netdev - [PATCH] - trivial - Improve appletalk checksum calculation

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Date:	Mon, 22 Oct 2007 12:36:19 -0700
From:	Joe Perches <joe@...ches.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: [PATCH] - trivial - Improve appletalk checksum calculation

It's a bit after 2.6.1 now...

Removes unnecessary if, uses 16 bit rotate left.
Performance improves ~30%

Signed-off-by: Joe Perches <joe@...ches.com>

diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 7c0b515..1c50f4c 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -925,15 +925,9 @@ static int atrtr_ioctl(unsigned int cmd, void __user *arg)
 static unsigned long atalk_sum_partial(const unsigned char *data,
 				       int len, unsigned long sum)
 {
-	/* This ought to be unwrapped neatly. I'll trust gcc for now */
 	while (len--) {
-		sum += *data;
-		sum <<= 1;
-		if (sum & 0x10000) {
-			sum++;
-			sum &= 0xffff;
-		}
-		data++;
+		sum += *data++;
+		sum = ((sum & 0x8000)>>15) | ((sum & 0x7fff)<<1);
 	}
 	return sum;
 }


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