def get_mcs_index(mcs):
    """http://git.kernel.org/cgit/linux/kernel/git/jberg/iw.git/tree/util.c?id=v3.17#n453

    Positional arguments:
    mcs -- bytearray

    Returns:
    List.
    """
    answers = list()
    for mcs_bit in range(77):
        mcs_octet = int(mcs_bit / 8)
        mcs_rate_bit = 1 << mcs_bit % 8
        mcs_rate_idx_set = not not mcs[mcs_octet] & mcs_rate_bit
        if not mcs_rate_idx_set:
            continue
        answers.append(mcs_bit)
    return answers
