libstdc++
mask_based_range_hashing.hpp
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1 // -*- C++ -*-
2 
3 // Copyright (C) 2005, 2006, 2009 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.
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11 // This library is distributed in the hope that it will be useful, but
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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.
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20 // You should have received a copy of the GNU General Public License and
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24 
25 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
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28 // is hereby granted without fee, provided that the above copyright
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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>
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
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
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