A class for calculating discrete fourier transforms using fast fourier transform. This class mimics std.numeric.Fft, but works a bit differently internally. The Fft in phobos does all the initialization when the constructor is called. Because pfft uses different tables for each combination of type and size, it can't do all the initialization up front. Instead, it calculates a table for a combination of type T and size n the first time the fft method is called with a template parameter T and a parameter of size n and then stores this table for later use.