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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 hash_load_set_change_example.cpp | |
44 | * An example of setting and changing the load factor of a hash-based | |
45 | * container object. | |
46 | */ | |
47 | ||
48 | /** | |
49 | * This example shows how to set and change the load-factor of | |
50 | * a hash-based container object through its resize-policy object. | |
51 | */ | |
52 | ||
53 | #include <functional> | |
54 | #include <cassert> | |
55 | #include <ext/pb_ds/assoc_container.hpp> | |
56 | #include <ext/pb_ds/hash_policy.hpp> | |
57 | ||
58 | using namespace std; | |
5e11f978 | 59 | using namespace __gnu_pbds; |
4569a895 AT |
60 | |
61 | // A simple hash functor. | |
62 | // hash could serve instead of this functor, but it is not yet | |
63 | // standard everywhere. | |
64 | struct int_hash : public unary_function<int, size_t> | |
65 | { | |
66 | inline size_t | |
67 | operator()(int i) const | |
68 | { return i; } | |
69 | }; | |
70 | ||
71 | int main() | |
72 | { | |
73 | // A trigger policy type. | |
74 | typedef hash_load_check_resize_trigger< true> trigger_t; | |
75 | ||
76 | // A resize policy type. | |
77 | typedef | |
78 | hash_standard_resize_policy< | |
79 | hash_exponential_size_policy<>, | |
80 | // Trigger type. | |
81 | trigger_t, | |
82 | /* Allow external access to size. | |
83 | * This is not necessary for setting the load factor, | |
84 | * but it allows to call get_actual_size. | |
85 | */ | |
86 | true> | |
87 | resize_t; | |
88 | ||
89 | // A collision-chaining hash table mapping ints to chars. | |
90 | typedef | |
91 | cc_hash_table< | |
92 | int, | |
93 | char, | |
94 | int_hash, | |
95 | equal_to<int>, | |
96 | // Combining function. | |
97 | direct_mask_range_hashing<>, | |
98 | // Resize policy. | |
99 | resize_t> | |
100 | map_t; | |
101 | ||
102 | // A trigger policy object with load between 0.3 and 0.8. | |
103 | trigger_t trigger(static_cast<float>(0.3), static_cast<float>(0.8)); | |
104 | ||
105 | // A resize policy object with the above trigger. | |
106 | resize_t resize(hash_exponential_size_policy<>(), | |
107 | trigger); | |
108 | ||
109 | map_t r_c(int_hash(), | |
110 | equal_to<int>(), | |
111 | direct_mask_range_hashing<>(), | |
112 | resize); | |
113 | ||
114 | r_c[1] = 'a'; | |
115 | ||
116 | // Check the loads and sizes. | |
117 | assert(r_c.get_loads().first == static_cast<float>(0.3)); | |
118 | assert(r_c.get_loads().second == static_cast<float>(0.8)); | |
119 | assert(r_c.get_actual_size() == 8); | |
120 | assert(r_c.size() == 1); | |
121 | ||
122 | // Note that there is a discrepancy between the loads of the policy | |
123 | // object and the actual size of the container object. This is | |
124 | // because the container's construction performs an implicit | |
125 | // external resize. | |
126 | r_c[2] = 'b'; | |
127 | r_c[3] = 'c'; | |
128 | r_c[4] = 'd'; | |
129 | ||
130 | assert(r_c.get_actual_size() == 8); | |
131 | ||
132 | // Change the loads. This causes (potentially) a resize. | |
133 | r_c.set_loads(make_pair(static_cast<float>(0.01), | |
134 | static_cast<float>(0.05))); | |
135 | ||
136 | // The actual size should really change in this case. | |
137 | assert(r_c.get_actual_size() > 8); | |
138 | ||
139 | return 0; | |
140 | } | |
141 |