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diff --git a/Source/JavaScriptCore/wtf/RefCountedArray.h b/Source/JavaScriptCore/wtf/RefCountedArray.h
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+++ b/Source/JavaScriptCore/wtf/RefCountedArray.h
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+/*
+ * Copyright (C) 2011 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. ``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
+ * 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 RefCountedArray_h
+#define RefCountedArray_h
+
+#include <wtf/FastMalloc.h>
+#include <wtf/StdLibExtras.h>
+#include <wtf/Vector.h>
+
+// This implements a reference counted array for POD** values, which is optimized for:
+// - An empty array only uses one word.
+// - A copy of the array only uses one word (i.e. assignment means aliasing).
+// - The vector can't grow beyond 2^32-1 elements.
+// - In all other regards this has similar space usage to a Vector.
+//
+// ** This could be modified to support non-POD values quite easily. It just
+//    hasn't been, so far, because there has been no need. Moreover, even now,
+//    it's used for things that aren't quite POD according to the official
+//    defintion, such as JSC::Instruction.
+
+namespace WTF {
+
+template<typename T>
+class RefCountedArray {
+public:
+    RefCountedArray()
+        : m_data(0)
+    {
+    }
+    
+    RefCountedArray(const RefCountedArray& other)
+        : m_data(other.m_data)
+    {
+        if (m_data)
+            Header::fromPayload(m_data)->refCount++;
+    }
+    
+    explicit RefCountedArray(const Vector<T>& other)
+    {
+        if (other.isEmpty()) {
+            m_data = 0;
+            return;
+        }
+        
+        m_data = (static_cast<Header*>(fastMalloc(Header::size() + sizeof(T) * other.size())))->payload();
+        Header::fromPayload(m_data)->refCount = 1;
+        Header::fromPayload(m_data)->length = other.size();
+        ASSERT(Header::fromPayload(m_data)->length == other.size());
+        memcpy(m_data, other.begin(), sizeof(T) * other.size());
+    }
+    
+    RefCountedArray& operator=(const RefCountedArray& other)
+    {
+        T* oldData = m_data;
+        m_data = other.m_data;
+        if (m_data)
+            Header::fromPayload(m_data)->refCount++;
+        
+        if (!oldData)
+            return *this;
+        if (--Header::fromPayload(oldData)->refCount)
+            return *this;
+        fastFree(Header::fromPayload(oldData));
+        return *this;
+    }
+    
+    ~RefCountedArray()
+    {
+        if (!m_data)
+            return;
+        if (--Header::fromPayload(m_data)->refCount)
+            return;
+        fastFree(Header::fromPayload(m_data));
+    }
+    
+    size_t size() const
+    {
+        if (!m_data)
+            return 0;
+        return Header::fromPayload(m_data)->length;
+    }
+    
+    T* data() { return m_data; }
+    T* begin() { return m_data; }
+    T* end()
+    {
+        if (!m_data)
+            return 0;
+        return m_data + Header::fromPayload(m_data)->length;
+    }
+    
+    const T* data() const { return m_data; }
+    const T* begin() const { return m_data; }
+    const T* end() const { return const_cast<RefCountedArray*>(this)->end(); }
+    
+    T& at(size_t i)
+    {
+        ASSERT(i < size());
+        return begin()[i];
+    }
+    
+    const T& at(size_t i) const
+    {
+        ASSERT(i < size());
+        return begin()[i];
+    }
+    
+    T& operator[](size_t i) { return at(i); }
+    const T& operator[](size_t i) const { return at(i); }
+    
+private:
+    struct Header {
+        unsigned refCount;
+        unsigned length;
+        
+        static size_t size()
+        {
+            return (sizeof(Header) + 7) & ~7;
+        }
+        
+        T* payload()
+        {
+            char* result = reinterpret_cast<char*>(this) + size();
+            ASSERT(!(bitwise_cast<uintptr_t>(result) & 7));
+            return reinterpret_cast<T*>(result);
+        }
+        
+        static Header* fromPayload(T* payload)
+        {
+            return reinterpret_cast_ptr<Header*>(reinterpret_cast<char*>(payload) - size());
+        }
+    };
+    
+    T* m_data;
+};
+
+} // namespace WTF
+
+using WTF::RefCountedArray;
+
+#endif // RefCountedArray_h
+