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List:       kde-multimedia
Subject:    Re: MMX stuff
From:       Stefan Westerfeld <stefan () space ! twc ! de>
Date:       2001-02-27 11:30:29
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   Hi!

On Mon, Feb 26, 2001 at 05:36:33AM +0100, Malte Starostik wrote:
> thanks to Darian Lanx <bio@gmx.net> I have a small test routine that checks 
> for availability of MMX and ISSE/3DNow/Cyrix Extended MMX.
> IMHO it'd be a good idea to not do those checks at compile-time (as the 
> configure check for ISSE I added to noatun recently does), but to check at 
> run-time. That way there will be no problems with binary packages compiled on 
> some other processor than the target machine. I fancy to run the check 
> somewhen during startup and set a global variable to reflect the results. 
> What do you think?

Doing checks for features that some x86-processors have and some have not at
runtime seems to be the right thing to do.

> I'm asking here as I do think that in kdemultimedia there might be the one or 
> other algorithm that could gain from some assembler optimization and so the 
> check could be added somewhere available to all of kdemultimedia and not only 
> noatun?

I think that if there is the need for a *fast* fft, we might as well modify
the one in kdelibs/arts instead of adding an alternative "fast one" to
kdemultimedia/arts. We could export the API, so that noatun could simply use
the aRts one.

The same is probably true for the bandpass filter (wouldn't it be a good idea
to make it available as Synth_BANDPASS?). I don't mind optimizations in aRts
code, as long as they are done in a way that they don't obfuscate the original
code. I.e.

	void calculateBlock(long samples) {
		if(haveISSE) calculateBlockISSE(samples);

		/* original code */
	}

is probably fine, whereas cluttering up all the code in calculateBlock with
various levels of #ifdef's is not.

   Cu... Stefan
-- 
  -* Stefan Westerfeld, stefan@space.twc.de (PGP!), Hamburg/Germany
     KDE Developer, project infos at http://space.twc.de/~stefan/kde *-         
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