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/*
* Copyright (C) 2013 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef CollectionIndexCache_h
#define CollectionIndexCache_h
namespace WebCore {
template <class Collection, class NodeType>
class CollectionIndexCache {
public:
CollectionIndexCache();
unsigned nodeCount(const Collection&);
NodeType* nodeAt(const Collection&, unsigned index);
void invalidate();
private:
NodeType* nodeBeforeCached(const Collection&, unsigned);
NodeType* nodeAfterCached(const Collection&, unsigned);
NodeType* m_currentNode;
unsigned m_currentIndex;
unsigned m_nodeCount;
bool m_nodeCountValid;
};
template <class Collection, class NodeType>
inline CollectionIndexCache<Collection, NodeType>::CollectionIndexCache()
: m_currentNode(nullptr)
, m_currentIndex(0)
, m_nodeCount(0)
, m_nodeCountValid(false)
{
}
template <class Collection, class NodeType>
inline unsigned CollectionIndexCache<Collection, NodeType>::nodeCount(const Collection& collection)
{
if (!m_nodeCountValid) {
if (auto first = collection.collectionFirst()) {
unsigned count;
collection.collectionTraverseForward(*first, std::numeric_limits<unsigned>::max(), count);
m_nodeCount = count + 1;
} else
m_nodeCount = 0;
m_nodeCountValid = true;
}
return m_nodeCount;
}
template <class Collection, class NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeBeforeCached(const Collection& collection, unsigned index)
{
ASSERT(m_currentNode);
ASSERT(index < m_currentIndex);
bool firstIsCloser = index < m_currentIndex - index;
if (firstIsCloser || !collection.collectionCanTraverseBackward()) {
m_currentNode = collection.collectionFirst();
m_currentIndex = 0;
if (index)
m_currentNode = collection.collectionTraverseForward(*m_currentNode, index, m_currentIndex);
ASSERT(m_currentNode);
return m_currentNode;
}
m_currentNode = collection.collectionTraverseBackward(*m_currentNode, m_currentIndex - index);
m_currentIndex = index;
ASSERT(m_currentNode);
return m_currentNode;
}
template <class Collection, class NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeAfterCached(const Collection& collection, unsigned index)
{
ASSERT(m_currentNode);
ASSERT(index > m_currentIndex);
ASSERT(!m_nodeCountValid || index < m_nodeCount);
bool lastIsCloser = m_nodeCountValid && m_nodeCount - index < index - m_currentIndex;
if (lastIsCloser && collection.collectionCanTraverseBackward()) {
m_currentNode = collection.collectionLast();
if (index < m_nodeCount - 1)
m_currentNode = collection.collectionTraverseBackward(*m_currentNode, m_nodeCount - index - 1);
m_currentIndex = index;
ASSERT(m_currentNode);
return m_currentNode;
}
unsigned traversedCount;
m_currentNode = collection.collectionTraverseForward(*m_currentNode, index - m_currentIndex, traversedCount);
m_currentIndex = m_currentIndex + traversedCount;
ASSERT(m_currentNode || m_currentIndex < index);
if (!m_currentNode && !m_nodeCountValid) {
// Failed to find the index but at least we now know the size.
m_nodeCount = m_currentIndex + 1;
m_nodeCountValid = true;
}
return m_currentNode;
}
template <class Collection, class NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeAt(const Collection& collection, unsigned index)
{
if (m_nodeCountValid && index >= m_nodeCount)
return nullptr;
if (m_currentNode) {
if (index > m_currentIndex)
return nodeAfterCached(collection, index);
if (index < m_currentIndex)
return nodeBeforeCached(collection, index);
return m_currentNode;
}
bool lastIsCloser = m_nodeCountValid && m_nodeCount - index < index;
if (lastIsCloser && collection.collectionCanTraverseBackward()) {
m_currentNode = collection.collectionLast();
if (index < m_nodeCount - 1)
m_currentNode = collection.collectionTraverseBackward(*m_currentNode, m_nodeCount - index - 1);
m_currentIndex = index;
ASSERT(m_currentNode);
return m_currentNode;
}
m_currentNode = collection.collectionFirst();
m_currentIndex = 0;
if (index && m_currentNode) {
m_currentNode = collection.collectionTraverseForward(*m_currentNode, index, m_currentIndex);
ASSERT(m_currentNode || m_currentIndex < index);
}
return m_currentNode;
}
template <class Collection, class NodeType>
void CollectionIndexCache<Collection, NodeType>::invalidate()
{
m_currentNode = nullptr;
m_nodeCountValid = false;
}
}
#endif
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