += strlen(".");
+ const int abs_exponent = abs(scientific_exponent);
+ expected_output_length += (abs_exponent >= 1000 ? strlen("e+dddd")
+ : abs_exponent >= 100 ? strlen("e+ddd")
+ : strlen("e+dd"));
+ if (last - first < expected_output_length)
+ return {last, errc::value_too_large};
+
+ const int output_length = ryu::to_chars(fd, first);
+ __glibcxx_assert(output_length == expected_output_length);
+ return {first + output_length, errc{}};
+ }
+ else if (fmt == chars_format::fixed && fd.exponent >= 0)
+ {
+ // The Ryu exponent is positive, and so this number's shortest
+ // representation is a whole number, to be formatted in fixed instead
+ // of scientific notation "as if by std::printf". This means we may
+ // need to print more digits of the IEEE mantissa than what the
+ // shortest scientific form given by Ryu provides.
+ //
+ // For instance, the exactly representable number
+ // 12300000000000001048576.0 has as its shortest scientific
+ // representation 123e+22, so in this case fd.mantissa is 123 and
+ // fd.exponent is 22, which doesn't have enough information to format
+ // the number exactly. So we defer to Ryu's d2fixed_buffered_n with
+ // precision=0 to format the number in the general case here.
+
+ // To that end, first compute the output length and perform a bounds
+ // check.
+ int expected_output_length = fd.sign + mantissa_length + fd.exponent;
+ if (is_rounded_up_pow10_p<T>(fd))
+ --expected_output_length;
+ if (last - first < expected_output_length)
+ return {last, errc::value_too_large};
+
+ // Optimization: if the shortest representation fits inside the IEEE
+ // mantissa, then the number is certainly exactly-representable and
+ // its shortest scientific form must be equal to its exact form. So
+ // we can write the value in fixed form exactly via fd.mantissa and
+ // fd.exponent.
+ //
+ // Taking log2 of both sides of the desired condition
+ // fd.mantissa * 10^fd.exponent < 2^mantissa_bits
+ // we get
+ // log2 fd.mantissa + fd.exponent * log2 10 < mantissa_bits
+ // where log2 10 is slightly smaller than 10/3=3.333...
+ //
+ // After adding some wiggle room due to rounding we get the condition
+ // value_fits_inside_mantissa_p below.
+ const int log2_mantissa = __bit_width(fd.mantissa) - 1;
+ const bool value_fits_inside_mantissa_p
+ = (log2_mantissa + (fd.exponent*10 + 2) / 3
+ < floating_type_traits<T>::mantissa_bits - 2);
+ if (value_fits_inside_mantissa_p)
+ {
+ // Print the small exactly-represantable number in fixed form by
+ // writing out fd.mantissa followed by fd.exponent many 0s.
+ if (fd.sign)
+ *first++ = '-';
+ to_chars_result result = to_chars(first, last, fd.mantissa);
+ __glibcxx_assert(result.ec == errc{});
+ memset(result.ptr, '0', fd.exponent);
+ result.ptr += fd.exponent;
+ const int output_length = fd.sign + (result.ptr - first);
+ __glibcxx_assert(output_length == expected_output_length);
+ return result;
+ }
+ else if constexpr (is_same_v<T, long double>)
+ {
+ // We can't use d2fixed_buffered_n for types larger than double,
+ // so we instead format larger types through sprintf.
+ // TODO: We currently go through an intermediate buffer in order
+ // to accomodate the mandatory null terminator of sprintf, but we
+ // can avoid this if we use sprintf to write all but the last
+ // digit, and carefully compute and write the last digit
+ // ourselves.
+ char buffer[expected_output_length+1];
+#if _GLIBCXX_USE_C99_FENV_TR1
+ const int saved_rounding_mode = fegetround();
+ if (saved_rounding_mode != FE_TONEAREST)
+ fesetround(FE_TONEAREST); // We want round-to-nearest behavior.
