Skip to content

Use division by 100 in to_string for integers #5691

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
+111 −12
Open

Use division by 100 in to_string for integers #5691

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
86958ab
benchmark
AlexGuteniev Aug 23, 2025
8b6f863
100 branch in to_string impl
AlexGuteniev Aug 23, 2025
84b3d1a
sort better
AlexGuteniev Aug 23, 2025
08b83da
hack around some linker issue in C++14
AlexGuteniev Aug 24, 2025
068234b
Merge branch 'microsoft:main' into integers
AlexGuteniev Sep 15, 2025
5de9ae1
Merge branch 'microsoft:main' into integers
AlexGuteniev Oct 24, 2025
74815fc
Merge branch 'microsoft:main' into integers
AlexGuteniev Oct 31, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
1 change: 1 addition & 0 deletions benchmarks/CMakeLists.txt
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,7 @@ add_benchmark(find_and_count src/find_and_count.cpp)
add_benchmark(find_first_of src/find_first_of.cpp)
add_benchmark(has_single_bit src/has_single_bit.cpp)
add_benchmark(includes src/includes.cpp)
add_benchmark(integer_to_string src/integer_to_string.cpp)
add_benchmark(iota src/iota.cpp)
add_benchmark(is_sorted_until src/is_sorted_until.cpp)
add_benchmark(locale_classic src/locale_classic.cpp)
Expand Down
84 changes: 84 additions & 0 deletions benchmarks/src/integer_to_string.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,84 @@
// Copyright (c) Microsoft Corporation.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#include <algorithm>
#include <array>
#include <benchmark/benchmark.h>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <random>
#include <type_traits>

using namespace std;

template <class T, double M, double S>
auto generate_array() {
array<T, 2000> a;

mt19937 gen;
lognormal_distribution<double> dis(M, S);
ranges::generate(a, [&] { return static_cast<T>(dis(gen)); });

if constexpr (is_signed_v<T>) {
bernoulli_distribution b(0.5);
ranges::for_each(a, [&](T& v) { v *= (b(gen) ? -1 : 1); });
}

return a;
}

template <class T, double M, double S>
void internal_integer_to_buff(benchmark::State& state) {
auto a = generate_array<T, M, S>();

char buff[24];

auto it = a.begin();
for (auto _ : state) {
auto i = *it;
benchmark::DoNotOptimize(i);
auto s = std::_UIntegral_to_buff(buff, i);
benchmark::DoNotOptimize(s);

++it;
if (it == a.end()) {
it = a.begin();
}
}
}

template <class T, double M, double S>
void integer_to_string(benchmark::State& state) {
auto a = generate_array<T, M, S>();

auto it = a.begin();
for (auto _ : state) {
auto i = *it;
benchmark::DoNotOptimize(i);
auto s = to_string(i);
benchmark::DoNotOptimize(s);

++it;
if (it == a.end()) {
it = a.begin();
}
}
}

BENCHMARK(internal_integer_to_buff<uint8_t, 2.5, 1.5>);
BENCHMARK(internal_integer_to_buff<uint16_t, 5.0, 3.0>);
BENCHMARK(internal_integer_to_buff<uint32_t, 10.0, 6.0>);
BENCHMARK(internal_integer_to_buff<uint64_t, 20.0, 12.0>);

BENCHMARK(integer_to_string<uint8_t, 2.5, 1.5>);
BENCHMARK(integer_to_string<uint16_t, 5.0, 3.0>);
BENCHMARK(integer_to_string<uint32_t, 10.0, 6.0>);
BENCHMARK(integer_to_string<uint64_t, 20.0, 12.0>);

BENCHMARK(integer_to_string<int8_t, 2.5, 1.5>);
BENCHMARK(integer_to_string<int16_t, 5.0, 3.0>);
BENCHMARK(integer_to_string<int32_t, 10.0, 6.0>);
BENCHMARK(integer_to_string<int64_t, 20.0, 12.0>);

BENCHMARK_MAIN();
28 changes: 16 additions & 12 deletions stl/inc/xcharconv_ryu_tables.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -37,10 +37,6 @@
#include <yvals_core.h>
#if _STL_COMPILER_PREPROCESSOR

#if !_HAS_CXX17
#error The contents of <charconv> are only available with C++17. (Also, you should not include this internal header.)
#endif // !_HAS_CXX17

#include <cstdint>

#pragma pack(push, _CRT_PACKING)
Expand All @@ -60,11 +56,15 @@ _STD_BEGIN

// vvvvvvvvvv DERIVED FROM digit_table.h vvvvvvvvvv

#if !_HAS_CXX17
namespace { // work around Clang link issues
#endif // !_HAS_CXX17

