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diff --git a/Source/JavaScriptCore/runtime/JSString.cpp b/Source/JavaScriptCore/runtime/JSString.cpp
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+/*
+ *  Copyright (C) 1999-2002 Harri Porten (porten@kde.org)
+ *  Copyright (C) 2001 Peter Kelly (pmk@post.com)
+ *  Copyright (C) 2004, 2007, 2008 Apple Inc. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Library General Public License
+ *  along with this library; see the file COPYING.LIB.  If not, write to
+ *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA 02110-1301, USA.
+ *
+ */
+
+#include "config.h"
+#include "JSString.h"
+
+#include "JSGlobalObject.h"
+#include "JSGlobalObjectFunctions.h"
+#include "JSObject.h"
+#include "Operations.h"
+#include "StringObject.h"
+#include "StringPrototype.h"
+
+namespace JSC {
+    
+static const unsigned substringFromRopeCutoff = 4;
+
+// Overview: this methods converts a JSString from holding a string in rope form
+// down to a simple UString representation.  It does so by building up the string
+// backwards, since we want to avoid recursion, we expect that the tree structure
+// representing the rope is likely imbalanced with more nodes down the left side
+// (since appending to the string is likely more common) - and as such resolving
+// in this fashion should minimize work queue size.  (If we built the queue forwards
+// we would likely have to place all of the constituent StringImpls into the
+// Vector before performing any concatenation, but by working backwards we likely
+// only fill the queue with the number of substrings at any given level in a
+// rope-of-ropes.)
+void JSString::resolveRope(ExecState* exec) const
+{
+    ASSERT(isRope());
+
+    // Allocate the buffer to hold the final string, position initially points to the end.
+    UChar* buffer;
+    if (PassRefPtr<StringImpl> newImpl = StringImpl::tryCreateUninitialized(m_length, buffer))
+        m_value = newImpl;
+    else {
+        for (unsigned i = 0; i < m_fiberCount; ++i) {
+            RopeImpl::deref(m_other.m_fibers[i]);
+            m_other.m_fibers[i] = 0;
+        }
+        m_fiberCount = 0;
+        ASSERT(!isRope());
+        ASSERT(m_value == UString());
+        if (exec)
+            throwOutOfMemoryError(exec);
+        return;
+    }
+    UChar* position = buffer + m_length;
+
+    // Start with the current RopeImpl.
+    Vector<RopeImpl::Fiber, 32> workQueue;
+    RopeImpl::Fiber currentFiber;
+    for (unsigned i = 0; i < (m_fiberCount - 1); ++i)
+        workQueue.append(m_other.m_fibers[i]);
+    currentFiber = m_other.m_fibers[m_fiberCount - 1];
+    while (true) {
+        if (RopeImpl::isRope(currentFiber)) {
+            RopeImpl* rope = static_cast<RopeImpl*>(currentFiber);
+            // Copy the contents of the current rope into the workQueue, with the last item in 'currentFiber'
+            // (we will be working backwards over the rope).
+            unsigned fiberCountMinusOne = rope->fiberCount() - 1;
+            for (unsigned i = 0; i < fiberCountMinusOne; ++i)
+                workQueue.append(rope->fibers()[i]);
+            currentFiber = rope->fibers()[fiberCountMinusOne];
+        } else {
+            StringImpl* string = static_cast<StringImpl*>(currentFiber);
+            unsigned length = string->length();
+            position -= length;
+            StringImpl::copyChars(position, string->characters(), length);
+
+            // Was this the last item in the work queue?
+            if (workQueue.isEmpty()) {
+                // Create a string from the UChar buffer, clear the rope RefPtr.
+                ASSERT(buffer == position);
+                for (unsigned i = 0; i < m_fiberCount; ++i) {
+                    RopeImpl::deref(m_other.m_fibers[i]);
+                    m_other.m_fibers[i] = 0;
+                }
+                m_fiberCount = 0;
+
+                ASSERT(!isRope());
+                return;
+            }
+
+            // No! - set the next item up to process.
+            currentFiber = workQueue.last();
+            workQueue.removeLast();
+        }
+    }
+}
+    
+// This function construsts a substring out of a rope without flattening by reusing the existing fibers.
