llvm-project/libcxx/include/charconv

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_CHARCONV
#define _LIBCPP_CHARCONV

/*
    charconv synopsis

namespace std {

  // floating-point format for primitive numerical conversion
  enum class chars_format {
    scientific = unspecified,
    fixed = unspecified,
    hex = unspecified,
    general = fixed | scientific
  };

  // 23.20.2, primitive numerical output conversion
  struct to_chars_result {
    char* ptr;
    errc ec;
    friend bool operator==(const to_chars_result&, const to_chars_result&) = default; // since C++20
  };

  to_chars_result to_chars(char* first, char* last, see below value,
                           int base = 10);
  to_chars_result to_chars(char* first, char* last, bool value,
                           int base = 10) = delete;

  to_chars_result to_chars(char* first, char* last, float value);
  to_chars_result to_chars(char* first, char* last, double value);
  to_chars_result to_chars(char* first, char* last, long double value);

  to_chars_result to_chars(char* first, char* last, float value,
                           chars_format fmt);
  to_chars_result to_chars(char* first, char* last, double value,
                           chars_format fmt);
  to_chars_result to_chars(char* first, char* last, long double value,
                           chars_format fmt);

  to_chars_result to_chars(char* first, char* last, float value,
                           chars_format fmt, int precision);
  to_chars_result to_chars(char* first, char* last, double value,
                           chars_format fmt, int precision);
  to_chars_result to_chars(char* first, char* last, long double value,
                           chars_format fmt, int precision);

  // 23.20.3, primitive numerical input conversion
  struct from_chars_result {
    const char* ptr;
    errc ec;
    friend bool operator==(const from_chars_result&, const from_chars_result&) = default; // since C++20
  };

  from_chars_result from_chars(const char* first, const char* last,
                               see below& value, int base = 10);

  from_chars_result from_chars(const char* first, const char* last,
                               float& value,
                               chars_format fmt = chars_format::general);
  from_chars_result from_chars(const char* first, const char* last,
                               double& value,
                               chars_format fmt = chars_format::general);
  from_chars_result from_chars(const char* first, const char* last,
                               long double& value,
                               chars_format fmt = chars_format::general);

} // namespace std

*/

#include <__assert> // all public C++ headers provide the assertion handler
#include <__availability>
#include <__bits>
#include <__charconv/chars_format.h>
#include <__charconv/from_chars_result.h>
#include <__charconv/tables.h>
#include <__charconv/to_chars_base_10.h>
#include <__charconv/to_chars_result.h>
#include <__config>
#include <__debug>
#include <__errc>
#include <__type_traits/make_32_64_or_128_bit.h>
#include <__utility/unreachable.h>
#include <cmath> // for log2f
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <limits>
#include <type_traits>

#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
#  include <iosfwd>
#endif

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

#ifndef _LIBCPP_CXX03_LANG

to_chars_result to_chars(char*, char*, bool, int = 10) = delete;
from_chars_result from_chars(const char*, const char*, bool, int = 10) = delete;

namespace __itoa
{

template <typename _Tp, typename = void>
struct _LIBCPP_HIDDEN __traits_base;

template <typename _Tp>
struct _LIBCPP_HIDDEN __traits_base<_Tp, __enable_if_t<sizeof(_Tp) <= sizeof(uint32_t)>>
{
    using type = uint32_t;

    /// The width estimation using a log10 algorithm.
    ///
    /// The algorithm is based on
    /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
    /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
    /// function requires its input to have at least one bit set the value of
    /// zero is set to one. This means the first element of the lookup table is
    /// zero.
    static _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v)
    {
        auto __t = (32 - std::__libcpp_clz(static_cast<type>(__v | 1))) * 1233 >> 12;
        return __t - (__v < __table<>::__pow10_32[__t]) + 1;
    }

    static _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v)
    {
        return __itoa::__base_10_u32(__p, __v);
    }

    static _LIBCPP_HIDE_FROM_ABI decltype(__table<>::__pow10_32)& __pow() { return __table<>::__pow10_32; }
};

template <typename _Tp>
struct _LIBCPP_HIDDEN
    __traits_base<_Tp, __enable_if_t<sizeof(_Tp) == sizeof(uint64_t)>> {
  using type = uint64_t;

