mirror of
https://github.com/git/git
synced 2024-08-26 11:09:18 +00:00
![Derrick Stolee](/assets/img/avatar_default.png)
When consuming a priority queue, it can be convenient to inspect the next object that will be dequeued without actually dequeueing it. Our existing library did not have such a 'peek' operation, so add it as prio_queue_peek(). Add a reference-level comparison in t/helper/test-prio-queue.c so this method is exercised by t0009-prio-queue.sh. Further, add a test that checks the behavior when the compare function is NULL (i.e. the queue becomes a stack). Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
97 lines
2 KiB
C
97 lines
2 KiB
C
#include "cache.h"
|
|
#include "prio-queue.h"
|
|
|
|
static inline int compare(struct prio_queue *queue, int i, int j)
|
|
{
|
|
int cmp = queue->compare(queue->array[i].data, queue->array[j].data,
|
|
queue->cb_data);
|
|
if (!cmp)
|
|
cmp = queue->array[i].ctr - queue->array[j].ctr;
|
|
return cmp;
|
|
}
|
|
|
|
static inline void swap(struct prio_queue *queue, int i, int j)
|
|
{
|
|
SWAP(queue->array[i], queue->array[j]);
|
|
}
|
|
|
|
void prio_queue_reverse(struct prio_queue *queue)
|
|
{
|
|
int i, j;
|
|
|
|
if (queue->compare != NULL)
|
|
BUG("prio_queue_reverse() on non-LIFO queue");
|
|
for (i = 0; i < (j = (queue->nr - 1) - i); i++)
|
|
swap(queue, i, j);
|
|
}
|
|
|
|
void clear_prio_queue(struct prio_queue *queue)
|
|
{
|
|
FREE_AND_NULL(queue->array);
|
|
queue->nr = 0;
|
|
queue->alloc = 0;
|
|
queue->insertion_ctr = 0;
|
|
}
|
|
|
|
void prio_queue_put(struct prio_queue *queue, void *thing)
|
|
{
|
|
int ix, parent;
|
|
|
|
/* Append at the end */
|
|
ALLOC_GROW(queue->array, queue->nr + 1, queue->alloc);
|
|
queue->array[queue->nr].ctr = queue->insertion_ctr++;
|
|
queue->array[queue->nr].data = thing;
|
|
queue->nr++;
|
|
if (!queue->compare)
|
|
return; /* LIFO */
|
|
|
|
/* Bubble up the new one */
|
|
for (ix = queue->nr - 1; ix; ix = parent) {
|
|
parent = (ix - 1) / 2;
|
|
if (compare(queue, parent, ix) <= 0)
|
|
break;
|
|
|
|
swap(queue, parent, ix);
|
|
}
|
|
}
|
|
|
|
void *prio_queue_get(struct prio_queue *queue)
|
|
{
|
|
void *result;
|
|
int ix, child;
|
|
|
|
if (!queue->nr)
|
|
return NULL;
|
|
if (!queue->compare)
|
|
return queue->array[--queue->nr].data; /* LIFO */
|
|
|
|
result = queue->array[0].data;
|
|
if (!--queue->nr)
|
|
return result;
|
|
|
|
queue->array[0] = queue->array[queue->nr];
|
|
|
|
/* Push down the one at the root */
|
|
for (ix = 0; ix * 2 + 1 < queue->nr; ix = child) {
|
|
child = ix * 2 + 1; /* left */
|
|
if (child + 1 < queue->nr &&
|
|
compare(queue, child, child + 1) >= 0)
|
|
child++; /* use right child */
|
|
|
|
if (compare(queue, ix, child) <= 0)
|
|
break;
|
|
|
|
swap(queue, child, ix);
|
|
}
|
|
return result;
|
|
}
|
|
|
|
void *prio_queue_peek(struct prio_queue *queue)
|
|
{
|
|
if (!queue->nr)
|
|
return NULL;
|
|
if (!queue->compare)
|
|
return queue->array[queue->nr - 1].data;
|
|
return queue->array[0].data;
|
|
}
|