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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 store_hash_example.cpp | |
44 | * An example showing how to store hash-values with | |
45 | * each entry in a hash-based container. | |
46 | */ | |
47 | ||
48 | /** | |
49 | * This example shows how to configure a hash-based container to store | |
50 | * the hash value of each key along with each entry. This technique | |
51 | * is useful for complex keys (e.g., strings in this example), since | |
52 | * it lowers the cost of collisions. For simpler types (e.g., integers), | |
53 | * where the cost of comparing keys is of the same order as the cost | |
54 | * of comparing hash values, this technique adds unnecessary overhead. | |
55 | */ | |
56 | ||
57 | #include <functional> | |
58 | #include <string> | |
59 | #include <ext/pb_ds/assoc_container.hpp> | |
60 | #include <ext/pb_ds/hash_policy.hpp> | |
61 | ||
62 | using namespace std; | |
63 | using namespace pb_ds; | |
64 | ||
65 | // A string hash functor. | |
66 | struct string_hash : public unary_function<string, size_t> | |
67 | { | |
68 | inline size_t | |
69 | operator()(string str) const | |
70 | { | |
71 | string::const_iterator b = str.begin(); | |
72 | string::const_iterator e = str.end(); | |
73 | ||
74 | size_t hash = 0; | |
75 | while (b != e) | |
76 | { | |
77 | hash *= 5; | |
78 | hash += static_cast<size_t>(*b); | |
79 | ++b; | |
80 | } | |
81 | return hash; | |
82 | } | |
83 | }; | |
84 | ||
85 | int main() | |
86 | { | |
87 | // A collision-chaining hash table mapping strings to ints. | |
88 | typedef | |
89 | cc_hash_table< | |
90 | string, | |
91 | int, | |
92 | string_hash, | |
93 | equal_to<string>, | |
94 | direct_mask_range_hashing<>, | |
95 | hash_standard_resize_policy<>, | |
96 | true> | |
97 | map_t; | |
98 | ||
99 | map_t h; | |
100 | ||
101 | // Use regularly. | |
102 | h["Hello, "] = 0; | |
103 | h["world"] = 1; | |
104 | ||
105 | return 0; | |
106 | } | |
107 |