mask_based_range_hashing.hpp

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// -*- C++ -*-

// Copyright (C) 2005 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.

// Permission to use, copy, modify, sell, and distribute this software
// is hereby granted without fee, provided that the above copyright
// notice appears in all copies, and that both that copyright notice and
// this permission notice appear in supporting documentation. None of
// the above authors, nor IBM Haifa Research Laboratories, make any
// representation about the suitability of this software for any
// purpose. It is provided "as is" without express or implied warranty.

#ifndef MASK_BASED_RANGE_HASHING_HPP
#define MASK_BASED_RANGE_HASHING_HPP

namespace pb_assoc
{

  namespace detail
  {

#define PB_ASSOC_CLASS_T_DEC \
    template<typename Size_Type>

#define PB_ASSOC_CLASS_C_DEC \
    mask_based_range_hashing< \
        Size_Type>

    template<typename Size_Type>
    class mask_based_range_hashing
    {
    protected:
      typedef Size_Type size_type;

    protected:
      void
      swap(PB_ASSOC_CLASS_C_DEC& r_other);

      void
      notify_resized(size_type size);

      inline size_type
      range_hash(size_type hash) const;

    private:
      size_type m_mask;

      const static size_type s_num_bits_in_size_type;

      const static size_type s_highest_bit_1;
    };

    PB_ASSOC_CLASS_T_DEC
    const typename PB_ASSOC_CLASS_C_DEC::size_type
    PB_ASSOC_CLASS_C_DEC::s_num_bits_in_size_type =
    sizeof(typename PB_ASSOC_CLASS_C_DEC::size_type) << 3;

    PB_ASSOC_CLASS_T_DEC
    const typename PB_ASSOC_CLASS_C_DEC::size_type
    PB_ASSOC_CLASS_C_DEC::s_highest_bit_1 =
    (typename PB_ASSOC_CLASS_C_DEC::size_type) 1
      << (s_num_bits_in_size_type - 1);

    PB_ASSOC_CLASS_T_DEC
    void
    PB_ASSOC_CLASS_C_DEC::
    swap(PB_ASSOC_CLASS_C_DEC& r_other)
    {
      std::swap(m_mask, r_other.m_mask);
    }

    PB_ASSOC_CLASS_T_DEC
    void
    PB_ASSOC_CLASS_C_DEC::
    notify_resized(size_type size)
    {
      size_type i = 0;

      while (size ^ s_highest_bit_1)
    {
      size <<= 1;

      ++i;
    }

      m_mask = 1;

      i += 2;

      while (i++ < s_num_bits_in_size_type)
    m_mask = (m_mask << 1) ^ 1;
    }

    PB_ASSOC_CLASS_T_DEC
    inline typename PB_ASSOC_CLASS_C_DEC::size_type
    PB_ASSOC_CLASS_C_DEC::
    range_hash(size_type hash) const
    {
      return (hash&  m_mask);
    }

#undef PB_ASSOC_CLASS_T_DEC
#undef PB_ASSOC_CLASS_C_DEC

  } // namespace detail

} // namespace pb_assoc

#endif // #ifndef MASK_BASED_RANGE_HASHING_HPP

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