This package contains C and Fortran FFT codes. The same routines are in each C and Fortran file.
Simple versions use no work area, but fast versions use work areas.
Fast versions have the same specification. Usage Brief explanations are in block comments of each packages. The examples are given in the test programs. I routines perform the 2D FFTs directly, but version II routines use 1D FFT routines. Please refer to this package when you modify this code.