linux-kernel - strncpy optimalisation? (lib/string.c)

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Message-ID: <20061210205230.GB30197@vanheusden.com>
Date:	Sun, 10 Dec 2006 21:52:30 +0100
From:	Folkert van Heusden <folkert@...heusden.com>
To:	linux-kernel@...r.kernel.org
Subject: strncpy optimalisation? (lib/string.c)

Hi,

In lib/string.c we have:

char *strncpy(char *dest, const char *src, size_t count)
{
        char *tmp = dest;

        while (count) {
                if ((*tmp = *src) != 0)
                        src++;
                tmp++;
                count--;
        }
        return dest;
}

now I wonder isn't this ineffecient when strlen(src) < count? It would
then, if I'm correct, iterate count-strlen(src) times doing useless
increment/decrement. And since there are aprox. 580 instances in the
2.6.18.2 source, maybe some efficency can be won here.
Wouldn't it be better to do:
                if ((*tmp = *src) == 0x00)
                        break;

So that would be:
--- lib/string.c	2006-11-04 02:33:58.000000000 +0100
+++ string-new.c	2006-12-10 21:50:05.000000000 +0100
@@ -97,8 +97,8 @@
 	char *tmp = dest;
 
 	while (count) {
-		if ((*tmp = *src) != 0)
-			src++;
+		if ((*tmp = *src) == 0x00)
+			break;
 		tmp++;
 		count--;
 	}


Folkert van Heusden

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