+#endif
+ const int output_length = sprintf(buffer, "%.0Lf", value);
+#if _GLIBCXX_USE_C99_FENV_TR1
+ if (saved_rounding_mode != FE_TONEAREST)
+ fesetround(saved_rounding_mode);
+#endif
+ __glibcxx_assert(output_length == expected_output_length);
+ memcpy(first, buffer, output_length);
+ return {first + output_length, errc{}};
+ }
+ else
+ {
+ // Otherwise, the number is too big, so defer to d2fixed_buffered_n.
+ const int output_length = ryu::d2fixed_buffered_n(value, 0, first);
+ __glibcxx_assert(output_length == expected_output_length);
+ return {first + output_length, errc{}};
+ }
+ }
+ else if (fmt == chars_format::fixed && fd.exponent < 0)
+ {
+ // The Ryu exponent is negative, so fd.mantissa definitely contains
+ // all of the whole part of the number, and therefore fd.mantissa and
+ // fd.exponent contain all of the information needed to format the
+ // number in fixed notation "as if by std::printf" (with precision
+ // equal to -fd.exponent).
+ const int whole_digits = max(mantissa_length + fd.exponent, 1);
+ const int expected_output_length
+ = fd.sign + whole_digits + strlen(".") + -fd.exponent;
+ if (last - first < expected_output_length)
+ return {last, errc::value_too_large};
+ if (mantissa_length <= -fd.exponent)
+ {
+ // The magnitude of the number is less than one. Format the
+ // number appropriately.
+ const auto orig_first = first;
+ if (fd.sign)
+ *first++ = '-';
+ *first++ = '0';
+ *first++ = '.';
+ const int leading_zeros = -fd.exponent - mantissa_length;
+ memset(first, '0', leading_zeros);
+ first += leading_zeros;
+ const to_chars_result result = to_chars(first, last, fd.mantissa);
+ const int output_length = result.ptr - orig_first;
+ __glibcxx_assert(output_length == expected_output_length
+ && result.ec == errc{});
+ return result;
+ }
+ else
+ {
+ // The magnitude of the number is at least one.
+ const auto orig_first = first;
+ if (fd.sign)
+ *first++ = '-';
+ to_chars_result result = to_chars(first, last, fd.mantissa);
+ __glibcxx_assert(result.ec == errc{});
+ // Make space for and write the decimal point in the correct spot.
+ memmove(&result.ptr[fd.exponent+1], &result.ptr[fd.exponent],
+ -fd.exponent);
+ result.ptr[fd.exponent] = '.';
+ const int output_length = result.ptr + 1 - orig_first;
+ __glibcxx_assert(output_length == expected_output_length);
+ ++result.ptr;
+ return result;
+ }
+ }
+
+ __glibcxx_assert(false);
+ }
+
+template<typename T>
+ static to_chars_result
+ __floating_to_chars_precision(char* first, char* const last, const T value,
+ chars_format fmt, const int precision)
+ {
+ if (fmt == chars_format::hex)
+ return __floating_to_chars_hex(first, last, value, precision);
+
+ if (precision < 0) [[unlikely]]
+ // A negative precision argument is treated as if it were omitted, in
+ // which case the default precision of 6 applies, as per the printf
+ // specification.
+ return __floating_to_chars_precision(first, last, value, fmt, 6);
+
+ __glibcxx_assert(fmt == chars_format::fixed
+ || fmt == chars_format::scientific
+ || fmt == chars_format::general);
+ __glibcxx_requires_valid_range(first, last);
+
+ if (auto result = __handle_special_value(first, last, value,
+ fmt, precision))
+ return *result;
+
+ constexpr int mantissa_bits = floating_type_traits<T>::mantissa_bits;
+ constexpr int exponent_bits = floating_type_traits<T>::exponent_bits;
+ constexpr int exponent_bias = (1u << (exponent_bits - 1)) - 1;
+
+ // Extract the sign and exponent from the value.
+ const auto [mantissa, biased_exponent, sign] = get_ieee_repr(value);
+ const bool is_normal_number = (biased_exponent != 0);
+
+ // Calculate the unbiased exponent.
+ const int32_t unbiased_exponent = (is_normal_number
+ ? biased_exponent - exponent_bias
+ : 1 - exponent_bias);
+
+ // Obtain trunc(log2(abs(value))), which is just the unbiased exponent.
