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diff-delta.c: Rationalize culling of hash buckets

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The previous hash bucket culling resulted in a somewhat unpredictable
number of hash bucket entries in the order of magnitude of HASH_LIMIT.

Replace this with a Bresenham-like algorithm leaving us with exactly
HASH_LIMIT entries by uniform culling.

Signed-off-by: David Kastrup <dak@gnu.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
David Kastrup 2007-09-08 23:25:55 +02:00 committed by Junio C Hamano
parent d2100860fd
commit 02e665ce49
1 changed files with 31 additions and 10 deletions
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41
diff-delta.c
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@ -207,19 +207,40 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
* the reference buffer.
*/
for (i = 0; i < hsize; i++) {
if (hash_count[i] < HASH_LIMIT)
int acc;
if (hash_count[i] <= HASH_LIMIT)
continue;
entries -= hash_count[i] - HASH_LIMIT;
/* We leave exactly HASH_LIMIT entries in the bucket */
entry = hash[i];
acc = 0;
do {
struct unpacked_index_entry *keep = entry;
int skip = hash_count[i] / HASH_LIMIT;
do {
--entries;
entry = entry->next;
} while(--skip && entry);
++entries;
keep->next = entry;
} while(entry);
acc += hash_count[i] - HASH_LIMIT;
if (acc > 0) {
struct unpacked_index_entry *keep = entry;
do {
entry = entry->next;
acc -= HASH_LIMIT;
} while (acc > 0);
keep->next = entry->next;
}
entry = entry->next;
} while (entry);
/* Assume that this loop is gone through exactly
* HASH_LIMIT times and is entered and left with
* acc==0. So the first statement in the loop
* contributes (hash_count[i]-HASH_LIMIT)*HASH_LIMIT
* to the accumulator, and the inner loop consequently
* is run (hash_count[i]-HASH_LIMIT) times, removing
* one element from the list each time. Since acc
* balances out to 0 at the final run, the inner loop
* body can't be left with entry==NULL. So we indeed
* encounter entry==NULL in the outer loop only.
*/
}
free(hash_count);