[FFmpeg-devel] Fwd: Fixpoint FFT optimization, with MDCT and IMDCT wrappers for audio optimization

[Marc Hoffman]

On 8/21/07, Michael Niedermayer <michaelni at gmx.at> wrote:
> Hi
>
> On Tue, Aug 21, 2007 at 05:02:18PM -0400, Marc Hoffman wrote:
> > Hi,
> >
> > On 8/19/07, Justin Ruggles <justinruggles at bellsouth.net> wrote:
> > >
> > >                      256    512   1024   2048    4096
> > > -------------------------------------------------------
> > > (1) fft32           46.1   101.0  205.0  494.4  1169.3
> > > (2) fftr2            7.6    16.0   34.1  101.3   258.5
> > > (3) fft ffmpeg       7.4    16.4   33.8   82.4   187.7
> > > (4) fftr4/2          6.7    13.6   28.2   74.0   169.8
> > >
> > > (1) fixedpoint 32bit simple RAD2 fft
> > > (2) simple rad2 first stage rad4
> > > (3) current lavc RAD2, first 2 stages, and middle pulled
> > > (4) rad4/2 with last stage rad2 if needed
> >
> > I'm adding a split radix to the list.  Its a lot harder to optimize
> > because of the extra pointer manipulation and control structures.  I
> > did manage to unroll the W0 multipliers out but getting a clean
> > iteration space has not happened yet.
>
> could you also add the split radix fft from
> liba52-cvs/a52dec/liba52/imdct.c
> as comparission
>
> also djbfft and fftw2 would be interresting
> IIRC they all use split radix ffts
>
> and looking at them might help you with optimizing your code

Your right if we do those techniques we would have to implement a
different optimized FFT for every possible data size we need. Unless
I'm missing something please advise.

Marc