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// Copyright 2020-2022 Junekey Jeon
//
// The contents of this file may be used under the terms of
// the Apache License v2.0 with LLVM Exceptions.
//
// (See accompanying file LICENSE-Apache or copy at
// https://llvm.org/foundation/relicensing/LICENSE.txt)
//
// Alternatively, the contents of this file may be used under the terms of
// the Boost Software License, Version 1.0.
// (See accompanying file LICENSE-Boost or copy at
// https://www.boost.org/LICENSE_1_0.txt)
//
// Unless required by applicable law or agreed to in writing, this software
// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.
#include "dragonbox/dragonbox_to_chars.h"
#if defined(__GNUC__) || defined(__clang__)
#define JKJ_FORCEINLINE inline __attribute__((always_inline))
#elif defined(_MSC_VER)
#define JKJ_FORCEINLINE __forceinline
#else
#define JKJ_FORCEINLINE inline
#endif
namespace jkj::dragonbox {
namespace to_chars_detail {
// These "//"'s are to prevent clang-format to ruin this nice alignment.
// Thanks to reddit user u/mcmcc:
// https://www.reddit.com/r/cpp/comments/so3wx9/dragonbox_110_is_released_a_fast_floattostring/hw8z26r/?context=3
static constexpr char radix_100_table[] = {
'0', '0', '0', '1', '0', '2', '0', '3', '0', '4', //
'0', '5', '0', '6', '0', '7', '0', '8', '0', '9', //
'1', '0', '1', '1', '1', '2', '1', '3', '1', '4', //
'1', '5', '1', '6', '1', '7', '1', '8', '1', '9', //
'2', '0', '2', '1', '2', '2', '2', '3', '2', '4', //
'2', '5', '2', '6', '2', '7', '2', '8', '2', '9', //
'3', '0', '3', '1', '3', '2', '3', '3', '3', '4', //
'3', '5', '3', '6', '3', '7', '3', '8', '3', '9', //
'4', '0', '4', '1', '4', '2', '4', '3', '4', '4', //
'4', '5', '4', '6', '4', '7', '4', '8', '4', '9', //
'5', '0', '5', '1', '5', '2', '5', '3', '5', '4', //
'5', '5', '5', '6', '5', '7', '5', '8', '5', '9', //
'6', '0', '6', '1', '6', '2', '6', '3', '6', '4', //
'6', '5', '6', '6', '6', '7', '6', '8', '6', '9', //
'7', '0', '7', '1', '7', '2', '7', '3', '7', '4', //
'7', '5', '7', '6', '7', '7', '7', '8', '7', '9', //
'8', '0', '8', '1', '8', '2', '8', '3', '8', '4', //
'8', '5', '8', '6', '8', '7', '8', '8', '8', '9', //
'9', '0', '9', '1', '9', '2', '9', '3', '9', '4', //
'9', '5', '9', '6', '9', '7', '9', '8', '9', '9' //
};
// These digit generation routines are inspired by James Anhalt's itoa algorithm:
// https://github.com/jeaiii/itoa
// The main idea is for given n, find y such that floor(10^k * y / 2^32) = n holds,
// where k is an appropriate integer depending on the length of n.
// For example, if n = 1234567, we set k = 6. In this case, we have
// floor(y / 2^32) = 1,
// floor(10^2 * ((10^0 * y) mod 2^32) / 2^32) = 23,
// floor(10^2 * ((10^2 * y) mod 2^32) / 2^32) = 45, and
// floor(10^2 * ((10^4 * y) mod 2^32) / 2^32) = 67.
// See https://jk-jeon.github.io/posts/2022/02/jeaiii-algorithm/ for more explanation.
JKJ_FORCEINLINE static void print_9_digits(std::uint32_t s32, int& exponent,
char*& buffer) noexcept {
if (s32 < 100) {
if (s32 < 10) {
// 1 digit.
buffer[0] = char('0' + s32);
buffer += 1;
}
else {
// 2 digits.
buffer[0] = radix_100_table[int(s32) * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[int(s32) * 2 + 1];
buffer += 3;
exponent += 1;
}
}
else {
if (s32 < 100'0000) {
if (s32 < 1'0000) {
// 3 or 4 digits.
