From: lkcl <lkcl@web>
Date: Tue, 12 Jul 2022 16:05:16 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1205
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=717b2457d0c847cd2db0122965751d99c4569534;p=libreriscv.git

---

diff --git a/openpower/sv/remap.mdwn b/openpower/sv/remap.mdwn
index 777e26548..70f614777 100644
--- a/openpower/sv/remap.mdwn
+++ b/openpower/sv/remap.mdwn
@@ -160,13 +160,20 @@ 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.
+These can be found in the [[openpower/isa/svfparith]] page if performing
+IEEE754 FP transforms. *(For fixed-point transforms, equivalent 3-in 2-out
+integer operations would be required)*. These "butterfly" instructions
+avoid the need for a temporary register because the two array positions
+being overwritten will be "in-flight" in any In-Order or Out-of-Order
+micro-architecture.
 
 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.
+limit is not a problem.  A Bluestein convolution to compute arbitrary
+length is demonstrated
+by [Project Nayuki](https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.py)
 
 ## Indexed