+// This can reduce memory usage substantially. Since traversing ropes is slow the function will revert 
+// back to flattening if the rope turns out to be long.
+JSString* JSString::substringFromRope(ExecState* exec, unsigned substringStart, unsigned substringLength)
+{
+    ASSERT(isRope());
+    ASSERT(substringLength);
+    
+    JSGlobalData* globalData = &exec->globalData();
+
+    UString substringFibers[3];
+    
+    unsigned fiberCount = 0;
+    unsigned substringFiberCount = 0;
+    unsigned substringEnd = substringStart + substringLength;
+    unsigned fiberEnd = 0;
+
+    RopeIterator end;
+    for (RopeIterator it(m_other.m_fibers.data(), m_fiberCount); it != end; ++it) {
+        ++fiberCount;
+        StringImpl* fiberString = *it;
+        unsigned fiberStart = fiberEnd;
+        fiberEnd = fiberStart + fiberString->length();
+        if (fiberEnd <= substringStart)
+            continue;
+        unsigned copyStart = std::max(substringStart, fiberStart);
+        unsigned copyEnd = std::min(substringEnd, fiberEnd);
+        if (copyStart == fiberStart && copyEnd == fiberEnd)
+            substringFibers[substringFiberCount++] = UString(fiberString);
+        else
+            substringFibers[substringFiberCount++] = UString(StringImpl::create(fiberString, copyStart - fiberStart, copyEnd - copyStart));
+        if (fiberEnd >= substringEnd)
+            break;
+        if (fiberCount > substringFromRopeCutoff || substringFiberCount >= 3) {
+            // This turned out to be a really inefficient rope. Just flatten it.
+            resolveRope(exec);
+            return jsSubstring(&exec->globalData(), m_value, substringStart, substringLength);
+        }
+    }
+    ASSERT(substringFiberCount && substringFiberCount <= 3);
+
+    if (substringLength == 1) {
+        ASSERT(substringFiberCount == 1);
+        UChar c = substringFibers[0].characters()[0];
+        if (c <= 0xFF)
+            return globalData->smallStrings.singleCharacterString(globalData, c);
+    }
+    if (substringFiberCount == 1)
+        return new (globalData) JSString(globalData, substringFibers[0]);
+    if (substringFiberCount == 2)
+        return new (globalData) JSString(globalData, substringFibers[0], substringFibers[1]);
+    return new (globalData) JSString(globalData, substringFibers[0], substringFibers[1], substringFibers[2]);
+}
+
+JSValue JSString::replaceCharacter(ExecState* exec, UChar character, const UString& replacement)
+{
+    if (!isRope()) {
+        size_t matchPosition = m_value.find(character);
+        if (matchPosition == notFound)
+            return JSValue(this);
+        return jsString(exec, m_value.substringSharingImpl(0, matchPosition), replacement, m_value.substringSharingImpl(matchPosition + 1));
+    }
+
+    RopeIterator end;
+    
+    // Count total fibers and find matching string.
+    size_t fiberCount = 0;
+    StringImpl* matchString = 0;
+    size_t matchPosition = notFound;
+    for (RopeIterator it(m_other.m_fibers.data(), m_fiberCount); it != end; ++it) {
+        ++fiberCount;
+        if (matchString)
+            continue;
+
+        StringImpl* string = *it;
+        matchPosition = string->find(character);
+        if (matchPosition == notFound)
+            continue;
+        matchString = string;
+    }
+
+    if (!matchString)
+        return this;
+
+    RopeBuilder builder(replacement.length() ? fiberCount + 2 : fiberCount + 1);
+    if (UNLIKELY(builder.isOutOfMemory()))
+        return throwOutOfMemoryError(exec);
+
+    for (RopeIterator it(m_other.m_fibers.data(), m_fiberCount); it != end; ++it) {
+        StringImpl* string = *it;
+        if (string != matchString) {
+            builder.append(UString(string));
+            continue;
+        }
+
+        builder.append(UString(string).substringSharingImpl(0, matchPosition));
+        if (replacement.length())
+            builder.append(replacement);
+        builder.append(UString(string).substringSharingImpl(matchPosition + 1));
+        matchString = 0;
+    }
+
+    JSGlobalData* globalData = &exec->globalData();
+    return JSValue(new (globalData) JSString(globalData, builder.release()));
+}
+
+JSString* JSString::getIndexSlowCase(ExecState* exec, unsigned i)
+{
+    ASSERT(isRope());
+    resolveRope(exec);
+    // Return a safe no-value result, this should never be used, since the excetion will be thrown.
