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 *** |