From: lkcl <lkcl@web>
Date: Mon, 11 Jul 2022 19:32:13 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1216
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=9b9e2130019438a0ebbcf6c2f26d472329f48587;p=libreriscv.git

---

diff --git a/openpower/sv/remap.mdwn b/openpower/sv/remap.mdwn
index 59b332f69..777e26548 100644
--- a/openpower/sv/remap.mdwn
+++ b/openpower/sv/remap.mdwn
@@ -153,7 +153,20 @@ instructions.
 
 ## FFT/DCT Triple Loop
 
-TODO
+DCT and FFT are some of the most astonishingly used algorithms in
+Computer Science.  Radar, Audio, Video, R.F. Baseband and dozens more.  At least
+two DSPs, TMS320 and Hexagon, have VLIW instructions specially tailored
+to FFT.
+
+An in-depth analysis showed that it is possible to do in-place in-register
+DCT and FFT as long as twin-result "butterfly" instructions are provided.
+These can be found in the [[openpower/isa/svfparith]] page.
+
+DCT and FFT Schedules are currently limited to RADIX2 sizes and do not
+accept predicate masks.  Given that it is common to perform recursive
+convolutions
+combining smaller Power-2 DCT/FFT to create larger DCT/FFTs in practice the RADIX2
+limit is not a problem.
 
 ## Indexed