prio-queue.c

#include "git-compat-util.h"
#include "prio-queue.h"

static inline int compare(struct prio_queue *queue, size_t i, size_t 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) -
		      (queue->array[i].ctr < queue->array[j].ctr);
	return cmp;
}

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

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

	if (queue->compare)
		BUG("prio_queue_reverse() on non-LIFO queue");
	if (!queue->nr_)
		return;
	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;
	queue->get_pending = 0;
}

static void sift_down_root(struct prio_queue *queue)
{
	size_t ix, child;

	/* 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);
	}
}

static inline void flush_get(struct prio_queue *queue)
{
	if (!queue->get_pending)
		return;
	queue->get_pending = 0;
	queue->array[0] = queue->array[--queue->nr_];
	sift_down_root(queue);
}

void prio_queue_put(struct prio_queue *queue, void *thing)
{
	size_t ix, parent;

	if (queue->get_pending) {
		queue->get_pending = 0;
		queue->array[0].ctr = queue->insertion_ctr++;
		queue->array[0].data = thing;
		sift_down_root(queue);
		return;
	}

	/* 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)
{
	if (queue->nr_ <= queue->get_pending) {
		queue->nr_ = 0;
		queue->get_pending = 0;
		return NULL;
	}
	if (!queue->compare)
		return queue->array[--queue->nr_].data; /* LIFO */

	flush_get(queue);

	queue->get_pending = 1;
	return queue->array[0].data;
}

void *prio_queue_peek(struct prio_queue *queue)
{
	if (queue->nr_ <= queue->get_pending) {
		queue->nr_ = 0;
		queue->get_pending = 0;
		return NULL;
	}
	if (!queue->compare)
		return queue->array[queue->nr_ - 1].data;

	flush_get(queue);

	return queue->array[0].data;
}