fft_time.c  Windows XP home, 2.53GHz P4 
N=16 FFT time=1.55e-006 
     inv time=2.35e-006 
    both time=3.525e-006 

N=32 FFT time=3.9e-006 
     inv time=6.25e-006 
    both time=8.6e-006 

N=64 FFT time=7.8e-006 
     inv time=1.25e-005 
    both time=1.87e-005 

N=128 FFT time=2.2e-005 
     inv time=2.5e-005 
    both time=4.36e-005 

N=256 FFT time=4.4e-005 
     inv time=5.6e-005 
    both time=8.76e-005 

N=512 FFT time=9.4e-005 
     inv time=0.000126 
    both time=0.000218 

N=1024 FFT time=0.000188 
     inv time=0.000248 
    both time=0.00044 

N=2048 FFT time=0.00047 
     inv time=0.000625 
    both time=0.001015 

N=4096 FFT time=0.00094 
     inv time=0.00125 
    both time=0.00203