1f9e18b772
Our array-reverse algorithm does the usual "walk from both
ends, swapping elements". We can quit when the two indices
are equal, since:
1. Swapping an element with itself is a noop.
2. If i and j are equal, then in the next iteration i is
guaranteed to be bigge than j, and we will exit the
loop.
So exiting the loop on equality is slightly more efficient.
And more importantly, the new SWAP() macro does not expect
to handle noop swaps; it will call memcpy() with the same src
and dst pointers in this case. It's unclear whether that
causes a problem on any platforms by violating the
"overlapping memory" constraint of memcpy, but it does cause
valgrind to complain.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
91 lines
1.9 KiB
C
91 lines
1.9 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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struct prio_queue_entry tmp = queue->array[i];
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queue->array[i] = queue->array[j];
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queue->array[j] = tmp;
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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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die("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(queue->array);
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queue->nr = 0;
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queue->alloc = 0;
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queue->array = NULL;
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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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