libstdc++
functional_hash.h
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1 // functional_hash.h header -*- C++ -*-
2 
3 // Copyright (C) 2007-2021 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
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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  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0)
176  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned)
177 #endif
178 #ifdef __GLIBCXX_TYPE_INT_N_1
179  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1)
180  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned)
181 #endif
182 #ifdef __GLIBCXX_TYPE_INT_N_2
183  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2)
184  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned)
185 #endif
186 #ifdef __GLIBCXX_TYPE_INT_N_3
187  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3)
188  _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned)
189 #endif
190 
191 #undef _Cxx_hashtable_define_trivial_hash
192 
193  struct _Hash_impl
194  {
195  static size_t
196  hash(const void* __ptr, size_t __clength,
197  size_t __seed = static_cast<size_t>(0xc70f6907UL))
198  { return _Hash_bytes(__ptr, __clength, __seed); }
199 
200  template<typename _Tp>
201  static size_t
202  hash(const _Tp& __val)
203  { return hash(&__val, sizeof(__val)); }
204 
205  template<typename _Tp>
206  static size_t
207  __hash_combine(const _Tp& __val, size_t __hash)
208  { return hash(&__val, sizeof(__val), __hash); }
209  };
210 
211  // A hash function similar to FNV-1a (see PR59406 for how it differs).
212  struct _Fnv_hash_impl
213  {
214  static size_t
215  hash(const void* __ptr, size_t __clength,
216  size_t __seed = static_cast<size_t>(2166136261UL))
217  { return _Fnv_hash_bytes(__ptr, __clength, __seed); }
218 
219  template<typename _Tp>
220  static size_t
221  hash(const _Tp& __val)
222  { return hash(&__val, sizeof(__val)); }
223 
224  template<typename _Tp>
225  static size_t
226  __hash_combine(const _Tp& __val, size_t __hash)
227  { return hash(&__val, sizeof(__val), __hash); }
228  };
229 
230  /// Specialization for float.
231  template<>
232  struct hash<float> : public __hash_base<size_t, float>
233  {
234  size_t
235  operator()(float __val) const noexcept
236  {
237  // 0 and -0 both hash to zero.
238  return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0;
239  }
240  };
241 
242  /// Specialization for double.
243  template<>
244  struct hash<double> : public __hash_base<size_t, double>
245  {
246  size_t
247  operator()(double __val) const noexcept
248  {
249  // 0 and -0 both hash to zero.
250  return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0;
251  }
252  };
253 
254  /// Specialization for long double.
255  template<>
256  struct hash<long double>
257  : public __hash_base<size_t, long double>
258  {
259  _GLIBCXX_PURE size_t
260  operator()(long double __val) const noexcept;
261  };
262 
263 #if __cplusplus >= 201703L
264  template<>
265  struct hash<nullptr_t> : public __hash_base<size_t, nullptr_t>
266  {
267  size_t
268  operator()(nullptr_t) const noexcept
269  { return 0; }
270  };
271 #endif
272 
273  /// @} group hashes
274 
275  // Hint about performance of hash functor. If not fast the hash-based
276  // containers will cache the hash code.
277  // Default behavior is to consider that hashers are fast unless specified
278  // otherwise.
279  template<typename _Hash>
280  struct __is_fast_hash : public std::true_type
281  { };
282 
283  template<>
284  struct __is_fast_hash<hash<long double>> : public std::false_type
285  { };
286 
287 _GLIBCXX_END_NAMESPACE_VERSION
288 } // namespace
289 
290 #endif // _FUNCTIONAL_HASH_H
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition: type_traits:2364
ISO C++ entities toplevel namespace is std.
Primary class template hash.
integral_constant
Definition: type_traits:66