Edit - charconv

Edit: charconv

// Primitive numeric conversions (to_chars and from_chars) -*- C++ -*-

// Copyright (C) 2017-2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/charconv
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_CHARCONV
#define _GLIBCXX_CHARCONV 1

#pragma GCC system_header

#if __cplusplus >= 201402L

#include <type_traits>
#include <limits>
#include <cctype>
#include <bits/error_constants.h> // for std::errc

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/// Result type of std::to_chars
  struct to_chars_result
  {
    char* ptr;
    errc ec;
  };

/// Result type of std::from_chars
  struct from_chars_result
  {
    const char* ptr;
    errc ec;
  };

namespace __detail
{
  template<typename _Tp, typename... _Types>
    using __is_one_of = __or_<is_same<_Tp, _Types>...>;

template<typename _Tp>
    using __is_int_to_chars_type = __and_<is_integral<_Tp>,
	  __not_<__is_one_of<_Tp, bool, char16_t, char32_t
#if _GLIBCXX_USE_WCHAR_T
	  , wchar_t
#endif
	    >>>;

template<typename _Tp>
    using __integer_to_chars_result_type
      = enable_if_t<__is_int_to_chars_type<_Tp>::value, to_chars_result>;

template<typename _Tp>
    using __unsigned_least_t
      = conditional_t<(sizeof(_Tp) <= sizeof(int)), unsigned int,
	conditional_t<(sizeof(_Tp) <= sizeof(long)), unsigned long,
	conditional_t<(sizeof(_Tp) <= sizeof(long long)), unsigned long long,
#if _GLIBCXX_USE_INT128
	conditional_t<(sizeof(_Tp) <= sizeof(__int128)), unsigned __int128,
#endif
	void
#if _GLIBCXX_USE_INT128
	>
#endif
	>>>;

// Generic implementation for arbitrary bases.
  template<typename _Tp>
    constexpr unsigned
    __to_chars_len(_Tp __value, int __base = 10) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

unsigned __n = 1;
      const int __b2 = __base  * __base;
      const int __b3 = __b2 * __base;
      const int __b4 = __b3 * __base;
      for (;;)
	{
	  if (__value < __base) return __n;
	  if (__value < __b2) return __n + 1;
	  if (__value < __b3) return __n + 2;
	  if (__value < __b4) return __n + 3;
	  __value /= (unsigned)__b4;
	  __n += 4;
	}
    }

template<typename _Tp>
    constexpr unsigned
    __to_chars_len_2(_Tp __value) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

constexpr size_t __nbits = __CHAR_BIT__ * sizeof(_Tp);

// N.B. __builtin_clzll is undefined if __value == 0, but std::to_chars
      // handles zero values directly.

// For sizeof(_Tp) > 1 this is an order of magnitude faster than
      // the generic __to_chars_len.
      return __nbits
	- (__builtin_clzll(__value)
	    - ((__CHAR_BIT__ * sizeof(long long)) - __nbits));
    }

template<typename _Tp>
    constexpr unsigned
    __to_chars_len_8(_Tp __value) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

constexpr size_t __nbits = __CHAR_BIT__ * sizeof(_Tp);

if _GLIBCXX17_CONSTEXPR (__nbits <= 16)
	{
	  return __value > 077777u ? 6u
	    : __value > 07777u ? 5u
	    : __value > 0777u ? 4u
	    : __value > 077u ? 3u
	    : __value > 07u ? 2u
	    : 1u;
	}
      else
	return __to_chars_len(__value, 8);
    }

