[libc++] Optimize num_put integral functions (#120859)

```
-------------------------------------------------------
Benchmark                              old          new
-------------------------------------------------------
BM_num_put<bool>                   76.2 ns      32.0 ns
BM_num_put<long>                   76.9 ns      33.1 ns
BM_num_put<long long>              77.9 ns      34.2 ns
BM_num_put<unsigned long>          78.4 ns      33.1 ns
BM_num_put<unsigned long long>     78.0 ns      34.4 ns
BM_num_put<double>                  224 ns       228 ns
BM_num_put<long double>             239 ns       230 ns
BM_num_put<const void*>            68.7 ns      35.1 ns
```

Fixes #40109.

Author: philnik777

libcxx/docs/ReleaseNotes/20.rst

@@ -120,6 +120,8 @@ Improvements and New Features
 
 - Added :ref:`hardening mode <hardening>` support for ``forward_list`` and ``bitset``.
 
+- The ``num_get::do_put`` integral overloads have been optimized, resulting in a performance improvement of up to 2.4x.
+
 Deprecations and Removals
 -------------------------
 

libcxx/include/__charconv/tables.h

@@ -19,24 +19,22 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 17
-
 namespace __itoa {
 
-inline constexpr char __base_2_lut[64] = {
+inline _LIBCPP_CONSTEXPR const char __base_2_lut[64] = {
     '0', '0', '0', '0', '0', '0', '0', '1', '0', '0', '1', '0', '0', '0', '1', '1', '0', '1', '0', '0', '0', '1',
     '0', '1', '0', '1', '1', '0', '0', '1', '1', '1', '1', '0', '0', '0', '1', '0', '0', '1', '1', '0', '1', '0',
     '1', '0', '1', '1', '1', '1', '0', '0', '1', '1', '0', '1', '1', '1', '1', '0', '1', '1', '1', '1'};
 
-inline constexpr char __base_8_lut[128] = {
+inline _LIBCPP_CONSTEXPR const char __base_8_lut[128] = {
     '0', '0', '0', '1', '0', '2', '0', '3', '0', '4', '0', '5', '0', '6', '0', '7', '1', '0', '1', '1', '1', '2',
     '1', '3', '1', '4', '1', '5', '1', '6', '1', '7', '2', '0', '2', '1', '2', '2', '2', '3', '2', '4', '2', '5',
     '2', '6', '2', '7', '3', '0', '3', '1', '3', '2', '3', '3', '3', '4', '3', '5', '3', '6', '3', '7', '4', '0',
     '4', '1', '4', '2', '4', '3', '4', '4', '4', '5', '4', '6', '4', '7', '5', '0', '5', '1', '5', '2', '5', '3',
     '5', '4', '5', '5', '5', '6', '5', '7', '6', '0', '6', '1', '6', '2', '6', '3', '6', '4', '6', '5', '6', '6',
     '6', '7', '7', '0', '7', '1', '7', '2', '7', '3', '7', '4', '7', '5', '7', '6', '7', '7'};
 
-inline constexpr char __base_16_lut[512] = {
+inline _LIBCPP_CONSTEXPR const char __base_16_lut[512] = {
     '0', '0', '0', '1', '0', '2', '0', '3', '0', '4', '0', '5', '0', '6', '0', '7', '0', '8', '0', '9', '0', 'a', '0',
     'b', '0', 'c', '0', 'd', '0', 'e', '0', 'f', '1', '0', '1', '1', '1', '2', '1', '3', '1', '4', '1', '5', '1', '6',
     '1', '7', '1', '8', '1', '9', '1', 'a', '1', 'b', '1', 'c', '1', 'd', '1', 'e', '1', 'f', '2', '0', '2', '1', '2',
@@ -61,7 +59,7 @@ inline constexpr char __base_16_lut[512] = {
     '1', 'f', '2', 'f', '3', 'f', '4', 'f', '5', 'f', '6', 'f', '7', 'f', '8', 'f', '9', 'f', 'a', 'f', 'b', 'f', 'c',
     'f', 'd', 'f', 'e', 'f', 'f'};
 
