lkml.org 
[lkml]   [2006]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subjectoptimalisation 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@vanheusden.com>


Folkert van Heusden

--
www.vanheusden.com/multitail - multitail is tail on steroids. multiple
windows, filtering, coloring, anything you can think of
----------------------------------------------------------------------
Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2006-12-10 22:27    [W:0.069 / U:15.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site