| 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, tail); |
| 522 |
> |
} |
| 523 |
> |
return true; |
| 524 |
> |
} |
| 525 |
|
} |
| 526 |
|
|
| 527 |
|
// *** Collection Methods *** |
