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pickaxe -S: slightly optimize contains()

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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>
This commit is contained in:
Ævar Arnfjörð Bjarmason 2021-04-12 19:15:23 +02:00 committed by Junio C Hamano
parent 5d35a9531c
commit 5b0672a26e
1 changed files with 10 additions and 3 deletions
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13
diffcore-pickaxe.c
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@ -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;
}