[Libre-soc-dev] [RFC] REMAP, SHAPE, complex (full) FFT

[Luke Kenneth Casson Leighton]

On Tue, Jul 20, 2021 at 12:56 PM Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:
>
> ---
> crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
>
> On Tue, Jul 20, 2021 at 11:27 AM Luke Kenneth Casson Leighton
> <lkcl at lkcl.net> wrote:
>
> > Henriok, if you are happy to look at how the need for swap
> > instructions can be removed that would be fantastic.
>
> see attached patch: i suspect it's going to be something like this

it was - sorry Henriok, i had to tackle it: the DCT using Vertical-First
mode would have been far too complex, with having to pause one
type of Schedule and push it onto a stack.

the solution was indeed to do *double* levels of redirection of
the data:

https://git.libre-soc.org/?p=openpower-isa.git;a=commitdiff;h=bce43f51ab3aea260e5c5df3f85cbdcc4aaf6714

currently i have a reordering phase in the middle of the butterflies,
however i *believe* it will be possible to *pre-load* the data in just the
right inversed-order, and also set the "swapping" indices up in an
inversed-order...

such that on completion of the inner butterfly *the data arrives at
the correct positions*.

l.