reduced the number of multiplication #154503

Mjz86 · 2025-08-20T10:08:27Z

#152655
first i tested the different ways i can do this , i think this was the least modifications to make that would result in
improvement in my tests

llvm#152655 first i tested the different ways i can do this , i think this was the least modifications to make that would result in in improvement in my tests

github-actions · 2025-08-20T10:08:45Z

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llvmbot · 2025-08-20T10:09:22Z

@llvm/pr-subscribers-libcxx

Author: mjz (Mjz86)

Changes

#152655
first i tested the different ways i can do this , i think this was the least modifications to make that would result in in improvement in my tests

Full diff: https://github.com/llvm/llvm-project/pull/154503.diff

1 Files Affected:

(modified) libcxx/include/__charconv/to_chars_base_10.h (+78-7)

diff --git a/libcxx/include/__charconv/to_chars_base_10.h b/libcxx/include/__charconv/to_chars_base_10.h
index d90952ea71f35..94e9255ad79ba 100644
--- a/libcxx/include/__charconv/to_chars_base_10.h
+++ b/libcxx/include/__charconv/to_chars_base_10.h
@@ -38,31 +38,102 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char*
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append2(__itoa::__append1(__first, __value / 100), __value % 100);
+  const uint32_t __shift = 14;
+  const uint32_t __mul_inv10 = 1639;
+  const uint32_t __mask = (uint32_t(1) << __shift) - 1;
+  const uint32_t __n = __mul_inv10 * __value;
+  __append2(__first, __n >> __shift);
+  __append1(__firs + 2, ((__n & __mask) * 5) >> (__shift - 1));
+  return __first + 3;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append2(__itoa::__append2(__first, __value / 100), __value % 100);
+  const uint32_t __shift = 19;
+  const uint32_t __mul_inv10 = 5243;
+  const uint32_t __mask = (uint32_t(1) << __shift) - 1;
+  const uint32_t __n = __mul_inv10 * __value;
+  __append2(__first, __n >> __shift);
+  __append2(__first + 2, uint32_t((__n & __mask) * 25) >> (__shift - 2));
+  return __first + 4;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append4(__itoa::__append1(__first, __value / 10000), __value % 10000);
+  const uint64_t __inv1000_val = 67109;
+  const uint64_t __shift_val = 26;
+  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res = __inv1000_val * __value;
+  __append2(__first, __res >> __shift_val);
+  const uint64_t __second_res = uint64_t(__mask_val & __res) * 25;
+  const uint64_t __second_shift_val = __shift_val - 2;
+  const uint64_t __second_mask_val = (uint64_t(1) << __second_shift_val) - 1;
+  __append2(__first + 2, __second_res >> __second_shift_val);
+  const uint64_t __third_res = (__second_mask_val & (__second_res)) * 5;
+  const uint64_t __third_shift_val = __second_shift_val - 1;
+  __append1(__first + 4, __third_res >> __third_shift_val);
+  return __first + 5;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append4(__itoa::__append2(__first, __value / 10000), __value % 10000);
+  const uint64_t __inv10000_val = 1717987;
+  const uint64_t __shift_val = 34;
+  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res = __inv10000_val * __value;
+  __append2(__first, __res >> __shift_val);
+  const uint64_t __second_res = (__mask_val & __res) * 25;
+  const uint64_t __second_shift_val = __shift_val - 2;
+  const uint64_t __second_mask_val = (uint64_t(1) << __second_shift_val) - 1;
+  __append2(__first + 2, __second_res >> __second_shift_val);
+  const uint64_t __third_res = (__second_mask_val & (__second_res)) * 25;
+  const uint64_t __third_shift_val = __second_shift_val - 2;
+  __append2(__first + 4, __third_res >> __third_shift_val);
+  return __first + 6;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append6(__itoa::__append1(__first, __value / 1000000), __value % 1000000);
+  const uint64_t __inv100000_val = 21990233;
+  const uint64_t __shift_val = 41;
+  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res = __inv100000_val * __value;
+  __append2(__first, __res >> __shift_val);
+  const uint64_t __res2 = (__res & __mask_val) * 25;
+  __append2(__first + 2, __res2 >> (__shift_val - 2));
+  const uint64_t __res3 = (__res2 & (__mask_val >> 2)) * 25;
+  __append2(__first + 4, __res3 >> (__shift_val - 4));
+  const uint64_t __res4 = (__res3 & (__mask_val >> 4)) * 5;
+  __append1(__first + 6, __res4 >> (__shift_val - 5));
+  return __first + 7;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append6(__itoa::__append2(__first, __value / 1000000), __value % 1000000);
+  const uint64_t __inv1000000_val = 140737489;
+  const uint64_t __shift_val = 47;
+  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res = __inv1000000_val * __value;
+  __append2(__first, __res >> __shift_val);
+  const uint64_t __res2 = (__res & __mask_val) * 25;
+  __append2(__first + 2, __res2 >> (__shift_val - 2));
+  const uint64_t __res3 = (__res2 & (__mask_val >> 2)) * 25;
+  __append2(__first + 4, __res3 >> (__shift_val - 4));
+  const uint64_t __res4 = (__res3 & (__mask_val >> 4)) * 25;
+  __append2(__first + 6, __res4 >> (__shift_val - 6));
+  return __first + 8;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) _NOEXCEPT {
-  return __itoa::__append8(__itoa::__append1(__first, __value / 100000000), __value % 100000000);
+  const uint64_t __inv10000000_val = 1801439851;
+  const uint64_t __shift_val = 54;
+  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res = __inv10000000_val * __value;
+  __append2(__first, __res >> __shift_val);
+  const uint64_t __res2 = (__res & __mask_val) * 25;
+  __append2(__first + 2, __res2 >> (__shift_val - 2));
+  const uint64_t __res3 = (__res2 & (__mask_val >> 2)) * 25;
+  __append2(__first + 4, __res3 >> (__shift_val - 4));
+  const uint64_t __res4 = (__res3 & (__mask_val >> 4)) * 25;
+  __append2(__first + 6, __res4 >> (__shift_val - 6));
+  const uint64_t __res5 = (__res4 & (__mask_val >> 6)) * 5;
+  __append1(__first + 8, __res5 >> (__shift_val - 7));
+  return __first + 9;
 }
 
