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