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@xxxxxx>
---
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