// 42949673 = ceil(2^32 / 100)
auto prod = s32 * std::uint64_t(42949673);
auto two_digits = int(prod >> 32);
// 3 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 2;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 4;
}
// 4 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 3;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 5;
}
}
else {
// 5 or 6 digits.
// 429497 = ceil(2^32 / 1'0000)
auto prod = s32 * std::uint64_t(429497);
auto two_digits = int(prod >> 32);
// 5 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 4;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 6;
}
// 6 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 5;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 5, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 7;
}
}
}
else {
if (s32 < 1'0000'0000) {
// 7 or 8 digits.
// 281474978 = ceil(2^48 / 100'0000) + 1
auto prod = s32 * std::uint64_t(281474978);
prod >>= 16;
auto two_digits = int(prod >> 32);
// 7 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 6;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 8;
}
// 8 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 7;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 5, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 7, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 9;
}
}
else {
// 9 digits.
// 1441151882 = ceil(2^57 / 1'0000'0000) + 1
auto prod = s32 * std::uint64_t(1441151882);
prod >>= 25;
buffer[0] = char(int(prod >> 32) + '0');
buffer[1] = '.';
exponent += 8;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 8, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 10;
}
}
}
}
template <>
char* to_chars<float, default_float_traits<float>>(std::uint32_t s32, int exponent,
char* buffer) noexcept {
// Print significand.
print_9_digits(s32, exponent, buffer);
// Print exponent and return
if (exponent < 0) {
std::memcpy(buffer, "E-", 2);
buffer += 2;
exponent = -exponent;
}
else {
buffer[0] = 'E';
buffer += 1;
}
if (exponent >= 10) {
std::memcpy(buffer, &radix_100_table[exponent * 2], 2);
buffer += 2;
}
else {
buffer[0] = (char)('0' + exponent);
buffer += 1;
}
return buffer;
}
template <>
char* to_chars<double, default_float_traits<double>>(std::uint64_t const significand,
int exponent, char* buffer) noexcept {
std::uint32_t first_block, second_block;
bool have_second_block;
if (significand < 10'0000'0000) {
first_block = std::uint32_t(significand);
have_second_block = false;
}
else {
first_block = std::uint32_t(significand / 1'0000'0000);
second_block = std::uint32_t(significand) - first_block * 1'0000'0000;
have_second_block = true;
}
// Print the first block of significand.
print_9_digits(first_block, exponent, buffer);
// Print second block if necessary.
if (have_second_block) {
// 281474978 = ceil(2^48 / 100'0000) + 1
auto prod = second_block * std::uint64_t(281474978);
prod >>= 16;
prod += 1;
exponent += 8;
std::memcpy(buffer + 0, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 8;
}
// Print exponent and return
if (exponent < 0) {
std::memcpy(buffer, "E-", 2);
buffer += 2;
exponent = -exponent;
}
else {
buffer[0] = 'E';
buffer += 1;
}
if (exponent >= 100) {
// d1 = exponent / 10; d2 = exponent % 10;
// 6554 = ceil(2^16 / 10)
auto prod = std::uint32_t(exponent) * std::uint32_t(6554);
auto d1 = prod >> 16;
prod = std::uint16_t(prod) * std::uint32_t(5); // * 10
auto d2 = prod >> 15; // >> 16
std::memcpy(buffer, &radix_100_table[d1 * 2], 2);
buffer[2] = char('0' + d2);
buffer += 3;
}
else if (exponent >= 10) {
std::memcpy(buffer, &radix_100_table[exponent * 2], 2);
buffer += 2;
}
else {
buffer[0] = char('0' + exponent);
buffer += 1;
}
return buffer;
}
}
}
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