1// -*- C++ -*-
2
3// Copyright (C) 2005, 2006 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 2, 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// You should have received a copy of the GNU General Public License
17// along with this library; see the file COPYING.  If not, write to
18// the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
19// MA 02111-1307, USA.
20
21// As a special exception, you may use this file as part of a free
22// software library without restriction.  Specifically, if other files
23// instantiate templates or use macros or inline functions from this
24// file, or you compile this file and link it with other files to
25// produce an executable, this file does not by itself cause the
26// resulting executable to be covered by the GNU General Public
27// License.  This exception does not however invalidate any other
28// reasons why the executable file might be covered by the GNU General
29// Public License.
30
31// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
32
33// Permission to use, copy, modify, sell, and distribute this software
34// is hereby granted without fee, provided that the above copyright
35// notice appears in all copies, and that both that copyright notice
36// and this permission notice appear in supporting documentation. None
37// of the above authors, nor IBM Haifa Research Laboratories, make any
38// representation about the suitability of this software for any
39// purpose. It is provided "as is" without express or implied
40// warranty.
41
42/**
43 * @file mask_based_range_hashing.hpp
44 * Contains a range hashing policy base.
45 */
46
47#ifndef PB_DS_MASK_BASED_RANGE_HASHING_HPP
48#define PB_DS_MASK_BASED_RANGE_HASHING_HPP
49
50namespace pb_ds
51{
52  namespace detail
53  {
54#define PB_DS_CLASS_T_DEC template<typename Size_Type>
55#define PB_DS_CLASS_C_DEC mask_based_range_hashing<Size_Type>
56
57    template<typename Size_Type>
58    class mask_based_range_hashing
59    {
60    protected:
61      typedef Size_Type size_type;
62
63      void
64      swap(mask_based_range_hashing& other)
65      { std::swap(m_mask, other.m_mask); }
66
67      void
68      notify_resized(size_type size);
69
70      inline size_type
71      range_hash(size_type hash) const
72      { return size_type(hash & m_mask); }
73
74    private:
75      size_type 		m_mask;
76      const static size_type 	s_num_bits_in_size_type;
77      const static size_type 	s_highest_bit_1;
78    };
79
80    PB_DS_CLASS_T_DEC
81    const typename PB_DS_CLASS_C_DEC::size_type
82    PB_DS_CLASS_C_DEC::s_num_bits_in_size_type =
83      sizeof(typename PB_DS_CLASS_C_DEC::size_type) << 3;
84
85    PB_DS_CLASS_T_DEC
86    const typename PB_DS_CLASS_C_DEC::size_type PB_DS_CLASS_C_DEC::s_highest_bit_1 = static_cast<typename PB_DS_CLASS_C_DEC::size_type>(1) << (s_num_bits_in_size_type - 1);
87
88
89    PB_DS_CLASS_T_DEC
90    void
91    PB_DS_CLASS_C_DEC::
92    notify_resized(size_type size)
93    {
94      size_type i = 0;
95      while (size ^ s_highest_bit_1)
96	{
97	  size <<= 1;
98	  ++i;
99	}
100
101      m_mask = 1;
102      i += 2;
103      while (i++ < s_num_bits_in_size_type)
104        m_mask = (m_mask << 1) ^ 1;
105    }
106
107#undef PB_DS_CLASS_T_DEC
108#undef PB_DS_CLASS_C_DEC
109
110  } // namespace detail
111} // namespace pb_ds
112
113#endif
114