+ const int floor_log2_value = unbiased_exponent;
+ // This is within +-1 of log10(abs(value)). Note that log10 2 is 0.3010..
+ const int approx_log10_value = (floor_log2_value >= 0
+ ? (floor_log2_value*301 + 999)/1000
+ : (floor_log2_value*301 - 999)/1000);
+
+ // Compute (an upper bound of) the number's effective precision when it is
+ // formatted in scientific and fixed notation. Beyond this precision all
+ // digits are definitely zero, and this fact allows us to bound the sizes
+ // of any local output buffers that we may need to use. TODO: Consider
+ // the number of trailing zero bits in the mantissa to obtain finer upper
+ // bounds.
+ // ???: Using "mantissa_bits + 1" instead of just "mantissa_bits" in the
+ // bounds below is necessary only for __ibm128, it seems. Even though the
+ // type has 105 bits of precision, printf may output 106 fractional digits
+ // on some inputs, e.g. 0x1.bcd19f5d720d12a3513e3301028p+0.
+ const int max_eff_scientific_precision
+ = (floor_log2_value >= 0
+ ? max(mantissa_bits + 1, approx_log10_value + 1)
+ : -(7*floor_log2_value + 9)/10 + 2 + mantissa_bits + 1);
+ __glibcxx_assert(max_eff_scientific_precision > 0);
+
+ const int max_eff_fixed_precision
+ = (floor_log2_value >= 0
+ ? mantissa_bits + 1
+ : -floor_log2_value + mantissa_bits + 1);
+ __glibcxx_assert(max_eff_fixed_precision > 0);
+
+ // Ryu doesn't support formatting floating-point types larger than double
+ // with an explicit precision, so instead we just go through printf.
+ if constexpr (is_same_v<T, long double>)
+ {
+ int effective_precision;
+ const char* output_specifier;
+ if (fmt == chars_format::scientific)
+ {
+ effective_precision = min(precision, max_eff_scientific_precision);
+ output_specifier = "%.*Le";
+ }
+ else if (fmt == chars_format::fixed)
+ {
+ effective_precision = min(precision, max_eff_fixed_precision);
+ output_specifier = "%.*Lf";
+ }
+ else if (fmt == chars_format::general)
+ {
+ effective_precision = min(precision, max_eff_scientific_precision);
+ output_specifier = "%.*Lg";
+ }
+ const int excess_precision = (fmt != chars_format::general
+ ? precision - effective_precision : 0);
+
+ // Since the output of printf is locale-sensitive, we need to be able
+ // to handle a radix point that's different from '.'.
+ char radix[6] = {'.', '\0', '\0', '\0', '\0', '\0'};
+ if (effective_precision > 0)
+ // ???: Can nl_langinfo() ever return null?
+ if (const char* const radix_ptr = nl_langinfo(RADIXCHAR))
+ {
+ strncpy(radix, radix_ptr, sizeof(radix)-1);
+ // We accept only radix points which are at most 4 bytes (one
+ // UTF-8 character) wide.
+ __glibcxx_assert(radix[4] == '\0');
+ }
+
+ // Compute straightforward upper bounds on the output length.
+ int output_length_upper_bound;
+ if (fmt == chars_format::scientific || fmt == chars_format::general)
+ output_length_upper_bound = (strlen("-d") + sizeof(radix)
+ + effective_precision
+ + strlen("e+dddd"));
+ else if (fmt == chars_format::fixed)
+ {
+ if (approx_log10_value >= 0)
+ output_length_upper_bound = sign + approx_log10_value + 1;
+ else
+ output_length_upper_bound = sign + strlen("0");
+ output_length_upper_bound += sizeof(radix) + effective_precision;
+ }
+
+ // Do the sprintf into the local buffer.
+ char buffer[output_length_upper_bound+1];
+#if _GLIBCXX_USE_C99_FENV_TR1
+ const int saved_rounding_mode = fegetround();
+ if (saved_rounding_mode != FE_TONEAREST)
+ fesetround(FE_TONEAREST); // We want round-to-nearest behavior.