// A table of all two-digit numbers. This is used to speed up decimal digit
// generation by copying pairs of digits into the final output.
template <class _CharT> constexpr _CharT __DIGIT_TABLE[] = {_CharT{}};

template <> inline constexpr char __DIGIT_TABLE<char>[200] = {
template <> _INLINE_VAR constexpr char __DIGIT_TABLE<char>[200] = {
'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',
Expand All @@ -77,7 +77,7 @@ template <> inline constexpr char __DIGIT_TABLE<char>[200] = {
'9','0','9','1','9','2','9','3','9','4','9','5','9','6','9','7','9','8','9','9'
};

template <> inline constexpr wchar_t __DIGIT_TABLE<wchar_t>[200] = {
template <> _INLINE_VAR constexpr wchar_t __DIGIT_TABLE<wchar_t>[200] = {
L'0',L'0',L'0',L'1',L'0',L'2',L'0',L'3',L'0',L'4',L'0',L'5',L'0',L'6',L'0',L'7',L'0',L'8',L'0',L'9',
L'1',L'0',L'1',L'1',L'1',L'2',L'1',L'3',L'1',L'4',L'1',L'5',L'1',L'6',L'1',L'7',L'1',L'8',L'1',L'9',
L'2',L'0',L'2',L'1',L'2',L'2',L'2',L'3',L'2',L'4',L'2',L'5',L'2',L'6',L'2',L'7',L'2',L'8',L'2',L'9',
Expand All @@ -90,6 +90,10 @@ template <> inline constexpr wchar_t __DIGIT_TABLE<wchar_t>[200] = {
L'9',L'0',L'9',L'1',L'9',L'2',L'9',L'3',L'9',L'4',L'9',L'5',L'9',L'6',L'9',L'7',L'9',L'8',L'9',L'9'
};

#if !_HAS_CXX17
} // unnamed namespace
#endif // !_HAS_CXX17

// ^^^^^^^^^^ DERIVED FROM digit_table.h ^^^^^^^^^^

// vvvvvvvvvv DERIVED FROM d2s_full_table.h vvvvvvvvvv
Expand All @@ -103,9 +107,9 @@ extern const uint64_t __DOUBLE_POW5_SPLIT[326][2];

// vvvvvvvvvv DERIVED FROM d2fixed_full_table.h vvvvvvvvvv

inline constexpr int __TABLE_SIZE = 64;
_INLINE_VAR constexpr int __TABLE_SIZE = 64;

inline constexpr uint16_t __POW10_OFFSET[__TABLE_SIZE] = {
_INLINE_VAR constexpr uint16_t __POW10_OFFSET[__TABLE_SIZE] = {
0, 2, 5, 8, 12, 16, 21, 26, 32, 39,
46, 54, 62, 71, 80, 90, 100, 111, 122, 134,
146, 159, 173, 187, 202, 217, 233, 249, 266, 283,
Expand All @@ -117,10 +121,10 @@ inline constexpr uint16_t __POW10_OFFSET[__TABLE_SIZE] = {

extern const uint64_t __POW10_SPLIT[1224][3];

inline constexpr int __TABLE_SIZE_2 = 69;
inline constexpr int __ADDITIONAL_BITS_2 = 120;
_INLINE_VAR constexpr int __TABLE_SIZE_2 = 69;
_INLINE_VAR constexpr int __ADDITIONAL_BITS_2 = 120;

inline constexpr uint16_t __POW10_OFFSET_2[__TABLE_SIZE_2] = {
_INLINE_VAR constexpr uint16_t __POW10_OFFSET_2[__TABLE_SIZE_2] = {
0, 2, 6, 12, 20, 29, 40, 52, 66, 80,
95, 112, 130, 150, 170, 192, 215, 240, 265, 292,
320, 350, 381, 413, 446, 480, 516, 552, 590, 629,
Expand All @@ -130,7 +134,7 @@ inline constexpr uint16_t __POW10_OFFSET_2[__TABLE_SIZE_2] = {
2465, 2544, 2625, 2706, 2789, 2873, 2959, 3046, 3133
};

inline constexpr uint8_t __MIN_BLOCK_2[__TABLE_SIZE_2] = {
_INLINE_VAR constexpr uint8_t __MIN_BLOCK_2[__TABLE_SIZE_2] = {
0, 0, 0, 0, 0, 0, 1, 1, 2, 3,
3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
8, 9, 9, 10, 11, 11, 12, 12, 13, 13,
Expand Down
10 changes: 10 additions & 0 deletions stl/inc/xmemory
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
#include <limits> // TRANSITION, see GH-4634: Lots of user code assumes that <xmemory> drags in <limits>
#include <new>
#include <xatomic.h>
#include <xcharconv_ryu_tables.h>
#include <xutility>

#if _HAS_CXX20
Expand Down Expand Up @@ -2782,6 +2783,15 @@ _NODISCARD _Elem* _UIntegral_to_buff(_Elem* _RNext, _UTy _UVal) { // used by bot
auto _UVal_trunc = static_cast<unsigned long>(_UVal);
#endif // ^^^ !defined(_WIN64) ^^^

if constexpr (_Is_any_of_v<_Elem, char, wchar_t>) {
while (_UVal_trunc >= 100) {
const unsigned long _UVal_trunc_part = _UVal_trunc % 100;
_UVal_trunc /= 100;
*--_RNext = static_cast<_Elem>(__DIGIT_TABLE<_Elem>[_UVal_trunc_part * 2 + 1]);
*--_RNext = static_cast<_Elem>(__DIGIT_TABLE<_Elem>[_UVal_trunc_part * 2]);
Comment on lines +2790 to +2791
Copy link
Contributor Author

@AlexGuteniev AlexGuteniev Aug 24, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This can be further optimized to

            _RNext -= 2;
            _CSTD memcpy(_RNext, __DIGIT_TABLE<_Elem> + _UVal_trunc_part * 2, 2 * sizeof(_Elem))

still without much better results in the benchmark.

}
}

do {
*--_RNext = static_cast<_Elem>('0' + _UVal_trunc % 10);
_UVal_trunc /= 10;
Expand Down