xdiff: optimise for no whitespace difference when ignoring whitespace.

In xdl_recmatch, do the memcmp to check if the two lines are equal before
checking if whitespace flags are set.  If the lines are identical, then
there is no need to check if they differ only in whitespace.
This makes the common case (there is no whitespace difference) faster.
It costs the case where lines are the same length and contain
whitespace differences, but the common case is more than 20% faster.

Signed-off-by: Dylan Reid <dgreid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index bc12f298953a4e72b323f73607278028ec4a2805..22f9bd692c2706136b4938bbcb2e0fc3dab212b8 100644 (file)
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -190,8 +190,10 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
 {
        int i1, i2;
 
+       if (s1 == s2 && !memcmp(l1, l2, s1))
+               return 1;
        if (!(flags & XDF_WHITESPACE_FLAGS))
-               return s1 == s2 && !memcmp(l1, l2, s1);
+               return 0;
 
        i1 = 0;
        i2 = 0;