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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: Short Vectors Versus Long Vectors
Date: Fri, 3 May 2024 10:23:43 +0200
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Thomas Koenig wrote:
> Terje Mathisen <terje.mathisen@tmsw.no> schrieb:
>> 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.
> 
> I'm actually not sure how that would help.  Could you elaborate?

Just that all his code is scalar, but when you have a bunch of these 
complex mul/mac operations in a loop, his hw will figure out the 
recurrences and run them as fast as possible, with all the (Re,Im) SIMD 
flips becoming NOPs.

Terje


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