| 491 |
|
*/ |
| 492 |
|
private boolean delete(int i) { |
| 493 |
|
int mask = elements.length - 1; |
| 494 |
+ |
int front = (i - head) & mask; |
| 495 |
+ |
int back = (tail - i) & mask; |
| 496 |
|
|
| 497 |
|
// Invariant: head <= i < tail mod circularity |
| 498 |
< |
if (((i - head) & mask) >= ((tail - head) & mask)) |
| 498 |
> |
if (front >= ((tail - head) & mask)) |
| 499 |
|
throw new ConcurrentModificationException(); |
| 500 |
|
|
| 501 |
< |
// Case 1: Deque doesn't wrap |
| 502 |
< |
// Case 2: Deque does wrap and removed element is in the head portion |
| 503 |
< |
if (i >= head) { |
| 504 |
< |
System.arraycopy(elements, head, elements, head + 1, i - head); |
| 505 |
< |
elements[head] = null; |
| 506 |
< |
head = (head + 1) & mask; |
| 501 |
> |
// Optimize for least element motion |
| 502 |
> |
if (front < back) { |
| 503 |
> |
if (head <= i) { |
| 504 |
> |
System.arraycopy(elements, head, elements, head + 1, front); |
| 505 |
> |
} else { // Wrap around |
| 506 |
> |
elements[0] = elements[mask]; |
| 507 |
> |
System.arraycopy(elements, 0, elements, 1, i); |
| 508 |
> |
System.arraycopy(elements, head, elements, head + 1, mask - head); |
| 509 |
> |
} |
| 510 |
> |
elements[head] = null; |
| 511 |
> |
head = (head + 1) & mask; |
| 512 |
|
return false; |
| 513 |
< |
} |
| 514 |
< |
|
| 515 |
< |
// Case 3: Deque wraps and removed element is in the tail portion |
| 516 |
< |
tail--; |
| 517 |
< |
System.arraycopy(elements, i + 1, elements, i, tail - i); |
| 518 |
< |
elements[tail] = null; |
| 519 |
< |
return true; |
| 513 |
> |
} else { |
| 514 |
> |
int t = tail; |
| 515 |
> |
tail = (tail - 1) & mask; |
| 516 |
> |
if (i < t) { // Copy the null tail as well |
| 517 |
> |
System.arraycopy(elements, i + 1, elements, i, back); |
| 518 |
> |
} else { // Wrap around |
| 519 |
> |
elements[mask] = elements[0]; |
| 520 |
> |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
| 521 |
> |
System.arraycopy(elements, 1, elements, 0, t); |
| 522 |
> |
} |
| 523 |
> |
return true; |
| 524 |
> |
} |
| 525 |
|
} |
| 526 |
|
|
| 527 |
|
// *** Collection Methods *** |
| 550 |
|
* order that elements would be dequeued (via successive calls to |
| 551 |
|
* {@link #remove} or popped (via successive calls to {@link #pop}). |
| 552 |
|
* |
| 553 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
| 553 |
> |
* @return an iterator over the elements in this deque |
| 554 |
|
*/ |
| 555 |
|
public Iterator<E> iterator() { |
| 556 |
|
return new DeqIterator(); |
| 557 |
|
} |
| 558 |
|
|
| 547 |
– |
/** |
| 548 |
– |
* Returns an iterator over the elements in this deque in reverse |
| 549 |
– |
* sequential order. The elements will be returned in order from |
| 550 |
– |
* last (tail) to first (head). |
| 551 |
– |
* |
| 552 |
– |
* @return an iterator over the elements in this deque in reverse |
| 553 |
– |
* sequence |
| 554 |
– |
*/ |
| 559 |
|
public Iterator<E> descendingIterator() { |
| 560 |
|
return new DescendingIterator(); |
| 561 |
|
} |
| 598 |
|
public void remove() { |
| 599 |
|
