ref: d2763f063d7af268cfb7b64a29e7d3f87a9e2aae
dir: /libfaac/kiss_fft/TIPS/
Speed:
* experiment with compiler flags
Special thanks to Oscar Lesta. He suggested some compiler flags
for gcc that make a big difference. They shave 10-15% off
execution time on some systems. Try some combination of:
-march=pentiumpro
-ffast-math
-fomit-frame-pointer
* If the input data has no imaginary component, use the kiss_fftr code under tools/.
Real ffts are roughly twice as fast as complex.
Reducing code size:
* remove some of the butterflies. There are currently butterflies optimized for radices
2,3,4,5. It is worth mentioning that you can still use FFT sizes that contain
these factors, they just won't be quite as fast. You can decide for yourself
whether to keep radix 2 or 4. If you do some work in this area, let me
know what you find.
* For platforms where ROM/code space is more plentiful than RAM,
consider creating a hardcoded kiss_fft_state. In other words, decide which
FFT size(s) you want and make a structure with the correct factors and twiddles.