-inline constexpr uint32_t __pow10_32[10] = {
+inline _LIBCPP_CONSTEXPR const uint32_t __pow10_32[10] = {
     UINT32_C(0),
     UINT32_C(10),
     UINT32_C(100),
@@ -73,7 +71,7 @@ inline constexpr uint32_t __pow10_32[10] = {
     UINT32_C(100000000),
     UINT32_C(1000000000)};
 
-inline constexpr uint64_t __pow10_64[20] = {
+inline _LIBCPP_CONSTEXPR const uint64_t __pow10_64[20] = {
     UINT64_C(0),
     UINT64_C(10),
     UINT64_C(100),
@@ -96,8 +94,8 @@ inline constexpr uint64_t __pow10_64[20] = {
     UINT64_C(10000000000000000000)};
 
 #  if _LIBCPP_HAS_INT128
-inline constexpr int __pow10_128_offset      = 0;
-inline constexpr __uint128_t __pow10_128[40] = {
+inline _LIBCPP_CONSTEXPR const int __pow10_128_offset      = 0;
+inline _LIBCPP_CONSTEXPR const __uint128_t __pow10_128[40] = {
     UINT64_C(0),
     UINT64_C(10),
     UINT64_C(100),
@@ -140,7 +138,7 @@ inline constexpr __uint128_t __pow10_128[40] = {
     (__uint128_t(UINT64_C(10000000000000000000)) * UINT64_C(10000000000000000000)) * 10};
 #  endif
 
-inline constexpr char __digits_base_10[200] = {
+inline _LIBCPP_CONSTEXPR const char __digits_base_10[200] = {
     // clang-format off
     '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',
@@ -156,8 +154,6 @@ inline constexpr char __digits_base_10[200] = {
 
 } // namespace __itoa
 
-#endif // _LIBCPP_STD_VER >= 17
-
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHARCONV_TABLES

libcxx/include/__charconv/to_chars_base_10.h

@@ -26,55 +26,53 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 17
-
 namespace __itoa {
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append1(char* __first, uint32_t __value) noexcept {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append1(char* __first, uint32_t __value) _NOEXCEPT {
   *__first = '0' + static_cast<char>(__value);
   return __first + 1;
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char* __first, uint32_t __value) noexcept {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char* __first, uint32_t __value) _NOEXCEPT {
   return std::copy_n(&__digits_base_10[__value * 2], 2, __first);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) noexcept {
+_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);
 }
 
 template <class _Tp>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __append10(char* __first, _Tp __value) noexcept {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __append10(char* __first, _Tp __value) _NOEXCEPT {
   return __itoa::__append8(__itoa::__append2(__first, static_cast<uint32_t>(__value / 100000000)),
                            static_cast<uint32_t>(__value % 100000000));
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
-__base_10_u32(char* __first, uint32_t __value) noexcept {
+__base_10_u32(char* __first, uint32_t __value) _NOEXCEPT {
   if (__value < 1000000) {
     if (__value < 10000) {
       if (__value < 100) {
@@ -110,7 +108,7 @@ __base_10_u32(char* __first, uint32_t __value) noexcept {
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
-__base_10_u64(char* __buffer, uint64_t __value) noexcept {
+__base_10_u64(char* __buffer, uint64_t __value) _NOEXCEPT {
   if (__value <= UINT32_MAX)
     return __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value));
 
@@ -132,13 +130,13 @@ __base_10_u64(char* __buffer, uint64_t __value) noexcept {
 /// \note The lookup table contains a partial set of exponents limiting the
 /// range that can be used. However the range is sufficient for
 /// \ref __base_10_u128.
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline __uint128_t __pow_10(int __exp) noexcept {
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline __uint128_t __pow_10(int __exp) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(__exp >= __pow10_128_offset, "Index out of bounds");
   return __pow10_128[__exp - __pow10_128_offset];
 }
 
 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
-__base_10_u128(char* __buffer, __uint128_t __value) noexcept {
+__base_10_u128(char* __buffer, __uint128_t __value) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(
       __value > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fails when this isn't true.");
 
@@ -179,8 +177,6 @@ __base_10_u128(char* __buffer, __uint128_t __value) noexcept {
 #  endif
 } // namespace __itoa
 
