[libre-riscv-dev] [Bug 189] Create partitioned right shift using the existing partitioned left shift

bugzilla-daemon at libre-riscv.org bugzilla-daemon at libre-riscv.org
Thu Feb 27 21:47:59 GMT 2020


--- Comment #5 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Michael Nolan from comment #4)

> > ah, nice.  see how the cascade is no longer an O(N^2) thing?
> > just a simple O(N) one instead.
> Ah yes I see now. However it looks like yosys is able to optimize the first
> version into the second one, they both end up as the same number of gates.

yyeah, not completely happy relying on that happening.

> > next one, ROR? :)  or shall we leave that one to be a
> > micro-op, put data twice through the pipelines as a
> > FSM?  hmm, back to the other bugreport i think
> ROR shouldn't be as common as SHL and SHR in normal code right? 

it's more for crypto and other stuff.  however there's that POWER ISA

> I think
> doing it in microcode would be fine, at least for the first iteration.

see how it goes.

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