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The C and C++ Include Header Files

/usr/include/c++/13/bits/charconv.h


$ cat -n /usr/include/c++/13/bits/charconv.h

     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