libstdc++
mask_based_range_hashing.hpp
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00001 // -*- C++ -*-
00002 
00003 // Copyright (C) 2005, 2006, 2009 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the terms
00007 // of the GNU General Public License as published by the Free Software
00008 // Foundation; either version 3, or (at your option) any later
00009 // version.
00010 
00011 // This library is distributed in the hope that it will be useful, but
00012 // WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014 // General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
00026 
00027 // Permission to use, copy, modify, sell, and distribute this software
00028 // is hereby granted without fee, provided that the above copyright
00029 // notice appears in all copies, and that both that copyright notice
00030 // and this permission notice appear in supporting documentation. None
00031 // of the above authors, nor IBM Haifa Research Laboratories, make any
00032 // representation about the suitability of this software for any
00033 // purpose. It is provided "as is" without express or implied
00034 // warranty.
00035 
00036 /**
00037  * @file mask_based_range_hashing.hpp
00038  * Contains a range hashing policy base.
00039  */
00040 
00041 #ifndef PB_DS_MASK_BASED_RANGE_HASHING_HPP
00042 #define PB_DS_MASK_BASED_RANGE_HASHING_HPP
00043 
00044 namespace __gnu_pbds
00045 {
00046   namespace detail
00047   {
00048     /// Range hashing policy.
00049     template<typename Size_Type>
00050     class mask_based_range_hashing
00051     {
00052     protected:
00053       typedef Size_Type     size_type;
00054 
00055       void
00056       swap(mask_based_range_hashing& other)
00057       { std::swap(m_mask, other.m_mask); }
00058 
00059       void
00060       notify_resized(size_type size);
00061 
00062       inline size_type
00063       range_hash(size_type hash) const
00064       { return size_type(hash & m_mask); }
00065 
00066     private:
00067       size_type         m_mask;
00068       const static size_type    s_num_bits_in_size_type;
00069       const static size_type    s_highest_bit_1;
00070     };
00071 
00072     template<typename Size_Type>
00073     const typename mask_based_range_hashing<Size_Type>::size_type
00074     mask_based_range_hashing<Size_Type>::s_num_bits_in_size_type =
00075       sizeof(typename mask_based_range_hashing<Size_Type>::size_type) << 3;
00076 
00077     template<typename Size_Type>
00078     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);
00079 
00080  
00081     template<typename Size_Type>
00082     void
00083     mask_based_range_hashing<Size_Type>::
00084     notify_resized(size_type size)
00085     {
00086       size_type i = 0;
00087       while (size ^ s_highest_bit_1)
00088     {
00089       size <<= 1;
00090       ++i;
00091     }
00092 
00093       m_mask = 1;
00094       i += 2;
00095       while (i++ < s_num_bits_in_size_type)
00096         m_mask = (m_mask << 1) ^ 1;
00097     }
00098   } // namespace detail
00099 } // namespace __gnu_pbds
00100 
00101 #endif