Date: Sun, 12 Nov 2000 23:04:10 -0700 (MST) From: Charles Mott <cmott@scientech.com> To: Archie Cobbs <archie@dellroad.org> Cc: Ruslan Ermilov <ru@FreeBSD.ORG>, net@FreeBSD.ORG, Ari Suutari <ari@suutari.iki.fi> Subject: Re: libalias: Incremental Update of Internet Checksum Message-ID: <Pine.BSF.4.21.0011122254240.50684-100000@carcassonne.scientech.com> In-Reply-To: <200011130252.eAD2qED17117@curve.dellroad.org>
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On Sun, 12 Nov 2000, Archie Cobbs wrote: > Ruslan Ermilov writes: > > The DifferentialChecksum() function in libalias(3) is used > > to efficiently recompute the checksum for altered packets. > > Unfortunately, the implementation suffers from the problem > > described in RFC 1624. I have implemented the replacement > > for it, using the final formula [4] from the RFC. > > > > The attached C program demonstrates the problem as well as > > the new implementation. > > > > Comments? > > Wow.. seems like a pretty important thing to fix. > We should try to get this into 4.2 if possible. I haven't studied the arithmetic yet, but the problem cannot be too serious, or a lot of things would break. My guess is that this has to be an "edge effect". Since Ruslan's example program showed a delta of 1 for so many cases, I'm not sure what it means yet. I would agree that if there is a problem, it should be fixed. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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