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>

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 23362a23597e9e520c2507955034b8c28da910d2..b7494fdf89c22b317fff7e1f8aeacd7273e67ac5 100644 (file)
--- 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;
 }