-#endif // _LIBCPP_STD_VER >= 17
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS

libcxx/include/__charconv/to_chars_integral.h

@@ -39,16 +39,12 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER >= 17
-
-to_chars_result to_chars(char*, char*, bool, int = 10) = delete;
-
 template <typename _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_itoa(char* __first, char* __last, _Tp __value, false_type);
 
 template <typename _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_itoa(char* __first, char* __last, _Tp __value, true_type) {
   auto __x = std::__to_unsigned_like(__value);
   if (__value < 0 && __first != __last) {
@@ -60,7 +56,7 @@ __to_chars_itoa(char* __first, char* __last, _Tp __value, true_type) {
 }
 
 template <typename _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_itoa(char* __first, char* __last, _Tp __value, false_type) {
   using __tx  = __itoa::__traits<_Tp>;
   auto __diff = __last - __first;
@@ -73,7 +69,7 @@ __to_chars_itoa(char* __first, char* __last, _Tp __value, false_type) {
 
 #  if _LIBCPP_HAS_INT128
 template <>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_itoa(char* __first, char* __last, __uint128_t __value, false_type) {
   // When the value fits in 64-bits use the 64-bit code path. This reduces
   // the number of expensive calculations on 128-bit values.
@@ -92,20 +88,20 @@ __to_chars_itoa(char* __first, char* __last, __uint128_t __value, false_type) {
 }
 #  endif
 
-template <class _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
-__to_chars_integral(char* __first, char* __last, _Tp __value, int __base, false_type);
+template <class _Tp, __enable_if_t<!is_signed<_Tp>::value, int> = 0>
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
+__to_chars_integral(char* __first, char* __last, _Tp __value, int __base);
 
-template <typename _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
-__to_chars_integral(char* __first, char* __last, _Tp __value, int __base, true_type) {
+template <class _Tp, __enable_if_t<is_signed<_Tp>::value, int> = 0>
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
+__to_chars_integral(char* __first, char* __last, _Tp __value, int __base) {
   auto __x = std::__to_unsigned_like(__value);
   if (__value < 0 && __first != __last) {
     *__first++ = '-';
     __x        = std::__complement(__x);
   }
 
-  return std::__to_chars_integral(__first, __last, __x, __base, false_type());
+  return std::__to_chars_integral(__first, __last, __x, __base);
 }
 
 namespace __itoa {
@@ -116,15 +112,15 @@ struct _LIBCPP_HIDDEN __integral;
 template <>
 struct _LIBCPP_HIDDEN __integral<2> {
   template <typename _Tp>
-  _LIBCPP_HIDE_FROM_ABI static constexpr int __width(_Tp __value) noexcept {
+  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR int __width(_Tp __value) _NOEXCEPT {
     // If value == 0 still need one digit. If the value != this has no
     // effect since the code scans for the most significant bit set. (Note
     // that __libcpp_clz doesn't work for 0.)
     return numeric_limits<_Tp>::digits - std::__libcpp_clz(__value | 1);
   }
 
   template <typename _Tp>
-  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static to_chars_result
+  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static __to_chars_result
   __to_chars(char* __first, char* __last, _Tp __value) {
     ptrdiff_t __cap = __last - __first;
     int __n         = __width(__value);
@@ -152,15 +148,15 @@ struct _LIBCPP_HIDDEN __integral<2> {
 template <>
 struct _LIBCPP_HIDDEN __integral<8> {
   template <typename _Tp>
-  _LIBCPP_HIDE_FROM_ABI static constexpr int __width(_Tp __value) noexcept {
+  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR int __width(_Tp __value) _NOEXCEPT {
     // If value == 0 still need one digit. If the value != this has no
     // effect since the code scans for the most significat bit set. (Note
     // that __libcpp_clz doesn't work for 0.)
     return ((numeric_limits<_Tp>::digits - std::__libcpp_clz(__value | 1)) + 2) / 3;
   }
 
