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317 lines
13 KiB
C++
317 lines
13 KiB
C++
// Copyright 2020-2023 Junekey Jeon
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// Copyright 2022 Peter Dimov
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// Copyright 2023 Matt Borland
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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#include <boost/charconv/to_chars.hpp>
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#include <limits>
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#include <cstdio>
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#include <cstring>
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#include <cstdint>
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namespace boost { namespace charconv { namespace detail {
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// These "//"'s are to prevent clang-format to ruin this nice alignment.
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// Thanks to reddit user u/mcmcc:
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// https://www.reddit.com/r/cpp/comments/so3wx9/dragonbox_110_is_released_a_fast_floattostring/hw8z26r/?context=3
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static constexpr char radix_100_table[] = {
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'0', '0', '0', '1', '0', '2', '0', '3', '0', '4', //
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'0', '5', '0', '6', '0', '7', '0', '8', '0', '9', //
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'1', '0', '1', '1', '1', '2', '1', '3', '1', '4', //
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'1', '5', '1', '6', '1', '7', '1', '8', '1', '9', //
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'2', '0', '2', '1', '2', '2', '2', '3', '2', '4', //
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'2', '5', '2', '6', '2', '7', '2', '8', '2', '9', //
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'3', '0', '3', '1', '3', '2', '3', '3', '3', '4', //
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'3', '5', '3', '6', '3', '7', '3', '8', '3', '9', //
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'4', '0', '4', '1', '4', '2', '4', '3', '4', '4', //
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'4', '5', '4', '6', '4', '7', '4', '8', '4', '9', //
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'5', '0', '5', '1', '5', '2', '5', '3', '5', '4', //
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'5', '5', '5', '6', '5', '7', '5', '8', '5', '9', //
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'6', '0', '6', '1', '6', '2', '6', '3', '6', '4', //
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'6', '5', '6', '6', '6', '7', '6', '8', '6', '9', //
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'7', '0', '7', '1', '7', '2', '7', '3', '7', '4', //
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'7', '5', '7', '6', '7', '7', '7', '8', '7', '9', //
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'8', '0', '8', '1', '8', '2', '8', '3', '8', '4', //
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'8', '5', '8', '6', '8', '7', '8', '8', '8', '9', //
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'9', '0', '9', '1', '9', '2', '9', '3', '9', '4', //
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'9', '5', '9', '6', '9', '7', '9', '8', '9', '9' //
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};
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static constexpr char radix_100_head_table[] = {
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'0', '.', '1', '.', '2', '.', '3', '.', '4', '.', //
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'5', '.', '6', '.', '7', '.', '8', '.', '9', '.', //
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'1', '.', '1', '.', '1', '.', '1', '.', '1', '.', //
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'1', '.', '1', '.', '1', '.', '1', '.', '1', '.', //
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'2', '.', '2', '.', '2', '.', '2', '.', '2', '.', //
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'2', '.', '2', '.', '2', '.', '2', '.', '2', '.', //
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'3', '.', '3', '.', '3', '.', '3', '.', '3', '.', //
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'3', '.', '3', '.', '3', '.', '3', '.', '3', '.', //
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'4', '.', '4', '.', '4', '.', '4', '.', '4', '.', //
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'4', '.', '4', '.', '4', '.', '4', '.', '4', '.', //
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'5', '.', '5', '.', '5', '.', '5', '.', '5', '.', //
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'5', '.', '5', '.', '5', '.', '5', '.', '5', '.', //
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'6', '.', '6', '.', '6', '.', '6', '.', '6', '.', //
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'6', '.', '6', '.', '6', '.', '6', '.', '6', '.', //
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'7', '.', '7', '.', '7', '.', '7', '.', '7', '.', //
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'7', '.', '7', '.', '7', '.', '7', '.', '7', '.', //
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'8', '.', '8', '.', '8', '.', '8', '.', '8', '.', //
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'8', '.', '8', '.', '8', '.', '8', '.', '8', '.', //
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'9', '.', '9', '.', '9', '.', '9', '.', '9', '.', //
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'9', '.', '9', '.', '9', '.', '9', '.', '9', '.' //
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};
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void print_1_digit(std::uint32_t n, char* buffer) noexcept
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{
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*buffer = char('0' | n);
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}
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void print_2_digits(std::uint32_t n, char* buffer) noexcept
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{
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std::memcpy(buffer, radix_100_table + n * 2, 2);
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}
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// These digit generation routines are inspired by James Anhalt's itoa algorithm:
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// https://github.com/jeaiii/itoa
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// The main idea is for given n, find y such that floor(10^k * y / 2^32) = n holds,
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// where k is an appropriate integer depending on the length of n.
