/*
 *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
 *  Copyright (C) 2003, 2007, 2008, 2009 Apple Inc. All rights reserved.
 *  Copyright (C) 2003 Peter Kelly (pmk@post.com)
 *  Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include "config.h"
#include "JSArray.h"

#include "ArrayPrototype.h"
#include "CachedCall.h"
#include "Error.h"
#include "Executable.h"
#include "PropertyNameArray.h"
#include <wtf/AVLTree.h>
#include <wtf/Assertions.h>
#include <wtf/OwnPtr.h>
#include <Operations.h>

using namespace std;
using namespace WTF;

namespace JSC {

ASSERT_CLASS_FITS_IN_CELL(JSArray);

// Overview of JSArray
//
// Properties of JSArray objects may be stored in one of three locations:
//   * The regular JSObject property map.
//   * A storage vector.
//   * A sparse map of array entries.
//
// Properties with non-numeric identifiers, with identifiers that are not representable
// as an unsigned integer, or where the value is greater than  MAX_ARRAY_INDEX
// (specifically, this is only one property - the value 0xFFFFFFFFU as an unsigned 32-bit
// integer) are not considered array indices and will be stored in the JSObject property map.
//
// All properties with a numeric identifer, representable as an unsigned integer i,
// where (i <= MAX_ARRAY_INDEX), are an array index and will be stored in either the
// storage vector or the sparse map.  An array index i will be handled in the following
// fashion:
//
//   * Where (i < MIN_SPARSE_ARRAY_INDEX) the value will be stored in the storage vector,
//     unless the array is in SparseMode in which case all properties go into the map.
//   * Where (MIN_SPARSE_ARRAY_INDEX <= i <= MAX_STORAGE_VECTOR_INDEX) the value will either
//     be stored in the storage vector or in the sparse array, depending on the density of
//     data that would be stored in the vector (a vector being used where at least
//     (1 / minDensityMultiplier) of the entries would be populated).
//   * Where (MAX_STORAGE_VECTOR_INDEX < i <= MAX_ARRAY_INDEX) the value will always be stored
//     in the sparse array.

// The definition of MAX_STORAGE_VECTOR_LENGTH is dependant on the definition storageSize
// function below - the MAX_STORAGE_VECTOR_LENGTH limit is defined such that the storage
// size calculation cannot overflow.  (sizeof(ArrayStorage) - sizeof(WriteBarrier<Unknown>)) +
// (vectorLength * sizeof(WriteBarrier<Unknown>)) must be <= 0xFFFFFFFFU (which is maximum value of size_t).
#define MAX_STORAGE_VECTOR_LENGTH static_cast<unsigned>((0xFFFFFFFFU - (sizeof(ArrayStorage) - sizeof(WriteBarrier<Unknown>))) / sizeof(WriteBarrier<Unknown>))

// These values have to be macros to be used in max() and min() without introducing
// a PIC branch in Mach-O binaries, see <rdar://problem/5971391>.
#define MIN_SPARSE_ARRAY_INDEX 10000U
#define MAX_STORAGE_VECTOR_INDEX (MAX_STORAGE_VECTOR_LENGTH - 1)
// 0xFFFFFFFF is a bit weird -- is not an array index even though it's an integer.
#define MAX_ARRAY_INDEX 0xFFFFFFFEU

// The value BASE_VECTOR_LEN is the maximum number of vector elements we'll allocate
// for an array that was created with a sepcified length (e.g. a = new Array(123))
#define BASE_VECTOR_LEN 4U
    
// The upper bound to the size we'll grow a zero length array when the first element
// is added.
#define FIRST_VECTOR_GROW 4U

// Our policy for when to use a vector and when to use a sparse map.
// For all array indices under MIN_SPARSE_ARRAY_INDEX, we always use a vector.
// When indices greater than MIN_SPARSE_ARRAY_INDEX are involved, we use a vector
// as long as it is 1/8 full. If more sparse than that, we use a map.
static const unsigned minDensityMultiplier = 8;

const ClassInfo JSArray::s_info = {"Array", &JSNonFinalObject::s_info, 0, 0, CREATE_METHOD_TABLE(JSArray)};

// We keep track of the size of the last array after it was grown.  We use this
// as a simple heuristic for as the value to grow the next array from size 0.
// This value is capped by the constant FIRST_VECTOR_GROW defined above.
static unsigned lastArraySize = 0;

static inline size_t storageSize(unsigned vectorLength)
{
    ASSERT(vectorLength <= MAX_STORAGE_VECTOR_LENGTH);

    // MAX_STORAGE_VECTOR_LENGTH is defined such that provided (vectorLength <= MAX_STORAGE_VECTOR_LENGTH)
    // - as asserted above - the following calculation cannot overflow.
    size_t size = (sizeof(ArrayStorage) - sizeof(WriteBarrier<Unknown>)) + (vectorLength * sizeof(WriteBarrier<Unknown>));
    // Assertion to detect integer overflow in previous calculation (should not be possible, provided that
    // MAX_STORAGE_VECTOR_LENGTH is correctly defined).
    ASSERT(((size - (sizeof(ArrayStorage) - sizeof(WriteBarrier<Unknown>))) / sizeof(WriteBarrier<Unknown>) == vectorLength) && (size >= (sizeof(ArrayStorage) - sizeof(WriteBarrier<Unknown>))));

    return size;
}

static inline bool isDenseEnoughForVector(unsigned length, unsigned numValues)
{
    return length <= MIN_SPARSE_ARRAY_INDEX || length / minDensityMultiplier <= numValues;
}

#if !CHECK_ARRAY_CONSISTENCY

inline void JSArray::checkConsistency(ConsistencyCheckType)
{
}

#endif

JSArray::JSArray(JSGlobalData& globalData, Structure* structure)
    : JSNonFinalObject(globalData, structure)
    , m_storage(0)
{
}

void JSArray::finishCreation(JSGlobalData& globalData, unsigned initialLength)
{
    Base::finishCreation(globalData);
    ASSERT(inherits(&s_info));

    unsigned initialVectorLength = BASE_VECTOR_LEN;
    unsigned initialStorageSize = storageSize(initialVectorLength);

    m_storage = static_cast<ArrayStorage*>(fastMalloc(initialStorageSize));
    m_storage->m_allocBase = m_storage;
    m_storage->m_length = initialLength;
    m_indexBias = 0;
    m_vectorLength = initialVectorLength;
    m_storage->m_sparseValueMap = 0;
    m_storage->subclassData = 0;
    m_storage->m_numValuesInVector = 0;
#if CHECK_ARRAY_CONSISTENCY
    m_storage->m_inCompactInitialization = false;
#endif

