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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
#include "platform/heap/Handle.h"
namespace blink {
template <typename Collection, typename NodeType>
class CollectionIndexCache {
DISALLOW_NEW();
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 NodeInserted();
void NodeRemoved();
DEFINE_INLINE_VIRTUAL_TRACE() { visitor->Trace(current_node_); }
protected:
ALWAYS_INLINE NodeType* CachedNode() const { return current_node_; }
ALWAYS_INLINE unsigned CachedNodeIndex() const {
DCHECK(CachedNode());
return cached_node_index_;
}
ALWAYS_INLINE void SetCachedNode(NodeType* node, unsigned index) {
DCHECK(node);
current_node_ = node;
cached_node_index_ = index;
}
ALWAYS_INLINE bool IsCachedNodeCountValid() const {
return is_length_cache_valid_;
}
ALWAYS_INLINE unsigned CachedNodeCount() const { return cached_node_count_; }
ALWAYS_INLINE void SetCachedNodeCount(unsigned length) {
cached_node_count_ = length;
is_length_cache_valid_ = true;
}
private:
NodeType* NodeBeforeCachedNode(const Collection&, unsigned index);
NodeType* NodeAfterCachedNode(const Collection&, unsigned index);
Member<NodeType> current_node_;
unsigned cached_node_count_;
unsigned cached_node_index_ : 31;
unsigned is_length_cache_valid_ : 1;
};
template <typename Collection, typename NodeType>
CollectionIndexCache<Collection, NodeType>::CollectionIndexCache()
: current_node_(nullptr),
cached_node_count_(0),
cached_node_index_(0),
is_length_cache_valid_(false) {}
template <typename Collection, typename NodeType>
void CollectionIndexCache<Collection, NodeType>::Invalidate() {
current_node_ = nullptr;
is_length_cache_valid_ = false;
}
template <typename Collection, typename NodeType>
void CollectionIndexCache<Collection, NodeType>::NodeInserted() {
cached_node_count_++;
current_node_ = nullptr;
}
template <typename Collection, typename NodeType>
void CollectionIndexCache<Collection, NodeType>::NodeRemoved() {
cached_node_count_--;
current_node_ = nullptr;
}
template <typename Collection, typename NodeType>
inline unsigned CollectionIndexCache<Collection, NodeType>::NodeCount(
const Collection& collection) {
if (IsCachedNodeCountValid())
return CachedNodeCount();
NodeAt(collection, UINT_MAX);
DCHECK(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.
NodeType* first_node = collection.TraverseToFirst();
if (!first_node) {
// The collection is empty.
SetCachedNodeCount(0);
return nullptr;
}
SetCachedNode(first_node, 0);
return index ? NodeAfterCachedNode(collection, index) : first_node;
}
template <typename Collection, typename NodeType>
inline NodeType*
CollectionIndexCache<Collection, NodeType>::NodeBeforeCachedNode(
const Collection& collection,
unsigned index) {
DCHECK(CachedNode()); // Cache should be valid.
unsigned current_index = CachedNodeIndex();
DCHECK_GT(current_index, index);
// Determine if we should traverse from the beginning of the collection
// instead of the cached node.
bool first_is_closer = index < current_index - index;
if (first_is_closer || !collection.CanTraverseBackward()) {
NodeType* first_node = collection.TraverseToFirst();
DCHECK(first_node);
SetCachedNode(first_node, 0);
return index ? NodeAfterCachedNode(collection, index) : first_node;
}
// Backward traversal from the cached node to the requested index.
DCHECK(collection.CanTraverseBackward());
NodeType* current_node =
collection.TraverseBackwardToOffset(index, *CachedNode(), current_index);
DCHECK(current_node);
SetCachedNode(current_node, current_index);
return current_node;
}
template <typename Collection, typename NodeType>
inline NodeType*
CollectionIndexCache<Collection, NodeType>::NodeAfterCachedNode(
const Collection& collection,
unsigned index) {
DCHECK(CachedNode()); // Cache should be valid.
unsigned current_index = CachedNodeIndex();
DCHECK_LT(current_index, index);
// Determine if we should traverse from the end of the collection instead of
// the cached node.
bool last_is_closer = IsCachedNodeCountValid() &&
CachedNodeCount() - index < index - current_index;
if (last_is_closer && collection.CanTraverseBackward()) {
NodeType* last_item = collection.TraverseToLast();
DCHECK(last_item);
SetCachedNode(last_item, CachedNodeCount() - 1);
if (index < CachedNodeCount() - 1)
return NodeBeforeCachedNode(collection, index);
return last_item;
}
// Forward traversal from the cached node to the requested index.
NodeType* current_node =
collection.TraverseForwardToOffset(index, *CachedNode(), current_index);
if (!current_node) {
// Did not find the node. On plus side, we now know the length.
if (IsCachedNodeCountValid()) {
DCHECK_EQ(current_index + 1, CachedNodeCount());
}
SetCachedNodeCount(current_index + 1);
return nullptr;
}
SetCachedNode(current_node, current_index);
return current_node;
}
} // namespace blink
#endif // CollectionIndexCache_h
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