fwt,fwt2分别是一维、二维快速沃尔什变换函数,采用蝶形快速算法编写，要比利用矩阵相乘得到变换结果的离散沃尔什变换快很多-fwt, fwt2 are one-dimensional, two-dimensional fast Walsh transform function, the use of butterfly Fast Algorithm for the preparation of, than the use of transformation matrices to be the result of the discrete Walsh transform much faster