    WriteBarrier<Unknown>* vector = m_storage->m_vector;
    for (size_t i = 0; i < initialVectorLength; ++i)
        vector[i].clear();

    checkConsistency();
    
    Heap::heap(this)->reportExtraMemoryCost(initialStorageSize);
}

JSArray* JSArray::tryFinishCreationUninitialized(JSGlobalData& globalData, unsigned initialLength)
{
    Base::finishCreation(globalData);
    ASSERT(inherits(&s_info));

    // Check for lengths larger than we can handle with a vector.
    if (initialLength > MAX_STORAGE_VECTOR_LENGTH)
        return 0;

    unsigned initialVectorLength = max(initialLength, BASE_VECTOR_LEN);
    unsigned initialStorageSize = storageSize(initialVectorLength);

    m_storage = static_cast<ArrayStorage*>(fastMalloc(initialStorageSize));
    m_storage->m_allocBase = m_storage;
    m_storage->m_length = 0;
    m_indexBias = 0;
    m_vectorLength = initialVectorLength;
    m_storage->m_sparseValueMap = 0;
    m_storage->subclassData = 0;
    m_storage->m_numValuesInVector = initialLength;
#if CHECK_ARRAY_CONSISTENCY
    m_storage->m_inCompactInitialization = true;
#endif

    WriteBarrier<Unknown>* vector = m_storage->m_vector;
    for (size_t i = initialLength; i < initialVectorLength; ++i)
        vector[i].clear();

    Heap::heap(this)->reportExtraMemoryCost(initialStorageSize);
    return this;
}

JSArray::~JSArray()
{
    ASSERT(jsCast<JSArray*>(this));

    // If we are unable to allocate memory for m_storage then this may be null.
    if (!m_storage)
        return;

    checkConsistency(DestructorConsistencyCheck);
    delete m_storage->m_sparseValueMap;
    fastFree(m_storage->m_allocBase);
}

void JSArray::destroy(JSCell* cell)
{
    jsCast<JSArray*>(cell)->JSArray::~JSArray();
}

SparseArrayValueMap::iterator SparseArrayValueMap::find(unsigned i)
{
    return m_map.find(i);
}

inline void SparseArrayValueMap::put(JSGlobalData& globalData, JSArray* array, unsigned i, JSValue value)
{
    SparseArrayEntry temp;
    pair<Map::iterator, bool> result = m_map.add(i, temp);
    result.first->second.set(globalData, array, value);
    if (!result.second) // pre-existing entry
        return;

    size_t capacity = m_map.capacity();
    if (capacity != m_reportedCapacity) {
        Heap::heap(array)->reportExtraMemoryCost((capacity - m_reportedCapacity) * (sizeof(unsigned) + sizeof(WriteBarrier<Unknown>)));
        m_reportedCapacity = capacity;
    }
}

inline void SparseArrayValueMap::visitChildren(SlotVisitor& visitor)
{
    iterator end = m_map.end();
    for (iterator it = m_map.begin(); it != end; ++it)
        visitor.append(&it->second);
}

bool JSArray::getOwnPropertySlotByIndex(JSCell* cell, ExecState* exec, unsigned i, PropertySlot& slot)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    ArrayStorage* storage = thisObject->m_storage;
    
    if (i >= storage->m_length) {
        if (i > MAX_ARRAY_INDEX)
            return thisObject->methodTable()->getOwnPropertySlot(thisObject, exec, Identifier::from(exec, i), slot);
        return false;
    }

    if (i < thisObject->m_vectorLength) {
        JSValue value = storage->m_vector[i].get();
        if (value) {
            slot.setValue(value);
            return true;
        }
    } else if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
        SparseArrayValueMap::iterator it = map->find(i);
        if (it != map->notFound()) {
            slot.setValue(it->second.get());
            return true;
        }
    }

    return JSObject::getOwnPropertySlot(thisObject, exec, Identifier::from(exec, i), slot);
}

bool JSArray::getOwnPropertySlot(JSCell* cell, ExecState* exec, const Identifier& propertyName, PropertySlot& slot)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    if (propertyName == exec->propertyNames().length) {
        slot.setValue(jsNumber(thisObject->length()));
        return true;
    }

    bool isArrayIndex;
    unsigned i = propertyName.toArrayIndex(isArrayIndex);
    if (isArrayIndex)
        return JSArray::getOwnPropertySlotByIndex(thisObject, exec, i, slot);

    return JSObject::getOwnPropertySlot(thisObject, exec, propertyName, slot);
}

bool JSArray::getOwnPropertyDescriptor(JSObject* object, ExecState* exec, const Identifier& propertyName, PropertyDescriptor& descriptor)
{
    JSArray* thisObject = jsCast<JSArray*>(object);
    if (propertyName == exec->propertyNames().length) {
        descriptor.setDescriptor(jsNumber(thisObject->length()), DontDelete | DontEnum);
        return true;
    }

    ArrayStorage* storage = thisObject->m_storage;
    
    bool isArrayIndex;
    unsigned i = propertyName.toArrayIndex(isArrayIndex);
    if (isArrayIndex) {
        if (i >= storage->m_length)
            return false;
        if (i < thisObject->m_vectorLength) {
            WriteBarrier<Unknown>& value = storage->m_vector[i];
            if (value) {
                descriptor.setDescriptor(value.get(), 0);
                return true;
            }
        } else if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
            SparseArrayValueMap::iterator it = map->find(i);
            if (it != map->notFound()) {
                descriptor.setDescriptor(it->second.get(), 0);
                return true;
            }
        }
    }
    return JSObject::getOwnPropertyDescriptor(thisObject, exec, propertyName, descriptor);
}

// ECMA 15.4.5.1
void JSArray::put(JSCell* cell, ExecState* exec, const Identifier& propertyName, JSValue value, PutPropertySlot& slot)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    bool isArrayIndex;
    unsigned i = propertyName.toArrayIndex(isArrayIndex);
    if (isArrayIndex) {
        putByIndex(thisObject, exec, i, value);
        return;
    }

    if (propertyName == exec->propertyNames().length) {
        unsigned newLength = value.toUInt32(exec);
        if (value.toNumber(exec) != static_cast<double>(newLength)) {
            throwError(exec, createRangeError(exec, "Invalid array length"));
            return;
        }
        thisObject->setLength(newLength);
        return;
    }

    JSObject::put(thisObject, exec, propertyName, value, slot);
}

void JSArray::putByIndex(JSCell* cell, ExecState* exec, unsigned i, JSValue value)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    thisObject->checkConsistency();

