- case 0 is first, because this indicates that the modulo operation in the switch statement (count % 8) has no remainder, i.e., all 8 copy instructions should be executed. So, this is first because of the properties of the modulo operation.

- the to pointer is not incremented because it corresponds to a single memory mapped output register (http://en.wikipedia.org/wiki/Duff%27s_device#Original_versio...). It does not have anything to do with the use if Duff's device.

hth