1 files changed, 83 insertions, 0 deletions
diff --git a/layout/xul/tree/nsTreeStyleCache.h b/layout/xul/tree/nsTreeStyleCache.h
new file mode 100644
index 0000000000..19202ab2d3
--- /dev/null
+++ b/layout/xul/tree/nsTreeStyleCache.h
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsTreeStyleCache_h__
+#define nsTreeStyleCache_h__
+
+#include "mozilla/AtomArray.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMArray.h"
+#include "nsDataHashtable.h"
+#include "nsRefPtrHashtable.h"
+#include "mozilla/ComputedStyle.h"
+
+class nsIContent;
+
+class nsTreeStyleCache {
+ public:
+  nsTreeStyleCache() : mNextState(0) {}
+
+  ~nsTreeStyleCache() { Clear(); }
+
+  void Clear() {
+    mTransitionTable = nullptr;
+    mCache = nullptr;
+    mNextState = 0;
+  }
+
+  mozilla::ComputedStyle* GetComputedStyle(
+      nsPresContext* aPresContext, nsIContent* aContent,
+      mozilla::ComputedStyle* aStyle,
+      nsCSSAnonBoxPseudoStaticAtom* aPseudoElement,
+      const mozilla::AtomArray& aInputWord);
+
+ protected:
+  typedef uint32_t DFAState;
+
+  class Transition final {
+   public:
+    Transition(DFAState aState, nsAtom* aSymbol);
+    bool operator==(const Transition& aOther) const;
+    uint32_t Hash() const;
+
+   private:
+    DFAState mState;
+    RefPtr<nsAtom> mInputSymbol;
+  };
+
+  typedef nsDataHashtable<nsGenericHashKey<Transition>, DFAState>
+      TransitionTable;
+
+  // A transition table for a deterministic finite automaton.  The DFA
+  // takes as its input a single pseudoelement and an ordered set of properties.
+  // It transitions on an input word that is the concatenation of the
+  // pseudoelement supplied with the properties in the array.
+  //
+  // It transitions from state to state by looking up entries in the transition
+  // table (which is a mapping from (S,i)->S', where S is the current state, i
+  // is the next property in the input word, and S' is the state to transition
+  // to.
+  //
+  // If S' is not found, it is constructed and entered into the hashtable
+  // under the key (S,i).
+  //
+  // Once the entire word has been consumed, the final state is used
+  // to reference the cache table to locate the ComputedStyle.
+  mozilla::UniquePtr<TransitionTable> mTransitionTable;
+
+  // The cache of all active ComputedStyles.  This is a hash from
+  // a final state in the DFA, Sf, to the resultant ComputedStyle.
+  typedef nsRefPtrHashtable<nsUint32HashKey, mozilla::ComputedStyle>
+      ComputedStyleCache;
+  mozilla::UniquePtr<ComputedStyleCache> mCache;
+
+  // An integer counter that is used when we need to make new states in the
+  // DFA.
+  DFAState mNextState;
+};
+
+#endif  // nsTreeStyleCache_h__