1  // Numeric conversions (to_string, to_chars) -*- C++ -*-
       2  
       3  // Copyright (C) 2017-2023 Free Software Foundation, Inc.
       4  //
       5  // This file is part of the GNU ISO C++ Library.  This library is free
       6  // software; you can redistribute it and/or modify it under the
       7  // terms of the GNU General Public License as published by the
       8  // Free Software Foundation; either version 3, or (at your option)
       9  // any later version.
      10  
      11  // This library is distributed in the hope that it will be useful,
      12  // but WITHOUT ANY WARRANTY; without even the implied warranty of
      13  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14  // GNU General Public License for more details.
      15  
      16  // Under Section 7 of GPL version 3, you are granted additional
      17  // permissions described in the GCC Runtime Library Exception, version
      18  // 3.1, as published by the Free Software Foundation.
      19  
      20  // You should have received a copy of the GNU General Public License and
      21  // a copy of the GCC Runtime Library Exception along with this program;
      22  // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      23  // <http://www.gnu.org/licenses/>.
      24  
      25  /** @file bits/charconv.h
      26   *  This is an internal header file, included by other library headers.
      27   *  Do not attempt to use it directly. @headername{charconv}
      28   */
      29  
      30  #ifndef _GLIBCXX_CHARCONV_H
      31  #define _GLIBCXX_CHARCONV_H 1
      32  
      33  #pragma GCC system_header
      34  
      35  #if __cplusplus >= 201103L
      36  
      37  #include <type_traits>
      38  #include <ext/numeric_traits.h>
      39  
      40  namespace std _GLIBCXX_VISIBILITY(default)
      41  {
      42  _GLIBCXX_BEGIN_NAMESPACE_VERSION
      43  namespace __detail
      44  {
      45  #if __cpp_variable_templates
      46    // This accepts 128-bit integers even in strict mode.
      47    template<typename _Tp>
      48      constexpr bool __integer_to_chars_is_unsigned
      49        = ! __gnu_cxx::__int_traits<_Tp>::__is_signed;
      50  #endif
      51  
      52    // Generic implementation for arbitrary bases.
      53    template<typename _Tp>
      54      _GLIBCXX14_CONSTEXPR unsigned
      55      __to_chars_len(_Tp __value, int __base = 10) noexcept
      56      {
      57  #if __cpp_variable_templates
      58        static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
      59  #endif
      60  
      61        unsigned __n = 1;
      62        const unsigned __b2 = __base  * __base;
      63        const unsigned __b3 = __b2 * __base;
      64        const unsigned long __b4 = __b3 * __base;
      65        for (;;)
      66  	{
      67  	  if (__value < (unsigned)__base) return __n;
      68  	  if (__value < __b2) return __n + 1;
      69  	  if (__value < __b3) return __n + 2;
      70  	  if (__value < __b4) return __n + 3;
      71  	  __value /= __b4;
      72  	  __n += 4;
      73  	}
      74      }
      75  
      76    // Write an unsigned integer value to the range [first,first+len).
      77    // The caller is required to provide a buffer of exactly the right size
      78    // (which can be determined by the __to_chars_len function).
      79    template<typename _Tp>
      80      _GLIBCXX23_CONSTEXPR void
      81      __to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
      82      {
      83  #if __cpp_variable_templates
      84        static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
      85  #endif
      86  
      87        constexpr char __digits[201] =
      88  	"0001020304050607080910111213141516171819"
      89  	"2021222324252627282930313233343536373839"
      90  	"4041424344454647484950515253545556575859"
      91  	"6061626364656667686970717273747576777879"
      92  	"8081828384858687888990919293949596979899";
      93        unsigned __pos = __len - 1;
      94        while (__val >= 100)
      95  	{
      96  	  auto const __num = (__val % 100) * 2;
      97  	  __val /= 100;
      98  	  __first[__pos] = __digits[__num + 1];
      99  	  __first[__pos - 1] = __digits[__num];
     100  	  __pos -= 2;
     101  	}
     102        if (__val >= 10)
     103  	{
     104  	  auto const __num = __val * 2;
     105  	  __first[1] = __digits[__num + 1];
     106  	  __first[0] = __digits[__num];
     107  	}
     108        else
     109  	__first[0] = '0' + __val;
     110      }
     111  
     112  } // namespace __detail
     113  _GLIBCXX_END_NAMESPACE_VERSION
     114  } // namespace std
     115  #endif // C++11
     116  #endif // _GLIBCXX_CHARCONV_H