    ArrayStorage* storage = thisObject->m_storage;

    // Fast case - store to the vector.
    if (i < thisObject->m_vectorLength) {
        WriteBarrier<Unknown>& valueSlot = storage->m_vector[i];
        unsigned length = storage->m_length;

        // Update m_length & m_numValuesInVector as necessary.
        if (i >= length) {
            length = i + 1;
            storage->m_length = length;
            ++storage->m_numValuesInVector;
        } else if (!valueSlot)
            ++storage->m_numValuesInVector;

        valueSlot.set(exec->globalData(), thisObject, value);
        thisObject->checkConsistency();
        return;
    }

    // Handle 2^32-1 - this is not an array index (see ES5.1 15.4), and is treated as a regular property.
    if (UNLIKELY(i > MAX_ARRAY_INDEX)) {
        PutPropertySlot slot;
        thisObject->methodTable()->put(thisObject, exec, Identifier::from(exec, i), value, slot);
        return;
    }

    // For all other cases, call putByIndexBeyondVectorLength.
    thisObject->putByIndexBeyondVectorLength(exec->globalData(), i, value);
    thisObject->checkConsistency();
}

NEVER_INLINE void JSArray::putByIndexBeyondVectorLength(JSGlobalData& globalData, unsigned i, JSValue value)
{
    // i should be a valid array index that is outside of the current vector.
    ASSERT(i >= m_vectorLength);
    ASSERT(i <= MAX_ARRAY_INDEX);

    ArrayStorage* storage = m_storage;
    SparseArrayValueMap* map = storage->m_sparseValueMap;

    // Update m_length if necessary.
    unsigned length = storage->m_length;
    if (i >= length) {
        length = i + 1;
        storage->m_length = length;
    }

    // First, handle cases where we don't currently have a sparse map.
    if (LIKELY(!map)) {
        // Check that it is sensible to still be using a vector, and then try to grow the vector.
        if (LIKELY((isDenseEnoughForVector(i, storage->m_numValuesInVector)) && increaseVectorLength(i + 1))) {
            // success! - reread m_storage since it has likely been reallocated, and store to the vector.
            storage = m_storage;
            storage->m_vector[i].set(globalData, this, value);
            ++storage->m_numValuesInVector;
            return;
        }
        // We don't want to, or can't use a vector to hold this property - allocate a sparse map & add the value.
        map = new SparseArrayValueMap;
        storage->m_sparseValueMap = map;
        map->put(globalData, this, i, value);
        return;
    }

    // We are currently using a map - check whether we still want to be doing so.
    // We will continue  to use a sparse map if SparseMode is set, a vector would be too sparse, or if allocation fails.
    unsigned numValuesInArray = storage->m_numValuesInVector + map->size();
    if (map->sparseMode() || !isDenseEnoughForVector(length, numValuesInArray) || !increaseVectorLength(length)) {
        map->put(globalData, this, i, value);
        return;
    }

    // Reread m_storage afterincreaseVectorLength, update m_numValuesInVector.
    storage = m_storage;
    storage->m_numValuesInVector = numValuesInArray;

    // Copy all values from the map into the vector, and delete the map.
    WriteBarrier<Unknown>* vector = storage->m_vector;
    SparseArrayValueMap::const_iterator end = map->end();
    for (SparseArrayValueMap::const_iterator it = map->begin(); it != end; ++it)
        vector[it->first].set(globalData, this, it->second.get());
    delete map;
    storage->m_sparseValueMap = 0;

    // Store the new property into the vector.
    WriteBarrier<Unknown>& valueSlot = vector[i];
    if (!valueSlot)
        ++storage->m_numValuesInVector;
    valueSlot.set(globalData, this, value);
}

bool JSArray::deleteProperty(JSCell* cell, ExecState* exec, const Identifier& propertyName)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    bool isArrayIndex;
    unsigned i = propertyName.toArrayIndex(isArrayIndex);
    if (isArrayIndex)
        return thisObject->methodTable()->deletePropertyByIndex(thisObject, exec, i);

    if (propertyName == exec->propertyNames().length)
        return false;

    return JSObject::deleteProperty(thisObject, exec, propertyName);
}

bool JSArray::deletePropertyByIndex(JSCell* cell, ExecState* exec, unsigned i)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    thisObject->checkConsistency();

    ArrayStorage* storage = thisObject->m_storage;
    
    if (i < thisObject->m_vectorLength) {
        WriteBarrier<Unknown>& valueSlot = storage->m_vector[i];
        if (!valueSlot) {
            thisObject->checkConsistency();
            return false;
        }
        valueSlot.clear();
        --storage->m_numValuesInVector;
        thisObject->checkConsistency();
        return true;
    }

    if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
        SparseArrayValueMap::iterator it = map->find(i);
        if (it != map->notFound()) {
            map->remove(it);
            thisObject->checkConsistency();
            return true;
        }
    }

    thisObject->checkConsistency();

    if (i > MAX_ARRAY_INDEX)
        return thisObject->methodTable()->deleteProperty(thisObject, exec, Identifier::from(exec, i));

    return false;
}

void JSArray::getOwnPropertyNames(JSObject* object, ExecState* exec, PropertyNameArray& propertyNames, EnumerationMode mode)
{
    JSArray* thisObject = jsCast<JSArray*>(object);
    // FIXME: Filling PropertyNameArray with an identifier for every integer
    // is incredibly inefficient for large arrays. We need a different approach,
    // which almost certainly means a different structure for PropertyNameArray.

    ArrayStorage* storage = thisObject->m_storage;
    
    unsigned usedVectorLength = min(storage->m_length, thisObject->m_vectorLength);
    for (unsigned i = 0; i < usedVectorLength; ++i) {
        if (storage->m_vector[i])
            propertyNames.add(Identifier::from(exec, i));
    }

    if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
        SparseArrayValueMap::const_iterator end = map->end();
        for (SparseArrayValueMap::const_iterator it = map->begin(); it != end; ++it)
            propertyNames.add(Identifier::from(exec, it->first));
    }

    if (mode == IncludeDontEnumProperties)
        propertyNames.add(exec->propertyNames().length);