  /// The width estimation using a log10 algorithm.
  ///
  /// The algorithm is based on
  /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
  /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
  /// function requires its input to have at least one bit set the value of
  /// zero is set to one. This means the first element of the lookup table is
  /// zero.
  static _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v) {
    auto __t = (64 - std::__libcpp_clz(static_cast<type>(__v | 1))) * 1233 >> 12;
    return __t - (__v < __table<>::__pow10_64[__t]) + 1;
  }

  static _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v) { return __itoa::__base_10_u64(__p, __v); }

  static _LIBCPP_HIDE_FROM_ABI decltype(__table<>::__pow10_64)& __pow() { return __table<>::__pow10_64; }
};


#  ifndef _LIBCPP_HAS_NO_INT128
template <typename _Tp>
struct _LIBCPP_HIDDEN
    __traits_base<_Tp, __enable_if_t<sizeof(_Tp) == sizeof(__uint128_t)> > {
  using type = __uint128_t;

  /// The width estimation using a log10 algorithm.
  ///
  /// The algorithm is based on
  /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
  /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
  /// function requires its input to have at least one bit set the value of
  /// zero is set to one. This means the first element of the lookup table is
  /// zero.
  static _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v) {
    _LIBCPP_ASSERT(__v > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fail when this isn't true.");
    // There's always a bit set in the upper 64-bits.
    auto __t = (128 - std::__libcpp_clz(static_cast<uint64_t>(__v >> 64))) * 1233 >> 12;
    _LIBCPP_ASSERT(__t >= __table<>::__pow10_128_offset, "Index out of bounds");
    // __t is adjusted since the lookup table misses the lower entries.
    return __t - (__v < __table<>::__pow10_128[__t - __table<>::__pow10_128_offset]) + 1;
  }

  static _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v) { return __itoa::__base_10_u128(__p, __v); }

  // TODO FMT This pow function should get an index.
  // By moving this to its own header it can be reused by the pow function in to_chars_base_10.
  static _LIBCPP_HIDE_FROM_ABI decltype(__table<>::__pow10_128)& __pow() { return __table<>::__pow10_128; }
};
#endif

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool
__mul_overflowed(unsigned char __a, _Tp __b, unsigned char& __r)
{
    auto __c = __a * __b;
    __r = __c;
    return __c > numeric_limits<unsigned char>::max();
}

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool
__mul_overflowed(unsigned short __a, _Tp __b, unsigned short& __r)
{
    auto __c = __a * __b;
    __r = __c;
    return __c > numeric_limits<unsigned short>::max();
}

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool
__mul_overflowed(_Tp __a, _Tp __b, _Tp& __r)
{
    static_assert(is_unsigned<_Tp>::value, "");
#if !defined(_LIBCPP_COMPILER_MSVC)
    return __builtin_mul_overflow(__a, __b, &__r);
#else
    bool __did = __b && (numeric_limits<_Tp>::max() / __b) < __a;
    __r = __a * __b;
    return __did;
#endif
}

template <typename _Tp, typename _Up>
inline _LIBCPP_HIDE_FROM_ABI bool
__mul_overflowed(_Tp __a, _Up __b, _Tp& __r)
{
    return __mul_overflowed(__a, static_cast<_Tp>(__b), __r);
}

template <typename _Tp>
struct _LIBCPP_HIDDEN __traits : __traits_base<_Tp>
{
    static constexpr int digits = numeric_limits<_Tp>::digits10 + 1;
    using __traits_base<_Tp>::__pow;
    using typename __traits_base<_Tp>::type;

