Re: [PATCH v2 bpf-next] bpf: improve the general precision of tnum_mul

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2025-08-15 at 19:35 +0530, Nandakumar Edamana wrote:
> This commit addresses a challenge explained in an open question ("How
> can we incorporate correlation in unknown bits across partial
> products?") left by Harishankar et al. in their paper:
> https://arxiv.org/abs/2105.05398
> 
> When LSB(a) is uncertain, we know for sure that it is either 0 or 1,
> from which we could find two possible partial products and take a
> union. Experiment shows that applying this technique in long
> multiplication improves the precision in a significant number of cases
> (at the cost of losing precision in a relatively lower number of
> cases).
> 
> This commit also removes the value-mask decomposition technique
> employed by Harishankar et al., as its direct incorporation did not
> result in any improvements for the new algorithm.
> 
> Signed-off-by: Nandakumar Edamana <nandakumar@nandakumar.co.in>
> ---

Hi Nandakumar,

Could you please provide a selftest demonstrating a difference in behavior?
What technique did you employ to estimate the number of cases when
precision is improved vs worsened? If this is some kind of a program
doing randomized testing, could you please share a link to it?

Thanks,
Eduard