libstdc++

functional_hash.h
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1 // functional_hash.h header -*- C++ -*-
2
3 // Copyright (C) 2007-2013 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 /// Partial specializations for pointer types.
61 template<typename _Tp>
62 struct hash<_Tp*> : public __hash_base<size_t, _Tp*>
63 {
64 size_t
65 operator()(_Tp* __p) const noexcept
66 { return reinterpret_cast<size_t>(__p); }
67 };
68
69 // Explicit specializations for integer types.
70 #define _Cxx_hashtable_define_trivial_hash(_Tp) \
71 template<> \
72 struct hash<_Tp> : public __hash_base<size_t, _Tp> \
73 { \
74 size_t \
75 operator()(_Tp __val) const noexcept \
76 { return static_cast<size_t>(__val); } \
77 };
78
79 /// Explicit specialization for bool.
80 _Cxx_hashtable_define_trivial_hash(bool)
81
82 /// Explicit specialization for char.
83 _Cxx_hashtable_define_trivial_hash(char)
84
85 /// Explicit specialization for signed char.
86 _Cxx_hashtable_define_trivial_hash(signed char)
87
88 /// Explicit specialization for unsigned char.
89 _Cxx_hashtable_define_trivial_hash(unsigned char)
90
91 /// Explicit specialization for wchar_t.
92 _Cxx_hashtable_define_trivial_hash(wchar_t)
93
94 /// Explicit specialization for char16_t.
95 _Cxx_hashtable_define_trivial_hash(char16_t)
96
97 /// Explicit specialization for char32_t.
98 _Cxx_hashtable_define_trivial_hash(char32_t)
99
100 /// Explicit specialization for short.
101 _Cxx_hashtable_define_trivial_hash(short)
102
103 /// Explicit specialization for int.
104 _Cxx_hashtable_define_trivial_hash(int)
105
106 /// Explicit specialization for long.
107 _Cxx_hashtable_define_trivial_hash(long)
108
109 /// Explicit specialization for long long.
110 _Cxx_hashtable_define_trivial_hash(long long)
111
112 /// Explicit specialization for unsigned short.
113 _Cxx_hashtable_define_trivial_hash(unsigned short)
114
115 /// Explicit specialization for unsigned int.
116 _Cxx_hashtable_define_trivial_hash(unsigned int)
117
118 /// Explicit specialization for unsigned long.
119 _Cxx_hashtable_define_trivial_hash(unsigned long)
120
121 /// Explicit specialization for unsigned long long.
122 _Cxx_hashtable_define_trivial_hash(unsigned long long)
123
124 #undef _Cxx_hashtable_define_trivial_hash
125
126 struct _Hash_impl
127 {
128 static size_t
129 hash(const void* __ptr, size_t __clength,
130 size_t __seed = static_cast<size_t>(0xc70f6907UL))
131 { return _Hash_bytes(__ptr, __clength, __seed); }
132
133 template<typename _Tp>
134 static size_t
135 hash(const _Tp& __val)
136 { return hash(&__val, sizeof(__val)); }
137
138 template<typename _Tp>
139 static size_t
140 __hash_combine(const _Tp& __val, size_t __hash)
141 { return hash(&__val, sizeof(__val), __hash); }
142 };
143
144 struct _Fnv_hash_impl
145 {
146 static size_t
147 hash(const void* __ptr, size_t __clength,
148 size_t __seed = static_cast<size_t>(2166136261UL))
149 { return _Fnv_hash_bytes(__ptr, __clength, __seed); }
150
151 template<typename _Tp>
152 static size_t
153 hash(const _Tp& __val)
154 { return hash(&__val, sizeof(__val)); }
155
156 template<typename _Tp>
157 static size_t
158 __hash_combine(const _Tp& __val, size_t __hash)
159 { return hash(&__val, sizeof(__val), __hash); }
160 };
161
162 /// Specialization for float.
163 template<>
164 struct hash<float> : public __hash_base<size_t, float>
165 {
166 size_t
167 operator()(float __val) const noexcept
168 {
169 // 0 and -0 both hash to zero.
170 return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0;
171 }
172 };
173
174 /// Specialization for double.
175 template<>
176 struct hash<double> : public __hash_base<size_t, double>
177 {
178 size_t
179 operator()(double __val) const noexcept
180 {
181 // 0 and -0 both hash to zero.
182 return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0;
183 }
184 };
185
186 /// Specialization for long double.
187 template<>
188 struct hash<long double>
189 : public __hash_base<size_t, long double>
190 {
191 _GLIBCXX_PURE size_t
192 operator()(long double __val) const noexcept;
193 };
194
195 // @} group hashes
196
197 // Hint about performance of hash functor. If not fast the hash based
198 // containers will cache the hash code.
199 // Default behavior is to consider that hasher are fast unless specified
200 // otherwise.
201 template<typename _Hash>
202 struct __is_fast_hash : public std::true_type
203 { };
204
205 template<>
206 struct __is_fast_hash<hash<long double>> : public std::false_type
207 { };
208
209 _GLIBCXX_END_NAMESPACE_VERSION
210 } // namespace
211
212 #endif // _FUNCTIONAL_HASH_H