libstdc++-v3/testsuite/ext/pb_assoc/example/hash_shift_mask.cc

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005 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
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 2, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License along
  17 // with this library; see the file COPYING.  If not, write to the Free
  18 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  19 // USA.
  20
  21 // As a special exception, you may use this file as part of a free software
  22 // library without restriction.  Specifically, if other files instantiate
  23 // templates or use macros or inline functions from this file, or you compile
  24 // this file and link it with other files to produce an executable, this
  25 // file does not by itself cause the resulting executable to be covered by
  26 // the GNU General Public License.  This exception does not however
  27 // invalidate any other reasons why the executable file might be covered by
  28 // the GNU General Public License.
  29
  30 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
  31
  32 // Permission to use, copy, modify, sell, and distribute this software
  33 // is hereby granted without fee, provided that the above copyright
  34 // notice appears in all copies, and that both that copyright notice and
  35 // this permission notice appear in supporting documentation. None of
  36 // the above authors, nor IBM Haifa Research Laboratories, make any
  37 // representation about the suitability of this software for any
  38 // purpose. It is provided "as is" without express or implied warranty.
  39
  40 /**
  41  * @file hash_shift_mask_example.cpp
  42  * An example showing how to write a range-hasing functor.
  43  */
  44
  45 // For cc_hash_assoc_cntnr.
  46 #include <ext/pb_assoc/assoc_cntnr.hpp>
  47 // For hash-related policies.
  48 #include <ext/pb_assoc/hash_policy.hpp>
  49 // For unary_function and binary_function
  50 #include <functional>
  51
  52 /*
  53  * A simple hash functor.
  54  *      std::hash could serve instead of this functor,
  55  *      but it is not yet standard everywhere.
  56  */
  57 struct simple_int_hash : public std::unary_function<
  58   int,
  59              size_t>
  60 {
  61   inline size_t
  62   operator()(int i) const
  63   {
  64     return (i);
  65   }
  66 };
  67
  68 // A range-hashing function which shifts 2 bits right and then masks.
  69 class shift_two_mask_range_hashing : private pb_assoc::direct_mask_range_hashing<>
  70 {
  71 public:
  72   typedef size_t size_type;
  73
  74 public:
  75   /*
  76    * Swaps with a different instant.
  77    */
  78   void
  79   swap(shift_two_mask_range_hashing& r_other)
  80   {
  81     pb_assoc::direct_mask_range_hashing<>::swap(r_other);
  82   }
  83
  84   /*
  85    * Called by the container when internally resized.
  86    */
  87   void
  88   notify_resized(size_type size)
  89   {
  90     pb_assoc::direct_mask_range_hashing<>::notify_resized(size);
  91   }
  92
  93   /*
  94    * Given a hash value, returns a number in the range of the
  95    *    internal size of the container.
  96    */
  97   inline size_type
  98   operator()(size_type hash) const
  99   {
 100     return (pb_assoc::direct_mask_range_hashing<>::operator()(
 101                                                               hash >> 2));
 102   }
 103 };
 104
 105 int
 106 main()
 107 {
 108   /*
 109    * A collision-chaining hash table mapping ints to chars.
 110    */
 111   typedef
 112     pb_assoc::cc_hash_assoc_cntnr<
 113     int,
 114     char,
 115     // Hash function.
 116     simple_int_hash,
 117     std::equal_to<int>,
 118     // Range hashing function.
 119     shift_two_mask_range_hashing>
 120     map_t;
 121
 122   map_t h;
 123
 124   // Use normally.
 125
 126   h[16] = 'a';
 127   h[256] = 'e';
 128   h[4] = 'z';
 129 }
 130