    // precondition: at least one non-zero character available
    static _LIBCPP_HIDE_FROM_ABI char const*
    __read(char const* __p, char const* __ep, type& __a, type& __b)
    {
        type __cprod[digits];
        int __j = digits - 1;
        int __i = digits;
        do
        {
            if (!('0' <= *__p && *__p <= '9'))
                break;
            __cprod[--__i] = *__p++ - '0';
        } while (__p != __ep && __i != 0);

        __a = __inner_product(__cprod + __i + 1, __cprod + __j, __pow() + 1,
                              __cprod[__i]);
        if (__mul_overflowed(__cprod[__j], __pow()[__j - __i], __b))
            --__p;
        return __p;
    }

    template <typename _It1, typename _It2, class _Up>
    static _LIBCPP_HIDE_FROM_ABI _Up
    __inner_product(_It1 __first1, _It1 __last1, _It2 __first2, _Up __init)
    {
        for (; __first1 < __last1; ++__first1, ++__first2)
            __init = __init + *__first1 * *__first2;
        return __init;
    }
};

}  // namespace __itoa

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI _Tp
__complement(_Tp __x)
{
    static_assert(is_unsigned<_Tp>::value, "cast to unsigned first");
    return _Tp(~__x + 1);
}

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI to_chars_result
__to_chars_itoa(char* __first, char* __last, _Tp __value, true_type)
{
    auto __x = __to_unsigned_like(__value);
    if (__value < 0 && __first != __last)
    {
        *__first++ = '-';
        __x = __complement(__x);
    }

    return __to_chars_itoa(__first, __last, __x, false_type());
}

template <typename _Tp>
inline _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;

    if (__tx::digits <= __diff || __tx::__width(__value) <= __diff)
        return {__tx::__convert(__first, __value), errc(0)};
    else
        return {__last, errc::value_too_large};
}

#  ifndef _LIBCPP_HAS_NO_INT128
template <>
inline _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.
    //
    // NOTE the 128-bit code path requires this optimization.
    if(__value <= numeric_limits<uint64_t>::max())
        return __to_chars_itoa(__first, __last, static_cast<uint64_t>(__value), false_type());

    using __tx = __itoa::__traits<__uint128_t>;
    auto __diff = __last - __first;

    if (__tx::digits <= __diff || __tx::__width(__value) <= __diff)
        return {__tx::__convert(__first, __value), errc(0)};
    else
        return {__last, errc::value_too_large};
}
#endif

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI to_chars_result
__to_chars_integral(char* __first, char* __last, _Tp __value, int __base,
                    true_type)
{
    auto __x = __to_unsigned_like(__value);
    if (__value < 0 && __first != __last)
    {
        *__first++ = '-';
        __x = __complement(__x);
    }

    return __to_chars_integral(__first, __last, __x, __base, false_type());
}

namespace __itoa {

template <unsigned _Base>
struct _LIBCPP_HIDDEN __integral;

template <>
struct _LIBCPP_HIDDEN __integral<2> {
  template <typename _Tp>
  _LIBCPP_HIDE_FROM_ABI static 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_HIDE_FROM_ABI static to_chars_result __to_chars(char* __first, char* __last, _Tp __value) {
    ptrdiff_t __cap = __last - __first;
    int __n = __width(__value);
    if (__n > __cap)
      return {__last, errc::value_too_large};

    __last = __first + __n;
    char* __p = __last;
    const unsigned __divisor = 16;
    while (__value > __divisor) {
      unsigned __c = __value % __divisor;
      __value /= __divisor;
      __p -= 4;
      std::memcpy(__p, &__table<>::__base_2_lut[4 * __c], 4);
    }
    do {
      unsigned __c = __value % 2;
      __value /= 2;
      *--__p = "01"[__c];
    } while (__value != 0);
    return {__last, errc(0)};
  }
};

template <>
struct _LIBCPP_HIDDEN __integral<8> {
  template <typename _Tp>
  _LIBCPP_HIDE_FROM_ABI static 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_HIDE_FROM_ABI static to_chars_result __to_chars(char* __first, char* __last, _Tp __value) {
    ptrdiff_t __cap = __last - __first;
    int __n = __width(__value);
    if (__n > __cap)
      return {__last, errc::value_too_large};

