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

   1 // -*- C++ -*-
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   3 // Copyright (C) 2005, 2006 Free Software Foundation, Inc.
   4 //
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   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.
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  21 // As a special exception, you may use this file as part of a free
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  23 // instantiate templates or use macros or inline functions from this
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  26 // resulting executable to be covered by the GNU General Public
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  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
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  37 // of the above authors, nor IBM Haifa Research Laboratories, make any
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  40 // warranty.
  41
  42 /**
  43  * @file hash_resize_example.cpp
  44  * An example of externally resizing a map.
  45  */
  46
  47 /**
  48  * This example shows how to externally manipulate the size of a hash-based
  49  * container object throught its resize-policy object.
  50  **/
  51
  52 #include <functional>
  53 #include <cassert>
  54 #include <ext/pb_ds/assoc_container.hpp>
  55 #include <ext/pb_ds/hash_policy.hpp>
  56
  57 using namespace std;
  58 using namespace __gnu_pbds;
  59
  60 // A simple hash functor.
  61 // hash could serve instead of this functor, but it is not yet
  62 // standard everywhere.
  63 struct int_hash : public unary_function<int, size_t>
  64 {
  65   inline size_t
  66   operator()(const int& r_i) const
  67   { return r_i; }
  68 };
  69
  70 int main()
  71 {
  72   // A probing hash table mapping ints to chars.
  73   typedef
  74     gp_hash_table<
  75     int,
  76     char,
  77     int_hash,
  78     equal_to<
  79     int>,
  80     // Combining function.
  81     direct_mask_range_hashing<>,
  82     // Probe function.
  83     linear_probe_fn<>,
  84     // Resize policy.
  85     hash_standard_resize_policy<
  86     hash_exponential_size_policy<>,
  87     hash_load_check_resize_trigger<>,
  88     /* Allow external access to size.
  89      * Without setting this to true, external resizing
  90      * is not possible.
  91      */
  92     true> >
  93     map_t;
  94
  95   map_t g;
  96
  97   // Check the actual size of the container object. In this case, this
  98   // should be the initial size given by the size policy object.
  99   assert(g.get_actual_size() == 8);
 100
 101   // Insert some elements.
 102   g[1] = 'a';
 103   g[2] = 'b';
 104   g[3] = 'c';
 105
 106   // Now resize the table upward.
 107   g.resize(200);
 108
 109   // Check the actual size of the container object.
 110   // For the policy used in this example, the nearest larger size than
 111   // 200 is 256.
 112   assert(g.get_actual_size() == 256);
 113
 114   g[67] = 'g';
 115   g[22] = 'f';
 116
 117   // Regardless of the internal size, the logical size should be 5.
 118   assert(g.size() == 5);
 119
 120   // Now resize the table downward.
 121   g.resize(106);
 122
 123   // Check the actual size of the container object.
 124   // For the policy used in this example, the nearest larger size than
 125   // 106 is 128.
 126   assert(g.get_actual_size() == 128);
 127
 128   g[37] = 'f';
 129
 130   // Regardless of the internal size, the logical size should be 5.
 131   assert(g.size() == 6);
 132
 133   return 0;
 134 }
 135