From owner-freebsd-net  Wed Nov 15  5: 5:31 2000
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Date: Wed, 15 Nov 2000 15:04:33 +0200
From: Ruslan Ermilov <ru@FreeBSD.ORG>
To: Julian Elischer <julian@elischer.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: <20001115150433.A98014@sunbay.com>
Mail-Followup-To: Julian Elischer <julian@elischer.org>,
	Charles Mott <cmott@scientech.com>,
	Archie Cobbs <archie@dellroad.org>, net@FreeBSD.ORG,
	Ari Suutari <ari@suutari.iki.fi>
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>
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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.


-- 
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


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