[PD-dev] Re: pvoc example and rsqrt~
Miller Puckette
mpuckett at man104-1.ucsd.edu
Mon Dec 29 23:32:05 CET 2003
Whenever I can detect that something/s about to go NAN, I just put out
a zero instead... this is because NAN processing is apparently hundreds
of times slower on i86 hardware than processing with well-formed numbers!
This is bad about a "correct" rsqrt~ brealing the phase vocoder. I
should be "seeding" the division by adding a tiny number but must have
forgotten.
cheers
Miller
On Mon, Dec 29, 2003 at 12:53:03AM +0100, Thomas Grill wrote:
> Hi Miller, hi all,
>
> i came across a strange thing when testing the Altivec SIMD
> implementation with my favorite example, namely 04.fft/09.pvoc.pd .
> It seems that the phase propagation is dependent on the fact that
> rsqrt~ (0) delivers a valid non-zero value of about 1.e+19. (well,
> which non-zero value is irrelevant)
> If rsqrt~ (0) = 0, which would make more sense to me (given the zero
> checks in /~ ) the example is silent. (what almost drove me nuts, btw.
> )
>
> Although i already asked before, i'd be interested about the common
> behaviour of objects that are endangered to deliver NANs. Should these
> cases always be trapped and bashed to zero? To know that would help me
> a lot with the proper SIMD implementation.
>
> best greetings,
> Thomas
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