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
44namespace __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