libstdc++-v3/src/hash.cc

   1 //  std::hash and std::tr1::hash definitions -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2008, 2009 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   // For long double, careful with random padding bits (e.g., on x86,
  26   // 10 bytes -> 12 bytes) and resort to frexp.
  27   template<>
  28     size_t
  29     hash<long double>::operator()(long double __val) const
  30     {
  31       size_t __result = 0;
  32
  33       int __exponent;
  34       __val = std::frexp(__val, &__exponent);
  35       __val = __val < 0.0l ? -(__val + 0.5l) : __val;
  36
  37       const long double __mult =
  38       __gnu_cxx::__numeric_traits<size_t>::__max + 1.0l;
  39       __val *= __mult;
  40
  41       // Try to use all the bits of the mantissa (really necessary only
  42       // on 32-bit targets, at least for 80-bit floating point formats).
  43       const size_t __hibits = (size_t)__val;
  44       __val = (__val - (long double)__hibits) * __mult;
  45
  46       const size_t __coeff =
  47         __gnu_cxx::__numeric_traits<size_t>::__max / __LDBL_MAX_EXP__;
  48
  49       __result = __hibits + (size_t)__val + __coeff * __exponent;
  50
  51       return __result;
  52     };
  53
  54 #ifndef _GLIBCXX_LONG_DOUBLE_COMPAT_IMPL
  55   template<>
  56     size_t
  57     hash<string>::operator()(string __s) const
  58     { return _Fnv_hash<>::hash(__s.data(), __s.length()); }
  59
  60   template<>
  61     size_t
  62     hash<const string&>::operator()(const string& __s) const
  63     { return _Fnv_hash<>::hash(__s.data(), __s.length()); }
  64
  65 #ifdef _GLIBCXX_USE_WCHAR_T
  66   template<>
  67     size_t
  68     hash<wstring>::operator()(wstring __s) const
  69     {
  70       const char* __p = reinterpret_cast<const char*>(__s.data());
  71       return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
  72     }
  73
  74   template<>
  75     size_t
  76     hash<const wstring&>::operator()(const wstring& __s) const
  77     {
  78       const char* __p = reinterpret_cast<const char*>(__s.data());
  79       return _Fnv_hash<>::hash(__p, __s.length() * sizeof(wchar_t));
  80     }
  81 #endif
  82 #endif