Source/JavaScriptCore/runtime/JSString.cpp - WebKit - Git at Google

 /*
  *  Copyright (C) 1999-2002 Harri Porten (porten@kde.org)
  *  Copyright (C) 2001 Peter Kelly (pmk@post.com)
  *  Copyright (C) 2004, 2007, 2008, 2015 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 "JSCInlines.h"
 #include "StringObject.h"
 #include "StringPrototype.h"
 #include "StrongInlines.h"

 namespace JSC {

 const ClassInfo JSString::s_info = { "string", 0, 0, CREATE_METHOD_TABLE(JSString) };

 Structure* JSString::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue proto)
 {
     return Structure::create(vm, globalObject, proto, TypeInfo(StringType, StructureFlags), info());
 }

 void JSRopeString::RopeBuilder::expand()
 {
     ASSERT(m_index == JSRopeString::s_maxInternalRopeLength);
     JSString* jsString = m_jsString;
     RELEASE_ASSERT(jsString);
     m_jsString = jsStringBuilder(&m_vm);
     m_index = 0;
     append(jsString);
 }

 void JSString::destroy(JSCell* cell)
 {
     JSString* thisObject = static_cast<JSString*>(cell);
     thisObject->JSString::~JSString();
 }

 void JSString::dumpToStream(const JSCell* cell, PrintStream& out)
 {
     const JSString* thisObject = jsCast<const JSString*>(cell);
     out.printf("<%p, %s, [%u], ", thisObject, thisObject->className(), thisObject->length());
     if (thisObject->isRope())
         out.printf("[rope]");
     else {
         WTF::StringImpl* ourImpl = thisObject->m_value.impl();
         if (ourImpl->is8Bit())
             out.printf("[8 %p]", ourImpl->characters8());
         else
             out.printf("[16 %p]", ourImpl->characters16());
     }
     out.printf(">");
 }

 void JSString::visitChildren(JSCell* cell, SlotVisitor& visitor)
 {
     JSString* thisObject = jsCast<JSString*>(cell);
     Base::visitChildren(thisObject, visitor);

     if (thisObject->isRope())
         static_cast<JSRopeString*>(thisObject)->visitFibers(visitor);
     else {
         StringImpl* impl = thisObject->m_value.impl();
         ASSERT(impl);
         visitor.reportExtraMemoryVisited(impl->costDuringGC());
     }
 }

 void JSRopeString::visitFibers(SlotVisitor& visitor)
 {
     if (isSubstring()) {
         visitor.append(&substringBase());
         return;
     }
     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
         visitor.append(&fiber(i));
 }

 static const unsigned maxLengthForOnStackResolve = 2048;

 void JSRopeString::resolveRopeInternal8(LChar* buffer) const
 {
     if (isSubstring()) {
         StringImpl::copyChars(
             buffer, substringBase()->m_value.characters8() + substringOffset(), m_length);
         return;
     }

     resolveRopeInternal8NoSubstring(buffer);
 }

 void JSRopeString::resolveRopeInternal8NoSubstring(LChar* buffer) const
 {
     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
         if (fiber(i)->isRope()) {
             resolveRopeSlowCase8(buffer);
             return;
         }
     }

     LChar* position = buffer;
     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
         const StringImpl& fiberString = *fiber(i)->m_value.impl();
         unsigned length = fiberString.length();
         StringImpl::copyChars(position, fiberString.characters8(), length);
         position += length;
     }
     ASSERT((buffer + m_length) == position);
 }

 void JSRopeString::resolveRopeInternal16(UChar* buffer) const
 {
     if (isSubstring()) {
         StringImpl::copyChars(
             buffer, substringBase()->m_value.characters16() + substringOffset(), m_length);
         return;
     }

     resolveRopeInternal16NoSubstring(buffer);
 }

 void JSRopeString::resolveRopeInternal16NoSubstring(UChar* buffer) const
 {
     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
         if (fiber(i)->isRope()) {
             resolveRopeSlowCase(buffer);
             return;
         }
     }

