class AT3Helper:

    def calculate_checksum(message):
        r = 0
        for c in message:
            r += c
        r = (r % 256)
        return bytes([r])

    def bit8_in_byte_on(bin_value):
        return (bin_value & 0b10000000) > 0

    def bit7_in_byte_on(bin_value):
        return (bin_value & 0b01000000) > 0
