diff options
Diffstat (limited to 'odb.c')
| -rw-r--r-- | odb.c | 73 |
1 files changed, 73 insertions, 0 deletions
@@ -12,6 +12,7 @@ #include "midx.h" #include "object-file-convert.h" #include "object-file.h" +#include "object-name.h" #include "odb.h" #include "packfile.h" #include "path.h" @@ -964,6 +965,78 @@ out: return ret; } +/* + * Return the slot of the most-significant bit set in "val". There are various + * ways to do this quickly with fls() or __builtin_clzl(), but speed is + * probably not a big deal here. + */ +static unsigned msb(unsigned long val) +{ + unsigned r = 0; + while (val >>= 1) + r++; + return r; +} + +int odb_find_abbrev_len(struct object_database *odb, + const struct object_id *oid, + int min_length, + unsigned *out) +{ + const struct git_hash_algo *algo = + oid->algo ? &hash_algos[oid->algo] : odb->repo->hash_algo; + const unsigned hexsz = algo->hexsz; + unsigned len; + int ret; + + if (min_length < 0) { + unsigned long count; + + if (odb_count_objects(odb, ODB_COUNT_OBJECTS_APPROXIMATE, &count) < 0) + count = 0; + + /* + * Add one because the MSB only tells us the highest bit set, + * not including the value of all the _other_ bits (so "15" + * is only one off of 2^4, but the MSB is the 3rd bit. + */ + len = msb(count) + 1; + /* + * We now know we have on the order of 2^len objects, which + * expects a collision at 2^(len/2). But we also care about hex + * chars, not bits, and there are 4 bits per hex. So all + * together we need to divide by 2 and round up. + */ + len = DIV_ROUND_UP(len, 2); + /* + * For very small repos, we stick with our regular fallback. + */ + if (len < FALLBACK_DEFAULT_ABBREV) + len = FALLBACK_DEFAULT_ABBREV; + } else { + len = min_length; + } + + if (len >= hexsz || !len) { + *out = hexsz; + ret = 0; + goto out; + } + + odb_prepare_alternates(odb); + for (struct odb_source *source = odb->sources; source; source = source->next) { + ret = odb_source_find_abbrev_len(source, oid, len, &len); + if (ret) + goto out; + } + + ret = 0; + *out = len; + +out: + return ret; +} + void odb_assert_oid_type(struct object_database *odb, const struct object_id *oid, enum object_type expect) { |