// Generic implementation for arbitrary bases.
  template<typename _Tp>
    to_chars_result
    __to_chars(char* __first, char* __last, _Tp __val, int __base) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

to_chars_result __res;

const unsigned __len = __to_chars_len(__val, __base);

if (__builtin_expect((__last - __first) < __len, 0))
	{
	  __res.ptr = __last;
	  __res.ec = errc::value_too_large;
	  return __res;
	}

unsigned __pos = __len - 1;

static constexpr char __digits[]
	= "0123456789abcdefghijklmnopqrstuvwxyz";

while (__val >= __base)
	{
	  auto const __quo = __val / __base;
	  auto const __rem = __val % __base;
	  __first[__pos--] = __digits[__rem];
	  __val = __quo;
	}
      *__first = __digits[__val];

__res.ptr = __first + __len;
      __res.ec = {};
      return __res;
    }

template<typename _Tp>
    __integer_to_chars_result_type<_Tp>
    __to_chars_16(char* __first, char* __last, _Tp __val) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

to_chars_result __res;

const unsigned __len = __to_chars_len(__val, 0x10);

if (__builtin_expect((__last - __first) < __len, 0))
	{
	  __res.ptr = __last;
	  __res.ec = errc::value_too_large;
	  return __res;
	}

static constexpr char __digits[513] =
	"000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f"
	"202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f"
	"404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f"
	"606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f"
	"808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9f"
	"a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
	"c0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
	"e0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
      unsigned __pos = __len - 1;
      while (__val >= 0x100)
	{
	  auto const __num = (__val % 0x100) * 2;
	  __val /= 0x100;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	  __pos -= 2;
	}
      if (__val >= 0x10)
	{
	  auto const __num = __val * 2;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	}
      else
	__first[__pos] = "0123456789abcdef"[__val];
      __res.ptr = __first + __len;
      __res.ec = {};
      return __res;
    }

template<typename _Tp>
    __integer_to_chars_result_type<_Tp>
    __to_chars_10(char* __first, char* __last, _Tp __val) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

to_chars_result __res;

const unsigned __len = __to_chars_len(__val, 10);

if (__builtin_expect((__last - __first) < __len, 0))
	{
	  __res.ptr = __last;
	  __res.ec = errc::value_too_large;
	  return __res;
	}

static constexpr char __digits[201] =
	"0001020304050607080910111213141516171819"
	"2021222324252627282930313233343536373839"
	"4041424344454647484950515253545556575859"
	"6061626364656667686970717273747576777879"
	"8081828384858687888990919293949596979899";
      unsigned __pos = __len - 1;
      while (__val >= 100)
	{
	  auto const __num = (__val % 100) * 2;
	  __val /= 100;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	  __pos -= 2;
	}
      if (__val >= 10)
	{
	  auto const __num = __val * 2;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	}
      else
	__first[__pos] = '0' + __val;
      __res.ptr = __first + __len;
      __res.ec = {};
      return __res;
    }

template<typename _Tp>
    __integer_to_chars_result_type<_Tp>
    __to_chars_8(char* __first, char* __last, _Tp __val) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

to_chars_result __res;

const unsigned __len = __to_chars_len_8(__val);

if (__builtin_expect((__last - __first) < __len, 0))
	{
	  __res.ptr = __last;
	  __res.ec = errc::value_too_large;
	  return __res;
	}

static constexpr char __digits[129] =
	"00010203040506071011121314151617"
	"20212223242526273031323334353637"
	"40414243444546475051525354555657"
	"60616263646566677071727374757677";
      unsigned __pos = __len - 1;
      while (__val >= 0100)
	{
	  auto const __num = (__val % 0100) * 2;
	  __val /= 0100;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	  __pos -= 2;
	}
      if (__val >= 010)
	{
	  auto const __num = __val * 2;
	  __first[__pos] = __digits[__num + 1];
	  __first[__pos - 1] = __digits[__num];
	}
      else
	__first[__pos] = '0' + __val;
      __res.ptr = __first + __len;
      __res.ec = {};
      return __res;
    }

template<typename _Tp>
    __integer_to_chars_result_type<_Tp>
    __to_chars_2(char* __first, char* __last, _Tp __val) noexcept
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

to_chars_result __res;

const unsigned __len = __to_chars_len_2(__val);

if (__builtin_expect((__last - __first) < __len, 0))
	{
	  __res.ptr = __last;
	  __res.ec = errc::value_too_large;
	  return __res;
	}

unsigned __pos = __len - 1;

while (__pos)
	{
	  __first[__pos--] = '0' + (__val & 1);
	  __val >>= 1;
	}
      *__first = '0' + (__val & 1);