if (lastRet < 0) |
| 600 |
|
throw new IllegalStateException(); |
| 601 |
< |
if (delete(lastRet)) |
| 602 |
< |
cursor--; |
| 601 |
> |
if (delete(lastRet)) // if left-shifted, undo increment in next() |
| 602 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
| 603 |
|
lastRet = -1; |
| 604 |
|
fence = tail; |
| 605 |
|
} |
| 607 |
|
|
| 608 |
|
|
| 609 |
|
private class DescendingIterator implements Iterator<E> { |
| 610 |
< |
/* |
| 611 |
< |
* This class is nearly a mirror-image of DeqIterator. It |
| 612 |
< |
* shares the same structure, but not many actual lines of |
| 613 |
< |
* code. The only asymmetric part is that to simplify some |
| 614 |
< |
* checks, indices are anded with length mask only on array |
| 615 |
< |
* access rather than on each update. |
| 610 |
> |
/* |
| 611 |
> |
* This class is nearly a mirror-image of DeqIterator, using |
| 612 |
> |
* (tail-1) instead of head for initial cursor, (head-1) |
| 613 |
> |
* instead of tail for fence, and elements.length instead of -1 |
| 614 |
> |
* for sentinel. It shares the same structure, but not many |
| 615 |
> |
* actual lines of code. |
| 616 |
|
*/ |
| 617 |
< |
private int cursor = tail - 1; |
| 618 |
< |
private int fence = head - 1; |
| 617 |
> |
private int cursor = (tail - 1) & (elements.length - 1); |
| 618 |
> |
private int fence = (head - 1) & (elements.length - 1); |
| 619 |
|
private int lastRet = elements.length; |
| 620 |
|
|
| 621 |
|
public boolean hasNext() { |
| 626 |
|
E result; |
| 627 |
|
if (cursor == fence) |
| 628 |
|
throw new NoSuchElementException(); |
| 629 |
< |
if ((head - 1) != fence || |
| 630 |
< |
(result = elements[cursor & (elements.length-1)]) == null) |
| 629 |
> |
if (((head - 1) & (elements.length - 1)) != fence || |
| 630 |
> |
(result = elements[cursor]) == null) |
| 631 |
|
throw new ConcurrentModificationException(); |
| 632 |
|
lastRet = cursor; |
| 633 |
< |
cursor--; |
| 633 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
| 634 |
|
return result; |
| 635 |
|
} |
| 636 |
|
|
| 637 |
|
public void remove() { |
| 638 |
|
if (lastRet >= elements.length) |
| 639 |
|
throw new IllegalStateException(); |
| 640 |
< |
if (delete(lastRet & (elements.length-1))) |
| 641 |
< |
cursor++; |
| 640 |
> |
if (!delete(lastRet)) |
| 641 |
> |
cursor = (cursor + 1) & (elements.length - 1); |
| 642 |
|
lastRet = elements.length; |
| 643 |
< |
fence = head - 1; |
| 643 |
> |
fence = (head - 1) & (elements.length - 1); |
| 644 |
|
} |
| 645 |
|
} |
| 646 |
|
|
| 802 |
|
s.defaultWriteObject(); |
| 803 |
|
|
| 804 |
|
// Write out size |
| 805 |
< |
int size = size(); |
| 802 |
< |
s.writeInt(size); |
| 805 |
> |
s.writeInt(size()); |
| 806 |
|
|
| 807 |
|
// Write out elements in order. |
| 805 |
– |
int i = head; |
| 808 |
|
int mask = elements.length - 1; |
| 809 |
< |
for (int j = 0; j < size; j++) { |
| 809 |
> |
for (int i = head; i != tail; i = (i + 1) & mask) |
| 810 |
|
s.writeObject(elements[i]); |
| 809 |
– |
i = (i + 1) & mask; |
| 810 |
– |
} |
| 811 |
|
} |
| 812 |
|
|
| 813 |
|
/** |
