[Libre-soc-dev] pysvp64asm: opcode setvli not supported

Luke Kenneth Casson Leighton lkcl at lkcl.net
Wed Jun 16 11:24:58 BST 2021

crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

On Wed, Jun 16, 2021 at 6:36 AM Lauri Kasanen <cand at gmx.com> wrote:

> On Tue, 15 Jun 2021 19:19:56 +0100
> Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> > i replaced the fmuls and fadds with fmadds, and also took the
> > liberty of using fmsubs in appropriate locations, which also gave
> > the opportunity to remove tmpsum and tmpsum2 because with
> > fmsubs / fmadds both sum and sum2 can be directly used as
> > accumulators, carrying on the subtract (or add).
> I'm having some trouble understanding why fmsubs works at all.

hmm possibly because the buf0 coincidentally contains a lot of zeros
in exactly the right places?

sum is mulres1 - mulres0, when it should be -mulres1 - mulres0. Note
> the sign of the last mul res.

ok, i'm reverting the fmsubs and the removal of tmpsum and tmpsum2,
then copying the pattern of subtracting from something for MLSS
at the end sum.

it still passes on buf0 but fails on buf1000.


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