[Libre-soc-dev] next ISA WG RFC

Luke Kenneth Casson Leighton lkcl at lkcl.net
Tue Mar 7 10:20:22 GMT 2023

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On Tue, Mar 7, 2023 at 2:28 AM Jacob Lifshay <programmerjake at gmail.com> wrote:
> On Mon, Mar 6, 2023, 10:45 Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>> On Monday, March 6, 2023, Jacob Lifshay <programmerjake at gmail.com> wrote:
>> > On Mon, Mar 6, 2023, 04:10 Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>> >>
>> >> folks we need to discuss what RFCs should go in next, and plan
>> >> groupings
>> >> https://libre-soc.org/openpower/sv/bitmanip/
> <snip>
>> >>
>> >> * bmask (x86 BMI on steroids) and cprop (carry-propagation)
>> >> * bitmask ops (or/and/xor/get) actually shift operations
>> >
>> > aren't those just `crand` or `and` and similar? i'm guessing that's not what you meant, so links please.
> i'll note my comments throughout the full email only apply to the one bullet list item directly above, here i wasn't asking about bmask or cprop.

ah ok. inline error.  so, yes, crternlogi is not the same as crand/cror (etc),
and crbinlog is not the same either: they contain a "mask" which performs
up to four crand/cror/crxor/crnand operations at a time.  crand/cror/crnand
etc. whilst they are clearly based on the same principle as crbinlog (but
cut the table in half) only do a single bit of a single CR Field.

>> bmset, etc in the bitmanip page.
> ah, thx! found them. my only comment is that imho the bit-reversed versions are likely uncommon enough that using whatever combination of grevi and bmext or similar that that turns out to be is probably better.

i found them in a proposal from AndesSTAR as part of their
PackedSIMD proposal.  there must be some use that they
have/need in DSP / Audio.

> how about waiting to see what it looks like before deciding...

that works, i've plugged them in to the relevant top-level


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