libstdc++-v3/include/bits/functional_hash.h

   1 // functional_hash.h header -*- C++ -*-
   2
   3 // Copyright (C) 2007-2016 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   template<typename _Tp, typename = void>
  61     struct __poison_hash
  62     {
  63     private:
  64       // Private rather than deleted to be non-trivially-copyable.
  65       __poison_hash(__poison_hash&&);
  66       ~__poison_hash();
  67     };
  68
  69   template<typename _Tp>
  70     struct __poison_hash<_Tp, __void_t<decltype(hash<_Tp>()(declval<_Tp>()))>>
  71     {
  72     };
  73
  74   // Helper struct for SFINAE-poisoning non-enum types.
  75   template<typename _Tp, bool = is_enum<_Tp>::value>
  76     struct __hash_enum
  77     {
  78     private:
  79       // Private rather than deleted to be non-trivially-copyable.
  80       __hash_enum(__hash_enum&&);
  81       ~__hash_enum();
  82     };
  83
  84   // Helper struct for hash with enum types.
  85   template<typename _Tp>
  86     struct __hash_enum<_Tp, true> : public __hash_base<size_t, _Tp>
  87     {
  88       size_t
  89       operator()(_Tp __val) const noexcept
  90       {
  91        using __type = typename underlying_type<_Tp>::type;
  92        return hash<__type>{}(static_cast<__type>(__val));
  93       }
  94     };
  95
  96   /// Primary class template hash, usable for enum types only.
  97   // Use with non-enum types still SFINAES.
  98   template<typename _Tp>
  99     struct hash : __hash_enum<_Tp>
 100     { };
 101
 102   /// Partial specializations for pointer types.
 103   template<typename _Tp>
 104     struct hash<_Tp*> : public __hash_base<size_t, _Tp*>
 105     {
 106       size_t
 107       operator()(_Tp* __p) const noexcept
 108       { return reinterpret_cast<size_t>(__p); }
 109     };
 110
 111   // Explicit specializations for integer types.
 112 #define _Cxx_hashtable_define_trivial_hash(_Tp)         \
 113   template<>                                            \
 114     struct hash<_Tp> : public __hash_base<size_t, _Tp>  \
 115     {                                                   \
 116       size_t                                            \
 117       operator()(_Tp __val) const noexcept              \
 118       { return static_cast<size_t>(__val); }            \
 119     };
 120
 121   /// Explicit specialization for bool.
 122   _Cxx_hashtable_define_trivial_hash(bool)
 123
 124   /// Explicit specialization for char.
 125   _Cxx_hashtable_define_trivial_hash(char)
 126
 127   /// Explicit specialization for signed char.
 128   _Cxx_hashtable_define_trivial_hash(signed char)
 129
 130   /// Explicit specialization for unsigned char.
 131   _Cxx_hashtable_define_trivial_hash(unsigned char)
 132
 133   /// Explicit specialization for wchar_t.
 134   _Cxx_hashtable_define_trivial_hash(wchar_t)
 135
 136   /// Explicit specialization for char16_t.
 137   _Cxx_hashtable_define_trivial_hash(char16_t)
 138
 139   /// Explicit specialization for char32_t.
 140   _Cxx_hashtable_define_trivial_hash(char32_t)
 141
 142   /// Explicit specialization for short.
 143   _Cxx_hashtable_define_trivial_hash(short)
 144
 145   /// Explicit specialization for int.
 146   _Cxx_hashtable_define_trivial_hash(int)
 147
 148   /// Explicit specialization for long.
 149   _Cxx_hashtable_define_trivial_hash(long)
 150
 151   /// Explicit specialization for long long.
 152   _Cxx_hashtable_define_trivial_hash(long long)
 153
 154   /// Explicit specialization for unsigned short.
 155   _Cxx_hashtable_define_trivial_hash(unsigned short)
 156
 157   /// Explicit specialization for unsigned int.
 158   _Cxx_hashtable_define_trivial_hash(unsigned int)
 159
 160   /// Explicit specialization for unsigned long.