     UChar* position = buffer;
     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
         const StringImpl& fiberString = *fiber(i)->m_value.impl();
         unsigned length = fiberString.length();
         if (fiberString.is8Bit())
             StringImpl::copyChars(position, fiberString.characters8(), length);
         else
             StringImpl::copyChars(position, fiberString.characters16(), length);
         position += length;
     }
     ASSERT((buffer + m_length) == position);
 }

 void JSRopeString::resolveRopeToAtomicString(ExecState* exec) const
 {
     if (m_length > maxLengthForOnStackResolve) {
         resolveRope(exec);
         m_value = AtomicString(m_value);
         setIs8Bit(m_value.impl()->is8Bit());
         return;
     }

     if (is8Bit()) {
         LChar buffer[maxLengthForOnStackResolve];
         resolveRopeInternal8(buffer);
         m_value = AtomicString(buffer, m_length);
         setIs8Bit(m_value.impl()->is8Bit());
     } else {
         UChar buffer[maxLengthForOnStackResolve];
         resolveRopeInternal16(buffer);
         m_value = AtomicString(buffer, m_length);
         setIs8Bit(m_value.impl()->is8Bit());
     }

     clearFibers();

     // If we resolved a string that didn't previously exist, notify the heap that we've grown.
     if (m_value.impl()->hasOneRef())
         Heap::heap(this)->reportExtraMemoryAllocated(m_value.impl()->cost());
 }

 void JSRopeString::clearFibers() const
 {
     for (size_t i = 0; i < s_maxInternalRopeLength; ++i)
         u[i].number = 0;
 }

 RefPtr<AtomicStringImpl> JSRopeString::resolveRopeToExistingAtomicString(ExecState* exec) const
 {
     if (m_length > maxLengthForOnStackResolve) {
         resolveRope(exec);
         if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(m_value.impl())) {
             m_value = *existingAtomicString;
             setIs8Bit(m_value.impl()->is8Bit());
             clearFibers();
             return existingAtomicString;
         }
         return nullptr;
     }

     if (is8Bit()) {
         LChar buffer[maxLengthForOnStackResolve];
         resolveRopeInternal8(buffer);
         if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(buffer, m_length)) {
             m_value = *existingAtomicString;
             setIs8Bit(m_value.impl()->is8Bit());
             clearFibers();
             return existingAtomicString;
         }
     } else {
         UChar buffer[maxLengthForOnStackResolve];
         resolveRopeInternal16(buffer);
         if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(buffer, m_length)) {
             m_value = *existingAtomicString;
             setIs8Bit(m_value.impl()->is8Bit());
             clearFibers();
             return existingAtomicString;
         }
     }

     return nullptr;
 }

 void JSRopeString::resolveRope(ExecState* exec) const
 {
     ASSERT(isRope());

     if (isSubstring()) {
         ASSERT(!substringBase()->isRope());
         m_value = substringBase()->m_value.substring(substringOffset(), m_length);
         substringBase().clear();
         return;
     }

     if (is8Bit()) {
         LChar* buffer;
         if (RefPtr<StringImpl> newImpl = StringImpl::tryCreateUninitialized(m_length, buffer)) {
             Heap::heap(this)->reportExtraMemoryAllocated(newImpl->cost());
             m_value = newImpl.release();
         } else {
             outOfMemory(exec);
             return;
         }
         resolveRopeInternal8NoSubstring(buffer);
         clearFibers();
         ASSERT(!isRope());
         return;
     }

     UChar* buffer;
     if (RefPtr<StringImpl> newImpl = StringImpl::tryCreateUninitialized(m_length, buffer)) {
         Heap::heap(this)->reportExtraMemoryAllocated(newImpl->cost());
         m_value = newImpl.release();
     } else {
         outOfMemory(exec);
         return;
     }

     resolveRopeInternal16NoSubstring(buffer);
     clearFibers();
     ASSERT(!isRope());
 }

 // Overview: These functions convert a JSString from holding a string in rope form
 // down to a simple String 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 JSRopeString::resolveRopeSlowCase8(LChar* buffer) const
 {
     LChar* position = buffer + m_length; // We will be working backwards over the rope.
     Vector<JSString*, 32, UnsafeVectorOverflow> workQueue; // Putting strings into a Vector is only OK because there are no GC points in this method.

     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
         workQueue.append(fiber(i).get());

     while (!workQueue.isEmpty()) {
         JSString* currentFiber = workQueue.last();
         workQueue.removeLast();

         const LChar* characters;

         if (currentFiber->isRope()) {
             JSRopeString* currentFiberAsRope = static_cast<JSRopeString*>(currentFiber);
             if (!currentFiberAsRope->isSubstring()) {
                 for (size_t i = 0; i < s_maxInternalRopeLength && currentFiberAsRope->fiber(i); ++i)
                     workQueue.append(currentFiberAsRope->fiber(i).get());
                 continue;
             }
             ASSERT(!currentFiberAsRope->substringBase()->isRope());
             characters =
                 currentFiberAsRope->substringBase()->m_value.characters8() +
                 currentFiberAsRope->substringOffset();
         } else
             characters = currentFiber->m_value.characters8();

         unsigned length = currentFiber->length();
         position -= length;
         StringImpl::copyChars(position, characters, length);
     }

