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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: Short Vectors Versus Long Vectors
Date: Thu, 2 May 2024 10:13:33 +0200
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Thomas Koenig wrote:
> MitchAlsup1 <mitchalsup@aol.com> schrieb:
> 
>> Then contemplate for an instant that one would want SIMD instructions for
>> Complex numbers and Hamiltonian Quaterions......
> 
> Quaternions would be a bit over the top, I tink.  Complex
> multiplication... implementing (e,f) = (a*c-b*d,a*d+b*c) is
> 
>          fmul    Rt1,Rc,Rb
>          fmac    Re,Rd,Ra,Rt1
> 
>          fmul    Rt2,Rd,Rb
>          fmac    Rf,Rc,Ra,-Rt2
> 
> So, you'd need both operands on both lanes.  Not very SIMD-friendly,
> I would assume, but (probably) not impossible, either.
> 
If you have the four operands spread across two SIMD registers, so 
(Re,Im) in each, then you need an initial pair of permutes to make 
flipped copies before you can start the fmul/fmac ops, right?

This is exactly the kind of code where Mitch's transparent vector 
processing would be very nice to have.

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"