René Scharfe <l.s.r@xxxxxx> wrote: > cf0983213c (hash: add an algo member to struct object_id, 2021-04-26) > introduced the algo member as an int. This increased the size of struct > object_id by 4 bytes (12.5%) and imposed a 4-byte alignment. Currently > we only need to stored the values 0, 1 and 2 in it. Let's use an > unsigned char instead to reduce the size overhead and lift the alignment > requirement. I like it. Btw, would a bitfield enum be portable enough for us? enum git_hash_algo algo:8; /* or algo:2 */ I've used those in other projects, but AFAIK they were for gcc||clang-only. > Not sure how to measure the performance impact of this change. The perf > tests mentioned by cf0983213c don't show much of a difference with > GIT_PERF_REPEAT_COUNT=10 for me: Thanks for that info. I'm not familiar enough with most git internals to know if it ought to make a difference as-is. In my experience, changes like this open the door to further struct-packing opportunities (possibly combined with conditional use of __attribute__((packed)) ).
