1 // -*- C++ -*-
2
3 // Copyright (C) 2005-2021 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 // You should have received a copy of the GNU General Public License
17 // along with this library; see the file COPYING3. If not see
18 // <http://www.gnu.org/licenses/>.
19
20
21 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
22
23 // Permission to use, copy, modify, sell, and distribute this software
24 // is hereby granted without fee, provided that the above copyright
25 // notice appears in all copies, and that both that copyright notice
26 // and this permission notice appear in supporting documentation. None
27 // of the above authors, nor IBM Haifa Research Laboratories, make any
28 // representation about the suitability of this software for any
29 // purpose. It is provided "as is" without express or implied
30 // warranty.
31
32 /**
33 * @file hash_mod_example.cpp
34 * An example showing how to use a mod range-hasing function
35 */
36
37 /**
38 * This example shows how to use a hash-based container employing
39 * a modulo-based range-hashing function.
40 */
41
42 #include <functional>
43 #include <ext/pb_ds/assoc_container.hpp>
44 #include <ext/pb_ds/hash_policy.hpp>
45
46 using namespace std;
47 using namespace __gnu_pbds;
48
49 // A simple hash functor.
50 // hash could serve instead of this functor, but it is not yet
51 // standard everywhere.
52 struct int_hash
53 {
54 size_t
operator ()int_hash55 operator()(int i) const
56 { return i; }
57 };
58
main()59 int main()
60 {
61 // In this case, we are worried that the key distribution will be
62 // skewed. We wish to use a more robust combining function.
63
64 // A collision-chaining hash table mapping ints to chars.
65 typedef
66 cc_hash_table<
67 int,
68 char,
69 int_hash,
70 equal_to<int>,
71 // Combining function.
72 direct_mod_range_hashing<> >
73 map_t;
74
75 map_t r_c;
76
77 // Use regularly.
78 r_c[32] = 'b';
79 r_c[1024] = 'c';
80 r_c[4096] = 'd';
81
82 // The above keys are all powers of 2. A mask combining function
83 // would hamper performance in such a case.
84 return 0;
85 }
86
87