[PATCH] hash: reduce size of algo member of object ID
- From
René Scharfe <l.s.r@web.de>
- Date
- Oct 3, 2021, 05:51 UTC
- Message-ID
- <8da7bad2-b5a8-5aef-284b-dfa4e78556a9@web.de>
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.
Signed-off-by: René Scharfe <l.s.r@web.de> --- 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:
Test origin/master HEAD -------------------------------------------------------------------------------------------- 0001.1: rev-list --all 0.11(0.08+0.02) 0.11(0.08+0.02) +0.0% 0001.2: rev-list --all --objects 3.04(2.98+0.05) 3.04(2.98+0.05) +0.0% 0001.3: rev-list --parents 0.05(0.04+0.01) 0.05(0.03+0.01) +0.0% 0001.5: rev-list -- dummy 0.21(0.20+0.01) 0.21(0.19+0.01) +0.0% 0001.6: rev-list --parents -- dummy 0.22(0.20+0.01) 0.22(0.20+0.01) +0.0% 0001.8: rev-list $commit --not --all 0.06(0.05+0.00) 0.06(0.05+0.00) +0.0% 0001.9: rev-list --objects $commit --not --all 0.06(0.05+0.00) 0.06(0.05+0.00) +0.0% 1450.1: fsck 20.20(19.71+0.47) 20.18(19.70+0.48) -0.1%
hash.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/hash.h b/hash.h index 9e25c40e9a..24d8f7cd21 100644 --- a/hash.h +++ b/hash.h @@ -115,7 +115,7 @@ static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *s struct object_id { unsigned char hash[GIT_MAX_RAWSZ]; - int algo; /* XXX requires 4-byte alignment */ + unsigned char algo; }; /* A suitably aligned type for stack allocations of hash contexts. */ -- 2.33.0