libstdc++
charconv.h
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1 // Numeric conversions (to_string, to_chars) -*- C++ -*-
2 
3 // Copyright (C) 2017-2025 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 #ifdef _GLIBCXX_SYSHDR
34 #pragma GCC system_header
35 #endif
36 
37 #if __cplusplus >= 201103L
38 
39 #include <type_traits>
40 #include <ext/numeric_traits.h>
41 
42 namespace std _GLIBCXX_VISIBILITY(default)
43 {
44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
45 namespace __detail
46 {
47 #if __cpp_variable_templates
48  // This accepts 128-bit integers even in strict mode.
49  template<typename _Tp>
50  constexpr bool __integer_to_chars_is_unsigned
52 #endif
53 
54  // Generic implementation for arbitrary bases.
55  template<typename _Tp>
56  _GLIBCXX14_CONSTEXPR unsigned
57  __to_chars_len(_Tp __value, int __base = 10) noexcept
58  {
59 #if __cpp_variable_templates
60  static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
61 #endif
62 
63  unsigned __n = 1;
64  const unsigned __b2 = __base * __base;
65  const unsigned __b3 = __b2 * __base;
66  const unsigned long __b4 = __b3 * __base;
67  for (;;)
68  {
69  if (__value < (unsigned)__base) return __n;
70  if (__value < __b2) return __n + 1;
71  if (__value < __b3) return __n + 2;
72  if (__value < __b4) return __n + 3;
73  __value /= __b4;
74  __n += 4;
75  }
76  }
77 
78  // Write an unsigned integer value to the range [first,first+len).
79  // The caller is required to provide a buffer of exactly the right size
80  // (which can be determined by the __to_chars_len function).
81  template<typename _Tp>
82  _GLIBCXX23_CONSTEXPR void
83  __to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
84  {
85 #if __cpp_variable_templates
86  static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
87 #endif
88 
89  constexpr char __digits[201] =
90  "0001020304050607080910111213141516171819"
91  "2021222324252627282930313233343536373839"
92  "4041424344454647484950515253545556575859"
93  "6061626364656667686970717273747576777879"
94  "8081828384858687888990919293949596979899";
95  unsigned __pos = __len - 1;
96  while (__val >= 100)
97  {
98  auto const __num = (__val % 100) * 2;
99  __val /= 100;
100  __first[__pos] = __digits[__num + 1];
101  __first[__pos - 1] = __digits[__num];
102  __pos -= 2;
103  }
104  if (__val >= 10)
105  {
106  auto const __num = __val * 2;
107  __first[1] = __digits[__num + 1];
108  __first[0] = __digits[__num];
109  }
110  else
111  __first[0] = '0' + __val;
112  }
113 
114 } // namespace __detail
115 _GLIBCXX_END_NAMESPACE_VERSION
116 } // namespace std
117 #endif // C++11
118 #endif // _GLIBCXX_CHARCONV_H
ISO C++ entities toplevel namespace is std.
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.
constexpr _Iterator __base(_Iterator __it)