Re: Relative Checksum

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Wed, 2003-03-26 at 18:16, Ralf Baechle wrote:
> On Wed, Mar 26, 2003 at 08:33:21AM +0000, Gilad Benjamini wrote:
> 
> > ip_fast_csum provides an asm version for IP checksum.
> > Any available mips-asm implementation out there for 
> > a relative checksum?
> > 
> > i.e. I get a packet, change
> > a field or two, and want to compute just the 
> > change in the checksum.
> 
> I suggest to look at the code for IP masquerading which already does things
> like this when rewriting packets.

Also read the RFC material on the danger of relative checksum updates.
There are a couple of interesting gotcha's with some stacks