/**
* 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 nsDeque::PushFront(void* aItem, const fallible_t&) {
mOrigin--;
modasgn(mOrigin,mCapacity);
if (mSize==mCapacity) {
if (!GrowCapacity()) {
return false;
}
/* Comments explaining this are above*/
mData[mSize]=mData[mOrigin];
}
mData[mOrigin]=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
* @return *this
*/
nsDeque& nsDeque::PushFront(void* aItem) {
mOrigin--;
modasgn(mOrigin,mCapacity);
if (mSize==mCapacity) {
if (!GrowCapacity()) {
NS_WARNING("out of memory");
return *this;
}
/* Comments explaining this are above*/
mData[mSize]=mData[mOrigin];
}
mData[mOrigin]=aItem;
mSize++;
return *this;
}