     ASSERT(buffer == position);
 }

 void JSRopeString::resolveRopeSlowCase(UChar* buffer) const
 {
     UChar* position = buffer + m_length; // We will be working backwards over the rope.
     Vector<JSString*, 32, UnsafeVectorOverflow> workQueue; // These strings are kept alive by the parent rope, so using a Vector is OK.

     for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
         workQueue.append(fiber(i).get());

     while (!workQueue.isEmpty()) {
         JSString* currentFiber = workQueue.last();
         workQueue.removeLast();

         if (currentFiber->isRope()) {
             JSRopeString* currentFiberAsRope = static_cast<JSRopeString*>(currentFiber);
             if (currentFiberAsRope->isSubstring()) {
                 ASSERT(!currentFiberAsRope->substringBase()->isRope());
                 StringImpl* string = static_cast<StringImpl*>(
                     currentFiberAsRope->substringBase()->m_value.impl());
                 unsigned offset = currentFiberAsRope->substringOffset();
                 unsigned length = currentFiberAsRope->length();
                 position -= length;
                 if (string->is8Bit())
                     StringImpl::copyChars(position, string->characters8() + offset, length);
                 else
                     StringImpl::copyChars(position, string->characters16() + offset, length);
                 continue;
             }
             for (size_t i = 0; i < s_maxInternalRopeLength && currentFiberAsRope->fiber(i); ++i)
                 workQueue.append(currentFiberAsRope->fiber(i).get());
             continue;
         }

         StringImpl* string = static_cast<StringImpl*>(currentFiber->m_value.impl());
         unsigned length = string->length();
         position -= length;
         if (string->is8Bit())
             StringImpl::copyChars(position, string->characters8(), length);
         else
             StringImpl::copyChars(position, string->characters16(), length);
     }

     ASSERT(buffer == position);
 }

 void JSRopeString::outOfMemory(ExecState* exec) const
 {
     clearFibers();
     ASSERT(isRope());
     ASSERT(m_value.isNull());
     if (exec)
         throwOutOfMemoryError(exec);
 }

 JSValue JSString::toPrimitive(ExecState*, PreferredPrimitiveType) const
 {
     return const_cast<JSString*>(this);
 }

 bool JSString::getPrimitiveNumber(ExecState* exec, double& number, JSValue& result) const
 {
     result = this;
     number = jsToNumber(view(exec));
     return false;
 }

 double JSString::toNumber(ExecState* exec) const
 {
     return jsToNumber(view(exec));
 }

 inline StringObject* StringObject::create(VM& vm, JSGlobalObject* globalObject, JSString* string)
 {
     StringObject* object = new (NotNull, allocateCell<StringObject>(vm.heap)) StringObject(vm, globalObject->stringObjectStructure());
     object->finishCreation(vm, string);
     return object;
 }

 JSObject* JSString::toObject(ExecState* exec, JSGlobalObject* globalObject) const
 {
     return StringObject::create(exec->vm(), globalObject, const_cast<JSString*>(this));
 }

 JSValue JSString::toThis(JSCell* cell, ExecState* exec, ECMAMode ecmaMode)
 {
     if (ecmaMode == StrictMode)
         return cell;
     return StringObject::create(exec->vm(), exec->lexicalGlobalObject(), jsCast<JSString*>(cell));
 }

 bool JSString::getStringPropertyDescriptor(ExecState* exec, PropertyName propertyName, PropertyDescriptor& descriptor)
 {
     if (propertyName == exec->propertyNames().length) {
         descriptor.setDescriptor(jsNumber(m_length), DontEnum | DontDelete | ReadOnly);
         return true;
     }

     Optional<uint32_t> index = parseIndex(propertyName);
     if (index && index.value() < m_length) {
         descriptor.setDescriptor(getIndex(exec, index.value()), DontDelete | ReadOnly);
         return true;
     }

     return false;
 }

 JSString* jsStringWithCacheSlowCase(VM& vm, StringImpl& stringImpl)
 {
     if (JSString* string = vm.stringCache.get(&stringImpl))
         return string;

     JSString* string = jsString(&vm, String(stringImpl));
     vm.lastCachedString.set(vm, string);
     return string;
 }

