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1 | // -*- C++ -*- |
2 | ||
748086b7 | 3 | // Copyright (C) 2005, 2006, 2009 Free Software Foundation, Inc. |
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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 | |
748086b7 | 8 | // Foundation; either version 3, or (at your option) any later |
4569a895 AT |
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 | |
748086b7 JJ |
17 | // along with this library; see the file COPYING3. If not see |
18 | // <http://www.gnu.org/licenses/>. | |
19 | ||
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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; | |
5e11f978 | 47 | using namespace __gnu_pbds; |
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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 : public unary_function<int, size_t> | |
53 | { | |
54 | inline size_t | |
55 | operator()(int i) const | |
56 | { return i; } | |
57 | }; | |
58 | ||
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 |