__res.ptr = __first + __len;
      __res.ec = {};
      return __res;
    }

} // namespace __detail

template<typename _Tp>
    __detail::__integer_to_chars_result_type<_Tp>
    to_chars(char* __first, char* __last, _Tp __value, int __base = 10)
    {
      __glibcxx_assert(2 <= __base && __base <= 36);

using _Up = __detail::__unsigned_least_t<_Tp>;
      _Up __unsigned_val = __value;

if (__value == 0 && __first != __last)
	{
	  *__first = '0';
	  return { __first + 1, errc{} };
	}

if _GLIBCXX17_CONSTEXPR (std::is_signed<_Tp>::value)
	if (__value < 0)
	  {
	    if (__builtin_expect(__first != __last, 1))
	      *__first++ = '-';
	    __unsigned_val = _Up(~__value) + _Up(1);
	  }

switch (__base)
      {
      case 16:
	return __detail::__to_chars_16(__first, __last, __unsigned_val);
      case 10:
	return __detail::__to_chars_10(__first, __last, __unsigned_val);
      case 8:
	return __detail::__to_chars_8(__first, __last, __unsigned_val);
      case 2:
	return __detail::__to_chars_2(__first, __last, __unsigned_val);
      default:
	return __detail::__to_chars(__first, __last, __unsigned_val, __base);
      }
    }

namespace __detail
{
  template<typename _Tp>
    bool
    __raise_and_add(_Tp& __val, int __base, unsigned char __c)
    {
      if (__builtin_mul_overflow(__val, __base, &__val)
	  || __builtin_add_overflow(__val, __c, &__val))
	return false;
      return true;
    }

/// std::from_chars implementation for integers in base 2.
  template<typename _Tp>
    bool
    __from_chars_binary(const char*& __first, const char* __last, _Tp& __val)
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

const ptrdiff_t __len = __last - __first;
      int __i = 0;
      while (__i < __len)
	{
	  const unsigned char __c = (unsigned)__first[__i] - '0';
	  if (__c < 2)
	    __val = (__val << 1) | __c;
	  else
	    break;
	  __i++;
	}
      __first += __i;
      return __i <= (sizeof(_Tp) * __CHAR_BIT__);
    }

/// std::from_chars implementation for integers in bases 3 to 10.
  template<typename _Tp>
    bool
    __from_chars_digit(const char*& __first, const char* __last, _Tp& __val,
		       int __base)
    {
      static_assert(is_integral<_Tp>::value, "implementation bug");
      static_assert(is_unsigned<_Tp>::value, "implementation bug");

auto __matches = [__base](char __c) {
	  return '0' <= __c && __c <= ('0' + (__base - 1));
      };

while (__first != __last)
	{
	  const char __c = *__first;
	  if (__matches(__c))
	  {
	    if (!__raise_and_add(__val, __base, __c - '0'))
	      {
		while (++__first != __last && __matches(*__first))
		  ;
		return false;
	      }
	    __first++;
	  }
	  else
	    return true;
	}
      return true;
    }

