Re: [Discuss-gnuradio] patch to gcell fft

[Eric Blossom]

On Wed, Jul 09, 2008 at 04:38:20PM -0400, Charles Swiger wrote:
> Here is a patch to add windowing to
> gcell/src/lib/wrapper/spu/gcs_fft_1d_r2.c , seems quick and snappy:
> 
> 
> 24a25
> > #include <spu_intrinsics.h>
> 50a52
> >
> 52,53c54,69
> <     // FIXME pointwise multiply in *= window
> <     assert(0);
> ---
> >     /*  pointwise multiply:  in *= window
> >      *
> >      *  shuffle pattern to make float 'window' suitable for vector multiply
> >      *  by complex 'in'
> >      */
> >     vector unsigned char pattern[2];
> >     pattern[0] = (vector unsigned 
> > char){0x0,0x1,0x2,0x3,0x0,0x1,0x2,0x3,0x4,0x5,0x6,0x7,0x4,0x5,0x6,0x7};
> >     pattern[1] = (vector unsigned 
> > char){0x8,0x9,0xa,0xb,0x8,0x9,0xa,0xb,0xc,0xd,0xe,0xf,0xc,0xd,0xe,0xf};
> >     register vector float zeros = (vector float){0,0,0,0};
> >     register vector float tempwin;
> >
> >     int i;
> >     for (i=0; i<(1 << log2_fft_length)/2; i++) {
> >        tempwin = spu_shuffle(window[i/2],zeros,pattern[(i & 0x1)]);
> >        in[i] *= tempwin;
> >     }
> 
> 
> Seems to work, take a lot of 'spikeyness' out:
> 
> http://www.swigerco.com/fft_windowing.html
> 
> It will also break gr-gcell/src/qa_fft.py
> 
> --Chuck

No need for all this shuffling...

I'll see if I can't get something in later on today.

Eric