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The C and C++ Include Header Files
/usr/include/c++/11/bits/functional_hash.h
$ cat -n /usr/include/c++/11/bits/functional_hash.h 1 // functional_hash.h header -*- C++ -*- 2 3 // Copyright (C) 2007-2021 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/functional_hash.h 26 * This is an internal header file, included by other library headers. 27 * Do not attempt to use it directly. @headername{functional} 28 */ 29 30 #ifndef _FUNCTIONAL_HASH_H 31 #define _FUNCTIONAL_HASH_H 1 32 33 #pragma GCC system_header 34 35 #include <type_traits> 36 #include <bits/hash_bytes.h> 37 38 namespace std _GLIBCXX_VISIBILITY(default) 39 { 40 _GLIBCXX_BEGIN_NAMESPACE_VERSION 41 42 /** @defgroup hashes Hashes 43 * @ingroup functors 44 * 45 * Hashing functors taking a variable type and returning a @c std::size_t. 46 * 47 * @{ 48 */ 49 50 template<typename _Result, typename _Arg> 51 struct __hash_base 52 { 53 typedef _Result result_type _GLIBCXX17_DEPRECATED; 54 typedef _Arg argument_type _GLIBCXX17_DEPRECATED; 55 }; 56 57 /// Primary class template hash. 58 template<typename _Tp> 59 struct hash; 60 61 template<typename _Tp, typename = void> 62 struct __poison_hash 63 { 64 static constexpr bool __enable_hash_call = false; 65 private: 66 // Private rather than deleted to be non-trivially-copyable. 67 __poison_hash(__poison_hash&&); 68 ~__poison_hash(); 69 }; 70 71 template<typename _Tp> 72 struct __poison_hash<_Tp, __void_t<decltype(hash<_Tp>()(declval<_Tp>()))>> 73 { 74 static constexpr bool __enable_hash_call = true; 75 }; 76 77 // Helper struct for SFINAE-poisoning non-enum types. 78 template<typename _Tp, bool = is_enum<_Tp>::value> 79 struct __hash_enum 80 { 81 private: 82 // Private rather than deleted to be non-trivially-copyable. 83 __hash_enum(__hash_enum&&); 84 ~__hash_enum(); 85 }; 86 87 // Helper struct for hash with enum types. 88 template<typename _Tp> 89 struct __hash_enum<_Tp, true> : public __hash_base<size_t, _Tp> 90 { 91 size_t 92 operator()(_Tp __val) const noexcept 93 { 94 using __type = typename underlying_type<_Tp>::type; 95 return hash<__type>{}(static_cast<__type>(__val)); 96 } 97 }; 98 99 /// Primary class template hash, usable for enum types only. 100 // Use with non-enum types still SFINAES. 101 template<typename _Tp> 102 struct hash : __hash_enum<_Tp> 103 { }; 104 105 /// Partial specializations for pointer types. 106 template<typename _Tp> 107 struct hash<_Tp*> : public __hash_base<size_t, _Tp*> 108 { 109 size_t 110 operator()(_Tp* __p) const noexcept 111 { return reinterpret_cast<size_t>(__p); } 112 }; 113 114 // Explicit specializations for integer types. 115 #define _Cxx_hashtable_define_trivial_hash(_Tp) \ 116 template<> \ 117 struct hash<_Tp> : public __hash_base<size_t, _Tp> \ 118 { \ 119 size_t \ 120 operator()(_Tp __val) const noexcept \ 121 { return static_cast<size_t>(__val); } \ 122 }; 123 124 /// Explicit specialization for bool. 125 _Cxx_hashtable_define_trivial_hash(bool) 126 127 /// Explicit specialization for char. 128 _Cxx_hashtable_define_trivial_hash(char) 129 130 /// Explicit specialization for signed char. 131 _Cxx_hashtable_define_trivial_hash(signed char) 132 133 /// Explicit specialization for unsigned char. 134 _Cxx_hashtable_define_trivial_hash(unsigned char) 135 136 /// Explicit specialization for wchar_t. 137 _Cxx_hashtable_define_trivial_hash(wchar_t) 138 139 #ifdef _GLIBCXX_USE_CHAR8_T 140 /// Explicit specialization for char8_t. 141 _Cxx_hashtable_define_trivial_hash(char8_t) 142 #endif 143 144 /// Explicit specialization for char16_t. 145 _Cxx_hashtable_define_trivial_hash(char16_t) 146 147 /// Explicit specialization for char32_t. 148 _Cxx_hashtable_define_trivial_hash(char32_t) 149 150 /// Explicit specialization for short. 