 161   _Cxx_hashtable_define_trivial_hash(unsigned long)
 162
 163   /// Explicit specialization for unsigned long long.
 164   _Cxx_hashtable_define_trivial_hash(unsigned long long)
 165
 166 #ifdef __GLIBCXX_TYPE_INT_N_0
 167   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0)
 168   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_0 unsigned)
 169 #endif
 170 #ifdef __GLIBCXX_TYPE_INT_N_1
 171   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1)
 172   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_1 unsigned)
 173 #endif
 174 #ifdef __GLIBCXX_TYPE_INT_N_2
 175   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2)
 176   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_2 unsigned)
 177 #endif
 178 #ifdef __GLIBCXX_TYPE_INT_N_3
 179   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3)
 180   _Cxx_hashtable_define_trivial_hash(__GLIBCXX_TYPE_INT_N_3 unsigned)
 181 #endif
 182
 183 #undef _Cxx_hashtable_define_trivial_hash
 184
 185   struct _Hash_impl
 186   {
 187     static size_t
 188     hash(const void* __ptr, size_t __clength,
 189          size_t __seed = static_cast<size_t>(0xc70f6907UL))
 190     { return _Hash_bytes(__ptr, __clength, __seed); }
 191
 192     template<typename _Tp>
 193       static size_t
 194       hash(const _Tp& __val)
 195       { return hash(&__val, sizeof(__val)); }
 196
 197     template<typename _Tp>
 198       static size_t
 199       __hash_combine(const _Tp& __val, size_t __hash)
 200       { return hash(&__val, sizeof(__val), __hash); }
 201   };
 202
 203   // A hash function similar to FNV-1a (see PR59406 for how it differs).
 204   struct _Fnv_hash_impl
 205   {
 206     static size_t
 207     hash(const void* __ptr, size_t __clength,
 208          size_t __seed = static_cast<size_t>(2166136261UL))
 209     { return _Fnv_hash_bytes(__ptr, __clength, __seed); }
 210
 211     template<typename _Tp>
 212       static size_t
 213       hash(const _Tp& __val)
 214       { return hash(&__val, sizeof(__val)); }
 215
 216     template<typename _Tp>
 217       static size_t
 218       __hash_combine(const _Tp& __val, size_t __hash)
 219       { return hash(&__val, sizeof(__val), __hash); }
 220   };
 221
 222   /// Specialization for float.
 223   template<>
 224     struct hash<float> : public __hash_base<size_t, float>
 225     {
 226       size_t
 227       operator()(float __val) const noexcept
 228       {
 229         // 0 and -0 both hash to zero.
 230         return __val != 0.0f ? std::_Hash_impl::hash(__val) : 0;
 231       }
 232     };
 233
 234   /// Specialization for double.
 235   template<>
 236     struct hash<double> : public __hash_base<size_t, double>
 237     {
 238       size_t
 239       operator()(double __val) const noexcept
 240       {
 241         // 0 and -0 both hash to zero.
 242         return __val != 0.0 ? std::_Hash_impl::hash(__val) : 0;
 243       }
 244     };
 245
 246   /// Specialization for long double.
 247   template<>
 248     struct hash<long double>
 249     : public __hash_base<size_t, long double>
 250     {
 251       _GLIBCXX_PURE size_t
 252       operator()(long double __val) const noexcept;
 253     };
 254
 255   // @} group hashes
 256
 257   // Hint about performance of hash functor. If not fast the hash-based
 258   // containers will cache the hash code.
 259   // Default behavior is to consider that hashers are fast unless specified
 260   // otherwise.
 261   template<typename _Hash>
 262     struct __is_fast_hash : public std::true_type
 263     { };
 264
 265   template<>
 266     struct __is_fast_hash<hash<long double>> : public std::false_type
 267     { };
 268
 269 _GLIBCXX_END_NAMESPACE_VERSION
 270 } // namespace
 271
 272 #endif // _FUNCTIONAL_HASH_H