If the signal is less than the length of N, and the need to xr xi behind complement 0, The results of x (k) the real and imaginary parts were still stored in the array xr and xi China.

• 如果信号长度小于N，需要给xr和xi后面补足0，计算结果x(k)的实部和虚部仍然分别存放在数组xr和xi中。-DIT - FFT subroutine FFT length of 2m； m is a positive integer.