c@409: Speed:
c@409:     * If you want to use multiple cores, then compile with -openmp or -fopenmp (see your compiler docs).
c@409: 	Realize that larger FFTs will reap more benefit than smaller FFTs. This generally uses more CPU time, but
c@409: 	less wall time.
c@409: 
c@409:     * experiment with compiler flags
c@409:         Special thanks to Oscar Lesta. He suggested some compiler flags 
c@409:         for gcc that make a big difference. They shave 10-15% off
c@409:         execution time on some systems.  Try some combination of:
c@409:                 -march=pentiumpro
c@409:                 -ffast-math
c@409:                 -fomit-frame-pointer
c@409: 
c@409:     * If the input data has no imaginary component, use the kiss_fftr code under tools/.
c@409:       Real ffts are roughly twice as fast as complex.
c@409: 
c@409:     * If you can rearrange your code to do 4 FFTs in parallel and you are on a recent Intel or AMD machine,
c@409:     then you might want to experiment with the USE_SIMD code.  See README.simd
c@409: 
c@409: 
c@409: Reducing code size:
c@409:     * remove some of the butterflies. There are currently butterflies optimized for radices
c@409:         2,3,4,5.  It is worth mentioning that you can still use FFT sizes that contain 
c@409:         other factors, they just won't be quite as fast.  You can decide for yourself 
c@409:         whether to keep radix 2 or 4.  If you do some work in this area, let me 
c@409:         know what you find.
c@409: 
c@409:     * For platforms where ROM/code space is more plentiful than RAM,
c@409:      consider creating a hardcoded kiss_fft_state. In other words, decide which 
c@409:      FFT size(s) you want and make a structure with the correct factors and twiddles.
c@409: 
c@409:     * Frank van der Hulst offered numerous suggestions for smaller code size and correct operation 
c@409:     on embedded targets.  "I'm happy to help anyone who is trying to implement KISSFFT on a micro"
c@409: 
c@409:     Some of these were rolled into the mainline code base:
c@409:         - using long casts to promote intermediate results of short*short multiplication
c@409:         - delaying allocation of buffers that are sometimes unused.
c@409:     In some cases, it may be desirable to limit capability in order to better suit the target:
c@409:         - predefining the twiddle tables for the desired fft size.