[libre-riscv-dev] partitioned compare and mux

[Michael Nolan]

Michael Nolan <mtnolan2640 at gmail.com> writes:

>
> I agree, this makes more sense than a separate subtractor. I need to
> check this for POWER, but I remember the PowerPC has a true carry bit,
> so a subtract with borrow is exactly the same as an add with carry,
> except that the B (actually A, because it only has a "subtract from")
> input is inverted.

Just checked, POWER's subtract instructions look just like PowerPC's,
they use a true carry bit for their subtractions, so subtraction is
~a+b+carry

--Michael