    JSObject::getOwnPropertyNames(thisObject, exec, propertyNames, mode);
}

ALWAYS_INLINE unsigned JSArray::getNewVectorLength(unsigned desiredLength)
{
    ASSERT(desiredLength <= MAX_STORAGE_VECTOR_LENGTH);

    unsigned increasedLength;
    unsigned maxInitLength = min(m_storage->m_length, 100000U);

    if (desiredLength < maxInitLength)
        increasedLength = maxInitLength;
    else if (!m_vectorLength)
        increasedLength = max(desiredLength, lastArraySize);
    else {
        // Mathematically equivalent to:
        //   increasedLength = (newLength * 3 + 1) / 2;
        // or:
        //   increasedLength = (unsigned)ceil(newLength * 1.5));
        // This form is not prone to internal overflow.
        increasedLength = desiredLength + (desiredLength >> 1) + (desiredLength & 1);
    }

    ASSERT(increasedLength >= desiredLength);

    lastArraySize = min(increasedLength, FIRST_VECTOR_GROW);

    return min(increasedLength, MAX_STORAGE_VECTOR_LENGTH);
}

bool JSArray::increaseVectorLength(unsigned newLength)
{
    // This function leaves the array in an internally inconsistent state, because it does not move any values from sparse value map
    // to the vector. Callers have to account for that, because they can do it more efficiently.
    if (newLength > MAX_STORAGE_VECTOR_LENGTH)
        return false;

    ArrayStorage* storage = m_storage;

    unsigned vectorLength = m_vectorLength;
    ASSERT(newLength > vectorLength);
    unsigned newVectorLength = getNewVectorLength(newLength);
    void* baseStorage = storage->m_allocBase;

    // Fast case - there is no precapacity. In these cases a realloc makes sense.
    if (LIKELY(!m_indexBias)) {
        if (!tryFastRealloc(baseStorage, storageSize(newVectorLength)).getValue(baseStorage))
            return false;

        storage = m_storage = reinterpret_cast_ptr<ArrayStorage*>(baseStorage);
        m_storage->m_allocBase = baseStorage;

        WriteBarrier<Unknown>* vector = storage->m_vector;
        for (unsigned i = vectorLength; i < newVectorLength; ++i)
            vector[i].clear();

        m_vectorLength = newVectorLength;
        
        Heap::heap(this)->reportExtraMemoryCost(storageSize(newVectorLength) - storageSize(vectorLength));
        return true;
    }

    // Remove some, but not all of the precapacity. Atomic decay, & capped to not overflow array length.
    unsigned newIndexBias = min(m_indexBias >> 1, MAX_STORAGE_VECTOR_LENGTH - newVectorLength);
    // Calculate new stoarge capcity, allowing room for the pre-capacity.
    unsigned newStorageCapacity = newVectorLength + newIndexBias;
    void* newAllocBase;
    if (!tryFastMalloc(storageSize(newStorageCapacity)).getValue(newAllocBase))
        return false;
    // The sum of m_vectorLength and m_indexBias will never exceed MAX_STORAGE_VECTOR_LENGTH.
    ASSERT(m_vectorLength <= MAX_STORAGE_VECTOR_LENGTH && (MAX_STORAGE_VECTOR_LENGTH - m_vectorLength) >= m_indexBias);
    unsigned currentCapacity = m_vectorLength + m_indexBias;
    // Currently there is no way to report to the heap that the extra capacity is shrinking!
    if (newStorageCapacity > currentCapacity)
        Heap::heap(this)->reportExtraMemoryCost((newStorageCapacity - currentCapacity) * sizeof(WriteBarrier<Unknown>));

    m_vectorLength = newVectorLength;
    m_indexBias = newIndexBias;
    m_storage = reinterpret_cast_ptr<ArrayStorage*>(reinterpret_cast<WriteBarrier<Unknown>*>(newAllocBase) + m_indexBias);

    // Copy the ArrayStorage header & current contents of the vector, clear the new post-capacity.
    memmove(m_storage, storage, storageSize(vectorLength));
    for (unsigned i = vectorLength; i < m_vectorLength; ++i)
        m_storage->m_vector[i].clear();

    // Free the old allocation, update m_allocBase.
    fastFree(m_storage->m_allocBase);
    m_storage->m_allocBase = newAllocBase;

    return true;
}

// This method makes room in the vector, but leaves the new space uncleared.
bool JSArray::unshiftCountSlowCase(unsigned count)
{
    // If not, we should have handled this on the fast path.
    ASSERT(count > m_indexBias);

    ArrayStorage* storage = m_storage;

    // Step 1:
    // Gather 4 key metrics:
    //  * usedVectorLength - how many entries are currently in the vector (conservative estimate - fewer may be in use in sparse vectors).
    //  * requiredVectorLength - how many entries are will there be in the vector, after allocating space for 'count' more.
    //  * currentCapacity - what is the current size of the vector, including any pre-capacity.
    //  * desiredCapacity - how large should we like to grow the vector to - based on 2x requiredVectorLength.

    unsigned length = storage->m_length;
    unsigned usedVectorLength = min(m_vectorLength, length);
    ASSERT(usedVectorLength <= MAX_STORAGE_VECTOR_LENGTH);
    // Check that required vector length is possible, in an overflow-safe fashion.
    if (count > MAX_STORAGE_VECTOR_LENGTH - usedVectorLength)
        return false;
    unsigned requiredVectorLength = usedVectorLength + count;
    ASSERT(requiredVectorLength <= MAX_STORAGE_VECTOR_LENGTH);
    // The sum of m_vectorLength and m_indexBias will never exceed MAX_STORAGE_VECTOR_LENGTH.
    ASSERT(m_vectorLength <= MAX_STORAGE_VECTOR_LENGTH && (MAX_STORAGE_VECTOR_LENGTH - m_vectorLength) >= m_indexBias);
    unsigned currentCapacity = m_vectorLength + m_indexBias;
    // The calculation of desiredCapacity won't overflow, due to the range of MAX_STORAGE_VECTOR_LENGTH.
    unsigned desiredCapacity = min(MAX_STORAGE_VECTOR_LENGTH, max(BASE_VECTOR_LEN, requiredVectorLength) << 1);

    // Step 2:
    // We're either going to choose to allocate a new ArrayStorage, or we're going to reuse the existing on.

    void* newAllocBase;
    unsigned newStorageCapacity;
    // If the current storage array is sufficiently large (but not too large!) then just keep using it.
    if (currentCapacity > desiredCapacity && isDenseEnoughForVector(currentCapacity, requiredVectorLength)) {
        newAllocBase = storage->m_allocBase;
        newStorageCapacity = currentCapacity;
    } else {
        if (!tryFastMalloc(storageSize(desiredCapacity)).getValue(newAllocBase))
            return false;
        newStorageCapacity = desiredCapacity;
        // Currently there is no way to report to the heap that the extra capacity is shrinking!
        if (desiredCapacity > currentCapacity)
            Heap::heap(this)->reportExtraMemoryCost((desiredCapacity - currentCapacity) * sizeof(WriteBarrier<Unknown>));
    }

    // Step 3:
    // Work out where we're going to move things to.

