Four types of RPN

[Thomas Klemm]

(09-03-2014 04:45 PM)Marcus von Cube Wrote:  The duplication of the value is just a side effect of the drop, not an extra operation.

The classical RPN calculators don't really use a stack but use 4 registers to emulate a stack. Thus roll-up and roll-down become expensive operations whereas when using what I consider a real stack drop is very cheap:
you just move the stack-pointer and don't move registers.

I think it's interesting that in the older HP calculators (e.g. HP-35) a special machine instruction was used for down-rotate while in later calculators (e.g. HP-41C) this was implemented using multiple read and write operations.

Does anybody know why and when this was changed?

Cheers
Thomas