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

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2014 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_mod_example.cpp
  34  * An example showing how to use a mod range-hasing function
  35  */
  36
  37 /**
  38  * This example shows how to use a hash-based container employing
  39  * a modulo-based range-hashing function.
  40  */
  41
  42 #include <functional>
  43 #include <ext/pb_ds/assoc_container.hpp>
  44 #include <ext/pb_ds/hash_policy.hpp>
  45
  46 using namespace std;
  47 using namespace __gnu_pbds;
  48
  49 // A simple hash functor.
  50 // hash could serve instead of this functor, but it is not yet
  51 // standard everywhere.
  52 struct int_hash : public unary_function<int, size_t>
  53 {
  54   inline size_t
  55   operator()(int i) const
  56   { return i; }
  57 };
  58
  59 int main()
  60 {
  61   // In this case, we are worried that the key distribution will be
  62   // skewed. We wish to use a more robust combining function.
  63
  64   // A collision-chaining hash table mapping ints to chars.
  65   typedef
  66     cc_hash_table<
  67     int,
  68     char,
  69     int_hash,
  70     equal_to<int>,
  71     // Combining function.
  72     direct_mod_range_hashing<> >
  73     map_t;
  74
  75   map_t r_c;
  76
  77   // Use regularly.
  78   r_c[32] = 'b';
  79   r_c[1024] = 'c';
  80   r_c[4096] = 'd';
  81
  82   // The above keys are all powers of 2. A mask combining function
  83   // would hamper performance in such a case.
  84   return 0;
  85 }
  86