@matheusbsbs / matheus-bagliano / commits / 1a2842d1b1

object-name: simplify computing common prefixes

The function `extend_abbrev_len()` computes the length of common hex characters between two object IDs. This is done by: - Making the caller provide the `hex` string for the needle object ID. - Comparing every hex position of the haystack object ID with `get_hex_char_from_oid()`. Turning the binary representation into hex first is roundabout though: we can simply compare the binary representation and give some special attention to the final nibble. Introduce a new function `oid_common_prefix_hexlen()` that does exactly this and refactor the code to use the new function. This allows us to drop the `struct min_abbrev_data::hex` field. Furthermore, this function will be used in by some other callsites in subsequent commits. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Patrick Steinhardt committed Mar 20, 2026 at 08:07 UTC 1a2842d1b1e91d5e068d231cf4df4e783bdf9205

3 files changed +24 -20

hash.c

+18

@@ -317,3 +317,21 @@ const struct git_hash_algo *unsafe_hash_algo(const struct git_hash_algo *algop)

317 /* Otherwise use the default one. */

318 return algop;

319 }

320 +

321 +unsigned oid_common_prefix_hexlen(const struct object_id *a,

322 + const struct object_id *b)

323 +{

324 + unsigned rawsz = hash_algos[a->algo].rawsz;

325 +

326 + for (unsigned i = 0; i < rawsz; i++) {

327 + if (a->hash[i] == b->hash[i])

328 + continue;

329 +

330 + if ((a->hash[i] ^ b->hash[i]) & 0xf0)

331 + return i * 2;

332 + else

333 + return i * 2 + 1;

334 + }

335 +

336 + return rawsz * 2;

337 +}

hash.h

@@ -396,6 +396,9 @@ static inline int oideq(const struct object_id *oid1, const struct object_id *oi

396 return !memcmp(oid1->hash, oid2->hash, GIT_MAX_RAWSZ);

397 }

398

399 +unsigned oid_common_prefix_hexlen(const struct object_id *a,

400 + const struct object_id *b);

401 +

402 static inline void oidcpy(struct object_id *dst, const struct object_id *src)

403 {

404 memcpy(dst->hash, src->hash, GIT_MAX_RAWSZ);

object-name.c

+3 -20

@@ -585,32 +585,16 @@ static unsigned msb(unsigned long val)

585 struct min_abbrev_data {

586 unsigned int init_len;

587 unsigned int cur_len;

588 - char *hex;

588 struct repository *repo;

589 const struct object_id *oid;

590 };

591

593 -static inline char get_hex_char_from_oid(const struct object_id *oid,

594 - unsigned int pos)

595 -{

596 - static const char hex[] = "0123456789abcdef";

597 -

598 - if ((pos & 1) == 0)

599 - return hex[oid->hash[pos >> 1] >> 4];

600 - else

601 - return hex[oid->hash[pos >> 1] & 0xf];

602 -}

603 -

592 static int extend_abbrev_len(const struct object_id *oid,

593 struct min_abbrev_data *mad)

594 {

607 - unsigned int i = mad->init_len;

608 - while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))

609 - i++;

610 -

611 - if (mad->hex[i] && i >= mad->cur_len)

612 - mad->cur_len = i + 1;

613 -

595 + unsigned len = oid_common_prefix_hexlen(oid, mad->oid);

596 + if (len != hash_algos[oid->algo].hexsz && len >= mad->cur_len)

597 + mad->cur_len = len + 1;

598 return 0;

599 }

600

@@ -785,7 +769,6 @@ int repo_find_unique_abbrev_r(struct repository *r, char *hex,

769 mad.repo = r;

770 mad.init_len = len;

771 mad.cur_len = len;

788 - mad.hex = hex;

772 mad.oid = oid;

773

774 find_abbrev_len_packed(&mad);