 } // namespace JSC
	/*
	* Copyright (C) 1999-2002 Harri Porten (porten@kde.org)
	* Copyright (C) 2001 Peter Kelly (pmk@post.com)
	* Copyright (C) 2004, 2007, 2008, 2015 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 "JSCInlines.h"
	#include "StringObject.h"
	#include "StringPrototype.h"
	#include "StrongInlines.h"

	namespace JSC {

	const ClassInfo JSString::s_info = { "string", 0, 0, CREATE_METHOD_TABLE(JSString) };

	Structure* JSString::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue proto)
	{
	return Structure::create(vm, globalObject, proto, TypeInfo(StringType, StructureFlags), info());
	}

	void JSRopeString::RopeBuilder::expand()
	{
	ASSERT(m_index == JSRopeString::s_maxInternalRopeLength);
	JSString* jsString = m_jsString;
	RELEASE_ASSERT(jsString);
	m_jsString = jsStringBuilder(&m_vm);
	m_index = 0;
	append(jsString);
	}

	void JSString::destroy(JSCell* cell)
	{
	JSString* thisObject = static_cast<JSString*>(cell);
	thisObject->JSString::~JSString();
	}

	void JSString::dumpToStream(const JSCell* cell, PrintStream& out)
	{
	const JSString* thisObject = jsCast<const JSString*>(cell);
	out.printf("<%p, %s, [%u], ", thisObject, thisObject->className(), thisObject->length());
	if (thisObject->isRope())
	out.printf("[rope]");
	else {
	WTF::StringImpl* ourImpl = thisObject->m_value.impl();
	if (ourImpl->is8Bit())
	out.printf("[8 %p]", ourImpl->characters8());
	else
	out.printf("[16 %p]", ourImpl->characters16());
	}
	out.printf(">");
	}

	void JSString::visitChildren(JSCell* cell, SlotVisitor& visitor)
	{
	JSString* thisObject = jsCast<JSString*>(cell);
	Base::visitChildren(thisObject, visitor);

	if (thisObject->isRope())
	static_cast<JSRopeString*>(thisObject)->visitFibers(visitor);
	else {
	StringImpl* impl = thisObject->m_value.impl();
	ASSERT(impl);
	visitor.reportExtraMemoryVisited(impl->costDuringGC());
	}
	}

	void JSRopeString::visitFibers(SlotVisitor& visitor)
	{
	if (isSubstring()) {
	visitor.append(&substringBase());
	return;
	}
	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
	visitor.append(&fiber(i));
	}

	static const unsigned maxLengthForOnStackResolve = 2048;

	void JSRopeString::resolveRopeInternal8(LChar* buffer) const
	{
	if (isSubstring()) {
	StringImpl::copyChars(
	buffer, substringBase()->m_value.characters8() + substringOffset(), m_length);
	return;
	}

	resolveRopeInternal8NoSubstring(buffer);
	}

	void JSRopeString::resolveRopeInternal8NoSubstring(LChar* buffer) const
	{
	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
	if (fiber(i)->isRope()) {
	resolveRopeSlowCase8(buffer);
	return;
	}
	}

	LChar* position = buffer;
	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
	const StringImpl& fiberString = *fiber(i)->m_value.impl();
	unsigned length = fiberString.length();
	StringImpl::copyChars(position, fiberString.characters8(), length);
	position += length;
	}
	ASSERT((buffer + m_length) == position);
	}

	void JSRopeString::resolveRopeInternal16(UChar* buffer) const
	{
	if (isSubstring()) {
	StringImpl::copyChars(
	buffer, substringBase()->m_value.characters16() + substringOffset(), m_length);
	return;
	}

	resolveRopeInternal16NoSubstring(buffer);
	}

	void JSRopeString::resolveRopeInternal16NoSubstring(UChar* buffer) const
	{
	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
	if (fiber(i)->isRope()) {
	resolveRopeSlowCase(buffer);
	return;
	}
	}

	UChar* position = buffer;
	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i) {
	const StringImpl& fiberString = *fiber(i)->m_value.impl();
	unsigned length = fiberString.length();
	if (fiberString.is8Bit())
	StringImpl::copyChars(position, fiberString.characters8(), length);
	else
	StringImpl::copyChars(position, fiberString.characters16(), length);
	position += length;
	}
	ASSERT((buffer + m_length) == position);
	}

	void JSRopeString::resolveRopeToAtomicString(ExecState* exec) const
	{
	if (m_length > maxLengthForOnStackResolve) {
	resolveRope(exec);
	m_value = AtomicString(m_value);
	setIs8Bit(m_value.impl()->is8Bit());
	return;
	}

	if (is8Bit()) {
	LChar buffer[maxLengthForOnStackResolve];
	resolveRopeInternal8(buffer);
	m_value = AtomicString(buffer, m_length);
	setIs8Bit(m_value.impl()->is8Bit());
	} else {
	UChar buffer[maxLengthForOnStackResolve];
	resolveRopeInternal16(buffer);
	m_value = AtomicString(buffer, m_length);
	setIs8Bit(m_value.impl()->is8Bit());
	}

	clearFibers();

