libstdc++-v3/src/hash.cc

   1 //  std::hash and std::tr1::hash definitions -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2008 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 2, 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 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  19 // Boston, MA 02110-1301, USA.
  20
  21 // As a special exception, you may use this file as part of a free software
  22 // library without restriction.  Specifically, if other files instantiate
  23 // templates or use macros or inline functions from this file, or you compile
  24 // this file and link it with other files to produce an executable, this
  25 // file does not by itself cause the resulting executable to be covered by
  26 // the GNU General Public License.  This exception does not however
  27 // invalidate any other reasons why the executable file might be covered by
  28 // the GNU General Public License.
  29
  30 #include <cstddef>
  31 #include <string>
  32 #include <cmath>
  33
  34 #ifdef __GXX_EXPERIMENTAL_CXX0X__
  35 #include <functional>
  36 #  define _GLIBCXX_BEGIN_NAMESPACE_TR1
  37 #  define _GLIBCXX_END_NAMESPACE_TR1
  38 #else
  39 #include <tr1/functional>
  40 #  define _GLIBCXX_BEGIN_NAMESPACE_TR1 namespace tr1 {
  41 #  define _GLIBCXX_END_NAMESPACE_TR1 }
  42 #endif
  43
  44 namespace std
  45 {
  46 _GLIBCXX_BEGIN_NAMESPACE_TR1
  47
  48   // For long double, careful with random padding bits (e.g., on x86,
  49   // 10 bytes -> 12 bytes) and resort to frexp.
  50   template<>
  51     size_t
  52     hash<long double>::operator()(long double __val) const
  53     {
  54       size_t __result = 0;
  55
  56       int __exponent;
  57       __val = std::frexp(__val, &__exponent);
  58       __val = __val < 0.0l ? -(__val + 0.5l) : __val;
  59
  60       const long double __mult =
  61       __gnu_cxx::__numeric_traits<size_t>::__max + 1.0l;
  62       __val *= __mult;
  63
  64       // Try to use all the bits of the mantissa (really necessary only
  65       // on 32-bit targets, at least for 80-bit floating point formats).
  66       const size_t __hibits = (size_t)__val;
  67       __val = (__val - (long double)__hibits) * __mult;
  68
  69       const size_t __coeff =
  70         __gnu_cxx::__numeric_traits<size_t>::__max / __LDBL_MAX_EXP__;
  71
  72       __result = __hibits + (size_t)__val + __coeff * __exponent;
  73
  74       return __result;
  75     };
  76
  77 #ifndef _GLIBCXX_LONG_DOUBLE_COMPAT_IMPL
  78   template<>
  79     size_t
  80     hash<string>::operator()(string __s) const
  81     { return _Fnv_hash<>::hash(__s.data(), __s.length()); }
  82
  83   template<>
  84     size_t
  85     hash<const string&>::operator()(const string& __s) const
  86     { return _Fnv_hash<>::hash(__s.data(), __s.length()); }
  87
  88 #ifdef _GLIBCXX_USE_WCHAR_T
  89   template<>
  90     size_t
  91     hash<wstring>::operator()(wstring __s) const
  92     {
  93       const char* __p = reinterpret_cast<const char*>(__s.data());
  94       return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
  95     }
  96
  97   template<>
  98     size_t
  99     hash<const wstring&>::operator()(const wstring& __s) const
 100     {
 101       const char* __p = reinterpret_cast<const char*>(__s.data());
 102       return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
 103     }
 104 #endif
 105 #endif
 106
 107 _GLIBCXX_END_NAMESPACE_TR1
 108 }