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diff --git a/Source/JavaScriptCore/runtime/StructureIDTable.h b/Source/JavaScriptCore/runtime/StructureIDTable.h
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+++ b/Source/JavaScriptCore/runtime/StructureIDTable.h
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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 StructureIDTable_h
+#define StructureIDTable_h
+
+#include "UnusedPointer.h"
+#include <wtf/Vector.h>
+
+namespace JSC {
+
+class Structure;
+
+#if USE(JSVALUE64)
+typedef uint32_t StructureID;
+#else
+typedef Structure* StructureID;
+#endif
+
+class StructureIDTable {
+    friend class LLIntOffsetsExtractor;
+public:
+    StructureIDTable();
+
+    void** base() { return reinterpret_cast<void**>(&m_table); }
+
+    Structure* get(StructureID);
+    void deallocateID(Structure*, StructureID);
+    StructureID allocateID(Structure*);
+
+    void flushOldTables();
+
+private:
+    void resize(size_t newCapacity);
+
+    union StructureOrOffset {
+        WTF_MAKE_FAST_ALLOCATED;
+    public:
+        Structure* structure;
+        StructureID offset;
+    };
+
+    StructureOrOffset* table() const { return m_table.get(); }
+    
+    static const size_t s_initialSize = 256;
+
+    Vector<std::unique_ptr<StructureOrOffset[]>> m_oldTables;
+
+    uint32_t m_firstFreeOffset;
+    std::unique_ptr<StructureOrOffset[]> m_table;
+
+    size_t m_size;
+    size_t m_capacity;
+
+#if USE(JSVALUE64)
+    static const StructureID s_unusedID = unusedPointer;
+#endif
+};
+
+inline Structure* StructureIDTable::get(StructureID structureID)
+{
+#if USE(JSVALUE64)
+    ASSERT_WITH_SECURITY_IMPLICATION(structureID && structureID < m_capacity);
+    return table()[structureID].structure;
+#else
+    return structureID;
+#endif
+}
+
+} // namespace JSC
+
+#endif // StructureIDTable_h