[Libre-soc-bugs] [Bug 782] add galois field bitmanip instructions

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=782

--- Comment #24 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #22)

> I picked gfpmuladdsubr overwriting one of the factors (RA) because that
> makes it more flexible since there's another identical input (RB) if you
> need your factor to not be overwritten, whereas you can't do that with the
> term input (RC) cuz there's only one of them, so I had that result go to RT
> instead of overwriting the term input.

to reiterate: you really, *really* do not want to modify the FFT REMAP
algorithm.  as in, really. don't. do it.

that means working out which reg was the coefficient, which the add, which
the sub, from the ffmaddsub instruction and copying it
verbatim but moving to GF.

yes it really was that much of a deep dive.

there is literally no difference in the schedules
between FFT and NTT so there is absolutely no technical
reason to modify the FFT REMAP system, either.

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