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

   1 // functional_hash.h header -*- C++ -*-
   2
   3 // Copyright (C) 2007-2014 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