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diff --git a/Source/JavaScriptCore/runtime/WriteBarrier.h b/Source/JavaScriptCore/runtime/WriteBarrier.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. 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 WriteBarrier_h
+#define WriteBarrier_h
+
+#include "JSValue.h"
+
+namespace JSC {
+class JSCell;
+class JSGlobalData;
+
+typedef enum { } Unknown;
+
+template <class T> class DeprecatedPtr {
+public:
+    DeprecatedPtr() : m_cell(0) { }
+    DeprecatedPtr(T* cell) : m_cell(reinterpret_cast<JSCell*>(cell)) { }
+    T* get() const { return reinterpret_cast<T*>(m_cell); }
+    T* operator*() const { return static_cast<T*>(m_cell); }
+    T* operator->() const { return static_cast<T*>(m_cell); }
+    
+    JSCell** slot() { return &m_cell; }
+    
+    typedef T* (DeprecatedPtr::*UnspecifiedBoolType);
+    operator UnspecifiedBoolType*() const { return m_cell ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
+
+    bool operator!() const { return !m_cell; }
+
+protected:
+    JSCell* m_cell;
+};
+
+template <> class DeprecatedPtr<Unknown> {
+public:
+    DeprecatedPtr() { }
+    DeprecatedPtr(JSValue value) : m_value(value) { }
+    DeprecatedPtr(JSCell* value) : m_value(value) { }
+    const JSValue& get() const { return m_value; }
+    const JSValue* operator*() const { return &m_value; }
+    const JSValue* operator->() const { return &m_value; }
+    
+    JSValue* slot() { return &m_value; }
+    
+    typedef JSValue (DeprecatedPtr::*UnspecifiedBoolType);
+    operator UnspecifiedBoolType*() const { return m_value ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
+    bool operator!() const { return !m_value; }
+    
+private:
+    JSValue m_value;
+};
+
+template <typename T> struct WriteBarrierCheck {
+    static const bool IsJSValue = false;
+};
+
+template <> struct WriteBarrierCheck<JSValue> {
+    static const bool IsJSValue = true;
+};
+
+template <typename T> class WriteBarrierBase {
+public:
+    COMPILE_ASSERT(!WriteBarrierCheck<T>::IsJSValue, WriteBarrier_JSValue_is_invalid__use_unknown);
+    void set(JSGlobalData&, const JSCell*, T* value) { this->m_cell = reinterpret_cast<JSCell*>(value); }
+    
+    T* get() const { return reinterpret_cast<T*>(m_cell); }
+    T* operator*() const { return static_cast<T*>(m_cell); }
+    T* operator->() const { return static_cast<T*>(m_cell); }
+    void clear() { m_cell = 0; }
+    
+    JSCell** slot() { return &m_cell; }
+    
+    typedef T* (WriteBarrierBase::*UnspecifiedBoolType);
+    operator UnspecifiedBoolType*() const { return m_cell ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
+    
+    bool operator!() const { return !m_cell; }
+
+    void setWithoutWriteBarrier(T* value) { this->m_cell = reinterpret_cast<JSCell*>(value); }
+
+protected:
+    JSCell* m_cell;
+};
+
+template <typename T> class WriteBarrier : public WriteBarrierBase<T> {
+public:
+    WriteBarrier() { this->m_cell = 0; }
+    WriteBarrier(JSGlobalData& globalData, const JSCell* owner, T* value)
+    {
+        this->set(globalData, owner, value);
+    }
+
+};
+
+template <> class WriteBarrierBase<Unknown> {
+public:
+    void set(JSGlobalData&, const JSCell*, JSValue value) { m_value = JSValue::encode(value); }
+    void setWithoutWriteBarrier(JSValue value) { m_value = JSValue::encode(value); }
+    JSValue get() const { return JSValue::decode(m_value); }
+    void clear() { m_value = JSValue::encode(JSValue()); }
+    void setUndefined() { m_value = JSValue::encode(jsUndefined()); }
+    bool isNumber() const { return get().isNumber(); }
+    bool isGetterSetter() const { return get().isGetterSetter(); }
+    
+    JSValue* slot()
+    { 
+        union {
+            EncodedJSValue* v;
+            JSValue* slot;
+        } u;
+        u.v = &m_value;
+        return u.slot;
+    }
+    
+    typedef JSValue (WriteBarrierBase::*UnspecifiedBoolType);
+    operator UnspecifiedBoolType*() const { return get() ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
+    bool operator!() const { return !get(); } 
+    
+protected:
+    EncodedJSValue m_value;
+};
+
+template <> class WriteBarrier<Unknown> : public WriteBarrierBase<Unknown> {
+public:
+    WriteBarrier() { m_value = JSValue::encode(JSValue()); }
+    WriteBarrier(JSGlobalData& globalData, const JSCell* owner, JSValue value)
+    {
+        this->set(globalData, owner, value);
+    }
+};
+
+template <typename U, typename V> inline bool operator==(const DeprecatedPtr<U>& lhs, const DeprecatedPtr<V>& rhs)
+{
+    return lhs.get() == rhs.get();
+}
+
+template <typename U, typename V> inline bool operator==(const WriteBarrierBase<U>& lhs, const WriteBarrierBase<V>& rhs)
+{
+    return lhs.get() == rhs.get();
+}
+
+}
+
+#endif // WriteBarrier_h