Microoptimize strbuf_cmp

It can be less object code and may be even faster, even if at the
moment there is no callers to take an advantage of that. This
implementation can be trivially made inlinable later.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -139,14 +139,11 @@ void strbuf_list_free(struct strbuf **sbs)
 
 int strbuf_cmp(const struct strbuf *a, const struct strbuf *b)
 {
-	int cmp;
-	if (a->len < b->len) {
-		cmp = memcmp(a->buf, b->buf, a->len);
-		return cmp ? cmp : -1;
-	} else {
-		cmp = memcmp(a->buf, b->buf, b->len);
-		return cmp ? cmp : a->len != b->len;
-	}
+	int len = a->len < b->len ? a->len: b->len;
+	int cmp = memcmp(a->buf, b->buf, len);
+	if (cmp)
+		return cmp;
+	return a->len < b->len ? -1: a->len != b->len;
 }
 
 void strbuf_splice(struct strbuf *sb, size_t pos, size_t len,