+#endif
+ int output_length
+ = sprintf(buffer, output_specifier, effective_precision, value);
+#if _GLIBCXX_USE_C99_FENV_TR1
+ if (saved_rounding_mode != FE_TONEAREST)
+ fesetround(saved_rounding_mode);
+#endif
+ __glibcxx_assert(output_length <= output_length_upper_bound);
+
+ if (effective_precision > 0)
+ // We need to replace a radix that is different from '.' with '.'.
+ if (const string_view radix_sv = {radix}; radix_sv != ".")
+ {
+ const string_view buffer_sv = {buffer, (size_t)output_length};
+ const size_t radix_index = buffer_sv.find(radix_sv);
+ if (radix_index != string_view::npos)
+ {
+ buffer[radix_index] = '.';
+ if (radix_sv.length() > 1)
+ {
+ memmove(&buffer[radix_index + 1],
+ &buffer[radix_index + radix_sv.length()],
+ output_length - radix_index - radix_sv.length());
+ output_length -= radix_sv.length() - 1;
+ }
+ }
+ }
+
+ // Copy the string from the buffer over to the output range.
+ if (last - first < output_length + excess_precision)
+ return {last, errc::value_too_large};
+ memcpy(first, buffer, output_length);
+ first += output_length;
+
+ // Add the excess 0s to the result.
+ if (excess_precision > 0)
+ {
+ if (fmt == chars_format::scientific)
+ {
+ char* const significand_end
+ = (output_length >= 6 && first[-6] == 'e' ? &first[-6]
+ : first[-5] == 'e' ? &first[-5]
+ : &first[-4]);
+ __glibcxx_assert(*significand_end == 'e');
+ memmove(significand_end + excess_precision, significand_end,
+ first - significand_end);
+ memset(significand_end, '0', excess_precision);
+ first += excess_precision;
+ }
+ else if (fmt == chars_format::fixed)
+ {
+ memset(first, '0', excess_precision);
+ first += excess_precision;
+ }
+ }
+ return {first, errc{}};
+ }
+ else if (fmt == chars_format::scientific)
+ {
+ const int effective_precision
+ = min(precision, max_eff_scientific_precision);
+ const int excess_precision = precision - effective_precision;
+
+ // We can easily compute the output length exactly whenever the
+ // scientific exponent is far enough away from +-100. But if it's
+ // near +-100, then our log2 approximation is too coarse (and doesn't
+ // consider precision-dependent rounding) in order to accurately
+ // distinguish between a scientific exponent of +-100 and +-99.
+ const bool scientific_exponent_near_100_p
+ = abs(abs(floor_log2_value) - 332) <= 4;
+
+ // Compute an upper bound on the output length. TODO: Maybe also
+ // consider a lower bound on the output length.
+ int output_length_upper_bound = sign + strlen("d");
+ if (effective_precision > 0)
+ output_length_upper_bound += strlen(".") + effective_precision;
+ if (scientific_exponent_near_100_p
+ || (floor_log2_value >= 332 || floor_log2_value <= -333))
+ output_length_upper_bound += strlen("e+ddd");
+ else
+ output_length_upper_bound += strlen("e+dd");
+
+ int output_length;
+ if (last - first >= output_length_upper_bound + excess_precision)
+ {
+ // The result will definitely fit into the output range, so we can
+ // write directly into it.
+ output_length = ryu::d2exp_buffered_n(value, effective_precision,
+ first, nullptr);
+ __glibcxx_assert(output_length == output_length_upper_bound
+ || (scientific_exponent_near_100_p
+ && (output_length
+ == output_length_upper_bound - 1)));
+ }
+ else if (scientific_exponent_near_100_p)
+ {
+ // Write the result of d2exp_buffered_n into an intermediate
+ // buffer, do a bounds check, and copy the result into the output
+ // range.
+ char buffer[output_length_upper_bound];
+ output_length = ryu::d2exp_buffered_n(value, effective_precision,
+ buffer, nullptr);
+ __glibcxx_assert(output_length == output_length_upper_bound - 1
+ || output_length == output_length_upper_bound);
+ if (last - first < output_length + excess_precision)
+ return {last, errc::value_too_large};
+ memcpy(first, buffer, output_length);
+ }
+ else
+ // If the scientific exponent is not near 100, then the upper bound
+ // is actually the exact length, and so the result will definitely
+ // not fit into the output range.
