grep: use REG_STARTEND (if available) to speed up regexec

BSD and glibc have an extension to regexec which takes a buffer + length pair
instead of a NUL-terminated string. Since we already have the length computed
this can save us a strlen call inside regexec.

Signed-off-by: Benjamin Kramer <benny.kra@googlemail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/grep.c b/grep.c
index 8e1f7de77..452c2cbae 100644
--- a/grep.c
+++ b/grep.c
@@ -640,8 +640,15 @@ static int look_ahead(struct grep_opt *opt,
 
 		if (p->fixed)
 			hit = !fixmatch(p->pattern, bol, p->ignore_case, &m);
-		else
+		else {
+#ifdef REG_STARTEND
+			m.rm_so = 0;
+			m.rm_eo = *left_p;
+			hit = !regexec(&p->regexp, bol, 1, &m, REG_STARTEND);
+#else
 			hit = !regexec(&p->regexp, bol, 1, &m, 0);
+#endif
+		}
 		if (!hit || m.rm_so < 0 || m.rm_eo < 0)
 			continue;
 		if (earliest < 0 || m.rm_so < earliest)