    // Determine how much of the vector to use as pre-capacity, and how much as post-capacity.
    // If the vector had no free post-capacity (length >= m_vectorLength), don't give it any.
    // If it did, we calculate the amount that will remain based on an atomic decay - leave the
    // vector with half the post-capacity it had previously.
    unsigned postCapacity = 0;
    if (length < m_vectorLength) {
        // Atomic decay, + the post-capacity cannot be greater than what is available.
        postCapacity = min((m_vectorLength - length) >> 1, newStorageCapacity - requiredVectorLength);
        // If we're moving contents within the same allocation, the post-capacity is being reduced.
        ASSERT(newAllocBase != storage->m_allocBase || postCapacity < m_vectorLength - length);
    }

    m_vectorLength = requiredVectorLength + postCapacity;
    m_indexBias = newStorageCapacity - m_vectorLength;
    m_storage = reinterpret_cast_ptr<ArrayStorage*>(reinterpret_cast<WriteBarrier<Unknown>*>(newAllocBase) + m_indexBias);

    // Step 4:
    // Copy array data / header into their new locations, clear post-capacity & free any old allocation.

    // If this is being moved within the existing buffer of memory, we are always shifting data
    // to the right (since count > m_indexBias). As such this memmove cannot trample the header.
    memmove(m_storage->m_vector + count, storage->m_vector, sizeof(WriteBarrier<Unknown>) * usedVectorLength);
    memmove(m_storage, storage, storageSize(0));

    // Are we copying into a new allocation?
    if (newAllocBase != m_storage->m_allocBase) {
        // Free the old allocation, update m_allocBase.
        fastFree(m_storage->m_allocBase);
        m_storage->m_allocBase = newAllocBase;

        // We need to clear any entries in the vector beyond length. We only need to
        // do this if this was a new allocation, because if we're using an existing
        // allocation the post-capacity will already be cleared, and in an existing
        // allocation we can only beshrinking the amount of post capacity.
        for (unsigned i = requiredVectorLength; i < m_vectorLength; ++i)
            m_storage->m_vector[i].clear();
    }

    return true;
}

void JSArray::setLength(unsigned newLength)
{
    checkConsistency();

    ArrayStorage* storage = m_storage;
    
    unsigned length = storage->m_length;

    if (newLength < length) {
        unsigned usedVectorLength = min(length, m_vectorLength);
        for (unsigned i = newLength; i < usedVectorLength; ++i) {
            WriteBarrier<Unknown>& valueSlot = storage->m_vector[i];
            bool hadValue = valueSlot;
            valueSlot.clear();
            storage->m_numValuesInVector -= hadValue;
        }

        if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
            SparseArrayValueMap copy = *map;
            SparseArrayValueMap::const_iterator end = copy.end();
            for (SparseArrayValueMap::const_iterator it = copy.begin(); it != end; ++it) {
                if (it->first >= newLength)
                    map->remove(it->first);
            }
            if (map->isEmpty() && !map->sparseMode()) {
                delete map;
                storage->m_sparseValueMap = 0;
            }
        }
    }

    storage->m_length = newLength;

    checkConsistency();
}

JSValue JSArray::pop()
{
    checkConsistency();

    ArrayStorage* storage = m_storage;
    
    unsigned length = storage->m_length;
    if (!length)
        return jsUndefined();

    --length;

    JSValue result;

    if (length < m_vectorLength) {
        WriteBarrier<Unknown>& valueSlot = storage->m_vector[length];
        if (valueSlot) {
            --storage->m_numValuesInVector;
            result = valueSlot.get();
            valueSlot.clear();
        } else
            result = jsUndefined();
    } else {
        result = jsUndefined();
        if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
            SparseArrayValueMap::iterator it = map->find(length);
            if (it != map->end()) {
                result = it->second.get();
                map->remove(it);
                if (map->isEmpty() && !map->sparseMode()) {
                    delete map;
                    storage->m_sparseValueMap = 0;
                }
            }
        }
    }

    storage->m_length = length;

    checkConsistency();

    return result;
}

// Push & putIndex are almost identical, with two small differences.
//  - we always are writing beyond the current array bounds, so it is always necessary to update m_length & m_numValuesInVector.
//  - pushing to an array of length 2^32-1 stores the property, but throws a range error.
void JSArray::push(ExecState* exec, JSValue value)
{
    checkConsistency();
    ArrayStorage* storage = m_storage;

    // Fast case - push within vector, always update m_length & m_numValuesInVector.
    unsigned length = storage->m_length;
    if (length < m_vectorLength) {
        storage->m_vector[length].set(exec->globalData(), this, value);
        storage->m_length = length + 1;
        ++storage->m_numValuesInVector;
        checkConsistency();
        return;
    }

    // Pushing to an array of length 2^32-1 stores the property, but throws a range error.
    if (UNLIKELY(storage->m_length == 0xFFFFFFFFu)) {
        methodTable()->putByIndex(this, exec, storage->m_length, value);
        // Per ES5.1 15.4.4.7 step 6 & 15.4.5.1 step 3.d.
        throwError(exec, createRangeError(exec, "Invalid array length"));
        return;
    }

    // Handled the same as putIndex.
    putByIndexBeyondVectorLength(exec->globalData(), storage->m_length, value);
    checkConsistency();
}

void JSArray::shiftCount(ExecState* exec, unsigned count)
{
    ASSERT(count > 0);
    
    ArrayStorage* storage = m_storage;
    
    unsigned oldLength = storage->m_length;
    
    if (!oldLength)
        return;
    
    if (oldLength != storage->m_numValuesInVector) {
        // If m_length and m_numValuesInVector aren't the same, we have a sparse vector
        // which means we need to go through each entry looking for the the "empty"
        // slots and then fill them with possible properties.  See ECMA spec.
        // 15.4.4.9 steps 11 through 13.
        for (unsigned i = count; i < oldLength; ++i) {
            if ((i >= m_vectorLength) || (!m_storage->m_vector[i])) {
                PropertySlot slot(this);
                JSValue p = prototype();
                if ((!p.isNull()) && (asObject(p)->getPropertySlot(exec, i, slot)))
                    methodTable()->putByIndex(this, exec, i, slot.getValue(exec, i));
            }
        }

        storage = m_storage; // The put() above could have grown the vector and realloc'ed storage.

