libstdc++
functional_hash.h
Go to the documentation of this file.
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 
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
Primary class template hash.
Definition: system_error:142
integral_constant
Definition: type_traits:57
ISO C++ entities toplevel namespace is std.