[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




More information about the Pd-dev mailing list