说明：  一个圆周卷积的代码~调用形式为y=juanji(h,x1,M) 其中，h和x1为输入，h为滤波器系数，x1为输入采样信号，输出为y,M为输入信号x1的长度。
(A circular convolution of the code to call the form of y = juanji (h, x1, M) of them, h, and x1 for the input, h for the filter coefficient, x1 sampling input signals, output y, M for the input signal x1 length.)