        // Need to decrement numValuesInvector based on number of real entries
        for (unsigned i = 0; i < (unsigned)count; ++i)
            if ((i < m_vectorLength) && (storage->m_vector[i]))
                --storage->m_numValuesInVector;
    } else
        storage->m_numValuesInVector -= count;
    
    storage->m_length -= count;
    
    if (m_vectorLength) {
        count = min(m_vectorLength, (unsigned)count);
        
        m_vectorLength -= count;
        
        if (m_vectorLength) {
            char* newBaseStorage = reinterpret_cast<char*>(storage) + count * sizeof(WriteBarrier<Unknown>);
            memmove(newBaseStorage, storage, storageSize(0));
            m_storage = reinterpret_cast_ptr<ArrayStorage*>(newBaseStorage);

            m_indexBias += count;
        }
    }
}
    
void JSArray::unshiftCount(ExecState* exec, unsigned count)
{
    ArrayStorage* storage = m_storage;
    unsigned length = storage->m_length;

    if (length != storage->m_numValuesInVector) {
        // If m_length and m_numValuesInVector aren't the same, we have a sparse vector
        // which means we need to go through each entry looking for the the "empty"
        // slots and then fill them with possible properties.  See ECMA spec.
        // 15.4.4.13 steps 8 through 10.
        for (unsigned i = 0; i < length; ++i) {
            if ((i >= m_vectorLength) || (!m_storage->m_vector[i])) {
                PropertySlot slot(this);
                JSValue p = prototype();
                if ((!p.isNull()) && (asObject(p)->getPropertySlot(exec, i, slot)))
                    methodTable()->putByIndex(this, exec, i, slot.getValue(exec, i));
            }
        }
    }
    
    storage = m_storage; // The put() above could have grown the vector and realloc'ed storage.
    
    if (m_indexBias >= count) {
        m_indexBias -= count;
        char* newBaseStorage = reinterpret_cast<char*>(storage) - count * sizeof(WriteBarrier<Unknown>);
        memmove(newBaseStorage, storage, storageSize(0));
        m_storage = reinterpret_cast_ptr<ArrayStorage*>(newBaseStorage);
        m_vectorLength += count;
    } else if (!unshiftCountSlowCase(count)) {
        throwOutOfMemoryError(exec);
        return;
    }

    WriteBarrier<Unknown>* vector = m_storage->m_vector;
    for (unsigned i = 0; i < count; i++)
        vector[i].clear();
}

void JSArray::visitChildren(JSCell* cell, SlotVisitor& visitor)
{
    JSArray* thisObject = jsCast<JSArray*>(cell);
    ASSERT_GC_OBJECT_INHERITS(thisObject, &s_info);
    COMPILE_ASSERT(StructureFlags & OverridesVisitChildren, OverridesVisitChildrenWithoutSettingFlag);
    ASSERT(thisObject->structure()->typeInfo().overridesVisitChildren());

    JSNonFinalObject::visitChildren(thisObject, visitor);
    
    ArrayStorage* storage = thisObject->m_storage;

    unsigned usedVectorLength = std::min(storage->m_length, thisObject->m_vectorLength);
    visitor.appendValues(storage->m_vector, usedVectorLength);

    if (SparseArrayValueMap* map = storage->m_sparseValueMap)
        map->visitChildren(visitor);
}

static int compareNumbersForQSort(const void* a, const void* b)
{
    double da = static_cast<const JSValue*>(a)->asNumber();
    double db = static_cast<const JSValue*>(b)->asNumber();
    return (da > db) - (da < db);
}

static int compareByStringPairForQSort(const void* a, const void* b)
{
    const ValueStringPair* va = static_cast<const ValueStringPair*>(a);
    const ValueStringPair* vb = static_cast<const ValueStringPair*>(b);
    return codePointCompare(va->second, vb->second);
}

void JSArray::sortNumeric(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
{
    ASSERT(!inSparseMode());

    ArrayStorage* storage = m_storage;

    unsigned lengthNotIncludingUndefined = compactForSorting();
    if (storage->m_sparseValueMap) {
        throwOutOfMemoryError(exec);
        return;
    }

    if (!lengthNotIncludingUndefined)
        return;
        
    bool allValuesAreNumbers = true;
    size_t size = storage->m_numValuesInVector;
    for (size_t i = 0; i < size; ++i) {
        if (!storage->m_vector[i].isNumber()) {
            allValuesAreNumbers = false;
            break;
        }
    }

    if (!allValuesAreNumbers)
        return sort(exec, compareFunction, callType, callData);

    // For numeric comparison, which is fast, qsort is faster than mergesort. We
    // also don't require mergesort's stability, since there's no user visible
    // side-effect from swapping the order of equal primitive values.
    qsort(storage->m_vector, size, sizeof(WriteBarrier<Unknown>), compareNumbersForQSort);

    checkConsistency(SortConsistencyCheck);
}

void JSArray::sort(ExecState* exec)
{
    ASSERT(!inSparseMode());

    ArrayStorage* storage = m_storage;

    unsigned lengthNotIncludingUndefined = compactForSorting();
    if (storage->m_sparseValueMap) {
        throwOutOfMemoryError(exec);
        return;
    }

    if (!lengthNotIncludingUndefined)
        return;

    // Converting JavaScript values to strings can be expensive, so we do it once up front and sort based on that.
    // This is a considerable improvement over doing it twice per comparison, though it requires a large temporary
    // buffer. Besides, this protects us from crashing if some objects have custom toString methods that return
    // random or otherwise changing results, effectively making compare function inconsistent.

    Vector<ValueStringPair> values(lengthNotIncludingUndefined);
    if (!values.begin()) {
        throwOutOfMemoryError(exec);
        return;
    }
    
    Heap::heap(this)->pushTempSortVector(&values);

    for (size_t i = 0; i < lengthNotIncludingUndefined; i++) {
        JSValue value = storage->m_vector[i].get();
        ASSERT(!value.isUndefined());
        values[i].first = value;
    }

    // FIXME: The following loop continues to call toString on subsequent values even after
    // a toString call raises an exception.

    for (size_t i = 0; i < lengthNotIncludingUndefined; i++)
        values[i].second = values[i].first.toString(exec);

    if (exec->hadException()) {
        Heap::heap(this)->popTempSortVector(&values);
        return;
    }

    // FIXME: Since we sort by string value, a fast algorithm might be to use a radix sort. That would be O(N) rather
    // than O(N log N).

