Subject: [PATCH 3/5] tree-walk: micro-optimization in tree_entry_interesting

From: Dan McGee <[email-masked]>
Date: Wed, 30 Mar 2011 20:37:59 -0500

In the case of a wide breadth top-level tree (~2400 entries, all trees
in this case), we can see a noticeable cost in the profiler calling
strncmp() here. Most of the time we are at the base level of the
repository, so base is "" and baselen == 0, which means we will always
test true. Break out this one tiny case so we can short circuit the
strncmp() call.

This resulted in an ~11% improvement (43 to 38 secs) for a reasonable
log operation on the Arch Linux Packages SVN clone repository, which
contained 117220 commits and the aforementioned 2400 top-level objects:
    git log -- autogen/trunk pacman/trunk/ wget/trunk/

Negligible slowdown was noted with other repositories (e.g. linux-2.6).

Signed-off-by: Dan McGee <[email-masked]>
---
 tree-walk.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tree-walk.c b/tree-walk.c
index 9be8007..f386151 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -591,8 +591,8 @@ int tree_entry_interesting(const struct name_entry *entry,
 					      ps->max_depth);
 		}
 
-		/* Does the base match? */
-		if (!strncmp(base_str, match, baselen)) {
+		/* Either there must be no base, or the base must match. */
+		if (baselen == 0 || !strncmp(base_str, match, baselen)) {
 			if (match_entry(entry, pathlen,
 					match + baselen, matchlen - baselen,
 					&never_interesting))
-- 
1.7.4.2