libstdc++: numeric_traits.h Source File

libstdc++

ext/numeric_traits.h
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1// -*- C++ -*-
2
3// Copyright (C) 2007-2026 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 terms
7// of the GNU General Public License as published by the Free Software
8// Foundation; either version 3, or (at your option) any later
9// version.
10
11// This library is distributed in the hope that it will be useful, but
12// WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14// 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.
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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 ext/numeric_traits.h
26 * This file is a GNU extension to the Standard C++ Library.
27 */
28
29#ifndef _EXT_NUMERIC_TRAITS
30#define _EXT_NUMERIC_TRAITS 1
31
32#ifdef _GLIBCXX_SYSHDR
33#pragma GCC system_header
34#endif
35
36#include <bits/cpp_type_traits.h>
37#include <ext/type_traits.h>
38
39namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
40{
41_GLIBCXX_BEGIN_NAMESPACE_VERSION
42
43 // Compile time constants for builtin types.
44 // In C++98 std::numeric_limits member functions are not constant expressions
45 // (that changed in C++11 with the addition of 'constexpr').
46 // Even for C++11, this header is smaller than <limits> and can be used
47 // when only is_signed, digits, min, or max values are needed for integers,
48 // or is_signed, digits10, max_digits10, or max_exponent10 for floats.
49
50 // Unlike __is_integer (and std::is_integral) this trait is true for
51 // non-standard built-in integer types such as __int20.
52 template<typename _Tp>
53 struct __is_integer_nonstrict
54 : public std::__is_integer<_Tp>
55 {
56 using std::__is_integer<_Tp>::__value;
57
58 // The number of bits in the value representation.
59 enum { __width = __value ? sizeof(_Tp) * __CHAR_BIT__ : 0 };
60 };
61
62 template<typename _Value>
63 struct __numeric_traits_integer
64 {
65#if __cplusplus >= 201103L
66 static_assert(__is_integer_nonstrict<_Value>::__value,
67 "invalid specialization");
68#endif
69
70 // NB: these two are also available in std::numeric_limits as compile
71 // time constants, but <limits> is big and we can avoid including it.
72 static const bool __is_signed = (_Value)(-1) < 0;
73 static const int __digits
74 = __is_integer_nonstrict<_Value>::__width - __is_signed;
75
76 // The initializers must be constants so that __max and __min are too.
77 static const _Value __max = __is_signed
78 ? (((((_Value)1 << (__digits - 1)) - 1) << 1) + 1)
79 : ~(_Value)0;
80 static const _Value __min = __is_signed ? -__max - 1 : (_Value)0;
81 };
82
83 template<typename _Value>
84 const _Value __numeric_traits_integer<_Value>::__min;
85
86 template<typename _Value>
87 const _Value __numeric_traits_integer<_Value>::__max;
88
89 template<typename _Value>
90 const bool __numeric_traits_integer<_Value>::__is_signed;
91
92 template<typename _Value>
93 const int __numeric_traits_integer<_Value>::__digits;
94
95 // Enable __numeric_traits_integer for types where the __is_integer_nonstrict
96 // primary template doesn't give the right answer.
97#define _GLIBCXX_INT_N_TRAITS(T, WIDTH) \
98 __extension__ \
99 template<> struct __is_integer_nonstrict<T> \
100 { \
101 enum { __value = 1 }; \
102 typedef std::__true_type __type; \
103 enum { __width = WIDTH }; \
104 }; \
105 __extension__ \
106 template<> struct __is_integer_nonstrict<unsigned T> \
107 { \
108 enum { __value = 1 }; \
109 typedef std::__true_type __type; \
110 enum { __width = WIDTH }; \
111 };
112
113 // We need to specify the width for some __intNN types because they
114 // have padding bits, e.g. the object representation of __int20 has 32 bits,
115 // but its width (number of bits in the value representation) is only 20.
116#if defined __GLIBCXX_TYPE_INT_N_0 && __GLIBCXX_BITSIZE_INT_N_0 % __CHAR_BIT__
117 _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_0, __GLIBCXX_BITSIZE_INT_N_0)
118#endif
119#if defined __GLIBCXX_TYPE_INT_N_1 && __GLIBCXX_BITSIZE_INT_N_1 % __CHAR_BIT__
120 _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_1, __GLIBCXX_BITSIZE_INT_N_1)
121#endif
122#if defined __GLIBCXX_TYPE_INT_N_2 && __GLIBCXX_BITSIZE_INT_N_2 % __CHAR_BIT__
123 _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_2, __GLIBCXX_BITSIZE_INT_N_2)
124#endif
125#if defined __GLIBCXX_TYPE_INT_N_3 && __GLIBCXX_BITSIZE_INT_N_3 % __CHAR_BIT__
126 _GLIBCXX_INT_N_TRAITS(__GLIBCXX_TYPE_INT_N_3, __GLIBCXX_BITSIZE_INT_N_3)
127#endif
128
129#undef _GLIBCXX_INT_N_TRAITS
130
131#if __cplusplus >= 201103L
132 /// Convenience alias for __numeric_traits<integer-type>.
