Re: Short Vectors Versus Long Vectors

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"