Re: absurdly slow git-diff

From

Linus Torvalds <torvalds@linux-foundation.org>

Date

Nov 7, 2008, 23:42 UTC

Message-ID

<alpine.LFD.2.00.0811071540340.3468@nehalem.linux-foundation.org>

In-Reply-To

<alpine.DEB.1.10.0811071517280.8736@alien.or.mcafeemobile.com>

On Fri, 7 Nov 2008, Davide Libenzi wrote:

> 
> With +/- 100 lines (200 lines window):
> 
> davide@alien:~$ time ./xdiff_test --diff 1 2 > /dev/null 
> 
> real    0m1.534s
> user    0m1.466s
> sys     0m0.040s

I assume the patch is something like the appended?

		Linus

---
 xdiff/xprepare.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index e87ab57..4bebd76 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -318,7 +318,7 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
 	 * Note that we always call this function with dis[i] > 1, so the
 	 * current line (i) is already a multimatch line.
 	 */
-	for (r = 1, rdis0 = 0, rpdis0 = 1; (i - r) >= s; r++) {
+	for (r = 1, rdis0 = 0, rpdis0 = 1; r < 100 && (i - r) >= s; r++) {
 		if (!dis[i - r])
 			rdis0++;
 		else if (dis[i - r] == 2)
@@ -334,7 +334,7 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
 	 */
 	if (rdis0 == 0)
 		return 0;
-	for (r = 1, rdis1 = 0, rpdis1 = 1; (i + r) <= e; r++) {
+	for (r = 1, rdis1 = 0, rpdis1 = 1; r < 100 && (i + r) <= e; r++) {
 		if (!dis[i + r])
 			rdis1++;
 		else if (dis[i + r] == 2)