133 template<typename _Tp>
134 using __int_traits = __numeric_traits_integer<_Tp>;
135#endif
136
137#define __glibcxx_floating(_Tp, _Fval, _Dval, _LDval) \
138 (std::__are_same<_Tp, float>::__value ? _Fval \
139 : std::__are_same<_Tp, double>::__value ? _Dval : _LDval)
140
141#define __glibcxx_max_digits10(_Tp) \
142 (2 + __glibcxx_floating(_Tp, __FLT_MANT_DIG__, __DBL_MANT_DIG__, \
143 __LDBL_MANT_DIG__) * 643L / 2136)
144
145#define __glibcxx_digits10(_Tp) \
146 __glibcxx_floating(_Tp, __FLT_DIG__, __DBL_DIG__, __LDBL_DIG__)
147
148#define __glibcxx_max_exponent10(_Tp) \
149 __glibcxx_floating(_Tp, __FLT_MAX_10_EXP__, __DBL_MAX_10_EXP__, \
150 __LDBL_MAX_10_EXP__)
151
152 // N.B. this only supports float, double and long double (no __float128 etc.)
153 template<typename _Value>
154 struct __numeric_traits_floating
155 {
156 // Only floating point types. See N1822.
157 static const int __max_digits10 = __glibcxx_max_digits10(_Value);
158
159 // See above comment...
160 static const bool __is_signed = true;
161 static const int __digits10 = __glibcxx_digits10(_Value);
162 static const int __max_exponent10 = __glibcxx_max_exponent10(_Value);
163 };
164
165 template<typename _Value>
166 const int __numeric_traits_floating<_Value>::__max_digits10;
167
168 template<typename _Value>
169 const bool __numeric_traits_floating<_Value>::__is_signed;
170
171 template<typename _Value>
172 const int __numeric_traits_floating<_Value>::__digits10;
173
174 template<typename _Value>
175 const int __numeric_traits_floating<_Value>::__max_exponent10;
176
177#undef __glibcxx_floating
178#undef __glibcxx_max_digits10
179#undef __glibcxx_digits10
180#undef __glibcxx_max_exponent10
181
182 template<typename _Value>
183 struct __numeric_traits
184 : public __numeric_traits_integer<_Value>
185 { };
186
187 template<>
188 struct __numeric_traits<float>
189 : public __numeric_traits_floating<float>
190 { };
191
192 template<>
193 struct __numeric_traits<double>
194 : public __numeric_traits_floating<double>
195 { };
196
197 template<>
198 struct __numeric_traits<long double>
199 : public __numeric_traits_floating<long double>
200 { };
201
202#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
203# if defined __LONG_DOUBLE_IEEE128__
204 // long double is __ieee128, define traits for __ibm128
205 template<>
206 struct __numeric_traits_floating<__ibm128>
207 {
208 static const int __max_digits10 = 33;
209 static const bool __is_signed = true;
210 static const int __digits10 = 31;
211 static const int __max_exponent10 = 308;
212 };
213 template<>
214 struct __numeric_traits<__ibm128>
215 : public __numeric_traits_floating<__ibm128>
216 { };
217# elif defined __LONG_DOUBLE_IBM128__
218 // long double is __ibm128, define traits for __ieee128
219 template<>
220 struct __numeric_traits_floating<__ieee128>
221 {
222 static const int __max_digits10 = 36;
223 static const bool __is_signed = true;
224 static const int __digits10 = 33;
225 static const int __max_exponent10 = 4932;
226 };
227 template<>
228 struct __numeric_traits<__ieee128>
229 : public __numeric_traits_floating<__ieee128>
230 { };
231# endif
232#endif
233
234_GLIBCXX_END_NAMESPACE_VERSION
235} // namespace
236
237#endif
cpp_type_traits.h
type_traits.h
__gnu_cxx
GNU extensions for public use.
__gnu_cxx::__int_traits
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.
Definition ext/numeric_traits.h:134