libstdc++-v3/testsuite/ext/pb_ds/example/hash_resize.cc

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2013 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 throught 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
  47 using namespace std;
  48 using 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.
  53 struct 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
  60 int 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