[Libre-soc-isa] [Bug 960] OPF ISA External RFC ls003 - maddedu and divmod2du

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=960

--- Comment #10 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #9)
> table 13 p1353 1357 1358 Public v3.1, there are 12 spaces available.
> using a large percentage of them would be unwise.

yes, hence why I said:

(In reply to Jacob Lifshay from comment #7)
>  if encoding space is an issue, imho Rc should be removed from dsld/dsrd as
> that is imho much less useful.

one other option is using a spr (ctr? maybe a new 64-bit spr named carry?)
instead of rs/rc for those operations that aren't very useful without carrying,
such as the muled* and maddedu operations, since the existing maddld/maddhd[u]
can just be used instead. maddedus (because it's signed/unsigned mul which
doesn't currently exist in PowerISA), divmod2du, dsld/dsrd, and pcdec are quite
useful for 128-bit arithmetic without VSX, prefix-code dec/enc, etc. and should
still be 4-arg operations.

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