[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 #68 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #67)
> (In reply to Jacob Lifshay from comment #65)
> > (In reply to Luke Kenneth Casson Leighton from comment #63)
> > > (In reply to Jacob Lifshay from comment #61)
> > > > we could change the madd ops to be 3-arg rather than 4:
> > > 
> > > i already explained clearly and non-negotiably the damaging
> > > consequences and cost of that.
> > 
> > I meant the non-twin madd ops (which aren't used for fft iirc).
> 
> ah yes, so sorry, yes those are used in Horizontal-First FFT REMAP
> mode.  that was related to complex numbers, where the "usual"
> single-for-loop-on-an-instruction would only work if we had actual
> complex-mul-and-add [which would be complete overkill and swamp
> us with work]

well, since complex numbers don't use cl*, gfb*, or gfp*, are you aware of any
other issues we might encounter? if not, I don't see why changing the madd ops
to 3-arg wouldn't work.

if we're too low on encoding space, we could have just the most widely used
*madd be 4-arg for extra flexibility, and *msub and *msubr would be 3-arg.

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