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.
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   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 #pragma once
  21
  22 #include <sal/config.h>
  23
  24 #include <cassert>
  25 #include <cstddef>
  26 #include <map>
  27 #include <list>
  28
  29 #include <sal/types.h>
  30
  31 namespace binaryurp {
  32
  33 namespace cache {
  34
  35 enum { size = 256, ignore = 0xFFFF };
  36
  37 }
  38
  39 template< typename T > class Cache {
  40 public:
  41     typedef sal_uInt16 IdxType;
  42
  43     explicit Cache(std::size_t size):
  44         size_(size)
  45     {
  46         assert(size < cache::ignore);
  47     }
  48
  49     IdxType add( const T& rContent, bool* pbFound) {
  50         assert( pbFound != nullptr);
  51         if( !size_) {
  52             *pbFound = false;
  53             return cache::ignore;
  54         }
  55         // try to insert into the map
  56         list_.push_front( rContent); // create a temp entry
  57         auto const [it, inserted] = map_.emplace( list_.begin(), 0 );
  58         *pbFound = !inserted;
  59
  60         if( !inserted) { // insertion not needed => found the entry
  61             list_.pop_front(); // remove the temp entry
  62             list_.splice( list_.begin(), list_, it->first); // the found entry is moved to front
  63             return it->second;
  64         }
  65
  66         // test insertion successful => it was new so we keep it
  67         IdxType n = static_cast<IdxType>( map_.size() - 1);
  68         if( n >= size_) { // cache full => replace the LRU entry
  69             // find the least recently used element in the map
  70             typename LruItMap::iterator lru = map_.find( --list_.end());
  71             n = lru->second;
  72             map_.erase( lru); // remove it from the map
  73             list_.pop_back(); // remove from the list
  74         }
  75         it->second = n;
  76         return n;
  77     }
  78
  79 private:
  80     Cache(const Cache&) = delete;
  81     Cache& operator=(const Cache&) = delete;
  82
  83     typedef std::list<T> LruList; // last recently used list
  84     typedef typename LruList::iterator LruListIt;
  85     struct CmpT{ bool operator()( const LruListIt& rA, const LruListIt& rB) const { return (*rA<*rB);}};
  86     typedef std::map< LruListIt, IdxType, CmpT > LruItMap; // a map into a LruList
  87
  88     std::size_t size_;
  89     LruItMap map_;
  90     LruList list_;
  91 };
  92
  93 }
  94
  95 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */