1 // functional_hash.h header -*- C++ -*-
2 
3 // Copyright (C) 2007-2018 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   /// 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   _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   _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
275