[FFmpeg-devel] [PATCH] libavutil: add an FFT & MDCT implementation

[Lynne]

May 4, 2019, 10:00 PM by dev at lynne.ee:

> May 4, 2019, 8:10 PM by > michael at niedermayer.cc <mailto:michael at niedermayer.cc>> :
>
>> On Fri, May 03, 2019 at 09:08:57PM +0200, Lynne wrote:
>>
>>> This commit adds a new API to libavutil to allow for arbitrary transformations
>>> on various types of data.
>>>
>> breaks build on mips
>>
>> CC	libavutil/fft.o
>> src/libavutil/fft.c:47: error: redefinition of typedef ‘AVFFTContext’
>> src/libavutil/fft.h:25: note: previous declaration of ‘AVFFTContext’ was here
>> make: *** [libavutil/fft.o] Error 1
>>
>> [...]
>>
>
> Fixed, v2 attached. Changes:
> -Stride really is in bytes now.
> -Corrected some comments (stride supported by all (i)mdcts, not just compound
>  ones, some clarifications regarding the scale).
>
> Also that 28-point FFT comparison was a typo, its 128.
>

Managed to further optimize the 15-point transform by rewriting it as an exptab-less
compound 3x5 transform and embedding its input map into the parent transform's map.
Updated comparisons to libfftw3f:
120:
  22353 decicycles in     fftwf_execute,     1024 runs,      0 skips
  21836 decicycles in compound_fft_15x8,     1024 runs,      0 skips

480:
  103998 decicycles in       fftwf_execute,    1024 runs,      0 skips
  102747 decicycles in compound_fft_15x32,    1024 runs,      0 skips
960:
  186210 decicycles in      fftwf_execute,    1024 runs,      0 skips
  215256 decicycles in compound_fft_15x64,    1024 runs,      0 skips

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