1 // functional_hash.h header -*- C++ -*-
2
3 // Copyright (C) 2007-2020 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 <bits/hash_bytes.h>
36
_GLIBCXX_VISIBILITY(default)37 namespace std _GLIBCXX_VISIBILITY(default)
38 {
39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
40
41 /** @defgroup hashes Hashes
42 * @ingroup functors
43 *
44 * Hashing functors taking a variable type and returning a @c std::size_t.
45 *
46 * @{
47 */
48
49 template<typename _Result, typename _Arg>
50 struct __hash_base
51 {
52 typedef _Result result_type _GLIBCXX17_DEPRECATED;
53 typedef _Arg argument_type _GLIBCXX17_DEPRECATED;
54 };
55
56 /// Primary class template hash.
57 template<typename _Tp>
58 struct hash;
59
60 template<typename _Tp, typename = void>
61 struct __poison_hash
62 {
63 static constexpr bool __enable_hash_call = false;
64 private:
65 // Private rather than deleted to be non-trivially-copyable.
66 __poison_hash(__poison_hash&&);
67 ~__poison_hash();
68 };
69
70 template<typename _Tp>
71 struct __poison_hash<_Tp, __void_t<decltype(hash<_Tp>()(declval<_Tp>()))>>
72 {
73 static constexpr bool __enable_hash_call = true;
74 };
75
76 // Helper struct for SFINAE-poisoning non-enum types.
77 template<typename _Tp, bool = is_enum<_Tp>::value>
78 struct __hash_enum
79 {
80 private:
81 // Private rather than deleted to be non-trivially-copyable.
82 __hash_enum(__hash_enum&&);
83 ~__hash_enum();
84 };
85
86 // Helper struct for hash with enum types.
87 template<typename _Tp>
88 struct __hash_enum<_Tp, true> : public __hash_base<size_t, _Tp>
89 {
90 size_t
91 operator()(_Tp __val) const noexcept
92 {
93 using __type = typename underlying_type<_Tp>::type;
94 return hash<__type>{}(static_cast<__type>(__val));
95 }
96 };
97
98 /// Primary class template hash, usable for enum types only.
99 // Use with non-enum types still SFINAES.
100 template<typename _Tp>
101 struct hash : __hash_enum<_Tp>
102 { };
103
104 /// Partial specializations for pointer types.
105 template<typename _Tp>
106 struct hash<_Tp*> : public __hash_base<size_t, _Tp*>
107 {
108 size_t
109 operator()(_Tp* __p) const noexcept
110 { return reinterpret_cast<size_t>(__p); }
111 };
112
113 // Explicit specializations for integer types.
114 #define _Cxx_hashtable_define_trivial_hash(_Tp) \
115 template<> \
116 struct hash<_Tp> : public __hash_base<size_t, _Tp> \
117 { \
118 size_t \
119 operator()(_Tp __val) const noexcept \
120 { return static_cast<size_t>(__val); } \
121 };
122
123 /// Explicit specialization for bool.
124 _Cxx_hashtable_define_trivial_hash(bool)
125
126 /// Explicit specialization for char.
127 _Cxx_hashtable_define_trivial_hash(char)
128
129 /// Explicit specialization for signed char.
130 _Cxx_hashtable_define_trivial_hash(signed char)
131
132 /// Explicit specialization for unsigned char.
133 _Cxx_hashtable_define_trivial_hash(unsigned char)
134
135 /// Explicit specialization for wchar_t.
136 _Cxx_hashtable_define_trivial_hash(wchar_t)
137
138 #ifdef _GLIBCXX_USE_CHAR8_T
139 /// Explicit specialization for char8_t.
140 _Cxx_hashtable_define_trivial_hash(char8_t)
141 #endif
142
143 /// Explicit specialization for char16_t.
144 _Cxx_hashtable_define_trivial_hash(char16_t)
145
146 /// Explicit specialization for char32_t.
147 _Cxx_hashtable_define_trivial_hash(char32_t)
148
149 /// Explicit specialization for short.
150 _Cxx_hashtable_define_trivial_hash(short)
151
152 /// Explicit specialization for int.
153 _Cxx_hashtable_define_trivial_hash(int)
154
155 /// Explicit specialization for long.
