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diff-delta: cull collided hash bucket more aggressively.

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This tries to limit collided hash buckets by removing identical
three-byte prefix from the same hashbucket.
This commit is contained in:
Junio C Hamano 2006-02-27 23:38:50 -08:00
parent d00e0f8101
commit c436eb8cf1
1 changed files with 25 additions and 12 deletions
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37
diff-delta.c
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@ -88,22 +88,35 @@ static struct index ** delta_index(const unsigned char *buf,
/*
* Now make sure none of the hash buckets has more entries than
* we're willing to test. Otherwise we short-circuit the entry
* list uniformly to still preserve a good repartition across
* the reference buffer.
* we're willing to test. Otherwise we cull the entry list to
* limit identical three byte prefixes to still preserve a good
* repartition across the reference buffer.
*/
for (i = 0; i < hsize; i++) {
struct index **list, *bucket, *remaining;
int cnt;
if (hash_count[i] < hlimit)
continue;
entry = hash[i];
do {
struct index *keep = entry;
int skip = hash_count[i] / hlimit / 2;
do {
entry = entry->next;
} while(--skip && entry);
keep->next = entry;
} while(entry);
bucket = NULL;
list = &bucket;
remaining = hash[i];
cnt = 0;
while (cnt < hlimit && remaining) {
struct index *this = remaining, *that;
remaining = remaining->next;
for (that = bucket; that; that = that->next) {
if (!memcmp(that->ptr, this->ptr, 3))
break;
}
if (that)
continue; /* discard */
cnt++;
*list = this;
list = &(this->next);
this->next = NULL;
}
hash[i] = bucket;
}
free(hash_count);