[P4-dev] Incremental checksum with v1model?

Andy Fingerhut andy.fingerhut at gmail.com
Fri Feb 14 13:20:08 EST 2020

I do not have source code to point you at, but the PSA specification has
some sample P4-like pseudocode for the implementation of the
InternetChecksum extern that should be correct (I won't bet $1000 on it,
but I will bet $100 on it :-).  Look here:


I did some very careful reading of RFCs related to the Internet checksum
involving prior bugs in older RFCs specifying how it was specified
incorrectly in earlier versions, and tried hard to follow them, and used
some formal proof techniques for small cases that looked promising that it
should be correct.


On Fri, Feb 14, 2020 at 6:43 AM Tom Barbette <barbette at kth.se> wrote:

> Hi all,
> Does anyone have an example of incremental checksum correction (in my
> case for TCP) in P4 with the v1model? I know PSA has the
> InternetChecksum.substract, but I'd like to run it with v1.
> I tried a few common tricks, but I have a one compilment's bug from time
> to time.
> Thanks,
> Tom
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