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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "nsDeque.h"
#include "nsISupportsImpl.h"
#include <string.h>
#include "mozilla/CheckedInt.h"
#define modulus(x, y) ((x) % (y))
namespace mozilla {
namespace detail {
/**
* Standard constructor
* @param deallocator, called by Erase and ~nsDequeBase
*/
nsDequeBase::nsDequeBase() {
MOZ_COUNT_CTOR(nsDequeBase);
mOrigin = mSize = 0;
mData = mBuffer; // don't allocate space until you must
mCapacity = sizeof(mBuffer) / sizeof(mBuffer[0]);
memset(mData, 0, mCapacity * sizeof(mBuffer[0]));
}
/**
* Destructor
*/
nsDequeBase::~nsDequeBase() {
MOZ_COUNT_DTOR(nsDequeBase);
if (mData && mData != mBuffer) {
free(mData);
}
mData = nullptr;
}
size_t nsDequeBase::SizeOfExcludingThis(
mozilla::MallocSizeOf aMallocSizeOf) const {
size_t size = 0;
if (mData != mBuffer) {
size += aMallocSizeOf(mData);
}
return size;
}
/**
* Remove all items from container without destroying them.
*/
void nsDequeBase::Empty() {
if (mSize && mData) {
memset(mData, 0, mCapacity * sizeof(*mData));
}
mSize = 0;
mOrigin = 0;
}
/**
* This method quadruples the size of the deque
* Elements in the deque are resequenced so that elements
* in the deque are stored sequentially
*
* @return whether growing succeeded
*/
bool nsDequeBase::GrowCapacity() {
mozilla::CheckedInt<size_t> newCapacity = mCapacity;
newCapacity *= 4;
NS_ASSERTION(newCapacity.isValid(), "Overflow");
if (!newCapacity.isValid()) {
return false;
}
// Sanity check the new byte size.
mozilla::CheckedInt<size_t> newByteSize = newCapacity;
newByteSize *= sizeof(void*);
NS_ASSERTION(newByteSize.isValid(), "Overflow");
if (!newByteSize.isValid()) {
return false;
}
void** temp = (void**)malloc(newByteSize.value());
if (!temp) {
return false;
}
// Here's the interesting part: You can't just move the elements
// directly (in situ) from the old buffer to the new one.
// Since capacity has changed, the old origin doesn't make
// sense anymore. It's better to resequence the elements now.
memcpy(temp, mData + mOrigin, sizeof(void*) * (mCapacity - mOrigin));
memcpy(temp + (mCapacity - mOrigin), mData, sizeof(void*) * mOrigin);
if (mData != mBuffer) {
free(mData);
}
mCapacity = newCapacity.value();
mOrigin = 0; // now realign the origin...
mData = temp;
return true;
}
/**
* This method adds an item to the end of the deque.
* This operation has the potential to cause the
* underlying buffer to resize.
*
* @param aItem: new item to be added to deque
*/
bool nsDequeBase::Push(void* aItem, const fallible_t&) {
if (mSize == mCapacity && !GrowCapacity()) {
return false;
}
mData[modulus(mOrigin + mSize, mCapacity)] = aItem;
mSize++;
return true;
}
/**
* This method adds an item to the front of the deque.
* This operation has the potential to cause the
* underlying buffer to resize.
*
* --Commments for GrowCapacity() case
* We've grown and shifted which means that the old
* final element in the deque is now the first element
* in the deque. This is temporary.
* We haven't inserted the new element at the front.
*
* To continue with the idea of having the front at zero
* after a grow, we move the old final item (which through
* the voodoo of mOrigin-- is now the first) to its final
* position which is conveniently the old length.
*
* Note that this case only happens when the deque is full.
* [And that pieces of this magic only work if the deque is full.]
* picture:
* [ABCDEFGH] @[mOrigin:3]:D.
* Task: PushFront("Z")
* shift mOrigin so, @[mOrigin:2]:C
* stretch and rearrange: (mOrigin:0)
* [CDEFGHAB ________ ________ ________]
* copy: (The second C is currently out of bounds)
* [CDEFGHAB C_______ ________ ________]
* later we will insert Z:
* [ZDEFGHAB C_______ ________ ________]
* and increment size: 9. (C is no longer out of bounds)
* --
* @param aItem: new item to be added to deque
*/
bool nsDequeBase::PushFront(void* aItem, const fallible_t&) {
if (mOrigin == 0) {
mOrigin = mCapacity - 1;
} else {
mOrigin--;
}
if (mSize == mCapacity) {
if (!GrowCapacity()) {
return false;
}
/* Comments explaining this are above*/
mData[mSize] = mData[mOrigin];
}
mData[mOrigin] = aItem;
mSize++;
return true;
}
/**
* Remove and return the last item in the container.
*
* @return ptr to last item in container
*/
void* nsDequeBase::Pop() {
void* result = nullptr;
if (mSize > 0) {
--mSize;
size_t offset = modulus(mSize + mOrigin, mCapacity);
result = mData[offset];
mData[offset] = nullptr;
if (!mSize) {
mOrigin = 0;
}
}
return result;
}
/**
* This method gets called you want to remove and return
* the first member in the container.
*
* @return last item in container
*/
void* nsDequeBase::PopFront() {
void* result = nullptr;
if (mSize > 0) {
NS_ASSERTION(mOrigin < mCapacity, "Error: Bad origin");
result = mData[mOrigin];
mData[mOrigin++] = nullptr; // zero it out for debugging purposes.
mSize--;
// Cycle around if we pop off the end
// and reset origin if when we pop the last element
if (mCapacity == mOrigin || !mSize) {
mOrigin = 0;
}
}
return result;
}
/**
* This method gets called you want to peek at the bottom
* member without removing it.
*
* @return last item in container
*/
void* nsDequeBase::Peek() const {
void* result = nullptr;
if (mSize > 0) {
result = mData[modulus(mSize - 1 + mOrigin, mCapacity)];
}
return result;
}
/**
* This method gets called you want to peek at the topmost
* member without removing it.
*
* @return last item in container
*/
void* nsDequeBase::PeekFront() const {
void* result = nullptr;
if (mSize > 0) {
result = mData[mOrigin];
}
return result;
}
/**
* Call this to retrieve the ith element from this container.
* Keep in mind that accessing the underlying elements is
* done in a relative fashion. Object 0 is not necessarily
* the first element (the first element is at mOrigin).
*
* @param aIndex : 0 relative offset of item you want
* @return void* or null
*/
void* nsDequeBase::ObjectAt(size_t aIndex) const {
void* result = nullptr;
if (aIndex < mSize) {
result = mData[modulus(mOrigin + aIndex, mCapacity)];
}
return result;
}
} // namespace detail
} // namespace mozilla