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diff --git a/Source/JavaScriptCore/runtime/GenericOffset.h b/Source/JavaScriptCore/runtime/GenericOffset.h
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+/*
+ * Copyright (C) 2015 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 GenericOffset_h
+#define GenericOffset_h
+
+#include <limits.h>
+#include <wtf/Assertions.h>
+
+namespace JSC {
+
+// A mixin for creating the various kinds of variable offsets that our engine supports.
+template<typename T>
+class GenericOffset {
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    static const unsigned invalidOffset = UINT_MAX;
+    
+    GenericOffset()
+        : m_offset(invalidOffset)
+    {
+    }
+    
+    explicit GenericOffset(unsigned offset)
+        : m_offset(offset)
+    {
+    }
+    
+    bool operator!() const { return m_offset == invalidOffset; }
+    
+    unsigned offsetUnchecked() const
+    {
+        return m_offset;
+    }
+    
+    unsigned offset() const
+    {
+        ASSERT(m_offset != invalidOffset);
+        return m_offset;
+    }
+    
+    bool operator==(const T& other) const
+    {
+        return m_offset == other.offsetUnchecked();
+    }
+    bool operator!=(const T& other) const
+    {
+        return m_offset != other.offsetUnchecked();
+    }
+    bool operator<(const T& other) const
+    {
+        return m_offset < other.offsetUnchecked();
+    }
+    bool operator>(const T& other) const
+    {
+        return m_offset > other.offsetUnchecked();
+    }
+    bool operator<=(const T& other) const
+    {
+        return m_offset <= other.offsetUnchecked();
+    }
+    bool operator>=(const T& other) const
+    {
+        return m_offset >= other.offsetUnchecked();
+    }
+    
+    T operator+(int value) const
+    {
+        return T(offset() + value);
+    }
+    T operator-(int value) const
+    {
+        return T(offset() - value);
+    }
+    T& operator+=(int value)
+    {
+        return *this = *this + value;
+    }
+    T& operator-=(int value)
+    {
+        return *this = *this - value;
+    }
+    
+private:
+    unsigned m_offset;
+};
+
+} // namespace JSC
+
+#endif // GenericOffset_h
+