[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date: Thu, 7 Jul 2011 12:18:49 +0100
From: Ian Abbott <abbotti@....co.uk>
To: <netdev@...r.kernel.org>
CC: Ian Abbott <abbotti@....co.uk>,
"David S. Miller" <davem@...emloft.net>,
Arnd Bergmann <arnd@...db.de>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] lib/checksum.c: optimize do_csum a bit
Reduce the number of variables modified by the loop in do_csum() by 1,
which seems like a good idea. On Nios II (a RISC CPU with 3-operand
instruction set) it reduces the loop from 7 to 6 instructions, including
the conditional branch.
Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
lib/checksum.c | 13 +++++--------
1 files changed, 5 insertions(+), 8 deletions(-)
diff --git a/lib/checksum.c b/lib/checksum.c
index 0975087..8df2f91 100644
--- a/lib/checksum.c
+++ b/lib/checksum.c
@@ -49,7 +49,7 @@ static inline unsigned short from32to16(unsigned int x)
static unsigned int do_csum(const unsigned char *buff, int len)
{
- int odd, count;
+ int odd;
unsigned int result = 0;
if (len <= 0)
@@ -64,25 +64,22 @@ static unsigned int do_csum(const unsigned char *buff, int len)
len--;
buff++;
}
- count = len >> 1; /* nr of 16-bit words.. */
- if (count) {
+ if (len >= 2) {
if (2 & (unsigned long) buff) {
result += *(unsigned short *) buff;
- count--;
len -= 2;
buff += 2;
}
- count >>= 1; /* nr of 32-bit words.. */
- if (count) {
+ if (len >= 4) {
+ const unsigned char *end = buff + ((unsigned)len & ~3);
unsigned int carry = 0;
do {
unsigned int w = *(unsigned int *) buff;
- count--;
buff += 4;
result += carry;
result += w;
carry = (w > result);
- } while (count);
+ } while (buff < end);
result += carry;
result = (result & 0xffff) + (result >> 16);
}
--
1.7.6
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists