libstdc++
functional_hash.h
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1 // functional_hash.h header -*- C++ -*-
2 
3 // Copyright (C) 2007-2015 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
Primary class template hash.
ISO C++ entities toplevel namespace is std.