   template <typename _Tp>
-  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static to_chars_result
+  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static __to_chars_result
   __to_chars(char* __first, char* __last, _Tp __value) {
     ptrdiff_t __cap = __last - __first;
     int __n         = __width(__value);
@@ -188,15 +184,15 @@ struct _LIBCPP_HIDDEN __integral<8> {
 template <>
 struct _LIBCPP_HIDDEN __integral<16> {
   template <typename _Tp>
-  _LIBCPP_HIDE_FROM_ABI static constexpr int __width(_Tp __value) noexcept {
+  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR int __width(_Tp __value) _NOEXCEPT {
     // If value == 0 still need one digit. If the value != this has no
     // effect since the code scans for the most significat bit set. (Note
     // that __libcpp_clz doesn't work for 0.)
     return (numeric_limits<_Tp>::digits - std::__libcpp_clz(__value | 1) + 3) / 4;
   }
 
   template <typename _Tp>
-  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static to_chars_result
+  _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI static __to_chars_result
   __to_chars(char* __first, char* __last, _Tp __value) {
     ptrdiff_t __cap = __last - __first;
     int __n         = __width(__value);
@@ -235,13 +231,13 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI int __to_chars_integral_widt
 }
 
 template <unsigned _Base, typename _Tp, __enable_if_t<(sizeof(_Tp) >= sizeof(unsigned)), int> = 0>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_integral(char* __first, char* __last, _Tp __value) {
   return __itoa::__integral<_Base>::__to_chars(__first, __last, __value);
 }
 
 template <unsigned _Base, typename _Tp, __enable_if_t<(sizeof(_Tp) < sizeof(unsigned)), int> = 0>
-_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
+_LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
 __to_chars_integral(char* __first, char* __last, _Tp __value) {
   return std::__to_chars_integral<_Base>(__first, __last, static_cast<unsigned>(__value));
 }
@@ -272,9 +268,9 @@ _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI int __to_chars_integral_widt
   __libcpp_unreachable();
 }
 
-template <typename _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
-__to_chars_integral(char* __first, char* __last, _Tp __value, int __base, false_type) {
+template <class _Tp, __enable_if_t<!is_signed<_Tp>::value, int> >
+inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI __to_chars_result
+__to_chars_integral(char* __first, char* __last, _Tp __value, int __base) {
   if (__base == 10) [[likely]]
     return std::__to_chars_itoa(__first, __last, __value, false_type());
 
@@ -302,6 +298,28 @@ __to_chars_integral(char* __first, char* __last, _Tp __value, int __base, false_
   return {__last, errc(0)};
 }
 
+_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR_SINCE_CXX14 char __hex_to_upper(char __c) {
+  switch (__c) {
+  case 'a':
+    return 'A';
+  case 'b':
+    return 'B';
+  case 'c':
+    return 'C';
+  case 'd':
+    return 'D';
+  case 'e':
+    return 'E';
+  case 'f':
+    return 'F';
+  }
+  return __c;
+}
+
+#if _LIBCPP_STD_VER >= 17
+
+to_chars_result to_chars(char*, char*, bool, int = 10) = delete;
+
 template <typename _Tp, __enable_if_t<is_integral<_Tp>::value, int> = 0>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI to_chars_result
 to_chars(char* __first, char* __last, _Tp __value) {
@@ -316,7 +334,7 @@ to_chars(char* __first, char* __last, _Tp __value, int __base) {
   _LIBCPP_ASSERT_UNCATEGORIZED(2 <= __base && __base <= 36, "base not in [2, 36]");
 
   using _Type = __make_32_64_or_128_bit_t<_Tp>;
-  return std::__to_chars_integral(__first, __last, static_cast<_Type>(__value), __base, is_signed<_Tp>());
+  return std::__to_chars_integral(__first, __last, static_cast<_Type>(__value), __base);
 }
 
 #endif // _LIBCPP_STD_VER >= 17

libcxx/include/__charconv/to_chars_result.h

@@ -34,6 +34,15 @@ struct _LIBCPP_EXPORTED_FROM_ABI to_chars_result {
 
 #endif // _LIBCPP_STD_VER >= 17
 
+struct __to_chars_result {
+  char* __ptr;
+  errc __ec;
+
+#if _LIBCPP_STD_VER >= 17
+  _LIBCPP_HIDE_FROM_ABI constexpr operator to_chars_result() { return {__ptr, __ec}; }
+#endif
+};
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHARCONV_TO_CHARS_RESULT_H