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Unified Diff: Source/core/dom/NthIndexCache.h

Issue 1023393002: Cache element indices for :nth-child and :nth-last-child selectors. (Closed) Base URL: https://chromium.googlesource.com/chromium/blink.git@master
Patch Set: Moved nth-index-cache scope to updateStyle Created 5 years, 9 months ago
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Index: Source/core/dom/NthIndexCache.h
diff --git a/Source/core/dom/NthIndexCache.h b/Source/core/dom/NthIndexCache.h
new file mode 100644
index 0000000000000000000000000000000000000000..50636506a98527dd20e4040cc597df0142387923
--- /dev/null
+++ b/Source/core/dom/NthIndexCache.h
@@ -0,0 +1,97 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NthIndexCache_h
+#define NthIndexCache_h
+
+#include "core/dom/Element.h"
+#include "core/dom/ElementTraversal.h"
+#include "platform/heap/Handle.h"
+#include "wtf/HashMap.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/RefPtr.h"
+
+namespace blink {
+
+class Document;
+
+class NthIndexCache : NoBaseWillBeGarbageCollected<NthIndexCache> {
+ WTF_MAKE_NONCOPYABLE(NthIndexCache);
+public:
+ static PassOwnPtr<NthIndexCache> create(Document& document)
+ {
+ return adoptPtr(new NthIndexCache(document));
+ }
+
+ unsigned nthChildIndex(Element&);
+ unsigned nthLastChildIndex(Element&);
+
+ void clear();
+
+ DECLARE_TRACE();
+
+private:
+ NthIndexCache(Document& document)
+ : m_document(document) { }
+
+ class NthIndexData : public NoBaseWillBeGarbageCollected<NthIndexData> {
+ WTF_MAKE_NONCOPYABLE(NthIndexData);
+ public:
+ NthIndexData() : m_count(0) { }
+
+ inline unsigned nthIndex(Element&);
+ inline unsigned nthLastIndex(Element&);
+
+ unsigned cacheNthIndices(Element&);
+
+ WillBeHeapHashMap<RawPtrWillBeMember<Element>, unsigned> m_elementIndexMap;
+ unsigned m_count;
+
+ DECLARE_TRACE();
+ };
+
+ NthIndexData& ensureNthIndexDataFor(Node&);
+ inline unsigned nthIndex(Element&);
+
+ using ParentMap = WillBeHeapHashMap<RefPtrWillBeMember<Node>, OwnPtrWillBeMember<NthIndexData>>;
+
+ OwnPtrWillBeMember<ParentMap> m_parentMap;
+ RawPtrWillBeMember<Document> m_document;
+};
+
+inline unsigned NthIndexCache::NthIndexData::nthIndex(Element& element)
+{
+ if (!m_count)
+ return cacheNthIndices(element);
+
+ unsigned index = 0;
+ for (Element* sibling = &element; sibling; sibling = ElementTraversal::previousSibling(*sibling), index++) {
+ auto it = m_elementIndexMap.find(sibling);
+ if (it != m_elementIndexMap.end())
+ return it->value + index;
+ }
+ return index;
+}
+
+inline unsigned NthIndexCache::NthIndexData::nthLastIndex(Element& element)
+{
+ unsigned index = nthIndex(element);
+ return m_count - index + 1;
+}
+
+inline unsigned NthIndexCache::nthChildIndex(Element& element)
+{
+ ASSERT(element.parentNode());
+ return ensureNthIndexDataFor(*element.parentNode()).nthIndex(element);
+}
+
+inline unsigned NthIndexCache::nthLastChildIndex(Element& element)
+{
+ ASSERT(element.parentNode());
+ return ensureNthIndexDataFor(*element.parentNode()).nthLastIndex(element);
+}
+
+} // namespace blink
+
+#endif // NthIndexCache_h

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