The basic fortran fft code comes from:

  https://web.pa.msu.edu/people/edmunds/Code/ADF_2/freq_space/


To compile and run it you need to do this:

>  gfortran  -c  -fdec  convert_4096.for

>  gfortran  -c  -fdec  forward_fourier_4096.for

>  gfortran  -o  convert_4096.exe  convert_4096.o  forward_fourier_4096.o

>  ./convert_4096.exe