	// If we resolved a string that didn't previously exist, notify the heap that we've grown.
	if (m_value.impl()->hasOneRef())
	Heap::heap(this)->reportExtraMemoryAllocated(m_value.impl()->cost());
	}

	void JSRopeString::clearFibers() const
	{
	for (size_t i = 0; i < s_maxInternalRopeLength; ++i)
	u[i].number = 0;
	}

	RefPtr<AtomicStringImpl> JSRopeString::resolveRopeToExistingAtomicString(ExecState* exec) const
	{
	if (m_length > maxLengthForOnStackResolve) {
	resolveRope(exec);
	if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(m_value.impl())) {
	m_value = *existingAtomicString;
	setIs8Bit(m_value.impl()->is8Bit());
	clearFibers();
	return existingAtomicString;
	}
	return nullptr;
	}

	if (is8Bit()) {
	LChar buffer[maxLengthForOnStackResolve];
	resolveRopeInternal8(buffer);
	if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(buffer, m_length)) {
	m_value = *existingAtomicString;
	setIs8Bit(m_value.impl()->is8Bit());
	clearFibers();
	return existingAtomicString;
	}
	} else {
	UChar buffer[maxLengthForOnStackResolve];
	resolveRopeInternal16(buffer);
	if (RefPtr<AtomicStringImpl> existingAtomicString = AtomicStringImpl::lookUp(buffer, m_length)) {
	m_value = *existingAtomicString;
	setIs8Bit(m_value.impl()->is8Bit());
	clearFibers();
	return existingAtomicString;
	}
	}

	return nullptr;
	}

	void JSRopeString::resolveRope(ExecState* exec) const
	{
	ASSERT(isRope());

	if (isSubstring()) {
	ASSERT(!substringBase()->isRope());
	m_value = substringBase()->m_value.substring(substringOffset(), m_length);
	substringBase().clear();
	return;
	}

	if (is8Bit()) {
	LChar* buffer;
	if (RefPtr<StringImpl> newImpl = StringImpl::tryCreateUninitialized(m_length, buffer)) {
	Heap::heap(this)->reportExtraMemoryAllocated(newImpl->cost());
	m_value = newImpl.release();
	} else {
	outOfMemory(exec);
	return;
	}
	resolveRopeInternal8NoSubstring(buffer);
	clearFibers();
	ASSERT(!isRope());
	return;
	}

	UChar* buffer;
	if (RefPtr<StringImpl> newImpl = StringImpl::tryCreateUninitialized(m_length, buffer)) {
	Heap::heap(this)->reportExtraMemoryAllocated(newImpl->cost());
	m_value = newImpl.release();
	} else {
	outOfMemory(exec);
	return;
	}

	resolveRopeInternal16NoSubstring(buffer);
	clearFibers();
	ASSERT(!isRope());
	}

	// Overview: These functions convert a JSString from holding a string in rope form
	// down to a simple String 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 JSRopeString::resolveRopeSlowCase8(LChar* buffer) const
	{
	LChar* position = buffer + m_length; // We will be working backwards over the rope.
	Vector<JSString*, 32, UnsafeVectorOverflow> workQueue; // Putting strings into a Vector is only OK because there are no GC points in this method.

	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
	workQueue.append(fiber(i).get());

	while (!workQueue.isEmpty()) {
	JSString* currentFiber = workQueue.last();
	workQueue.removeLast();

	const LChar* characters;

	if (currentFiber->isRope()) {
	JSRopeString* currentFiberAsRope = static_cast<JSRopeString*>(currentFiber);
	if (!currentFiberAsRope->isSubstring()) {
	for (size_t i = 0; i < s_maxInternalRopeLength && currentFiberAsRope->fiber(i); ++i)
	workQueue.append(currentFiberAsRope->fiber(i).get());
	continue;
	}
	ASSERT(!currentFiberAsRope->substringBase()->isRope());
	characters =
	currentFiberAsRope->substringBase()->m_value.characters8() +
	currentFiberAsRope->substringOffset();
	} else
	characters = currentFiber->m_value.characters8();

	unsigned length = currentFiber->length();
	position -= length;
	StringImpl::copyChars(position, characters, length);
	}

