libstdc++

mask_based_range_hashing.hpp
Go to the documentation of this file.
1 // -*- C++ -*-
2
3 // Copyright (C) 2005-2013 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