Date: Wed, 15 Nov 2000 05:55:42 -0800 From: Julian Elischer <julian@elischer.org> 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 Message-ID: <3A1295DE.6930D125@elischer.org> 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
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