    __last = __first + __n;
    char* __p = __last;
    unsigned __divisor = 64;
    while (__value > __divisor) {
      unsigned __c = __value % __divisor;
      __value /= __divisor;
      __p -= 2;
      std::memcpy(__p, &__table<>::__base_8_lut[2 * __c], 2);
    }
    do {
      unsigned __c = __value % 8;
      __value /= 8;
      *--__p = "01234567"[__c];
    } while (__value != 0);
    return {__last, errc(0)};
  }

};

template <>
struct _LIBCPP_HIDDEN __integral<16> {
  template <typename _Tp>
  _LIBCPP_HIDE_FROM_ABI static 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_HIDE_FROM_ABI static to_chars_result __to_chars(char* __first, char* __last, _Tp __value) {
    ptrdiff_t __cap = __last - __first;
    int __n = __width(__value);
    if (__n > __cap)
      return {__last, errc::value_too_large};

    __last = __first + __n;
    char* __p = __last;
    unsigned __divisor = 256;
    while (__value > __divisor) {
      unsigned __c = __value % __divisor;
      __value /= __divisor;
      __p -= 2;
      std::memcpy(__p, &__table<>::__base_16_lut[2 * __c], 2);
    }
    if (__first != __last)
      do {
        unsigned __c = __value % 16;
        __value /= 16;
        *--__p = "0123456789abcdef"[__c];
      } while (__value != 0);
    return {__last, errc(0)};
  }
};

} // namespace __itoa

template <unsigned _Base, typename _Tp,
          typename enable_if<(sizeof(_Tp) >= sizeof(unsigned)), int>::type = 0>
_LIBCPP_HIDE_FROM_ABI int
__to_chars_integral_width(_Tp __value) {
  return __itoa::__integral<_Base>::__width(__value);
}

template <unsigned _Base, typename _Tp,
          typename enable_if<(sizeof(_Tp) < sizeof(unsigned)), int>::type = 0>
_LIBCPP_HIDE_FROM_ABI int
__to_chars_integral_width(_Tp __value) {
  return std::__to_chars_integral_width<_Base>(static_cast<unsigned>(__value));
}

template <unsigned _Base, typename _Tp,
          typename enable_if<(sizeof(_Tp) >= sizeof(unsigned)), int>::type = 0>
_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,
          typename enable_if<(sizeof(_Tp) < sizeof(unsigned)), int>::type = 0>
_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));
}

template <typename _Tp>
_LIBCPP_HIDE_FROM_ABI int
__to_chars_integral_width(_Tp __value, unsigned __base) {
  _LIBCPP_ASSERT(__value >= 0, "The function requires a non-negative value.");

  unsigned __base_2 = __base * __base;
  unsigned __base_3 = __base_2 * __base;
  unsigned __base_4 = __base_2 * __base_2;

  int __r = 0;
  while (true) {
    if (__value < __base)
      return __r + 1;
    if (__value < __base_2)
      return __r + 2;
    if (__value < __base_3)
      return __r + 3;
    if (__value < __base_4)
      return __r + 4;

    __value /= __base_4;
    __r += 4;
  }

  __libcpp_unreachable();
}

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI to_chars_result
__to_chars_integral(char* __first, char* __last, _Tp __value, int __base,
                    false_type)
{
  if (__base == 10) [[likely]]
    return __to_chars_itoa(__first, __last, __value, false_type());

  switch (__base) {
  case 2:
    return __to_chars_integral<2>(__first, __last, __value);
  case 8:
    return __to_chars_integral<8>(__first, __last, __value);
  case 16:
    return __to_chars_integral<16>(__first, __last, __value);
  }

  ptrdiff_t __cap = __last - __first;
  int __n = __to_chars_integral_width(__value, __base);
  if (__n > __cap)
    return {__last, errc::value_too_large};

