1 // functional_hash.h header -*- C++ -*- 2 3 // Copyright (C) 2007-2024 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 __extension__ 176 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0) 177 __extension__ 178 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned) 179 #endif 180 #ifdef __GLIBCXX_TYPE_INT_N_1 181 __extension__ 182 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1) 183 __extension__ 184 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned) 185 #endif 186 #ifdef __GLIBCXX_TYPE_INT_N_2 187 __extension__ 188 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2) 189 __extension__ 190 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned) 191 #endif 192 #ifdef __GLIBCXX_TYPE_INT_N_3 193 __extension__ 194 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3) 195 __extension__ 196 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned) 197 #endif 198 199 #undef _Cxx_hashtable_define_trivial_hash 200 201 struct _Hash_impl 202 { 203 static size_t 204 hash(const void* __ptr, size_t __clength, 205 size_t __seed = static_cast<size_t>(0xc70f6907UL)) 206 { return _Hash_bytes(__ptr, __clength, __seed); } 207 208 template<typename _Tp> 209 static size_t 210 hash(const _Tp& __val) 211 { return hash(&__val, sizeof(__val)); } 212 213 template<typename _Tp> 214 static size_t 215 __hash_combine(const _Tp& __val, size_t __hash) 216 { return hash(&__val, sizeof(__val), __hash); } 217 }; 218 219 // A hash function similar to FNV-1a (see PR59406 for how it differs). 220 struct _Fnv_hash_impl 221 { 222 static size_t 223 hash(const void* __ptr, size_t __clength, 224 size_t __seed = static_cast<size_t>(2166136261UL)) 225 { return _Fnv_hash_bytes(__ptr, __clength, __seed); } 226 227 template<typename _Tp> 228 static size_t 229 hash(const _Tp& __val) 230 { return hash(&__val, sizeof(__val)); } 231 232 template<typename _Tp> 233 static size_t 234 __hash_combine(const _Tp& __val, size_t __hash) 235 { return hash(&__val, sizeof(__val), __hash); } 236 }; 237 238 /// Specialization for float. 239 template<> 240 struct hash<float> : public __hash_base<size_t, float> 241 { 242 size_t 243 operator()(float __val) const noexcept 244 { 245 // 0 and -0 both hash to zero. 246 return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0; 247 } 248 }; 249 250 /// Specialization for double. 251 template<> 252 struct hash<double> : public __hash_base<size_t, double> 253 { 254 size_t 255 operator()(double __val) const noexcept 256 { 257 // 0 and -0 both hash to zero. 258 return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0; 259 } 260 }; 261 262 /// Specialization for long double. 263 template<> 264 struct hash<long double> 265 : public __hash_base<size_t, long double> 266 { 267 _GLIBCXX_PURE size_t 268 operator()(long double __val) const noexcept; 269 }; 270 271 #if __cplusplus >= 201703L 272 template<> 273 struct hash<nullptr_t> : public __hash_base<size_t, nullptr_t> 274 { 275 size_t 276 operator()(nullptr_t) const noexcept 277 { return 0; } 278 }; 279 #endif 280 281 /// @} group hashes 282 283 /** Hint about performance of hash functions. 284 * 285 * If a given hash function object is not fast, the hash-based containers 286 * will cache the hash code. 287 * The default behavior is to consider that hashers are fast unless specified 288 * otherwise. 289 * 290 * Users can specialize this for their own hash functions in order to force 291 * caching of hash codes in unordered containers. Specializing this trait 292 * affects the ABI of the unordered containers, so use it carefully. 293 */ 294 template<typename _Hash> 295 struct __is_fast_hash : public std::true_type 296 { }; 297 298 template<> 299 struct __is_fast_hash<hash<long double>> : public std::false_type 300 { }; 301 302 _GLIBCXX_END_NAMESPACE_VERSION 303 } // namespace 304 305 #endif // _FUNCTIONAL_HASH_H 306
Indexes created Sat Feb 28 05:31:39 UTC 2026