1 // functional_hash.h header -*- C++ -*-
2
3 // Copyright (C) 2007-2023 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