+ return {last, errc::value_too_large};
+ first += output_length;
+ if (excess_precision > 0)
+ {
+ // Splice the excess zeros into the result.
+ char* const significand_end = (first[-5] == 'e'
+ ? &first[-5] : &first[-4]);
+ __glibcxx_assert(*significand_end == 'e');
+ memmove(significand_end + excess_precision, significand_end,
+ first - significand_end);
+ memset(significand_end, '0', excess_precision);
+ first += excess_precision;
+ }
+ return {first, errc{}};
+ }
+ else if (fmt == chars_format::fixed)
+ {
+ const int effective_precision
+ = min(precision, max_eff_fixed_precision);
+ const int excess_precision = precision - effective_precision;
+
+ // Compute an upper bound on the output length. TODO: Maybe also
+ // consider a lower bound on the output length.
+ int output_length_upper_bound;
+ if (approx_log10_value >= 0)
+ output_length_upper_bound = sign + approx_log10_value + 1;
+ else
+ output_length_upper_bound = sign + strlen("0");
+ if (effective_precision > 0)
+ output_length_upper_bound += strlen(".") + effective_precision;
+
+ int output_length;
+ if (last - first >= output_length_upper_bound + excess_precision)
+ {
+ // The result will definitely fit into the output range, so we can
+ // write directly into it.
+ output_length = ryu::d2fixed_buffered_n(value, effective_precision,
+ first);
+ __glibcxx_assert(output_length <= output_length_upper_bound);
+ }
+ else
+ {
+ // Write the result of d2fixed_buffered_n into an intermediate
+ // buffer, do a bounds check, and copy the result into the output
+ // range.
+ char buffer[output_length_upper_bound];
+ output_length = ryu::d2fixed_buffered_n(value, effective_precision,
+ buffer);
+ __glibcxx_assert(output_length <= output_length_upper_bound);
+ if (last - first < output_length + excess_precision)
+ return {last, errc::value_too_large};
+ memcpy(first, buffer, output_length);
+ }
+ first += output_length;
+ if (excess_precision > 0)
+ {
+ // Append the excess zeros into the result.
+ memset(first, '0', excess_precision);
+ first += excess_precision;
+ }
+ return {first, errc{}};
+ }
+ else if (fmt == chars_format::general)
+ {
+ // Handle the 'general' formatting mode as per C11 printf's %g output
+ // specifier. Since Ryu doesn't do zero-trimming, we always write to
+ // an intermediate buffer and manually perform zero-trimming there
+ // before copying the result over to the output range.
+ int effective_precision
+ = min(precision, max_eff_scientific_precision + 1);
+ const int output_length_upper_bound
+ = strlen("-d.") + effective_precision + strlen("e+ddd");
+ // The four bytes of headroom is to avoid needing to do a memmove when
+ // rewriting a scientific form such as 1.00e-2 into the equivalent
+ // fixed form 0.001.
+ char buffer[4 + output_length_upper_bound];
+
+ // 7.21.6.1/8: "Let P equal ... 1 if the precision is zero."
+ if (effective_precision == 0)
+ effective_precision = 1;
+
+ // Perform a trial formatting in scientific form, and obtain the
+ // scientific exponent.
+ int scientific_exponent;
+ char* buffer_start = buffer + 4;
+ int output_length
+ = ryu::d2exp_buffered_n(value, effective_precision - 1,
+ buffer_start, &scientific_exponent);
+ __glibcxx_assert(output_length <= output_length_upper_bound);
+
+ // 7.21.6.1/8: "Then, if a conversion with style E would have an
+ // exponent of X:
+ // if P > X >= -4, the conversion is with style f and
+ // precision P - (X + 1).
+ // otherwise, the conversion is with style e and precision P - 1."
