fft_time.c  448MHz P3 Linux
N=16 FFT time=3e-06 
     inv time=4e-06 
    both time=7e-06 

N=32 FFT time=8e-06 
     inv time=9e-06 
    both time=1.6e-05 

N=64 FFT time=1.6e-05 
     inv time=2e-05 
    both time=3.4e-05 

N=128 FFT time=3.5e-05 
     inv time=4e-05 
    both time=8e-05 

N=256 FFT time=8e-05 
     inv time=9e-05 
    both time=0.00017 

N=512 FFT time=0.00018 
     inv time=0.00018 
    both time=0.00038 

N=1024 FFT time=0.0004 
     inv time=0.0004 
    both time=0.0008 

N=2048 FFT time=0.0012 
     inv time=0.0009 
    both time=0.0021 

N=4096 FFT time=0.0024 
     inv time=0.0042 
    both time=0.0064