The opposite of splitclass(). Joins a (service, major, minor) class-of-
    device tuple into a whole class of device value.

def _joinclass(codtuple):
    """
    The opposite of splitclass(). Joins a (service, major, minor) class-of-
    device tuple into a whole class of device value.
    """
    if not isinstance(codtuple, tuple):
        raise TypeError("argument must be tuple, was %s" % type(codtuple))
    if len(codtuple) != 3:
        raise ValueError("tuple must have 3 items, has %d" % len(codtuple))

    serviceclass = codtuple[0] << 2 << 11
    majorclass = codtuple[1] << 2 << 6
    minorclass = codtuple[2] << 2
    return (serviceclass | majorclass | minorclass)