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/*
* Copyright (C) 2013 Apple Inc. All rights reserved.
* Copyright (C) 2014 Samsung Electronics. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
* OWNER OR 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 blink {
template <typename Collection, typename NodeType>
class CollectionIndexCache {
DISALLOW_ALLOCATION();
public:
CollectionIndexCache();
bool isEmpty(const Collection& collection)
{
if (isCachedNodeCountValid())
return !cachedNodeCount();
if (cachedNode())
return false;
return !nodeAt(collection, 0);
}
bool hasExactlyOneNode(const Collection& collection)
{
if (isCachedNodeCountValid())
return cachedNodeCount() == 1;
if (cachedNode())
return !cachedNodeIndex() && !nodeAt(collection, 1);
return nodeAt(collection, 0) && !nodeAt(collection, 1);
}
unsigned nodeCount(const Collection&);
NodeType* nodeAt(const Collection&, unsigned index);
void invalidate();
void trace(Visitor* visitor)
{
visitor->trace(m_currentNode);
}
protected:
ALWAYS_INLINE NodeType* cachedNode() const { return m_currentNode; }
ALWAYS_INLINE unsigned cachedNodeIndex() const { ASSERT(cachedNode()); return m_cachedNodeIndex; }
ALWAYS_INLINE void setCachedNode(NodeType* node, unsigned index)
{
ASSERT(node);
m_currentNode = node;
m_cachedNodeIndex = index;
}
ALWAYS_INLINE bool isCachedNodeCountValid() const { return m_isLengthCacheValid; }
ALWAYS_INLINE unsigned cachedNodeCount() const { return m_cachedNodeCount; }
ALWAYS_INLINE void setCachedNodeCount(unsigned length)
{
m_cachedNodeCount = length;
m_isLengthCacheValid = true;
}
private:
NodeType* nodeBeforeCachedNode(const Collection&, unsigned index);
NodeType* nodeAfterCachedNode(const Collection&, unsigned index);
RawPtrWillBeMember<NodeType> m_currentNode;
unsigned m_cachedNodeCount;
unsigned m_cachedNodeIndex : 31;
unsigned m_isLengthCacheValid : 1;
};
template <typename Collection, typename NodeType>
CollectionIndexCache<Collection, NodeType>::CollectionIndexCache()
: m_currentNode(nullptr)
, m_cachedNodeCount(0)
, m_cachedNodeIndex(0)
, m_isLengthCacheValid(false)
{
}
template <typename Collection, typename NodeType>
void CollectionIndexCache<Collection, NodeType>::invalidate()
{
m_currentNode = nullptr;
m_isLengthCacheValid = false;
}
template <typename Collection, typename NodeType>
inline unsigned CollectionIndexCache<Collection, NodeType>::nodeCount(const Collection& collection)
{
if (isCachedNodeCountValid())
return cachedNodeCount();
nodeAt(collection, UINT_MAX);
ASSERT(isCachedNodeCountValid());
return cachedNodeCount();
}
template <typename Collection, typename NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeAt(const Collection& collection, unsigned index)
{
if (isCachedNodeCountValid() && index >= cachedNodeCount())
return nullptr;
if (cachedNode()) {
if (index > cachedNodeIndex())
return nodeAfterCachedNode(collection, index);
if (index < cachedNodeIndex())
return nodeBeforeCachedNode(collection, index);
return cachedNode();
}
// No valid cache yet, let's find the first matching element.
ASSERT(!isCachedNodeCountValid());
NodeType* firstNode = collection.traverseToFirst();
if (!firstNode) {
// The collection is empty.
setCachedNodeCount(0);
return nullptr;
}
setCachedNode(firstNode, 0);
return index ? nodeAfterCachedNode(collection, index) : firstNode;
}
template <typename Collection, typename NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeBeforeCachedNode(const Collection& collection, unsigned index)
{
ASSERT(cachedNode()); // Cache should be valid.
unsigned currentIndex = cachedNodeIndex();
ASSERT(currentIndex > index);
// Determine if we should traverse from the beginning of the collection instead of the cached node.
bool firstIsCloser = index < currentIndex - index;
if (firstIsCloser || !collection.canTraverseBackward()) {
NodeType* firstNode = collection.traverseToFirst();
ASSERT(firstNode);
setCachedNode(firstNode, 0);
return index ? nodeAfterCachedNode(collection, index) : firstNode;
}
// Backward traversal from the cached node to the requested index.
ASSERT(collection.canTraverseBackward());
NodeType* currentNode = collection.traverseBackwardToOffset(index, *cachedNode(), currentIndex);
ASSERT(currentNode);
setCachedNode(currentNode, currentIndex);
return currentNode;
}
template <typename Collection, typename NodeType>
inline NodeType* CollectionIndexCache<Collection, NodeType>::nodeAfterCachedNode(const Collection& collection, unsigned index)
{
ASSERT(cachedNode()); // Cache should be valid.
unsigned currentIndex = cachedNodeIndex();
ASSERT(currentIndex < index);
// Determine if we should traverse from the end of the collection instead of the cached node.
bool lastIsCloser = isCachedNodeCountValid() && cachedNodeCount() - index < index - currentIndex;
if (lastIsCloser && collection.canTraverseBackward()) {
NodeType* lastItem = collection.traverseToLast();
ASSERT(lastItem);
setCachedNode(lastItem, cachedNodeCount() - 1);
if (index < cachedNodeCount() - 1)
return nodeBeforeCachedNode(collection, index);
return lastItem;
}
// Forward traversal from the cached node to the requested index.
NodeType* currentNode = collection.traverseForwardToOffset(index, *cachedNode(), currentIndex);
if (!currentNode) {
// Did not find the node. On plus side, we now know the length.
setCachedNodeCount(currentIndex + 1);
return nullptr;
}
setCachedNode(currentNode, currentIndex);
return currentNode;
}
} // namespace blink
#endif // CollectionIndexCache_h
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