# -*- coding: utf-8 -*-

#GP: Generator Polynomial, MP: Message Polynomial
# test:
GP_list = {
        7: [0, 87, 229, 146, 149, 238, 102, 21],
        10: [0, 251, 67, 46, 61, 118, 70, 64, 94, 32, 45],
        13: [0, 74, 152, 176, 100, 86, 100, 106, 104, 130, 218, 206, 140, 78],
        15: [0, 8, 183, 61, 91, 202, 37, 51, 58, 58, 237, 140, 124, 5, 99, 105],
        16: [0, 120, 104, 107, 109, 102, 161, 76, 3, 91, 191, 147, 169, 182, 194, 225, 120],
        17: [0, 43, 139, 206, 78, 43, 239, 123, 206, 214, 147, 24, 99, 150, 39, 243, 163, 136],
        18: [0, 215, 234, 158, 94, 184, 97, 118, 170, 79, 187, 152, 148, 252, 179, 5, 98, 96, 153],
        20: [0, 17, 60, 79, 50, 61, 163, 26, 187, 202, 180, 221, 225, 83, 239, 156, 164, 212, 212, 188, 190],
        22: [0, 210, 171, 247, 242, 93, 230, 14, 109, 221, 53, 200, 74, 8, 172, 98, 80, 219, 134, 160, 105, 165, 231],
        23: [0, 229, 121, 135, 48, 211, 117, 251, 126, 159, 180, 169, 152, 192, 226, 228, 218, 111, 117, 232, 87, 96, 227, 21],
        26: [0, 173, 125, 158, 2, 103, 182, 118, 17, 145, 201, 111, 28, 165, 53, 161, 21, 245, 142, 13, 102, 48, 227, 153, 145, 218, 70],
        28: [0, 168, 223, 200, 104, 224, 234, 108, 180, 110, 190, 195, 147, 205, 27, 232, 201, 21, 43, 245, 87, 42, 195, 212, 119, 242, 37, 9, 123],
        30: [0, 41, 173, 145, 152, 216, 31, 179, 182, 50, 48, 110, 86, 239, 96, 222, 125, 42, 173, 226, 193, 224, 130, 156, 37, 251, 216, 238, 40, 192, 180]
        }

#DC: Data Codewords, ECC: Error Correction Codewords
def get_ECC(DC, ECC_num):
    GP = GP_list[ECC_num]    
    remainder = DC
    for i in range(len(DC)):
        remainder = divide(remainder, *GP)
    return remainder
    
def divide(MP, *GP):
    po2 = get_power_of_2_list()
    log = get_log_list(po2)
    GP = list(GP)
    for i in range(len(GP)):
        GP[i] += log[MP[0]]
        if GP[i] > 255:
            GP[i] %= 255
        GP[i] = po2[GP[i]]
    
    return XOR(MP, GP)
    
    
def XOR(MP, GP):
    a = len(MP) - len(GP)
    if a < 0:
        MP += [0] * (-a)
    elif a > 0:
        GP += [0] * a
    
    remainder = []
    for i in range(1, len(MP)):
        remainder.append(MP[i]^GP[i])
    return remainder
    
def get_power_of_2_list():
    po2 = [1]
    for i in range(255):
        a = po2[i] * 2
        if a > 255:
            a ^= 285
        po2.append(a)
    return po2
    
def get_log_list(po2):
    log = [None]*256
    for i in range(255):
        log[po2[i]] = i
    return log