fft_time.c 
N=16 FFT time=5e-07 
     inv time=1e-06 
    both time=1.5e-06 

N=32 FFT time=1e-06 
     inv time=2e-06 
    both time=3e-06 

N=64 FFT time=2e-06 
     inv time=6e-06 
    both time=8e-06 

N=128 FFT time=5e-06 
     inv time=1e-05 
    both time=1.5e-05 

N=256 FFT time=1e-05 
     inv time=2e-05 
    both time=4e-05 

N=512 FFT time=2e-05 
     inv time=4e-05 
    both time=8e-05 

N=1024 FFT time=5e-05 
     inv time=0.0001 
    both time=0.00015 

N=2048 FFT time=1e-04 
     inv time=0.0003 
    both time=0.0003 

N=4096 FFT time=0.0002 
     inv time=0.0006 
    both time=0.0008