1// -*- C++ -*-
2
3// Copyright (C) 2005-2015 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_resize_example.cpp
34 * An example of externally resizing a map.
35 */
36
37/**
38 * This example shows how to externally manipulate the size of a hash-based
39 * container object through its resize-policy object.
40 **/
41
42#include <functional>
43#include <cassert>
44#include <ext/pb_ds/assoc_container.hpp>
45#include <ext/pb_ds/hash_policy.hpp>
46
47using namespace std;
48using namespace __gnu_pbds;
49
50// A simple hash functor.
51// hash could serve instead of this functor, but it is not yet
52// standard everywhere.
53struct int_hash : public unary_function<int, size_t>
54{
55  inline size_t
56  operator()(const int& r_i) const
57  { return r_i; }
58};
59
60int main()
61{
62  // A probing hash table mapping ints to chars.
63  typedef
64    gp_hash_table<
65    int,
66    char,
67    int_hash,
68    equal_to<
69    int>,
70    // Combining function.
71    direct_mask_range_hashing<>,
72    // Probe function.
73    linear_probe_fn<>,
74    // Resize policy.
75    hash_standard_resize_policy<
76    hash_exponential_size_policy<>,
77    hash_load_check_resize_trigger<>,
78    /* Allow external access to size.
79     * Without setting this to true, external resizing
80     * is not possible.
81     */
82    true> >
83    map_t;
84
85  map_t g;
86
87  // Check the actual size of the container object. In this case, this
88  // should be the initial size given by the size policy object.
89  assert(g.get_actual_size() == 8);
90
91  // Insert some elements.
92  g[1] = 'a';
93  g[2] = 'b';
94  g[3] = 'c';
95
96  // Now resize the table upward.
97  g.resize(200);
98
99  // Check the actual size of the container object.
100  // For the policy used in this example, the nearest larger size than
101  // 200 is 256.
102  assert(g.get_actual_size() == 256);
103
104  g[67] = 'g';
105  g[22] = 'f';
106
107  // Regardless of the internal size, the logical size should be 5.
108  assert(g.size() == 5);
109
110  // Now resize the table downward.
111  g.resize(106);
112
113  // Check the actual size of the container object.
114  // For the policy used in this example, the nearest larger size than
115  // 106 is 128.
116  assert(g.get_actual_size() == 128);
117
118  g[37] = 'f';
119
120  // Regardless of the internal size, the logical size should be 5.
121  assert(g.size() == 6);
122
123  return 0;
124}
125
126