[libre-riscv-dev] partitioned compare and mux

[Jacob Lifshay]

On Fri, Feb 7, 2020, 14:23 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
wrote:

> ... damn, you're right.  yes.  we'll need to have the ability to
> drop-in multiple extra carry bits in at various points.
>
> oh wait: i know.  yes, if you look at the way that the partitioning
> works, extended-A is set up to have the partition points (inverted)
> inserted in, however B very deliberately has *zeros* inserted in.  if
> instead the "carry_in" is inserted into those points (the carry_in[0]
> still has to be added in as a "pre-LSB") then that solves that one.


we need to make sure that carry isn't accidentally propagated from the
previous partition, also, if a particular partition is merged with the
previous partition, the carry in needs to be masked off to avoid
accidentally adding a carry when there was none.

Jacob