[FFmpeg-devel] suggestions for debugging ff_fft_calc_altivec?

Pavel Koshevoy pkoshevoy at gmail.com
Sun Aug 11 06:27:27 CEST 2013


I've decided to take a closer look at OSX 10.5 PPC build with
gas-preprocessor.pl.  The last time I tried it more than half a year
ago the result was that some audio decoders didn't sound right (AAC,
AC3 -- both sound like loud white noise).

I tried again today and compared decoder output from builds with and
without gas-preprocessor.  I've narrowed it down to output of
fft_calc_c (called in ff_imdct_half_c) being different from output of
ff_fft_calc_altivec (called in imdct_half_altivec).

I am not a PPC assembly expert, nor am I familiar with FFT
implementation details to be able to easily spot what the problem is
with ff_fft_calc_altivec.  Can anyone offer some suggestions to
proceed further?

Thank you,

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