  __last = __first + __n;
  char* __p = __last;
  do {
    unsigned __c = __value % __base;
    __value /= __base;
    *--__p = "0123456789abcdefghijklmnopqrstuvwxyz"[__c];
  } while (__value != 0);
  return {__last, errc(0)};
}

template <typename _Tp, typename enable_if<is_integral<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI to_chars_result
to_chars(char* __first, char* __last, _Tp __value)
{
  using _Type = __make_32_64_or_128_bit_t<_Tp>;
  static_assert(!is_same<_Type, void>::value, "unsupported integral type used in to_chars");
  return std::__to_chars_itoa(__first, __last, static_cast<_Type>(__value), is_signed<_Tp>());
}

template <typename _Tp, typename enable_if<is_integral<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI to_chars_result
to_chars(char* __first, char* __last, _Tp __value, int __base)
{
  _LIBCPP_ASSERT(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>());
}

template <typename _It, typename _Tp, typename _Fn, typename... _Ts>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__sign_combinator(_It __first, _It __last, _Tp& __value, _Fn __f, _Ts... __args)
{
    using __tl = numeric_limits<_Tp>;
    decltype(__to_unsigned_like(__value)) __x;

    bool __neg = (__first != __last && *__first == '-');
    auto __r = __f(__neg ? __first + 1 : __first, __last, __x, __args...);
    switch (__r.ec)
    {
    case errc::invalid_argument:
        return {__first, __r.ec};
    case errc::result_out_of_range:
        return __r;
    default:
        break;
    }

    if (__neg)
    {
        if (__x <= __complement(__to_unsigned_like(__tl::min())))
        {
            __x = __complement(__x);
            std::memcpy(&__value, &__x, sizeof(__x));
            return __r;
        }
    }
    else
    {
        if (__x <= __to_unsigned_like(__tl::max()))
        {
            __value = __x;
            return __r;
        }
    }

    return {__r.ptr, errc::result_out_of_range};
}

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI bool
__in_pattern(_Tp __c)
{
    return '0' <= __c && __c <= '9';
}

struct _LIBCPP_HIDDEN __in_pattern_result
{
    bool __ok;
    int __val;

    explicit _LIBCPP_HIDE_FROM_ABI operator bool() const { return __ok; }
};

template <typename _Tp>
inline _LIBCPP_HIDE_FROM_ABI __in_pattern_result
__in_pattern(_Tp __c, int __base)
{
    if (__base <= 10)
        return {'0' <= __c && __c < '0' + __base, __c - '0'};
    else if (__in_pattern(__c))
        return {true, __c - '0'};
    else if ('a' <= __c && __c < 'a' + __base - 10)
        return {true, __c - 'a' + 10};
    else
        return {'A' <= __c && __c < 'A' + __base - 10, __c - 'A' + 10};
}

template <typename _It, typename _Tp, typename _Fn, typename... _Ts>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__subject_seq_combinator(_It __first, _It __last, _Tp& __value, _Fn __f,
                         _Ts... __args)
{
    auto __find_non_zero = [](_It __firstit, _It __lastit) {
        for (; __firstit != __lastit; ++__firstit)
            if (*__firstit != '0')
                break;
        return __firstit;
    };

    auto __p = __find_non_zero(__first, __last);
    if (__p == __last || !__in_pattern(*__p, __args...))
    {
        if (__p == __first)
            return {__first, errc::invalid_argument};
        else
        {
            __value = 0;
            return {__p, {}};
        }
    }

    auto __r = __f(__p, __last, __value, __args...);
    if (__r.ec == errc::result_out_of_range)
    {
        for (; __r.ptr != __last; ++__r.ptr)
        {
            if (!__in_pattern(*__r.ptr, __args...))
                break;
        }
    }