	ASSERT(buffer == position);
	}

	void JSRopeString::resolveRopeSlowCase(UChar* buffer) const
	{
	UChar* position = buffer + m_length; // We will be working backwards over the rope.
	Vector<JSString*, 32, UnsafeVectorOverflow> workQueue; // These strings are kept alive by the parent rope, so using a Vector is OK.

	for (size_t i = 0; i < s_maxInternalRopeLength && fiber(i); ++i)
	workQueue.append(fiber(i).get());

	while (!workQueue.isEmpty()) {
	JSString* currentFiber = workQueue.last();
	workQueue.removeLast();

	if (currentFiber->isRope()) {
	JSRopeString* currentFiberAsRope = static_cast<JSRopeString*>(currentFiber);
	if (currentFiberAsRope->isSubstring()) {
	ASSERT(!currentFiberAsRope->substringBase()->isRope());
	StringImpl* string = static_cast<StringImpl*>(
	currentFiberAsRope->substringBase()->m_value.impl());
	unsigned offset = currentFiberAsRope->substringOffset();
	unsigned length = currentFiberAsRope->length();
	position -= length;
	if (string->is8Bit())
	StringImpl::copyChars(position, string->characters8() + offset, length);
	else
	StringImpl::copyChars(position, string->characters16() + offset, length);
	continue;
	}
	for (size_t i = 0; i < s_maxInternalRopeLength && currentFiberAsRope->fiber(i); ++i)
	workQueue.append(currentFiberAsRope->fiber(i).get());
	continue;
	}

	StringImpl* string = static_cast<StringImpl*>(currentFiber->m_value.impl());
	unsigned length = string->length();
	position -= length;
	if (string->is8Bit())
	StringImpl::copyChars(position, string->characters8(), length);
	else
	StringImpl::copyChars(position, string->characters16(), length);
	}

	ASSERT(buffer == position);
	}

	void JSRopeString::outOfMemory(ExecState* exec) const
	{
	clearFibers();
	ASSERT(isRope());
	ASSERT(m_value.isNull());
	if (exec)
	throwOutOfMemoryError(exec);
	}

	JSValue JSString::toPrimitive(ExecState*, PreferredPrimitiveType) const
	{
	return const_cast<JSString*>(this);
	}

	bool JSString::getPrimitiveNumber(ExecState* exec, double& number, JSValue& result) const
	{
	result = this;
	number = jsToNumber(view(exec));
	return false;
	}

	double JSString::toNumber(ExecState* exec) const
	{
	return jsToNumber(view(exec));
	}

	inline StringObject* StringObject::create(VM& vm, JSGlobalObject* globalObject, JSString* string)
	{
	StringObject* object = new (NotNull, allocateCell<StringObject>(vm.heap)) StringObject(vm, globalObject->stringObjectStructure());
	object->finishCreation(vm, string);
	return object;
	}

	JSObject* JSString::toObject(ExecState* exec, JSGlobalObject* globalObject) const
	{
	return StringObject::create(exec->vm(), globalObject, const_cast<JSString*>(this));
	}

	JSValue JSString::toThis(JSCell* cell, ExecState* exec, ECMAMode ecmaMode)
	{
	if (ecmaMode == StrictMode)
	return cell;
	return StringObject::create(exec->vm(), exec->lexicalGlobalObject(), jsCast<JSString*>(cell));
	}

	bool JSString::getStringPropertyDescriptor(ExecState* exec, PropertyName propertyName, PropertyDescriptor& descriptor)
	{
	if (propertyName == exec->propertyNames().length) {
	descriptor.setDescriptor(jsNumber(m_length), DontEnum \| DontDelete \| ReadOnly);
	return true;
	}

	Optional<uint32_t> index = parseIndex(propertyName);
	if (index && index.value() < m_length) {
	descriptor.setDescriptor(getIndex(exec, index.value()), DontDelete \| ReadOnly);
	return true;
	}

	return false;
	}

	JSString* jsStringWithCacheSlowCase(VM& vm, StringImpl& stringImpl)
	{
	if (JSString* string = vm.stringCache.get(&stringImpl))
	return string;

	JSString* string = jsString(&vm, String(stringImpl));
	vm.lastCachedString.set(vm, string);
	return string;
	}

	} // namespace JSC