def gen_m_sequence(taps, init=0x2):
degree = utils.get_highest_set_bit(taps)
mask = (2 ** (1+degree)) - 1
bins = init
done = 0
output = []
while not done:
output.append(1 if bins & 1 else 0)
bins = ((bins >> 1) +
((utils.count_bits(taps & bins) % 2) << (degree-1))) & mask
if bins == init or bins == 0:
done = 1
return numpy.array(output)
def berlekamp_factorisation_check(a):
# Check for two or more irreducable factors
# from http://www.diva-portal.org/smash/get/diva2:414578/FULLTEXT01.pdf
# gcd(f(x), f'(x))
# (a >> 1) & 0x77777777 is a quick way of differentiating a gf2 poly < 32 bits
if utils.gf2_gcd(a, (a >> 1) & 0x77777777) != 1:
return False
degree = utils.get_highest_set_bit(a)
polys = [utils.gf2_mod(1 << (2*i), a) ^ (1 << i) for i in xrange(degree)]
for i, div in enumerate(polys[:i]):
for j in range(len(polys[i+1:])):
polys[j+i+1] ^= div
if polys[j+i+1] == 0:
# Matrix of polys is not full rank
return False
return True
