[Libre-soc-bugs] [Bug 1044] SVP64 implementation of pow(x,y,z)

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1044

--- Comment #15 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from bug #1175 comment #2)
> (In reply to Jacob Lifshay from bug #1175 comment #0)
> > since I want to use [mcrxrx].
> 
> ahh what for? can you put something about it on the mailing list
> and as usual crossref to bugreport(s)

I'm using mcrxrx to check if an unsigned bigint subtraction has a result that's
less than zero (aka. it underflowed) .. the sv.subfe leaves XER.CA set if the
result is >= 0, otherwise it's cleared. mcrxrx moves CA to a CR field, so I can
branch on it.

basically, it's a combined subtraction-comparison all-in-one.

https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=src/openpower/test/bigint/powmod.py;h=c0d5e3161cf0421f2c829aa9ae7b36fe837004dc;hb=8444282d4c29bbeb19e84612c5f075d078d27f3b#l112

see the corresponding lines in the python algorithm:
https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=src/openpower/test/bigint/powmod.py;h=c0d5e3161cf0421f2c829aa9ae7b36fe837004dc;hb=8444282d4c29bbeb19e84612c5f075d078d27f3b#l138

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