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 
39namespace std _GLIBCXX_VISIBILITY(default) 
40{ 
41_GLIBCXX_BEGIN_NAMESPACE_VERSION 
42namespace __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 
107