From owner-freebsd-net  Wed Nov 15  5:56:24 2000
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Message-ID: <3A1295DE.6930D125@elischer.org>
Date: Wed, 15 Nov 2000 05:55:42 -0800
From: Julian Elischer <julian@elischer.org>
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To: Ruslan Ermilov <ru@FreeBSD.ORG>
Cc: Charles Mott <cmott@scientech.com>,
	Archie Cobbs <archie@dellroad.org>, net@FreeBSD.ORG,
	Ari Suutari <ari@suutari.iki.fi>
Subject: Re: libalias: Incremental Update of Internet Checksum
References: <Pine.BSF.4.21.0011122254240.50684-100000@carcassonne.scientech.com> <Pine.BSF.4.21.0011130015100.50906-100000@carcassonne.scientech.com> <20001113103852.E34671@sunbay.com> <3A126F63.8EB0D49@elischer.org> <20001115150433.A98014@sunbay.com>
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Ruslan Ermilov wrote:
> 
> On Wed, Nov 15, 2000 at 03:11:31AM -0800, Julian Elischer wrote:
> > Ruslan Ermilov wrote:
> > >
> > Here's the version I wrote some years ago..
> >
> >   #define FIXSUM16(c, op, np)                                          \
> >     do {                                                               \
> >       (c) -= (u_int16_t) ~*((u_int16_t *) (op));                       \
> >       if ((c) < 0) {                                                   \
> >         (c) += 0xffff;                                                 \
> >       }                                                                \
> >       (c) -= (u_int16_t)  *((u_int16_t *) (np));                       \
> >       if ((c) < 0) {                                                   \
> >         (c) += 0xffff;                                                 \
> >       }                                                                \
> >     } while (0)
> >
> > it replaces the 16 bit word at *op with the new value at *np and updates
> > the checksum c
> >
> The above is the implementation of 4th equation from RFC 1624, right?
> But we are talking about the version that allows updating of N 16-bit
> words, not exactly one word.

I can't remember which it was, but I also had a version that did N
words..
the same math applies though..
you just do it in a loop :-)

I wrote this myself but read the RFCs
does it pass your test cases?


> 
> --
> Ruslan Ermilov          Oracle Developer/DBA,
> ru@sunbay.com           Sunbay Software AG,
> ru@FreeBSD.org          FreeBSD committer,
> +380.652.512.251        Simferopol, Ukraine
> 
> http://www.FreeBSD.org  The Power To Serve
> http://www.oracle.com   Enabling The Information Age

-- 
      __--_|\  Julian Elischer
     /       \ julian@elischer.org
    (   OZ    ) World tour 2000
---> X_.---._/  presently in:  Budapest
            v


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