151 _Cxx_hashtable_define_trivial_hash(short) 152 153 /// Explicit specialization for int. 154 _Cxx_hashtable_define_trivial_hash(int) 155 156 /// Explicit specialization for long. 157 _Cxx_hashtable_define_trivial_hash(long) 158 159 /// Explicit specialization for long long. 160 _Cxx_hashtable_define_trivial_hash(long long) 161 162 /// Explicit specialization for unsigned short. 163 _Cxx_hashtable_define_trivial_hash(unsigned short) 164 165 /// Explicit specialization for unsigned int. 166 _Cxx_hashtable_define_trivial_hash(unsigned int) 167 168 /// Explicit specialization for unsigned long. 169 _Cxx_hashtable_define_trivial_hash(unsigned long) 170 171 /// Explicit specialization for unsigned long long. 172 _Cxx_hashtable_define_trivial_hash(unsigned long long) 173 174 #ifdef __GLIBCXX_TYPE_INT_N_0 175 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0) 176 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned) 177 #endif 178 #ifdef __GLIBCXX_TYPE_INT_N_1 179 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1) 180 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned) 181 #endif 182 #ifdef __GLIBCXX_TYPE_INT_N_2 183 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2) 184 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned) 185 #endif 186 #ifdef __GLIBCXX_TYPE_INT_N_3 187 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3) 188 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned) 189 #endif 190 191 #undef _Cxx_hashtable_define_trivial_hash 192 193 struct _Hash_impl 194 { 195 static size_t 196 hash(const void* __ptr, size_t __clength, 197 size_t __seed = static_cast<size_t>(0xc70f6907UL)) 198 { return _Hash_bytes(__ptr, __clength, __seed); } 199 200 template<typename _Tp> 201 static size_t 202 hash(const _Tp& __val) 203 { return hash(&__val, sizeof(__val)); } 204 205 template<typename _Tp> 206 static size_t 207 __hash_combine(const _Tp& __val, size_t __hash) 208 { return hash(&__val, sizeof(__val), __hash); } 209 }; 210 211 // A hash function similar to FNV-1a (see PR59406 for how it differs). 212 struct _Fnv_hash_impl 213 { 214 static size_t 215 hash(const void* __ptr, size_t __clength, 216 size_t __seed = static_cast<size_t>(2166136261UL)) 217 { return _Fnv_hash_bytes(__ptr, __clength, __seed); } 218 219 template<typename _Tp> 220 static size_t 221 hash(const _Tp& __val) 222 { return hash(&__val, sizeof(__val)); } 223 224 template<typename _Tp> 225 static size_t 226 __hash_combine(const _Tp& __val, size_t __hash) 227 { return hash(&__val, sizeof(__val), __hash); } 228 }; 229 230 /// Specialization for float. 231 template<> 232 struct hash<float> : public __hash_base<size_t, float> 233 { 234 size_t 235 operator()(float __val) const noexcept 236 { 237 // 0 and -0 both hash to zero. 238 return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0; 239 } 240 }; 241 242 /// Specialization for double. 243 template<> 244 struct hash<double> : public __hash_base<size_t, double> 245 { 246 size_t 247 operator()(double __val) const noexcept 248 { 249 // 0 and -0 both hash to zero. 250 return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0; 251 } 252 }; 253 254 /// Specialization for long double. 255 template<> 256 struct hash<long double> 257 : public __hash_base<size_t, long double> 258 { 259 _GLIBCXX_PURE size_t 260 operator()(long double __val) const noexcept; 261 }; 262 263 #if __cplusplus >= 201703L 264 template<> 265 struct hash<nullptr_t> : public __hash_base<size_t, nullptr_t> 266 { 267 size_t 268 operator()(nullptr_t) const noexcept 269 { return 0; } 270 }; 271 #endif 272 273 /// @} group hashes 274 275 // Hint about performance of hash functor. If not fast the hash-based 276 // containers will cache the hash code. 277 // Default behavior is to consider that hashers are fast unless specified 278 // otherwise. 279 template<typename _Hash> 280 struct __is_fast_hash : public std::true_type 281 { }; 282 283 template<> 284 struct __is_fast_hash<hash<long double>> : public std::false_type 285 { }; 286 287 _GLIBCXX_END_NAMESPACE_VERSION 288 } // namespace 289 290 #endif // _FUNCTIONAL_HASH_H
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