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  1. // -*- C++ -*-
  2.  
  3. // Copyright (C) 2005-2015 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
  102.