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

   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
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  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
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  37 // of the above authors, nor IBM Haifa Research Laboratories, make any
  38 // representation about the suitability of this software for any
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  40 // warranty.
  41
  42 /**
  43  * @file hash_mod_example.cpp
  44  * An example showing how to use a mod range-hasing function
  45  */
  46
  47 /**
  48  * This example shows how to use a hash-based container employing
  49  * a modulo-based range-hashing function.
  50  */
  51
  52 #include <functional>
  53 #include <ext/pb_ds/assoc_container.hpp>
  54 #include <ext/pb_ds/hash_policy.hpp>
  55
  56 using namespace std;
  57 using namespace __gnu_pbds;
  58
  59 // A simple hash functor.
  60 // hash could serve instead of this functor, but it is not yet
  61 // standard everywhere.
  62 struct int_hash : public unary_function<int, size_t>
  63 {
  64   inline size_t
  65   operator()(int i) const
  66   { return i; }
  67 };
  68
  69 int main()
  70 {
  71   // In this case, we are worried that the key distribution will be
  72   // skewed. We wish to use a more robust combining function.
  73
  74   // A collision-chaining hash table mapping ints to chars.
  75   typedef
  76     cc_hash_table<
  77     int,
  78     char,
  79     int_hash,
  80     equal_to<int>,
  81     // Combining function.
  82     direct_mod_range_hashing<> >
  83     map_t;
  84
  85   map_t r_c;
  86
  87   // Use regularly.
  88   r_c[32] = 'b';
  89   r_c[1024] = 'c';
  90   r_c[4096] = 'd';
  91
  92   // The above keys are all powers of 2. A mask combining function
  93   // would hamper performance in such a case.
  94   return 0;
  95 }
  96