char* del_option(bucketmap* bucket)
{
char* input = read();
char* output = concat(input, " returned ");
return concat(output, remove_from_bucket(bucket, input));
}
/** Split a bucket.
* Returns the newly created bucket on success
* Returns NULL on failure (likely cause being out of memory)
*/
static ginthash_bucket *ginthash_splitbucket(void *db, ext_ginthash *tbl,
ginthash_bucket *bucket)
{
gint msbmask, lowbits;
int i;
ginthash_bucket *newbucket;
if(bucket->level == tbl->level) {
/* can't split at this level anymore, extend directory */
/*printf("grow: curr level %d\n", tbl->level);*/
if(grow_ginthash(db, (ext_ginthash *) tbl))
return NULL;
}
/* Hash values for the new level (0+lowbits, msb+lowbits) */
msbmask = (1<<(bucket->level++));
lowbits = GINTHASH_SCRAMBLE(bucket->key[0]) & (msbmask - 1);
/* Create a bucket to split into */
newbucket = ginthash_newbucket(db, tbl);
if(!newbucket)
return NULL;
newbucket->level = bucket->level;
/* Split the entries based on the most significant
* bit for the local level hash (the ones with msb set are relocated)
*/
for(i=bucket->fill-1; i>=0; i--) {
gint k_i = bucket->key[i];
if(GINTHASH_SCRAMBLE(k_i) & msbmask) {
add_to_bucket(newbucket, k_i, remove_from_bucket(bucket, i));
/* printf("reassign: %d hash %d --> %d\n",
k_i, lowbits, msbmask | lowbits); */
}
}
/* Update the directory */
if(bucket->level == tbl->level) {
/* There are just two pointers pointing to bucket,
* we can compute the location of the one that has the index
* with msb set. The other one's contents do not need to be
* modified.
*/
tbl->directory[msbmask | lowbits] = newbucket;
} else {
/* The pointers that need to be updated have indexes
* of xxx1yyyy where 1 is the msb in the index of the new
* bucket, yyyy is the hash value of the bucket masked
* by the previous level and xxx are all combinations of
* bits that still remain masked by the local level after
* the split. The pointers xxx0yyyy will remain pointing
* to the old bucket.
*/
size_t msbbuckets = 1<<(tbl->level - bucket->level), j;
for(j=0; j<msbbuckets; j++) {
size_t k = (j<<bucket->level) | msbmask | lowbits;
/* XXX: paranoia check, remove in production */
if(tbl->directory[k] != bucket)
return NULL;
tbl->directory[k] = newbucket;
}
}
return newbucket;
}
