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1 : // functional_hash.h header -*- C++ -*-
2 :
3 : // Copyright (C) 2007-2017 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 :
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;
53 : typedef _Arg argument_type;
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
91 213 : operator()(_Tp __val) const noexcept
92 : {
93 : using __type = typename underlying_type<_Tp>::type;
94 213 : 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 : /// Explicit specialization for char16_t.
139 : _Cxx_hashtable_define_trivial_hash(char16_t)
140 :
141 : /// Explicit specialization for char32_t.
142 : _Cxx_hashtable_define_trivial_hash(char32_t)
143 :
144 : /// Explicit specialization for short.
145 : _Cxx_hashtable_define_trivial_hash(short)
146 :
147 : /// Explicit specialization for int.
148 213 : _Cxx_hashtable_define_trivial_hash(int)
149 :
150 : /// Explicit specialization for long.
151 : _Cxx_hashtable_define_trivial_hash(long)
152 :
153 : /// Explicit specialization for long long.
154 : _Cxx_hashtable_define_trivial_hash(long long)
155 :
156 : /// Explicit specialization for unsigned short.
157 : _Cxx_hashtable_define_trivial_hash(unsigned short)
158 :
159 : /// Explicit specialization for unsigned int.
160 4335 : _Cxx_hashtable_define_trivial_hash(unsigned int)
161 :
162 : /// Explicit specialization for unsigned long.
163 : _Cxx_hashtable_define_trivial_hash(unsigned long)
164 :
165 : /// Explicit specialization for unsigned long long.
166 : _Cxx_hashtable_define_trivial_hash(unsigned long long)
167 :
168 : #ifdef __GLIBCXX_TYPE_INT_N_0
169 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0)
170 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned)
171 : #endif
172 : #ifdef __GLIBCXX_TYPE_INT_N_1
173 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1)
174 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned)
175 : #endif
176 : #ifdef __GLIBCXX_TYPE_INT_N_2
177 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2)
178 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned)
179 : #endif
180 : #ifdef __GLIBCXX_TYPE_INT_N_3
181 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3)
182 : _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned)
183 : #endif
184 :
185 : #undef _Cxx_hashtable_define_trivial_hash
186 :
187 : struct _Hash_impl
188 : {
189 : static size_t
190 : hash(const void* __ptr, size_t __clength,
191 : size_t __seed = static_cast<size_t>(0xc70f6907UL))
192 : { return _Hash_bytes(__ptr, __clength, __seed); }
193 :
194 : template<typename _Tp>
195 : static size_t
196 : hash(const _Tp& __val)
197 : { return hash(&__val, sizeof(__val)); }
198 :
199 : template<typename _Tp>
200 : static size_t
201 : __hash_combine(const _Tp& __val, size_t __hash)
202 : { return hash(&__val, sizeof(__val), __hash); }
203 : };
204 :
205 : // A hash function similar to FNV-1a (see PR59406 for how it differs).
206 : struct _Fnv_hash_impl
207 : {
208 : static size_t
209 : hash(const void* __ptr, size_t __clength,
210 : size_t __seed = static_cast<size_t>(2166136261UL))
211 : { return _Fnv_hash_bytes(__ptr, __clength, __seed); }
212 :
213 : template<typename _Tp>
214 : static size_t
215 : hash(const _Tp& __val)
216 : { return hash(&__val, sizeof(__val)); }
217 :
218 : template<typename _Tp>
219 : static size_t
220 : __hash_combine(const _Tp& __val, size_t __hash)
221 : { return hash(&__val, sizeof(__val), __hash); }
222 : };
223 :
224 : /// Specialization for float.
225 : template<>
226 : struct hash<float> : public __hash_base<size_t, float>
227 : {
228 : size_t
229 : operator()(float __val) const noexcept
230 : {
231 : // 0 and -0 both hash to zero.
232 : return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0;
233 : }
234 : };
235 :
236 : /// Specialization for double.
237 : template<>
238 : struct hash<double> : public __hash_base<size_t, double>
239 : {
240 : size_t
241 : operator()(double __val) const noexcept
242 : {
243 : // 0 and -0 both hash to zero.
244 : return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0;
245 : }
246 : };
247 :
248 : /// Specialization for long double.
249 : template<>
250 : struct hash<long double>
251 : : public __hash_base<size_t, long double>
252 : {
253 : _GLIBCXX_PURE size_t
254 : operator()(long double __val) const noexcept;
255 : };
256 :
257 : // @} group hashes
258 :
259 : // Hint about performance of hash functor. If not fast the hash-based
260 : // containers will cache the hash code.
261 : // Default behavior is to consider that hashers are fast unless specified
262 : // otherwise.
263 : template<typename _Hash>
264 : struct __is_fast_hash : public std::true_type
265 : { };
266 :
267 : template<>
268 : struct __is_fast_hash<hash<long double>> : public std::false_type
269 : { };
270 :
271 : _GLIBCXX_END_NAMESPACE_VERSION
272 : } // namespace
273 :
274 : #endif // _FUNCTIONAL_HASH_H
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