libstdc++-v3/include/bits/charconv.h

   1 // Numeric conversions (to_string, to_chars) -*- C++ -*-
   2
   3 // Copyright (C) 2017-2021 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
  39 namespace std _GLIBCXX_VISIBILITY(default)
  40 {
  41 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  42 namespace __detail
  43 {
  44   // Generic implementation for arbitrary bases.
  45   template<typename _Tp>
  46     _GLIBCXX14_CONSTEXPR unsigned
  47     __to_chars_len(_Tp __value, int __base = 10) noexcept
  48     {
  49       static_assert(is_integral<_Tp>::value, "implementation bug");
  50       static_assert(is_unsigned<_Tp>::value, "implementation bug");
  51
  52       unsigned __n = 1;
  53       const unsigned __b2 = __base  * __base;
  54       const unsigned __b3 = __b2 * __base;
  55       const unsigned long __b4 = __b3 * __base;
  56       for (;;)
  57         {
  58           if (__value < (unsigned)__base) return __n;
  59           if (__value < __b2) return __n + 1;
  60           if (__value < __b3) return __n + 2;
  61           if (__value < __b4) return __n + 3;
  62           __value /= __b4;
  63           __n += 4;
  64         }
  65     }
  66
  67   // Write an unsigned integer value to the range [first,first+len).
  68   // The caller is required to provide a buffer of exactly the right size
  69   // (which can be determined by the __to_chars_len function).
  70   template<typename _Tp>
  71     void
  72     __to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
  73     {
  74       static_assert(is_integral<_Tp>::value, "implementation bug");
  75       static_assert(is_unsigned<_Tp>::value, "implementation bug");
  76
  77       static constexpr char __digits[201] =
  78         "0001020304050607080910111213141516171819"
  79         "2021222324252627282930313233343536373839"
  80         "4041424344454647484950515253545556575859"
  81         "6061626364656667686970717273747576777879"
  82         "8081828384858687888990919293949596979899";
  83       unsigned __pos = __len - 1;
  84       while (__val >= 100)
  85         {
  86           auto const __num = (__val % 100) * 2;
  87           __val /= 100;
  88           __first[__pos] = __digits[__num + 1];
  89           __first[__pos - 1] = __digits[__num];
  90           __pos -= 2;
  91         }
  92       if (__val >= 10)
  93         {
  94           auto const __num = __val * 2;
  95           __first[1] = __digits[__num + 1];
  96           __first[0] = __digits[__num];
  97         }
  98       else
  99         __first[0] = '0' + __val;
 100     }
 101
 102 } // namespace __detail
 103 _GLIBCXX_END_NAMESPACE_VERSION
 104 } // namespace std
 105 #endif // C++11
 106 #endif // _GLIBCXX_CHARCONV_H