US has banned 'software patents' long time ago. However, you can still patent a software being performed by a processor or computer, which then becomes 'hardware'. NZ has now caught up with US. It is not what you think it is.
"A method of representing numbers as binary strings in the registers of a CPU, and manipulating those registers such that the output is the representation of the sum of the input numbers."
That is what happened in America when we "banned" math^H^H^H^Hsoftware patents. Software itself is not patentable, but the use of a machine to execute specific software is. So the NZ equivalent of "on a computer" will be "manipulating CPU registers" or some similar nonsense.