Fourier transform library is a dll that contains functionswhich calculate the fast fourier transform (FFT) and the inverse FFT (IFFT).

This FFT implementation accepts only real numbers as input and produces complex numbers as output (spectrum). Analogously, IFFT accepts complex numbers and produces real ones.

Therefore, IFFT requires only half of the spectrum as input (the other half can be reconstructed on the basis of symmetry, since we know that it is a spectrum of a real signal). Summarizing:

real �� FFT �� complex
complex �� IFFT �� real
The functions contain implementation of Cooley-Tukey algorithm, which requires that the number of samples be a power of 2. The algorithm used here is optimized for real input.

If one wants to use this library in their program, they can find function declarations in the header file, available below.

They have long comments and this is the only documentation that I have written for this library, and there will probably never be a better one, due to the author's laziness and/or lack of time.