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// For example, if n = 1234567, we set k = 6. In this case, we have
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// floor(y / 2^32) = 1,
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// floor(10^2 * ((10^0 * y) mod 2^32) / 2^32) = 23,
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// floor(10^2 * ((10^2 * y) mod 2^32) / 2^32) = 45, and
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// floor(10^2 * ((10^4 * y) mod 2^32) / 2^32) = 67.
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// See https://jk-jeon.github.io/posts/2022/02/jeaiii-algorithm/ for more explanation.
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void print_9_digits(std::uint32_t s32, int& exponent, char* buffer) noexcept
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{
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// -- IEEE-754 binary32
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// Since we do not cut trailing zeros in advance, s32 must be of 6~9 digits
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// unless the original input was subnormal.
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// In particular, when it is of 9 digits it shouldn't have any trailing zeros.
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// -- IEEE-754 binary64
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// In this case, s32 must be of 7~9 digits unless the input is subnormal,
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// and it shouldn't have any trailing zeros if it is of 9 digits.
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if (s32 >= 100000000)
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{
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// 9 digits.
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// 1441151882 = ceil(2^57 / 1'0000'0000) + 1
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auto prod = s32 * UINT64_C(1441151882);
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prod >>= 25;
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std::memcpy(buffer, radix_100_head_table + UINT32_C(prod >> 32) * 2, 2);
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 2);
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 4);
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 6);
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 8);
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exponent += 8;
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buffer += 10;
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}
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else if (s32 >= 1000000)
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{
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// 7 or 8 digits.
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// 281474978 = ceil(2^48 / 100'0000) + 1
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auto prod = s32 * UINT64_C(281474978);
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prod >>= 16;
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auto const head_digits = static_cast<std::uint32_t>(prod >> 32);
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// If s32 is of 8 digits, increase the exponent by 7.
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// Otherwise, increase it by 6.
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exponent += (6 + unsigned(head_digits >= 10));
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// Write the first digit and the decimal point.
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std::memcpy(buffer, radix_100_head_table + head_digits * 2, 2);
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// This third character may be overwritten later but we don't care.
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buffer[2] = radix_100_table[head_digits * 2 + 1];
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// Remaining 6 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 1000000))
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{
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// The number of characters actually need to be written is:
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// 1, if only the first digit is nonzero, which means that either s32 is of 7
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// digits or it is of 8 digits but the second digit is zero, or
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// 3, otherwise.
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// Note that buffer[2] is never '0' if s32 is of 7 digits, because the input is
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// never zero.
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buffer += (1 + (unsigned(head_digits >= 10) & unsigned(buffer[2] > '0')) * 2);
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}
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else
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{
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// At least one of the remaining 6 digits are nonzero.
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// After this adjustment, now the first destination becomes buffer + 2.
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buffer += unsigned(head_digits >= 10);
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// Obtain the next two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 2);
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// Remaining 4 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 10000))
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{
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buffer += (3 + unsigned(buffer[3] > '0'));
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}
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else
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{
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// At least one of the remaining 4 digits are nonzero.
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// Obtain the next two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 4);
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// Remaining 2 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 100))
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{
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buffer += (5 + unsigned(buffer[5] > '0'));
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}
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else
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{
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// Obtain the last two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 6);
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buffer += (7 + unsigned(buffer[7] > '0'));
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}
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}
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}
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}
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else if (s32 >= 10000)
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{
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// 5 or 6 digits.
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// 429497 = ceil(2^32 / 1'0000)
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auto prod = s32 * UINT64_C(429497);
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auto const head_digits = static_cast<std::uint32_t>(prod >> 32);
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// If s32 is of 6 digits, increase the exponent by 5.
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// Otherwise, increase it by 4.
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exponent += (4 + static_cast<unsigned>(head_digits >= 10));
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// Write the first digit and the decimal point.
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std::memcpy(buffer, radix_100_head_table + head_digits * 2, 2);
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// This third character may be overwritten later but we don't care.
