From: Joe Perches <joe@perches.com>
To: David Miller <davem@davemloft.net>
Cc: acme@ghostprotocols.net, netdev@vger.kernel.org
Subject: Re: [PATCH] - trivial - Improve appletalk checksum calculation
Date: Mon, 22 Oct 2007 18:36:28 -0700 [thread overview]
Message-ID: <1193103388.5132.38.camel@localhost> (raw)
In-Reply-To: <20071022.173545.74561992.davem@davemloft.net>
On Mon, 2007-10-22 at 17:35 -0700, David Miller wrote:
> Your code is rotating bit 15 down by one bit and bits 0-14 up by one
> bit.
Yes, a 16 bit rotate left.
There was a discussion a few years ago:
http://oss.sgi.com/archives/netdev/2003-10/msg00734.html
>From the spec:
Implementers of DDP should treat generating the checksum as an optional
feature. The 16-bit DDP checksum is computed as follows:
CkSum := 0 ;
FOR each datagram byte starting with the byte immediately following this
Checksum field
REPEAT the following algorithm:
CkSum := CkSum + byte; (unsigned addition)
Rotate CkSum left one bit, rotating the
most significant bit in least significant bit;
IF, at the end, CkSum = 0 THEN
CkSum := $FFFF (all ones).
Reception of a datagram with CkSum equal to 0 implies that a checksum is
not performed.
next prev parent reply other threads:[~2007-10-23 1:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-22 19:36 [PATCH] - trivial - Improve appletalk checksum calculation Joe Perches
2007-10-23 0:35 ` David Miller
2007-10-23 1:36 ` Joe Perches [this message]
2007-10-23 1:43 ` David Miller
2007-10-23 1:53 ` Joe Perches
2007-10-23 3:51 ` Herbert Xu
2007-10-28 20:18 ` Urs Thuermann
2007-10-28 21:01 ` Joe Perches
2007-10-29 2:40 ` Joe Perches
2007-10-23 3:30 ` Stephen Hemminger
2007-10-23 3:39 ` Joe Perches
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