+ const bool resolve_to_fixed_form
+ = (scientific_exponent >= -4
+ && scientific_exponent < effective_precision);
+ if (resolve_to_fixed_form)
+ {
+ // Rather than invoking d2fixed_buffered_n to reformat the number
+ // for us from scratch, we can just rewrite the scientific form
+ // into fixed form in-place. This is safe to do because whenever
+ // %g resolves to %f, the fixed form will be no larger than the
+ // corresponding scientific form, and it will also contain the
+ // same significant digits as the scientific form.
+ fmt = chars_format::fixed;
+ if (scientific_exponent < 0)
+ {
+ // e.g. buffer_start == "-1.234e-04"
+ char* leading_digit = &buffer_start[sign];
+ leading_digit[1] = leading_digit[0];
+ // buffer_start == "-11234e-04"
+ buffer_start -= -scientific_exponent;
+ __glibcxx_assert(buffer_start >= buffer);
+ // buffer_start == "????-11234e-04"
+ char* head = buffer_start;
+ if (sign)
+ *head++ = '-';
+ *head++ = '0';
+ *head++ = '.';
+ memset(head, '0', -scientific_exponent - 1);
+ // buffer_start == "-0.00011234e-04"
+
+ // Now drop the exponent suffix, and add the leading zeros to
+ // the output length.
+ output_length -= strlen("e-0d");
+ output_length += -scientific_exponent;
+ if (effective_precision - 1 == 0)
+ // The scientific form had no decimal point, but the fixed
+ // form now does.
+ output_length += strlen(".");
+ }
+ else if (effective_precision == 1)
+ {
+ // The scientific exponent must be 0, so the fixed form
+ // coincides with the scientific form (minus the exponent
+ // suffix).
+ __glibcxx_assert(scientific_exponent == 0);
+ output_length -= strlen("e+dd");
+ }
+ else
+ {
+ // We are dealing with a scientific form which has a
+ // non-empty fractional part and a nonnegative exponent,
+ // e.g. buffer_start == "1.234e+02".
+ __glibcxx_assert(effective_precision >= 1);
+ char* const decimal_point = &buffer_start[sign + 1];
+ __glibcxx_assert(*decimal_point == '.');
+ memmove(decimal_point, decimal_point+1,
+ scientific_exponent);
+ // buffer_start == "123.4e+02"
+ decimal_point[scientific_exponent] = '.';
+ if (scientific_exponent >= 100)
+ output_length -= strlen("e+ddd");
+ else
+ output_length -= strlen("e+dd");
+ if (effective_precision - 1 == scientific_exponent)
+ output_length -= strlen(".");
+ }
+ effective_precision -= 1 + scientific_exponent;
+
+ __glibcxx_assert(output_length <= output_length_upper_bound);
+ }
+ else
+ {
+ // We're sticking to the scientific form, so keep the output as-is.
+ fmt = chars_format::scientific;
+ effective_precision = effective_precision - 1;
+ }
+
+ // 7.21.6.1/8: "Finally ... any any trailing zeros are removed from
+ // the fractional portion of the result and the decimal-point
+ // character is removed if there is no fractional portion remaining."
+ if (effective_precision > 0)
+ {
+ char* decimal_point = nullptr;
+ if (fmt == chars_format::scientific)
+ decimal_point = &buffer_start[sign + 1];
+ else if (fmt == chars_format::fixed)
+ decimal_point
+ = &buffer_start[output_length] - effective_precision - 1;
+ __glibcxx_assert(*decimal_point == '.');
+
+ char* const fractional_part_start = decimal_point + 1;
+ char* fractional_part_end = nullptr;
+ if (fmt == chars_format::scientific)
+ {
+ fractional_part_end = (buffer_start[output_length-5] == 'e'
+ ? &buffer_start[output_length-5]
+ : &buffer_start[output_length-4]);
+ __glibcxx_assert(*fractional_part_end == 'e');
+ }
+ else if (fmt == chars_format::fixed)
+ fractional_part_end = &buffer_start[output_length];
+
+ const string_view fractional_part
+ = {fractional_part_start, (size_t)(fractional_part_end
+ - fractional_part_start) };
+ const size_t last_nonzero_digit_pos
+ = fractional_part.find_last_not_of('0');
+
+ char* trim_start;
+ if (last_nonzero_digit_pos == string_view::npos)
+ trim_start = decimal_point;
+ else
+ trim_start = &fractional_part_start[last_nonzero_digit_pos] + 1;
+ if (fmt == chars_format::scientific)
+ memmove(trim_start, fractional_part_end,
+ &buffer_start[output_length] - fractional_part_end);
+ output_length -= fractional_part_end - trim_start;
+ }
+
+ if (last - first < output_length)
+ return {last, errc::value_too_large};
+
+ memcpy(first, buffer_start, output_length);
+ return {first + output_length, errc{}};
+ }
+
+ __glibcxx_assert(false);
+ }
+
+// Define the overloads for float.
