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170 lines
4.2 KiB
170 lines
4.2 KiB
15 years ago
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/*
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Copyright (C) 2003 KSVG Team
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This file is part of the KDE project
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public License
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aint with this library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA.
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*/
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#ifndef LRUCACHE_H
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#define LRUCACHE_H
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#include <qvaluelist.h>
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namespace KSVG
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{
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// A value-based LRU cache with a maximum total cost constraint, but with the exception that the
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// most recently added item is kept in the cache even if its cost exceeds the maximum total cost.
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template<class keyType, class valueType>
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class MinOneLRUCache
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{
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public:
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MinOneLRUCache(int maxTotalCost = 0) : m_maxTotalCost(maxTotalCost), m_totalCost(0) {}
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virtual ~MinOneLRUCache() {}
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void insert(const keyType& key, const valueType& value, int cost);
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bool find(const keyType& key, valueType& result);
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void setMaxTotalCost(int maxTotalCost);
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int maxTotalCost() const { return m_maxTotalCost; }
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int totalCost() const { return m_totalCost; }
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void clear();
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protected:
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class CacheItem
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{
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public:
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CacheItem() : m_cost(0) {}
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CacheItem(const keyType& key, const valueType& value, int cost) : m_key(key), m_value(value), m_cost(cost) {}
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const keyType& key() const { return m_key; }
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const valueType& value() const { return m_value; }
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int cost() const { return m_cost; }
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private:
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keyType m_key;
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valueType m_value;
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int m_cost;
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};
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typedef QValueList<CacheItem> CacheItemList;
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typename CacheItemList::iterator find(const keyType& key);
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void enforceCostConstraint();
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CacheItemList m_items;
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int m_maxTotalCost;
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int m_totalCost;
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};
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template<class keyType, class valueType>
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void MinOneLRUCache<keyType, valueType>::insert(const keyType& key, const valueType& value, int cost)
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{
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typename CacheItemList::iterator it = find(key);
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if(it != m_items.end())
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{
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// Replace the existing item.
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m_totalCost -= (*it).cost();
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m_items.erase(it);
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}
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// We always hold the most recently added item in the cache, even if it exceeds
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// the maximum total cost.
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m_items.push_front(CacheItem(key, value, cost));
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m_totalCost += cost;
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enforceCostConstraint();
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}
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template<class keyType, class valueType>
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bool MinOneLRUCache<keyType, valueType>::find(const keyType& key, valueType& result)
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{
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bool foundKey = false;
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typename CacheItemList::iterator it = find(key);
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if(it != m_items.end())
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{
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CacheItem item = *it;
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result = item.value();
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if(it != m_items.begin())
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{
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// This is now the most recently used item.
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m_items.erase(it);
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m_items.push_front(item);
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}
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foundKey = true;
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}
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return foundKey;
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}
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template<class keyType, class valueType>
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typename MinOneLRUCache<keyType, valueType>::CacheItemList::iterator MinOneLRUCache<keyType, valueType>::find(const keyType& key)
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{
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typename CacheItemList::iterator it;
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for(it = m_items.begin(); it != m_items.end(); it++)
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{
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if((*it).key() == key)
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break;
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}
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return it;
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}
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template<class keyType, class valueType>
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void MinOneLRUCache<keyType, valueType>::enforceCostConstraint()
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{
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if(m_totalCost > m_maxTotalCost && m_items.size() > 1)
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{
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typename CacheItemList::iterator it = m_items.begin();
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m_totalCost = (*it).cost();
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++it;
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while(it != m_items.end() && m_totalCost + (*it).cost() <= m_maxTotalCost)
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{
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m_totalCost += (*it).cost();
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++it;
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}
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// Remove the remainder
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while(it != m_items.end())
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it = m_items.erase(it);
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}
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}
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template<class keyType, class valueType>
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void MinOneLRUCache<keyType, valueType>::setMaxTotalCost(int maxTotalCost)
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{
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m_maxTotalCost = maxTotalCost;
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enforceCostConstraint();
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}
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template<class keyType, class valueType>
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void MinOneLRUCache<keyType, valueType>::clear()
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{
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m_items.clear();
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m_totalCost = 0;
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}
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}
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#endif
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