#if HAVE(MERGESORT)
    mergesort(values.begin(), values.size(), sizeof(ValueStringPair), compareByStringPairForQSort);
#else
    // FIXME: The qsort library function is likely to not be a stable sort.
    // ECMAScript-262 does not specify a stable sort, but in practice, browsers perform a stable sort.
    qsort(values.begin(), values.size(), sizeof(ValueStringPair), compareByStringPairForQSort);
#endif

    // If the toString function changed the length of the array or vector storage,
    // increase the length to handle the orignal number of actual values.
    if (m_vectorLength < lengthNotIncludingUndefined)
        increaseVectorLength(lengthNotIncludingUndefined);
    if (storage->m_length < lengthNotIncludingUndefined)
        storage->m_length = lengthNotIncludingUndefined;

    JSGlobalData& globalData = exec->globalData();
    for (size_t i = 0; i < lengthNotIncludingUndefined; i++)
        storage->m_vector[i].set(globalData, this, values[i].first);

    Heap::heap(this)->popTempSortVector(&values);
    
    checkConsistency(SortConsistencyCheck);
}

struct AVLTreeNodeForArrayCompare {
    JSValue value;

    // Child pointers.  The high bit of gt is robbed and used as the
    // balance factor sign.  The high bit of lt is robbed and used as
    // the magnitude of the balance factor.
    int32_t gt;
    int32_t lt;
};

struct AVLTreeAbstractorForArrayCompare {
    typedef int32_t handle; // Handle is an index into m_nodes vector.
    typedef JSValue key;
    typedef int32_t size;

    Vector<AVLTreeNodeForArrayCompare> m_nodes;
    ExecState* m_exec;
    JSValue m_compareFunction;
    CallType m_compareCallType;
    const CallData* m_compareCallData;
    OwnPtr<CachedCall> m_cachedCall;

    handle get_less(handle h) { return m_nodes[h].lt & 0x7FFFFFFF; }
    void set_less(handle h, handle lh) { m_nodes[h].lt &= 0x80000000; m_nodes[h].lt |= lh; }
    handle get_greater(handle h) { return m_nodes[h].gt & 0x7FFFFFFF; }
    void set_greater(handle h, handle gh) { m_nodes[h].gt &= 0x80000000; m_nodes[h].gt |= gh; }

    int get_balance_factor(handle h)
    {
        if (m_nodes[h].gt & 0x80000000)
            return -1;
        return static_cast<unsigned>(m_nodes[h].lt) >> 31;
    }

    void set_balance_factor(handle h, int bf)
    {
        if (bf == 0) {
            m_nodes[h].lt &= 0x7FFFFFFF;
            m_nodes[h].gt &= 0x7FFFFFFF;
        } else {
            m_nodes[h].lt |= 0x80000000;
            if (bf < 0)
                m_nodes[h].gt |= 0x80000000;
            else
                m_nodes[h].gt &= 0x7FFFFFFF;
        }
    }

    int compare_key_key(key va, key vb)
    {
        ASSERT(!va.isUndefined());
        ASSERT(!vb.isUndefined());

        if (m_exec->hadException())
            return 1;

        double compareResult;
        if (m_cachedCall) {
            m_cachedCall->setThis(jsUndefined());
            m_cachedCall->setArgument(0, va);
            m_cachedCall->setArgument(1, vb);
            compareResult = m_cachedCall->call().toNumber(m_cachedCall->newCallFrame(m_exec));
        } else {
            MarkedArgumentBuffer arguments;
            arguments.append(va);
            arguments.append(vb);
            compareResult = call(m_exec, m_compareFunction, m_compareCallType, *m_compareCallData, jsUndefined(), arguments).toNumber(m_exec);
        }
        return (compareResult < 0) ? -1 : 1; // Not passing equality through, because we need to store all values, even if equivalent.
    }

    int compare_key_node(key k, handle h) { return compare_key_key(k, m_nodes[h].value); }
    int compare_node_node(handle h1, handle h2) { return compare_key_key(m_nodes[h1].value, m_nodes[h2].value); }

    static handle null() { return 0x7FFFFFFF; }
};

void JSArray::sort(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
{
    ASSERT(!inSparseMode());

    checkConsistency();

    ArrayStorage* storage = m_storage;

    // FIXME: This ignores exceptions raised in the compare function or in toNumber.

    // The maximum tree depth is compiled in - but the caller is clearly up to no good
    // if a larger array is passed.
    ASSERT(storage->m_length <= static_cast<unsigned>(std::numeric_limits<int>::max()));
    if (storage->m_length > static_cast<unsigned>(std::numeric_limits<int>::max()))
        return;

    unsigned usedVectorLength = min(storage->m_length, m_vectorLength);
    unsigned nodeCount = usedVectorLength + (storage->m_sparseValueMap ? storage->m_sparseValueMap->size() : 0);

    if (!nodeCount)
        return;

    AVLTree<AVLTreeAbstractorForArrayCompare, 44> tree; // Depth 44 is enough for 2^31 items
    tree.abstractor().m_exec = exec;
    tree.abstractor().m_compareFunction = compareFunction;
    tree.abstractor().m_compareCallType = callType;
    tree.abstractor().m_compareCallData = &callData;
    tree.abstractor().m_nodes.grow(nodeCount);

    if (callType == CallTypeJS)
        tree.abstractor().m_cachedCall = adoptPtr(new CachedCall(exec, asFunction(compareFunction), 2));

    if (!tree.abstractor().m_nodes.begin()) {
        throwOutOfMemoryError(exec);
        return;
    }

    // FIXME: If the compare function modifies the array, the vector, map, etc. could be modified
    // right out from under us while we're building the tree here.

    unsigned numDefined = 0;
    unsigned numUndefined = 0;

    // Iterate over the array, ignoring missing values, counting undefined ones, and inserting all other ones into the tree.
    for (; numDefined < usedVectorLength; ++numDefined) {
        JSValue v = storage->m_vector[numDefined].get();
        if (!v || v.isUndefined())
            break;
        tree.abstractor().m_nodes[numDefined].value = v;
        tree.insert(numDefined);
    }
    for (unsigned i = numDefined; i < usedVectorLength; ++i) {
        JSValue v = storage->m_vector[i].get();
        if (v) {
            if (v.isUndefined())
                ++numUndefined;
            else {
                tree.abstractor().m_nodes[numDefined].value = v;
                tree.insert(numDefined);
                ++numDefined;
            }
        }
    }

    unsigned newUsedVectorLength = numDefined + numUndefined;

    if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
        newUsedVectorLength += map->size();
        if (newUsedVectorLength > m_vectorLength) {
            // Check that it is possible to allocate an array large enough to hold all the entries.
            if ((newUsedVectorLength > MAX_STORAGE_VECTOR_LENGTH) || !increaseVectorLength(newUsedVectorLength)) {
                throwOutOfMemoryError(exec);
                return;
            }
        }
        
        storage = m_storage;

        SparseArrayValueMap::const_iterator end = map->end();
        for (SparseArrayValueMap::const_iterator it = map->begin(); it != end; ++it) {
            tree.abstractor().m_nodes[numDefined].value = it->second.get();
            tree.insert(numDefined);
            ++numDefined;
        }

        delete map;
        storage->m_sparseValueMap = 0;
    }

    ASSERT(tree.abstractor().m_nodes.size() >= numDefined);

    // FIXME: If the compare function changed the length of the array, the following might be
    // modifying the vector incorrectly.

