Re: [ANNOUNCE] Git v2.19.0-rc0

Jeff King [off-list ref] writes:

On Wed, Aug 22, 2018 at 12:49:34PM -0400, Derrick Stolee wrote:

quoted

quoted

Yes, that was what I meant. We actually did switch to that hand-rolled
loop, but later we went back to memcmp in 0b006014c8 (hashcmp: use
memcmp instead of open-coded loop, 2017-08-09).

Looking at that commit, I'm surprised the old logic was just a for
loop, instead of a word-based approach, such as the following:
[...]
+struct object_id_20 {
+       uint64_t data0;
+       uint64_t data1;
+       uint32_t data2;
+};
+
 static inline int hashcmp(const unsigned char *sha1, const unsigned char
*sha2)
 {
-       return memcmp(sha1, sha2, the_hash_algo->rawsz);
+       if (the_hash_algo->rawsz == 20) {
+               struct object_id_20 *obj1 = (struct object_id_20 *)sha1;
+               struct object_id_20 *obj2 = (struct object_id_20 *)sha2;

I wonder if you're potentially running afoul of alignment requirements
here.

Yup, and I think that all was discussed in that old thread ;-)