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aca4240f6a
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>
96 lines
2 KiB
C
96 lines
2 KiB
C
#include "cache.h"
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#include "prio-queue.h"
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static inline int compare(struct prio_queue *queue, int i, int j)
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{
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int cmp = queue->compare(queue->array[i].data, queue->array[j].data,
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queue->cb_data);
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if (!cmp)
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cmp = queue->array[i].ctr - queue->array[j].ctr;
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return cmp;
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}
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static inline void swap(struct prio_queue *queue, int i, int j)
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{
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SWAP(queue->array[i], queue->array[j]);
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}
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void prio_queue_reverse(struct prio_queue *queue)
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{
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int i, j;
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if (queue->compare != NULL)
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BUG("prio_queue_reverse() on non-LIFO queue");
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for (i = 0; i < (j = (queue->nr - 1) - i); i++)
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swap(queue, i, j);
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}
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void clear_prio_queue(struct prio_queue *queue)
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{
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FREE_AND_NULL(queue->array);
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queue->nr = 0;
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queue->alloc = 0;
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queue->insertion_ctr = 0;
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}
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void prio_queue_put(struct prio_queue *queue, void *thing)
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{
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int ix, parent;
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/* Append at the end */
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ALLOC_GROW(queue->array, queue->nr + 1, queue->alloc);
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queue->array[queue->nr].ctr = queue->insertion_ctr++;
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queue->array[queue->nr].data = thing;
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queue->nr++;
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if (!queue->compare)
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return; /* LIFO */
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/* Bubble up the new one */
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for (ix = queue->nr - 1; ix; ix = parent) {
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parent = (ix - 1) / 2;
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if (compare(queue, parent, ix) <= 0)
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break;
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swap(queue, parent, ix);
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}
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}
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void *prio_queue_get(struct prio_queue *queue)
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{
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void *result;
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int ix, child;
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if (!queue->nr)
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return NULL;
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if (!queue->compare)
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return queue->array[--queue->nr].data; /* LIFO */
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result = queue->array[0].data;
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if (!--queue->nr)
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return result;
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queue->array[0] = queue->array[queue->nr];
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/* Push down the one at the root */
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for (ix = 0; ix * 2 + 1 < queue->nr; ix = child) {
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child = ix * 2 + 1; /* left */
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if (child + 1 < queue->nr &&
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compare(queue, child, child + 1) >= 0)
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child++; /* use right child */
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if (compare(queue, ix, child) <= 0)
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break;
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swap(queue, child, ix);
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}
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return result;
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}
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void *prio_queue_peek(struct prio_queue *queue)
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{
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if (!queue->nr)
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return NULL;
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if (!queue->compare)
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return queue->array[queue->nr - 1].data;
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return queue->array[0].data;
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}
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