156 _Cxx_hashtable_define_trivial_hash(long)
157
158 /// Explicit specialization for long long.
159 _Cxx_hashtable_define_trivial_hash(long long)
160
161 /// Explicit specialization for unsigned short.
162 _Cxx_hashtable_define_trivial_hash(unsigned short)
163
164 /// Explicit specialization for unsigned int.
165 _Cxx_hashtable_define_trivial_hash(unsigned int)
166
167 /// Explicit specialization for unsigned long.
168 _Cxx_hashtable_define_trivial_hash(unsigned long)
169
170 /// Explicit specialization for unsigned long long.
171 _Cxx_hashtable_define_trivial_hash(unsigned long long)
172
173 #ifdef __GLIBCXX_TYPE_INT_N_0
174 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0)
175 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned)
176 #endif
177 #ifdef __GLIBCXX_TYPE_INT_N_1
178 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1)
179 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned)
180 #endif
181 #ifdef __GLIBCXX_TYPE_INT_N_2
182 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2)
183 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned)
184 #endif
185 #ifdef __GLIBCXX_TYPE_INT_N_3
186 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3)
187 _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned)
188 #endif
189
190 #undef _Cxx_hashtable_define_trivial_hash
191
192 struct _Hash_impl
193 {
194 static size_t
195 hash(const void* __ptr, size_t __clength,
196 size_t __seed = static_cast<size_t>(0xc70f6907UL))
197 { return _Hash_bytes(__ptr, __clength, __seed); }
198
199 template<typename _Tp>
200 static size_t
201 hash(const _Tp& __val)
202 { return hash(&__val, sizeof(__val)); }
203
204 template<typename _Tp>
205 static size_t
206 __hash_combine(const _Tp& __val, size_t __hash)
207 { return hash(&__val, sizeof(__val), __hash); }
208 };
209
210 // A hash function similar to FNV-1a (see PR59406 for how it differs).
211 struct _Fnv_hash_impl
212 {
213 static size_t
214 hash(const void* __ptr, size_t __clength,
215 size_t __seed = static_cast<size_t>(2166136261UL))
216 { return _Fnv_hash_bytes(__ptr, __clength, __seed); }
217
218 template<typename _Tp>
219 static size_t
220 hash(const _Tp& __val)
221 { return hash(&__val, sizeof(__val)); }
222
223 template<typename _Tp>
224 static size_t
225 __hash_combine(const _Tp& __val, size_t __hash)
226 { return hash(&__val, sizeof(__val), __hash); }
227 };
228
229 /// Specialization for float.
230 template<>
231 struct hash<float> : public __hash_base<size_t, float>
232 {
233 size_t
234 operator()(float __val) const noexcept
235 {
236 // 0 and -0 both hash to zero.
237 return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0;
238 }
239 };
240
241 /// Specialization for double.
242 template<>
243 struct hash<double> : public __hash_base<size_t, double>
244 {
245 size_t
246 operator()(double __val) const noexcept
247 {
248 // 0 and -0 both hash to zero.
249 return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0;
250 }
251 };
252
253 /// Specialization for long double.
254 template<>
255 struct hash<long double>
256 : public __hash_base<size_t, long double>
257 {
258 _GLIBCXX_PURE size_t
259 operator()(long double __val) const noexcept;
260 };
261
262 #if __cplusplus >= 201703L
263 template<>
264 struct hash<nullptr_t> : public __hash_base<size_t, nullptr_t>
265 {
266 size_t
267 operator()(nullptr_t) const noexcept
268 { return 0; }
269 };
270 #endif
271
272 // @} group hashes
273
274 // Hint about performance of hash functor. If not fast the hash-based
275 // containers will cache the hash code.
276 // Default behavior is to consider that hashers are fast unless specified
277 // otherwise.
278 template<typename _Hash>
279 struct __is_fast_hash : public std::true_type
280 { };
281
282 template<>
283 struct __is_fast_hash<hash<long double>> : public std::false_type
284 { };
285
286 _GLIBCXX_END_NAMESPACE_VERSION
287 } // namespace
288
289 #endif // _FUNCTIONAL_HASH_H
290