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

   1 // functional_hash.h header -*- C++ -*-
   2
   3 // Copyright (C) 2007-2017 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