libstdc++-v3/include/ext/pb_assoc/detail/hash_fn/mask_based_range_hashing.hpp

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005 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 along
  17 // with this library; see the file COPYING.  If not, write to the Free
  18 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  19 // 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 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
  31
  32 // Permission to use, copy, modify, sell, and distribute this software
  33 // is hereby granted without fee, provided that the above copyright
  34 // notice appears in all copies, and that both that copyright notice and
  35 // this permission notice appear in supporting documentation. None of
  36 // the above authors, nor IBM Haifa Research Laboratories, make any
  37 // representation about the suitability of this software for any
  38 // purpose. It is provided "as is" without express or implied warranty.
  39
  40 /**
  41  * @file mask_based_range_hashing.hpp
  42  * Contains a range hashing policy base.
  43  */
  44
  45 #ifndef MASK_BASED_RANGE_HASHING_HPP
  46 #define MASK_BASED_RANGE_HASHING_HPP
  47
  48 namespace pb_assoc
  49 {
  50
  51   namespace detail
  52   {
  53
  54 #define PB_ASSOC_CLASS_T_DEC \
  55         template<typename Size_Type>
  56
  57 #define PB_ASSOC_CLASS_C_DEC \
  58         mask_based_range_hashing< \
  59                 Size_Type>
  60
  61     template<typename Size_Type>
  62     class mask_based_range_hashing
  63     {
  64     protected:
  65       typedef Size_Type size_type;
  66
  67     protected:
  68       void
  69       swap(PB_ASSOC_CLASS_C_DEC& r_other);
  70
  71       void
  72       notify_resized(size_type size);
  73
  74       inline size_type
  75       range_hash(size_type hash) const;
  76
  77     private:
  78       size_type m_mask;
  79
  80       const static size_type s_num_bits_in_size_type;
  81
  82       const static size_type s_highest_bit_1;
  83     };
  84
  85     PB_ASSOC_CLASS_T_DEC
  86     const typename PB_ASSOC_CLASS_C_DEC::size_type
  87     PB_ASSOC_CLASS_C_DEC::s_num_bits_in_size_type =
  88     sizeof(typename PB_ASSOC_CLASS_C_DEC::size_type) << 3;
  89
  90     PB_ASSOC_CLASS_T_DEC
  91     const typename PB_ASSOC_CLASS_C_DEC::size_type
  92     PB_ASSOC_CLASS_C_DEC::s_highest_bit_1 =
  93     (typename PB_ASSOC_CLASS_C_DEC::size_type) 1
  94       << (s_num_bits_in_size_type - 1);
  95
  96     PB_ASSOC_CLASS_T_DEC
  97     void
  98     PB_ASSOC_CLASS_C_DEC::
  99     swap(PB_ASSOC_CLASS_C_DEC& r_other)
 100     {
 101       std::swap(m_mask, r_other.m_mask);
 102     }
 103
 104     PB_ASSOC_CLASS_T_DEC
 105     void
 106     PB_ASSOC_CLASS_C_DEC::
 107     notify_resized(size_type size)
 108     {
 109       size_type i = 0;
 110
 111       while (size ^ s_highest_bit_1)
 112         {
 113           size <<= 1;
 114
 115           ++i;
 116         }
 117
 118       m_mask = 1;
 119
 120       i += 2;
 121
 122       while (i++ < s_num_bits_in_size_type)
 123         m_mask = (m_mask << 1) ^ 1;
 124     }
 125
 126     PB_ASSOC_CLASS_T_DEC
 127     inline typename PB_ASSOC_CLASS_C_DEC::size_type
 128     PB_ASSOC_CLASS_C_DEC::
 129     range_hash(size_type hash) const
 130     {
 131       return (hash&  m_mask);
 132     }
 133
 134 #undef PB_ASSOC_CLASS_T_DEC
 135 #undef PB_ASSOC_CLASS_C_DEC
 136
 137   } // namespace detail
 138
 139 } // namespace pb_assoc
 140
 141 #endif // #ifndef MASK_BASED_RANGE_HASHING_HPP