binaryurp/source/cache.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
  11  *   Licensed to the Apache Software Foundation (ASF) under one or more
  12  *   contributor license agreements. See the NOTICE file distributed
  13  *   with this work for additional information regarding copyright
  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 #ifndef INCLUDED_BINARYURP_SOURCE_CACHE_HXX
  21 #define INCLUDED_BINARYURP_SOURCE_CACHE_HXX
  22
  23 #include <sal/config.h>
  24
  25 #include <cassert>
  26 #include <cstddef>
  27 #include <map>
  28 #include <list>
  29
  30 #include <sal/types.h>
  31
  32 namespace binaryurp {
  33
  34 namespace cache {
  35
  36 enum { size = 256, ignore = 0xFFFF };
  37
  38 }
  39
  40 template< typename T > class Cache {
  41 public:
  42     typedef sal_uInt16 IdxType;
  43
  44     explicit Cache(std::size_t size):
  45         size_(size)
  46     {
  47         assert(size < cache::ignore);
  48     }
  49
  50     IdxType add( const T& rContent, bool* pbFound) {
  51         assert( pbFound != nullptr);
  52         if( !size_) {
  53             *pbFound = false;
  54             return cache::ignore;
  55         }
  56         // try to insert into the map
  57         list_.push_front( rContent); // create a temp entry
  58         typedef std::pair<typename LruItMap::iterator,bool> MapPair;
  59         MapPair aMP = map_.emplace( list_.begin(), 0 );
  60         *pbFound = !aMP.second;
  61
  62         if( !aMP.second) { // insertion not needed => found the entry
  63             list_.pop_front(); // remove the temp entry
  64             list_.splice( list_.begin(), list_, aMP.first->first); // the found entry is moved to front
  65             return aMP.first->second;
  66         }
  67
  68         // test insertion successful => it was new so we keep it
  69         IdxType n = static_cast<IdxType>( map_.size() - 1);
  70         if( n >= size_) { // cache full => replace the LRU entry
  71             // find the least recently used element in the map
  72             typename LruItMap::iterator it = map_.find( --list_.end());
  73             n = it->second;
  74             map_.erase( it); // remove it from the map
  75             list_.pop_back(); // remove from the list
  76         }
  77         aMP.first->second = n;
  78         return n;
  79     }
  80
  81 private:
  82     Cache(const Cache&) = delete;
  83     Cache& operator=(const Cache&) = delete;
  84
  85     typedef std::list<T> LruList; // last recently used list
  86     typedef typename LruList::iterator LruListIt;
  87     struct CmpT{ bool operator()( const LruListIt& rA, const LruListIt& rB) const { return (*rA<*rB);}};
  88     typedef std::map< LruListIt, IdxType, CmpT > LruItMap; // a map into a LruList
  89
  90     std::size_t size_;
  91     LruItMap map_;
  92     LruList list_;
  93 };
  94
  95 }
  96
  97 #endif
  98
  99 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */