Re: strange FFT timing

[Sergei Steshenko]

--- David Bateman <address@hidden> wrote:

> Sergei Steshenko wrote:
> > 1e6 is faster than 2^20.
> >
> > FFTW3 is with SSE2 support.
> >   
> But SSE2 instructions are only used if the block of memory passed to
> FFTW3 of type fftw_complex is 16 byte aligned. If its not then FFTW3
> falls back to a slower non SSE2 version... Octave attempts to flag
> memory blocks that have the correctly alignment for use of the SSE2
> instruction and force FFTW3 to use it. However Octave makes no attempt
> to enforce a 16byte alignment in its own Array class and so SSE2 can not
> always be used with Octave.. This is what I meant by "got lucky"..
> 
> D.
> 
> 
> -- 
> David Bateman                                address@hidden
> Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
> Parc Les Algorithmes, Commune de St Aubin    +33 6 72 01 06 33 (Mob) 
> 91193 Gif-Sur-Yvette FRANCE                  +33 1 69 35 77 01 (Fax) 
> 
> The information contained in this communication has been classified as: 
> 
> [x] General Business Information 
> [ ] Motorola Internal Use Only 
> [ ] Motorola Confidential Proprietary
> 
> 

David, I know what you've said, I simply put info on SSE2 for clarity.

Regards,
  Sergei.




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