prio-queue: factor out compare and swap operations

[thirdparty/git.git] / prio-queue.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], queue->array[j],
				 queue->cb_data);
	return cmp;
}

static inline void swap(struct prio_queue *queue, int i, int j)
{
	void *tmp = queue->array[i];
	queue->array[i] = queue->array[j];
	queue->array[j] = tmp;
}

void prio_queue_reverse(struct prio_queue *queue)
{
	int i, j;

	if (queue->compare != NULL)
		die("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(queue->array);
	queue->nr = 0;
	queue->alloc = 0;
	queue->array = NULL;
}

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++] = thing;
	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]; /* LIFO */

	result = queue->array[0];
	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;
}