linux-kernel - optimalisation for strlcpy (lib/string.c)

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Message-ID: <20061210212350.GC30197@vanheusden.com>
Date:	Sun, 10 Dec 2006 22:23:51 +0100
From:	Folkert van Heusden <folkert@...heusden.com>
To:	linux-kernel@...r.kernel.org
Subject: optimalisation for strlcpy (lib/string.c)

Hi,

Like the other patch (by that other person), I think it is faster to not
do a strlen first.
E.g. replace this:
ize_t strlcpy(char *dest, const char *src, size_t size)
{
        size_t ret = strlen(src);

        if (size) {
                size_t len = (ret >= size) ? size - 1 : ret;
                memcpy(dest, src, len);
                dest[len] = '\0';
        }
        return ret;
}
by this:
size_t strlcpy(char *dest, const char *src, size_t size)
{
        char *tmp = dest;

        for(;;)
        {
                *dest = *src;
                if (!*src)
                        break;

                if (--size == 0)
                        break;

                dest++;
                src++;
        }

        *dest = 0x00;

        return dest - tmp;
}
patch:
diff -uNrBbd lib/string.c string-new.c
--- lib/string.c        2006-11-04 02:33:58.000000000 +0100
+++ string-new.c        2006-12-10 22:22:08.000000000 +0100
@@ -121,14 +121,24 @@
  */
 size_t strlcpy(char *dest, const char *src, size_t size)
 {
-       size_t ret = strlen(src);
+        char *tmp = dest;

-       if (size) {
-               size_t len = (ret >= size) ? size - 1 : ret;
-               memcpy(dest, src, len);
-               dest[len] = '\0';
+        for(;;)
+        {
+                *dest = *src;
+                if (!*src)
+                        break;
+
+                if (--size == 0)
+                        break;
+
+                dest++;
+                src++;
        }
-       return ret;
+
+        *dest = 0x00;
+
+        return dest - tmp;
 }
 EXPORT_SYMBOL(strlcpy);
 #endif


I've tested the speed difference with this:
http://www.vanheusden.com/misc/kernel-strlcpy-opt-test.c
and the speed difference is quite a bit on a P4: 28% faster.


Signed-off by: Folkert van Heusden <folkert@...heusden.com>


Folkert van Heusden

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