    return __r;
}

template <typename _Tp, typename enable_if<is_unsigned<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__from_chars_atoi(const char* __first, const char* __last, _Tp& __value)
{
    using __tx = __itoa::__traits<_Tp>;
    using __output_type = typename __tx::type;

    return __subject_seq_combinator(
        __first, __last, __value,
        [](const char* __f, const char* __l,
           _Tp& __val) -> from_chars_result {
            __output_type __a, __b;
            auto __p = __tx::__read(__f, __l, __a, __b);
            if (__p == __l || !__in_pattern(*__p))
            {
                __output_type __m = numeric_limits<_Tp>::max();
                if (__m >= __a && __m - __a >= __b)
                {
                    __val = __a + __b;
                    return {__p, {}};
                }
            }
            return {__p, errc::result_out_of_range};
        });
}

template <typename _Tp, typename enable_if<is_signed<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__from_chars_atoi(const char* __first, const char* __last, _Tp& __value)
{
    using __t = decltype(__to_unsigned_like(__value));
    return __sign_combinator(__first, __last, __value, __from_chars_atoi<__t>);
}

template <typename _Tp, typename enable_if<is_unsigned<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__from_chars_integral(const char* __first, const char* __last, _Tp& __value,
                      int __base)
{
    if (__base == 10)
        return __from_chars_atoi(__first, __last, __value);

    return __subject_seq_combinator(
        __first, __last, __value,
        [](const char* __p, const char* __lastp, _Tp& __val,
           int __b) -> from_chars_result {
            using __tl = numeric_limits<_Tp>;
            auto __digits = __tl::digits / log2f(float(__b));
            _Tp __x = __in_pattern(*__p++, __b).__val, __y = 0;

            for (int __i = 1; __p != __lastp; ++__i, ++__p)
            {
                if (auto __c = __in_pattern(*__p, __b))
                {
                    if (__i < __digits - 1)
                        __x = __x * __b + __c.__val;
                    else
                    {
                        if (!__itoa::__mul_overflowed(__x, __b, __x))
                            ++__p;
                        __y = __c.__val;
                        break;
                    }
                }
                else
                    break;
            }

            if (__p == __lastp || !__in_pattern(*__p, __b))
            {
                if (__tl::max() - __x >= __y)
                {
                    __val = __x + __y;
                    return {__p, {}};
                }
            }
            return {__p, errc::result_out_of_range};
        },
        __base);
}

template <typename _Tp, typename enable_if<is_signed<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
__from_chars_integral(const char* __first, const char* __last, _Tp& __value,
                      int __base)
{
    using __t = decltype(__to_unsigned_like(__value));
    return __sign_combinator(__first, __last, __value,
                             __from_chars_integral<__t>, __base);
}

template <typename _Tp, typename enable_if<is_integral<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
from_chars(const char* __first, const char* __last, _Tp& __value)
{
    return __from_chars_atoi(__first, __last, __value);
}

template <typename _Tp, typename enable_if<is_integral<_Tp>::value, int>::type = 0>
inline _LIBCPP_HIDE_FROM_ABI from_chars_result
from_chars(const char* __first, const char* __last, _Tp& __value, int __base)
{
    _LIBCPP_ASSERT(2 <= __base && __base <= 36, "base not in [2, 36]");
    return __from_chars_integral(__first, __last, __value, __base);
}

// Floating-point implementation starts here.
// Unlike the other parts of charconv this is only available in C++17 and newer.
#if _LIBCPP_STD_VER > 14

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, float __value);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, double __value);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, long double __value);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, float __value, chars_format __fmt);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, double __value, chars_format __fmt);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, long double __value, chars_format __fmt);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, float __value, chars_format __fmt, int __precision);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, double __value, chars_format __fmt, int __precision);

_LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
to_chars_result to_chars(char* __first, char* __last, long double __value, chars_format __fmt, int __precision);

#  endif // _LIBCPP_STD_VER > 14
#endif // _LIBCPP_CXX03_LANG

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP_CHARCONV