pickaxe -S: slightly optimize contains()
When the "log -S<pat>" switch counts occurrences of <pat> on the pre-image and post-image of a change. As soon as we know we had e.g. 1 before and 2 now we can stop, we don't need to keep counting past 2. With this change a diff between A and B may have different performance characteristics than between B and A. That's OK in this case, since we'll emit the same output, and the effect is to make one of them better. I'm picking a check of "one" first on the assumption that it's a more common case to have files grow over time than not. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ævar Arnfjörð Bjarmason committed
Apr 12, 2021 at 19:15 UTC
5b0672a26e51387bc18adad89eaa3ebb131b2e33
1 file changed
+10
-3
diffcore-pickaxe.c
+10
-3
index 23362a2359..b7494fdf89 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -68,7 +68,8 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
return ecbdata.hit;
}
-static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
+static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws,
+ unsigned int limit)
{
unsigned int cnt = 0;
unsigned long sz = mf->size;
@@ -88,6 +89,9 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
sz--;
}
cnt++;
+
+ if (limit && cnt == limit)
+ return cnt;
}
} else { /* Classic exact string match */
@@ -99,6 +103,9 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
sz -= offset + kwsm.size[0];
data += offset + kwsm.size[0];
cnt++;
+
+ if (limit && cnt == limit)
+ return cnt;
}
}
return cnt;
@@ -108,8 +115,8 @@ static int has_changes(mmfile_t *one, mmfile_t *two,
struct diff_options *o,
regex_t *regexp, kwset_t kws)
{
- unsigned int c1 = one ? contains(one, regexp, kws) : 0;
- unsigned int c2 = two ? contains(two, regexp, kws) : 0;
+ unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
+ unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
return c1 != c2;
}