 template <class _Tp>

into char-conv-branch

Mjz86 · 2025-08-20T10:52:24Z

idk why this gives an error when built?!
i only changed the names in my https://github.com/Mjz86/String/blob/main/mjz_lib/mjz_uintconv.hpp at uint_to_dec_par_impl_exact_
mmmm which i tested and it was equivalent to std::to_string in my pc

github-actions · 2025-08-20T11:33:22Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions h -- libcxx/include/__charconv/to_chars_base_10.h

View the diff from clang-format here.

diff --git a/libcxx/include/__charconv/to_chars_base_10.h b/libcxx/include/__charconv/to_chars_base_10.h
index 27a8d98f3..c2df6845f 100644
--- a/libcxx/include/__charconv/to_chars_base_10.h
+++ b/libcxx/include/__charconv/to_chars_base_10.h
@@ -38,20 +38,20 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char*
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) _NOEXCEPT {
-  const uint32_t __shift = 14;
+  const uint32_t __shift     = 14;
   const uint32_t __mul_inv10 = 1639;
-  const uint32_t __mask = (uint32_t(1) << __shift) - 1;
-  const uint32_t __n = __mul_inv10 * __value;
+  const uint32_t __mask      = (uint32_t(1) << __shift) - 1;
+  const uint32_t __n         = __mul_inv10 * __value;
   __itoa::__append2(__first, __n >> __shift);
   __itoa::__append1(__first + 2, ((__n & __mask) * 5) >> (__shift - 1));
   return __first + 3;
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) _NOEXCEPT {
-  const uint32_t __shift = 19;
+  const uint32_t __shift     = 19;
   const uint32_t __mul_inv10 = 5243;
-  const uint32_t __mask = (uint32_t(1) << __shift) - 1;
-  const uint32_t __n = __mul_inv10 * __value;
+  const uint32_t __mask      = (uint32_t(1) << __shift) - 1;
+  const uint32_t __n         = __mul_inv10 * __value;
   __itoa::__append2(__first, __n >> __shift);
   __itoa::__append2(__first + 2, uint32_t((__n & __mask) * 25) >> (__shift - 2));
   return __first + 4;
@@ -59,15 +59,15 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char*
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) _NOEXCEPT {
   const uint64_t __inv1000_val = 67109;
-  const uint64_t __shift_val = 26;
-  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
-  const uint64_t __res = __inv1000_val * __value;
+  const uint64_t __shift_val   = 26;
+  const uint64_t __mask_val    = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res         = __inv1000_val * __value;
   __itoa::__append2(__first, __res >> __shift_val);
-  const uint64_t __second_res = uint64_t(__mask_val & __res) * 25;
+  const uint64_t __second_res       = uint64_t(__mask_val & __res) * 25;
   const uint64_t __second_shift_val = __shift_val - 2;
-  const uint64_t __second_mask_val = (uint64_t(1) << __second_shift_val) - 1;
+  const uint64_t __second_mask_val  = (uint64_t(1) << __second_shift_val) - 1;
   __itoa::__append2(__first + 2, __second_res >> __second_shift_val);
-  const uint64_t __third_res = (__second_mask_val & (__second_res)) * 5;
+  const uint64_t __third_res       = (__second_mask_val & (__second_res)) * 5;
   const uint64_t __third_shift_val = __second_shift_val - 1;
   __itoa::__append1(__first + 4, __third_res >> __third_shift_val);
   return __first + 5;
@@ -75,15 +75,15 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char*
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) _NOEXCEPT {
   const uint64_t __inv10000_val = 1717987;
-  const uint64_t __shift_val = 34;
-  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
-  const uint64_t __res = __inv10000_val * __value;
+  const uint64_t __shift_val    = 34;
+  const uint64_t __mask_val     = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res          = __inv10000_val * __value;
   __itoa::__append2(__first, __res >> __shift_val);
-  const uint64_t __second_res = (__mask_val & __res) * 25;
+  const uint64_t __second_res       = (__mask_val & __res) * 25;
   const uint64_t __second_shift_val = __shift_val - 2;
-  const uint64_t __second_mask_val = (uint64_t(1) << __second_shift_val) - 1;