+to_chars_result
+to_chars(char* first, char* last, float value) noexcept
+{ return __floating_to_chars_shortest(first, last, value, chars_format{}); }
+
+to_chars_result
+to_chars(char* first, char* last, float value, chars_format fmt) noexcept
+{ return __floating_to_chars_shortest(first, last, value, fmt); }
+
+to_chars_result
+to_chars(char* first, char* last, float value, chars_format fmt,
+ int precision) noexcept
+{ return __floating_to_chars_precision(first, last, value, fmt, precision); }
+
+// Define the overloads for double.
+to_chars_result
+to_chars(char* first, char* last, double value) noexcept
+{ return __floating_to_chars_shortest(first, last, value, chars_format{}); }
+
+to_chars_result
+to_chars(char* first, char* last, double value, chars_format fmt) noexcept
+{ return __floating_to_chars_shortest(first, last, value, fmt); }
+
+to_chars_result
+to_chars(char* first, char* last, double value, chars_format fmt,
+ int precision) noexcept
+{ return __floating_to_chars_precision(first, last, value, fmt, precision); }
+
+// Define the overloads for long double.
+to_chars_result
+to_chars(char* first, char* last, long double value) noexcept
+{
+ if constexpr (LONG_DOUBLE_KIND == LDK_BINARY64
+ || LONG_DOUBLE_KIND == LDK_UNSUPPORTED)
+ return __floating_to_chars_shortest(first, last, static_cast<double>(value),
+ chars_format{});
+ else
+ return __floating_to_chars_shortest(first, last, value, chars_format{});
+}
+
+to_chars_result
+to_chars(char* first, char* last, long double value, chars_format fmt) noexcept
+{
+ if constexpr (LONG_DOUBLE_KIND == LDK_BINARY64
+ || LONG_DOUBLE_KIND == LDK_UNSUPPORTED)
+ return __floating_to_chars_shortest(first, last, static_cast<double>(value),
+ fmt);
+ else
+ return __floating_to_chars_shortest(first, last, value, fmt);
+}
+
+to_chars_result
+to_chars(char* first, char* last, long double value, chars_format fmt,
+ int precision) noexcept
+{
+ if constexpr (LONG_DOUBLE_KIND == LDK_BINARY64
+ || LONG_DOUBLE_KIND == LDK_UNSUPPORTED)
+ return __floating_to_chars_precision(first, last, static_cast<double>(value),
+ fmt,
+ precision);
+ else
+ return __floating_to_chars_precision(first, last, value, fmt, precision);
+}
+
+#ifdef _GLIBCXX_LONG_DOUBLE_COMPAT
+// Map the -mlong-double-64 long double overloads to the double overloads.
+extern "C" to_chars_result
+_ZSt8to_charsPcS_e(char* first, char* last, double value) noexcept
+ __attribute__((alias ("_ZSt8to_charsPcS_d")));
+
+extern "C" to_chars_result
+_ZSt8to_charsPcS_eSt12chars_format(char* first, char* last, double value,
+ chars_format fmt) noexcept
+ __attribute__((alias ("_ZSt8to_charsPcS_dSt12chars_format")));
+
+extern "C" to_chars_result
+_ZSt8to_charsPcS_eSt12chars_formati(char* first, char* last, double value,
+ chars_format fmt, int precision) noexcept
+ __attribute__((alias ("_ZSt8to_charsPcS_dSt12chars_formati")));
+#endif
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
projects / gcc.git / commitdiff