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more comments for hashindex_lookup

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Thomas Waldmann 2023-02-08 15:33:58 +01:00 • committed by snsmac
parent 3a44894aca
commit 32519617b6
1 changed files with 12 additions and 4 deletions
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16
src/borg/_hashindex.c
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@ -148,22 +148,24 @@ static int
hashindex_lookup(HashIndex *index, const unsigned char *key, int *start_idx)
{
int didx = -1;
int start = hashindex_index(index, key);
int start = hashindex_index(index, key); /* perfect index for this key, if there is no collision. */
int idx = start;
for(;;) {
if(BUCKET_IS_EMPTY(index, idx))
{
break;
break; /* if we encounter an empty bucket, we do not need to look any further. */
}
if(BUCKET_IS_DELETED(index, idx)) {
if(didx == -1) {
didx = idx;
didx = idx; /* remember the index of the first deleted bucket. */
}
}
else if(BUCKET_MATCHES_KEY(index, idx, key)) {
/* we found the bucket with the key we are looking for! */
if (didx != -1) {
// note: although lookup is logically a read-only operation,
// we optimize (change) the hashindex here "on the fly".
// we optimize (change) the hashindex here "on the fly":
// swap this full bucket with a previous deleted/tombstone bucket.
memcpy(BUCKET_ADDR(index, didx), BUCKET_ADDR(index, idx), index->bucket_size);
BUCKET_MARK_DELETED(index, idx);
idx = didx;
@ -175,10 +177,16 @@ hashindex_lookup(HashIndex *index, const unsigned char *key, int *start_idx)
idx -= index->num_buckets;
}
if(idx == start) {
/* we have done a full pass over all buckets. */
break;
}
}
/* we get here if we did not find a bucket with the key we searched for. */
if (start_idx != NULL) {
/* by giving a non-NULL pointer in start_idx, caller can request to
* get the index of the first empty or deleted bucket we encountered,
* e.g. to add a new entry for that key into that bucket.
*/
(*start_idx) = (didx == -1) ? idx : didx;
}
return -1;