+  const uint64_t __second_mask_val  = (uint64_t(1) << __second_shift_val) - 1;
   __itoa::__append2(__first + 2, __second_res >> __second_shift_val);
-  const uint64_t __third_res = (__second_mask_val & (__second_res)) * 25;
+  const uint64_t __third_res       = (__second_mask_val & (__second_res)) * 25;
   const uint64_t __third_shift_val = __second_shift_val - 2;
   __itoa::__append2(__first + 4, __third_res >> __third_shift_val);
   return __first + 6;
@@ -91,9 +91,9 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char*
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) _NOEXCEPT {
   const uint64_t __inv100000_val = 21990233;
-  const uint64_t __shift_val = 41;
-  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
-  const uint64_t __res = __inv100000_val * __value;
+  const uint64_t __shift_val     = 41;
+  const uint64_t __mask_val      = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res           = __inv100000_val * __value;
   __itoa::__append2(__first, __res >> __shift_val);
   const uint64_t __res2 = (__res & __mask_val) * 25;
   __itoa::__append2(__first + 2, __res2 >> (__shift_val - 2));
@@ -106,9 +106,9 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char*
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) _NOEXCEPT {
   const uint64_t __inv1000000_val = 140737489;
-  const uint64_t __shift_val = 47;
-  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
-  const uint64_t __res = __inv1000000_val * __value;
+  const uint64_t __shift_val      = 47;
+  const uint64_t __mask_val       = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res            = __inv1000000_val * __value;
   __itoa::__append2(__first, __res >> __shift_val);
   const uint64_t __res2 = (__res & __mask_val) * 25;
   __itoa::__append2(__first + 2, __res2 >> (__shift_val - 2));
@@ -121,9 +121,9 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char*
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) _NOEXCEPT {
   const uint64_t __inv10000000_val = 1801439851;
-  const uint64_t __shift_val = 54;
-  const uint64_t __mask_val = (uint64_t(1) << __shift_val) - 1;
-  const uint64_t __res = __inv10000000_val * __value;
+  const uint64_t __shift_val       = 54;
+  const uint64_t __mask_val        = (uint64_t(1) << __shift_val) - 1;
+  const uint64_t __res             = __inv10000000_val * __value;
   __itoa::__append2(__first, __res >> __shift_val);
   const uint64_t __res2 = (__res & __mask_val) * 25;
   __itoa::__append2(__first + 2, __res2 >> (__shift_val - 2));

Zingam · 2025-08-20T12:02:40Z

#152655 first i tested the different ways i can do this , i think this was the least modifications to make that would result in improvement in my tests

Could you please improve the title and also the commit message, which is this top comment to what is this PR implementing. Also please use github syntax to associate the PR to the issue: "Closes #152655". The title should have a prefix [libc++].

reduced the number of multiplication

68477f5

llvm#152655 first i tested the different ways i can do this , i think this was the least modifications to make that would result in in improvement in my tests

Mjz86 requested a review from a team as a code owner August 20, 2025 10:08

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Aug 20, 2025

Mjz86 added 9 commits August 20, 2025 13:40

Merge branch 'main' into char-conv-branch

6a2e5be

Update to_chars_base_10.h

393f464

Merge branch 'char-conv-branch' of https://github.com/Mjz86/llvm-project

87b7a63

into char-conv-branch

Merge branch 'main' into char-conv-branch

594ddec

Update to_chars_base_10.h

7765133

Merge branch 'char-conv-branch' of https://github.com/Mjz86/llvm-project

5acbfa4

into char-conv-branch

Merge branch 'main' into char-conv-branch

aa88983

Merge branch 'char-conv-branch' of https://github.com/Mjz86/llvm-project

8a8f60a

into char-conv-branch

Merge branch 'main' into char-conv-branch

1bf96dc

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