+    if (exec->exception())
+        return jsString(exec, "");
+    ASSERT(!isRope());
+    ASSERT(i < m_value.length());
+    return jsSingleCharacterSubstring(exec, m_value, i);
+}
+
+JSValue JSString::toPrimitive(ExecState*, PreferredPrimitiveType) const
+{
+    return const_cast<JSString*>(this);
+}
+
+bool JSString::getPrimitiveNumber(ExecState* exec, double& number, JSValue& result)
+{
+    result = this;
+    number = jsToNumber(value(exec));
+    return false;
+}
+
+bool JSString::toBoolean(ExecState*) const
+{
+    return m_length;
+}
+
+double JSString::toNumber(ExecState* exec) const
+{
+    return jsToNumber(value(exec));
+}
+
+UString JSString::toString(ExecState* exec) const
+{
+    return value(exec);
+}
+
+inline StringObject* StringObject::create(ExecState* exec, JSString* string)
+{
+    return new (exec) StringObject(exec->lexicalGlobalObject()->stringObjectStructure(), string);
+}
+
+JSObject* JSString::toObject(ExecState* exec) const
+{
+    return StringObject::create(exec, const_cast<JSString*>(this));
+}
+
+JSObject* JSString::toThisObject(ExecState* exec) const
+{
+    return StringObject::create(exec, const_cast<JSString*>(this));
+}
+
+bool JSString::getOwnPropertySlot(ExecState* exec, const Identifier& propertyName, PropertySlot& slot)
+{
+    // The semantics here are really getPropertySlot, not getOwnPropertySlot.
+    // This function should only be called by JSValue::get.
+    if (getStringPropertySlot(exec, propertyName, slot))
+        return true;
+    if (propertyName == exec->propertyNames().underscoreProto) {
+        slot.setValue(exec->lexicalGlobalObject()->stringPrototype());
+        return true;
+    }
+    slot.setBase(this);
+    JSObject* object;
+    for (JSValue prototype = exec->lexicalGlobalObject()->stringPrototype(); !prototype.isNull(); prototype = object->prototype()) {
+        object = asObject(prototype);
+        if (object->getOwnPropertySlot(exec, propertyName, slot))
+            return true;
+    }
+    slot.setUndefined();
+    return true;
+}
+
+bool JSString::getStringPropertyDescriptor(ExecState* exec, const Identifier& propertyName, PropertyDescriptor& descriptor)
+{
+    if (propertyName == exec->propertyNames().length) {
+        descriptor.setDescriptor(jsNumber(m_length), DontEnum | DontDelete | ReadOnly);
+        return true;
+    }
+    
+    bool isStrictUInt32;
+    unsigned i = propertyName.toUInt32(isStrictUInt32);
+    if (isStrictUInt32 && i < m_length) {
+        descriptor.setDescriptor(getIndex(exec, i), DontDelete | ReadOnly);
+        return true;
+    }
+    
+    return false;
+}
+
+bool JSString::getOwnPropertyDescriptor(ExecState* exec, const Identifier& propertyName, PropertyDescriptor& descriptor)
+{
+    if (getStringPropertyDescriptor(exec, propertyName, descriptor))
+        return true;
+    if (propertyName != exec->propertyNames().underscoreProto)
+        return false;
+    descriptor.setDescriptor(exec->lexicalGlobalObject()->stringPrototype(), DontEnum);
+    return true;
+}
+
+bool JSString::getOwnPropertySlot(ExecState* exec, unsigned propertyName, PropertySlot& slot)
+{
+    // The semantics here are really getPropertySlot, not getOwnPropertySlot.
+    // This function should only be called by JSValue::get.
+    if (getStringPropertySlot(exec, propertyName, slot))
+        return true;
+    return JSString::getOwnPropertySlot(exec, Identifier::from(exec, propertyName), slot);
+}
+
+} // namespace JSC