    // Copy the values back into m_storage.
    AVLTree<AVLTreeAbstractorForArrayCompare, 44>::Iterator iter;
    iter.start_iter_least(tree);
    JSGlobalData& globalData = exec->globalData();
    for (unsigned i = 0; i < numDefined; ++i) {
        storage->m_vector[i].set(globalData, this, tree.abstractor().m_nodes[*iter].value);
        ++iter;
    }

    // Put undefined values back in.
    for (unsigned i = numDefined; i < newUsedVectorLength; ++i)
        storage->m_vector[i].setUndefined();

    // Ensure that unused values in the vector are zeroed out.
    for (unsigned i = newUsedVectorLength; i < usedVectorLength; ++i)
        storage->m_vector[i].clear();

    storage->m_numValuesInVector = newUsedVectorLength;

    checkConsistency(SortConsistencyCheck);
}

void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
{
    ArrayStorage* storage = m_storage;

    WriteBarrier<Unknown>* vector = storage->m_vector;
    unsigned vectorEnd = min(storage->m_length, m_vectorLength);
    unsigned i = 0;
    for (; i < vectorEnd; ++i) {
        WriteBarrier<Unknown>& v = vector[i];
        if (!v)
            break;
        args.append(v.get());
    }

    for (; i < storage->m_length; ++i)
        args.append(get(exec, i));
}

void JSArray::copyToArguments(ExecState* exec, CallFrame* callFrame, uint32_t length)
{
    ASSERT(length == this->length());
    UNUSED_PARAM(length);
    unsigned i = 0;
    WriteBarrier<Unknown>* vector = m_storage->m_vector;
    unsigned vectorEnd = min(length, m_vectorLength);
    for (; i < vectorEnd; ++i) {
        WriteBarrier<Unknown>& v = vector[i];
        if (!v)
            break;
        callFrame->setArgument(i, v.get());
    }

    for (; i < length; ++i)
        callFrame->setArgument(i, get(exec, i));
}

unsigned JSArray::compactForSorting()
{
    ASSERT(!inSparseMode());

    checkConsistency();

    ArrayStorage* storage = m_storage;

    unsigned usedVectorLength = min(storage->m_length, m_vectorLength);

    unsigned numDefined = 0;
    unsigned numUndefined = 0;

    for (; numDefined < usedVectorLength; ++numDefined) {
        JSValue v = storage->m_vector[numDefined].get();
        if (!v || v.isUndefined())
            break;
    }

    for (unsigned i = numDefined; i < usedVectorLength; ++i) {
        JSValue v = storage->m_vector[i].get();
        if (v) {
            if (v.isUndefined())
                ++numUndefined;
            else
                storage->m_vector[numDefined++].setWithoutWriteBarrier(v);
        }
    }

    unsigned newUsedVectorLength = numDefined + numUndefined;

    if (SparseArrayValueMap* map = storage->m_sparseValueMap) {
        newUsedVectorLength += map->size();
        if (newUsedVectorLength > m_vectorLength) {
            // Check that it is possible to allocate an array large enough to hold all the entries - if not,
            // exception is thrown by caller.
            if ((newUsedVectorLength > MAX_STORAGE_VECTOR_LENGTH) || !increaseVectorLength(newUsedVectorLength))
                return 0;

            storage = m_storage;
        }

        SparseArrayValueMap::const_iterator end = map->end();
        for (SparseArrayValueMap::const_iterator it = map->begin(); it != end; ++it)
            storage->m_vector[numDefined++].setWithoutWriteBarrier(it->second.get());

        delete map;
        storage->m_sparseValueMap = 0;
    }

    for (unsigned i = numDefined; i < newUsedVectorLength; ++i)
        storage->m_vector[i].setUndefined();
    for (unsigned i = newUsedVectorLength; i < usedVectorLength; ++i)
        storage->m_vector[i].clear();

    storage->m_numValuesInVector = newUsedVectorLength;

    checkConsistency(SortConsistencyCheck);

    return numDefined;
}

void* JSArray::subclassData() const
{
    return m_storage->subclassData;
}

void JSArray::setSubclassData(void* d)
{
    m_storage->subclassData = d;
}

#if CHECK_ARRAY_CONSISTENCY

void JSArray::checkConsistency(ConsistencyCheckType type)
{
    ArrayStorage* storage = m_storage;

    ASSERT(!storage->m_inCompactInitialization);

    ASSERT(storage);
    if (type == SortConsistencyCheck)
        ASSERT(!storage->m_sparseValueMap);

    unsigned numValuesInVector = 0;
    for (unsigned i = 0; i < m_vectorLength; ++i) {
        if (JSValue value = storage->m_vector[i]) {
            ASSERT(i < storage->m_length);
            if (type != DestructorConsistencyCheck)
                value.isUndefined(); // Likely to crash if the object was deallocated.
            ++numValuesInVector;
        } else {
            if (type == SortConsistencyCheck)
                ASSERT(i >= storage->m_numValuesInVector);
        }
    }
    ASSERT(numValuesInVector == storage->m_numValuesInVector);
    ASSERT(numValuesInVector <= storage->m_length);

    if (storage->m_sparseValueMap) {
        SparseArrayValueMap::iterator end = storage->m_sparseValueMap->end();
        for (SparseArrayValueMap::iterator it = storage->m_sparseValueMap->begin(); it != end; ++it) {
            unsigned index = it->first;
            ASSERT(index < storage->m_length);
            ASSERT(index >= storage->m_vectorLength);
            ASSERT(index <= MAX_ARRAY_INDEX);
            ASSERT(it->second);
            if (type != DestructorConsistencyCheck)
                it->second.isUndefined(); // Likely to crash if the object was deallocated.
        }
    }
}

#endif

} // namespace JSC