I have implemented Dutt & Rokhlin's FFT algorithm  for non-equispaced data but for some reason I am getting very large errors ($E_2=0.04$ and $E_\infty=0.1$). I was wondering if there are any freely available implementation of this method so I can compare my implementation.
 Dutt, Alok, and Vladimir Rokhlin. "Fast Fourier transforms for nonequispaced data." SIAM Journal on Scientific computing 14.6 (1993): 1368-1393.