mask_based_range_hashing.hpp

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// -*- C++ -*-
 
// Copyright (C) 2005-2022 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 3, 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.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
// 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
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// warranty.
 
/**
 * @file mask_based_range_hashing.hpp
 * Contains a range hashing policy base.
 */
 
#ifndef PB_DS_MASK_BASED_RANGE_HASHING_HPP
#define PB_DS_MASK_BASED_RANGE_HASHING_HPP
 
namespace __gnu_pbds
{
  namespace detail
  {
    /// Range hashing policy.
    template<typename Size_Type>
    class mask_based_range_hashing
    {
    protected:
      typedef Size_Type         size_type;
 
      void
      swap(mask_based_range_hashing& other)
      { std::swap(m_mask, other.m_mask); }
 
      void
      notify_resized(size_type size);
 
      inline size_type
      range_hash(size_type hash) const
      { return size_type(hash & m_mask); }
 
    private:
      size_type                 m_mask;
      const static size_type    s_num_bits_in_size_type;
      const static size_type    s_highest_bit_1;
    };
 
    template<typename Size_Type>
    const typename mask_based_range_hashing<Size_Type>::size_type
    mask_based_range_hashing<Size_Type>::s_num_bits_in_size_type =
      sizeof(typename mask_based_range_hashing<Size_Type>::size_type) << 3;
 
    template<typename Size_Type>
    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);
 
 
    template<typename Size_Type>
    void
    mask_based_range_hashing<Size_Type>::
    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;
    }
  } // namespace detail
} // namespace __gnu_pbds
 
#endif