def gen_pow_matrix(primpoly):
    q = int(math.log2(primpoly))
    res = np.zeros((2**(q) - 1, 2)).astype('int')
    res[-1, 1] = 1
    for i in range(2**(q) - 1):
        res[i, 1] = res[i-1, 1] * 2
        if res[i, 1] >= 2**q:
            res[i, 1] = primpoly ^ res[i, 1]

        res[res[i, 1]-1, 0] = i+1
        #print(res[i])
    return res