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buffer[2] = radix_100_table[head_digits * 2 + 1];
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// Remaining 4 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 10000))
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{
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// The number of characters actually written is 1 or 3, similarly to the case of
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// 7 or 8 digits.
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buffer += (1 + (unsigned(head_digits >= 10) & unsigned(buffer[2] > '0')) * 2);
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}
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else
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{
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// At least one of the remaining 4 digits are nonzero.
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// After this adjustment, now the first destination becomes buffer + 2.
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buffer += unsigned(head_digits >= 10);
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// Obtain the next two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 2);
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// Remaining 2 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 100))
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{
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buffer += (3 + unsigned(buffer[3] > '0'));
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}
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else
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{
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// Obtain the last two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 4);
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buffer += (5 + unsigned(buffer[5] > '0'));
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}
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}
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}
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else if (s32 >= 100)
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{
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// 3 or 4 digits.
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// 42949673 = ceil(2^32 / 100)
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auto prod = s32 * UINT64_C(42949673);
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auto const head_digits = static_cast<std::uint32_t>(prod >> 32);
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// If s32 is of 4 digits, increase the exponent by 3.
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// Otherwise, increase it by 2.
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exponent += (2 + int(head_digits >= 10));
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// Write the first digit and the decimal point.
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std::memcpy(buffer, radix_100_head_table + head_digits * 2, 2);
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// This third character may be overwritten later but we don't care.
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buffer[2] = radix_100_table[head_digits * 2 + 1];
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// Remaining 2 digits are all zero?
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if (static_cast<std::uint32_t>(prod) <= static_cast<std::uint32_t>((UINT64_C(1) << 32) / 100))
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{
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// The number of characters actually written is 1 or 3, similarly to the case of
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// 7 or 8 digits.
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buffer += (1 + (unsigned(head_digits >= 10) & unsigned(buffer[2] > '0')) * 2);
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}
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else
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{
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// At least one of the remaining 2 digits are nonzero.
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// After this adjustment, now the first destination becomes buffer + 2.
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buffer += unsigned(head_digits >= 10);
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// Obtain the last two digits.
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prod = static_cast<std::uint32_t>(prod) * UINT64_C(100);
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print_2_digits(static_cast<std::uint32_t>(prod >> 32), buffer + 2);
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buffer += (3 + unsigned(buffer[3] > '0'));
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}
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}
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else
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{
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// 1 or 2 digits.
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// If s32 is of 2 digits, increase the exponent by 1.
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exponent += int(s32 >= 10);
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// Write the first digit and the decimal point.
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std::memcpy(buffer, radix_100_head_table + s32 * 2, 2);
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// This third character may be overwritten later but we don't care.
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buffer[2] = radix_100_table[s32 * 2 + 1];
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// The number of characters actually written is 1 or 3, similarly to the case of
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// 7 or 8 digits.
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buffer += (1 + (unsigned(s32 >= 10) & unsigned(buffer[2] > '0')) * 2);
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}
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}
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}}} // Namespaces
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boost::charconv::to_chars_result boost::charconv::to_chars( char* first, char* last, float value ) noexcept
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{
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std::snprintf( first, last - first, "%.*g", std::numeric_limits<float>::max_digits10, value );
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return { first + std::strlen(first), 0 };
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}
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boost::charconv::to_chars_result boost::charconv::to_chars(char* first, char* last, double value, boost::charconv::chars_format fmt, int precision) noexcept
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{
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if (fmt == boost::charconv::chars_format::scientific)
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{
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if (precision == -1)
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{
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precision = std::numeric_limits<double>::max_digits10;
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}
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if (precision > static_cast<std::ptrdiff_t>(last - first))
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{
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return { first, EOVERFLOW };
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}
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auto* ptr = jkj::floff::floff<jkj::floff::main_cache_full, jkj::floff::extended_cache_long>(value, precision, first);
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return { ptr, 0 };
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}
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else
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{
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std::snprintf( first, last - first, "%.*g", std::numeric_limits<double>::max_digits10, value );
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return { first + std::strlen(first), 0 };
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}
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}
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boost::charconv::to_chars_result boost::charconv::to_chars( char* first, char* last, long double value ) noexcept
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{
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std::snprintf( first, last - first, "%.*Lg", std::numeric_limits<long double>::max_digits10, value );
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return { first + std::strlen(first), 0 };
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}
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