在本computes fft.c

代码说明：

fft.c--This computes an in-place complex-to-complex FFT x and y are the real and imaginary arrays of 2^m points. dir = 1 gives forward transform dir = -1 gives reverse transform -fft.c This computes an in-place complex-to-complex FFT x and y are the real and imaginary arrays of 2 ^ m points. dir = 1 gives forward transform dir =-1 gives reverse transform