[PATCH] Optimize prefixcmp()

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Dec 29, 2007, 19:22 UTC
Message-ID: <Pine.LNX.4.64.0712292019450.14355@wbgn129.biozentrum.uni-wuerzburg.de>
In-Reply-To: <e5bfff550712291001q5f246ceah6700b98308fb96f1@mail.gmail.com>

Certain codepaths (notably "git log --pretty=format...") use prefixcmp() extensively, with very short prefixes. In those cases, calling strlen() is a wasteful operation, so avoid it.

Initial patch by Marco Costalba.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	On Sat, 29 Dec 2007, Marco Costalba wrote:

	> In case the prefix string is a single char avoid a costly call 
	> to strlen() + strncmp()

	Could you test this patch, please?

	Not only does it avoid the strlen() call also for longer prefixes; 
	it also avoids a C++ comment.

 git-compat-util.h |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index 79eb10e..7059cbd 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -398,7 +398,11 @@ static inline int sane_case(int x, int high)
 
 static inline int prefixcmp(const char *str, const char *prefix)
 {
-	return strncmp(str, prefix, strlen(prefix));
+	for (; ; str++, prefix++)
+		if (!*prefix)
+			return 0;
+		else if (*str != *prefix)
+			return (unsigned char)*prefix - (unsigned char)*str;
 }
 
 static inline int strtoul_ui(char const *s, int base, unsigned int *result)

-- 
1.5.2.rc0.4321.gd618