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

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2014 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 terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 3, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // 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 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
  26
  27 // Permission to use, copy, modify, sell, and distribute this software
  28 // is hereby granted without fee, provided that the above copyright
  29 // notice appears in all copies, and that both that copyright notice
  30 // and this permission notice appear in supporting documentation. None
  31 // of the above authors, nor IBM Haifa Research Laboratories, make any
  32 // representation about the suitability of this software for any
  33 // purpose. It is provided "as is" without express or implied
  34 // warranty.
  35
  36 /**
  37  * @file mask_based_range_hashing.hpp
  38  * Contains a range hashing policy base.
  39  */
  40
  41 #ifndef PB_DS_MASK_BASED_RANGE_HASHING_HPP
  42 #define PB_DS_MASK_BASED_RANGE_HASHING_HPP
  43
  44 namespace __gnu_pbds
  45 {
  46   namespace detail
  47   {
  48     /// Range hashing policy.
  49     template<typename Size_Type>
  50     class mask_based_range_hashing
  51     {
  52     protected:
  53       typedef Size_Type         size_type;
  54
  55       void
  56       swap(mask_based_range_hashing& other)
  57       { std::swap(m_mask, other.m_mask); }
  58
  59       void
  60       notify_resized(size_type size);
  61
  62       inline size_type
  63       range_hash(size_type hash) const
  64       { return size_type(hash & m_mask); }
  65
  66     private:
  67       size_type                 m_mask;
  68       const static size_type    s_num_bits_in_size_type;
  69       const static size_type    s_highest_bit_1;
  70     };
  71
  72     template<typename Size_Type>
  73     const typename mask_based_range_hashing<Size_Type>::size_type
  74     mask_based_range_hashing<Size_Type>::s_num_bits_in_size_type =
  75       sizeof(typename mask_based_range_hashing<Size_Type>::size_type) << 3;
  76
  77     template<typename Size_Type>
  78     const typename mask_based_range_hashing<Size_Type>::size_type mask_based_range_hashing<Size_Type>::s_highest_bit_1 = static_cast<typename mask_based_range_hashing<Size_Type>::size_type>(1) << (s_num_bits_in_size_type - 1);
  79
  80
  81     template<typename Size_Type>
  82     void
  83     mask_based_range_hashing<Size_Type>::
  84     notify_resized(size_type size)
  85     {
  86       size_type i = 0;
  87       while (size ^ s_highest_bit_1)
  88         {
  89           size <<= 1;
  90           ++i;
  91         }
  92
  93       m_mask = 1;
  94       i += 2;
  95       while (i++ < s_num_bits_in_size_type)
  96         m_mask = (m_mask << 1) ^ 1;
  97     }
  98   } // namespace detail
  99 } // namespace __gnu_pbds
 100
 101 #endif