[Libre-soc-isa] [Bug 924] potential major opcode allocation for SVP64

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=924

--- Comment #17 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #16)

> afaict those are *new* encodings, so no, it's not 48-63, it's 248-263 (in
> your weird prefix * 100 + suffix scheme).

[the weird prefix+suffix scheme.  best to think of it in advance as not
 being "personally owned" given that it's to be transferred to the OPF]

>  it would be equally valid to pick
> po 200-215 (as i'm suggesting) as what you currently picked -- po 248-263.

ok, right, yes, that's much clearer

> I'm suggesting picking zeros rather than 11 because that's what is
> conventional for quite a few places in the power isa spec.

honestly it doesn't matter what it is. i'm happy for the OPF to pick the
digits.

two digits represents a 25% reservation of the new space.  i did say that
we could potentially go to three (12.5% - only 8 new POs) but it starts
to get dicey at that point, especially given that:

* at least one of those new POs are likely to be for large bitmanip  
* 22 new POs (!!) are needed for a full suite of LD-ST-with-shift!
  (which has to be done *really* carefully - if at all - just
   sticking with add-with-shift might be better)

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