You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
129 lines
3.2 KiB
129 lines
3.2 KiB
#include "cache.h" |
|
#include "hash-lookup.h" |
|
|
|
static uint32_t take2(const struct object_id *oid, size_t ofs) |
|
{ |
|
return ((oid->hash[ofs] << 8) | oid->hash[ofs + 1]); |
|
} |
|
|
|
/* |
|
* Conventional binary search loop looks like this: |
|
* |
|
* do { |
|
* int mi = lo + (hi - lo) / 2; |
|
* int cmp = "entry pointed at by mi" minus "target"; |
|
* if (!cmp) |
|
* return (mi is the wanted one) |
|
* if (cmp > 0) |
|
* hi = mi; "mi is larger than target" |
|
* else |
|
* lo = mi+1; "mi is smaller than target" |
|
* } while (lo < hi); |
|
* |
|
* The invariants are: |
|
* |
|
* - When entering the loop, lo points at a slot that is never |
|
* above the target (it could be at the target), hi points at a |
|
* slot that is guaranteed to be above the target (it can never |
|
* be at the target). |
|
* |
|
* - We find a point 'mi' between lo and hi (mi could be the same |
|
* as lo, but never can be the same as hi), and check if it hits |
|
* the target. There are three cases: |
|
* |
|
* - if it is a hit, we are happy. |
|
* |
|
* - if it is strictly higher than the target, we update hi with |
|
* it. |
|
* |
|
* - if it is strictly lower than the target, we update lo to be |
|
* one slot after it, because we allow lo to be at the target. |
|
* |
|
* When choosing 'mi', we do not have to take the "middle" but |
|
* anywhere in between lo and hi, as long as lo <= mi < hi is |
|
* satisfied. When we somehow know that the distance between the |
|
* target and lo is much shorter than the target and hi, we could |
|
* pick mi that is much closer to lo than the midway. |
|
*/ |
|
/* |
|
* The table should contain "nr" elements. |
|
* The oid of element i (between 0 and nr - 1) should be returned |
|
* by "fn(i, table)". |
|
*/ |
|
int oid_pos(const struct object_id *oid, const void *table, size_t nr, |
|
oid_access_fn fn) |
|
{ |
|
size_t hi = nr; |
|
size_t lo = 0; |
|
size_t mi = 0; |
|
|
|
if (!nr) |
|
return -1; |
|
|
|
if (nr != 1) { |
|
size_t lov, hiv, miv, ofs; |
|
|
|
for (ofs = 0; ofs < the_hash_algo->rawsz - 2; ofs += 2) { |
|
lov = take2(fn(0, table), ofs); |
|
hiv = take2(fn(nr - 1, table), ofs); |
|
miv = take2(oid, ofs); |
|
if (miv < lov) |
|
return -1; |
|
if (hiv < miv) |
|
return index_pos_to_insert_pos(nr); |
|
if (lov != hiv) { |
|
/* |
|
* At this point miv could be equal |
|
* to hiv (but hash could still be higher); |
|
* the invariant of (mi < hi) should be |
|
* kept. |
|
*/ |
|
mi = (nr - 1) * (miv - lov) / (hiv - lov); |
|
if (lo <= mi && mi < hi) |
|
break; |
|
BUG("assertion failed in binary search"); |
|
} |
|
} |
|
} |
|
|
|
do { |
|
int cmp; |
|
cmp = oidcmp(fn(mi, table), oid); |
|
if (!cmp) |
|
return mi; |
|
if (cmp > 0) |
|
hi = mi; |
|
else |
|
lo = mi + 1; |
|
mi = lo + (hi - lo) / 2; |
|
} while (lo < hi); |
|
return index_pos_to_insert_pos(lo); |
|
} |
|
|
|
int bsearch_hash(const unsigned char *hash, const uint32_t *fanout_nbo, |
|
const unsigned char *table, size_t stride, uint32_t *result) |
|
{ |
|
uint32_t hi, lo; |
|
|
|
hi = ntohl(fanout_nbo[*hash]); |
|
lo = ((*hash == 0x0) ? 0 : ntohl(fanout_nbo[*hash - 1])); |
|
|
|
while (lo < hi) { |
|
unsigned mi = lo + (hi - lo) / 2; |
|
int cmp = hashcmp(table + mi * stride, hash); |
|
|
|
if (!cmp) { |
|
if (result) |
|
*result = mi; |
|
return 1; |
|
} |
|
if (cmp > 0) |
|
hi = mi; |
|
else |
|
lo = mi + 1; |
|
} |
|
|
|
if (result) |
|
*result = lo; |
|
return 0; |
|
}
|
|
|