def _get_length_length(_bytes):
    """Returns a count of bytes in an Ion value's `length` field."""
    if (_bytes[0] & 0x0F) == 0x0E:
        # read subsequent byte(s) as the "length" field
        for i in range(1, len(_bytes)):
            if (_bytes[i] & 0x80) != 0:
                return i
        raise Exception("Problem while reading VarUInt!")
    return 0