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From: louie@sayshell.umd.edu (Louis A. Mamakos)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: TCP checksums
Message-ID: <1991Jun5.213556.13556@ni.umd.edu>
Date: 5 Jun 91 21:35:56 GMT
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In article <9105311628.AA24660@berserkly.cray.com> dab@BERSERKLY.CRAY.COM (David Borman) writes:
>So, just as addition will never yield a value of 0000, subtraction
>will never yield a value of FFFF.  Another way of stating it is that
>when the 1's sum wraps, it will give you -0, when the 1's difference
>wraps, it will give you +0.

Err.., excuse me.  Those of us with hardware that actually does one's
complement (horrors!) arithmentic can depend on the hardware never
generating a -0 as the result of any arithmetic operation.  So, in
fact, I do get checksums computed with a value of 0x0000, which might
be turned into a 0xffff when you take the one's complement.

Of course, my hardware also have 9 bit bytes...

louie