PRBS using linear feedback shift register implemented in Python

#! /usr/bin/env python3

def prbs_gen(msg, bitwidth, poly, seed, pam_mode):

    print(msg, 'poly=', poly, 'seed=', seed, ':')

    mask = ~((~0)<<bitwidth);

    lfsr = seed

    period = 0

    bit = 0

    while period < 32:

        for x in range(pam_mode+1):

            bit <<= 1

            bit |= cal_parity(mask&(poly&lfsr))

            lfsr = mask & ( (lfsr <<1) | (bit&1) )

        if pam_mode == 1 :

            bit &= 0x3

            gray_code_dict = {0:0, 1:1, 2:3, 3:2}

            bit = gray_code_dict[bit];

        else:

            bit &=0x1

        if period%4 == 0:

            print(' ', end='')

        print(bit, end='')

        period += 1

    print('\n')

    return period

def cal_parity(value):

    value ^= (value>>16)

    value ^= (value>>8)

    value ^= (value>>4)

    value &= 0xf

    return (0x6996>>value)&0x1

#below are example unction calls for some prbs types:

prbs_gen('LT136/LT162 prbs13Q 0', 13, 0x1803, 0x1aa0, 1);

prbs_gen('LT136/LT162 prbs13Q 1', 13, 0x1046, 0x105c, 1);

prbs_gen('LT136/LT162 prbs13Q 2', 13, 0x108a, 0x0689, 1);

prbs_gen('LT136/LT162 prbs13Q 3', 13, 0x1112, 0x0822, 1);

prbs_gen('LT93 prbs11 0', 11, 0x630, 0x3f5, 0);

prbs_gen('LT93 prbs11 1', 11, 0x530, 0x513, 0);

prbs_gen('LT93 prbs11 2', 11, 0x4a8, 0x5a7, 0);

prbs_gen('LT93 prbs11 3', 11, 0x468, 0x36f, 0);

prbs_gen('LT72 prbs11 0', 11, 0x503, 0x36f, 0);