constexpr unsigned char
  __from_chars_alpha_to_num(char __c)
  {
    switch (__c)
    {
    case 'a':
    case 'A':
      return 10;
    case 'b':
    case 'B':
      return 11;
    case 'c':
    case 'C':
      return 12;
    case 'd':
    case 'D':
      return 13;
    case 'e':
    case 'E':
      return 14;
    case 'f':
    case 'F':
      return 15;
    case 'g':
    case 'G':
      return 16;
    case 'h':
    case 'H':
      return 17;
    case 'i':
    case 'I':
      return 18;
    case 'j':
    case 'J':
      return 19;
    case 'k':
    case 'K':
      return 20;
    case 'l':
    case 'L':
      return 21;
    case 'm':
    case 'M':
      return 22;
    case 'n':
    case 'N':
      return 23;
    case 'o':
    case 'O':
      return 24;
    case 'p':
    case 'P':
      return 25;
    case 'q':
    case 'Q':
      return 26;
    case 'r':
    case 'R':
      return 27;
    case 's':
    case 'S':
      return 28;
    case 't':
    case 'T':
      return 29;
    case 'u':
    case 'U':
      return 30;
    case 'v':
    case 'V':
      return 31;
    case 'w':
    case 'W':
      return 32;
    case 'x':
    case 'X':
      return 33;
    case 'y':
    case 'Y':
      return 34;
    case 'z':
    case 'Z':
      return 35;
    }
    return std::numeric_limits<unsigned char>::max();
  }

/// std::from_chars implementation for integers in bases 11 to 26.
  template<typename _Tp>
    bool
    __from_chars_alnum(const char*& __first, const char* __last, _Tp& __val,
		       int __base)
    {
      bool __valid = true;
      while (__first != __last)
	{
	  unsigned char __c = *__first;
	  if (std::isdigit(__c))
	    __c -= '0';
	  else
	    {
	      __c = __from_chars_alpha_to_num(__c);
	      if (__c >= __base)
		break;
	    }

if (__builtin_expect(__valid, 1))
	    __valid = __raise_and_add(__val, __base, __c);
	  __first++;
	}
      return __valid;
    }

template<typename _Tp>
    using __integer_from_chars_result_type
      = enable_if_t<__is_int_to_chars_type<_Tp>::value, from_chars_result>;

} // namespace __detail

/// std::from_chars for integral types.
  template<typename _Tp>
    __detail::__integer_from_chars_result_type<_Tp>
    from_chars(const char* __first, const char* __last, _Tp& __value,
	       int __base = 10)
    {
      __glibcxx_assert(2 <= __base && __base <= 36);

from_chars_result __res{__first, {}};

int __sign = 1;
      if _GLIBCXX17_CONSTEXPR (std::is_signed<_Tp>::value)
	if (__first != __last && *__first == '-')
	  {
	    __sign = -1;
	    ++__first;
	  }

using _Up = __detail::__unsigned_least_t<_Tp>;
      _Up __val = 0;

const auto __start = __first;
      bool __valid;
      if (__base == 2)
	__valid = __detail::__from_chars_binary(__first, __last, __val);
      else if (__base <= 10)
	__valid = __detail::__from_chars_digit(__first, __last, __val, __base);
      else
	__valid = __detail::__from_chars_alnum(__first, __last, __val, __base);

if (__builtin_expect(__first == __start, 0))
	__res.ec = errc::invalid_argument;
      else
	{
	  __res.ptr = __first;
	  if (!__valid)
	    __res.ec = errc::result_out_of_range;
	  else
	    {
	      if _GLIBCXX17_CONSTEXPR (std::is_signed<_Tp>::value)
		{
		  _Tp __tmp;
		  if (__builtin_mul_overflow(__val, __sign, &__tmp))
		    __res.ec = errc::result_out_of_range;
		  else
		    __value = __tmp;
		}
	      else
		{
		  if _GLIBCXX17_CONSTEXPR
		    (numeric_limits<_Up>::max() > numeric_limits<_Tp>::max())
		    {
		      if (__val > numeric_limits<_Tp>::max())
			__res.ec = errc::result_out_of_range;
		      else
			__value = __val;
		    }
		  else
		    __value = __val;
		}
	    }
	}
      return __res;
    }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // C++14
#endif // _GLIBCXX_CHARCONV

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