HP-25/SR-56 Identical Conditionals

[Dave Britten]

(10-14-2021 04:49 PM)Valentin Albillo Wrote:  Excuse me but in your example you use "DSZ 4". At face value, I read this as "Decrement and Skip if Zero (Register 4)".

But I asked for an example of "DSNZ", i.e., "Decrement and Skip if Not Zero" ...

What gives ? Can you supply a non-contrived example using DSNZ, as asked, to see its usefulness and cleanness, please ?

Regards.
V.

Well, I did provide an example, but it was in the format seen on a TI where you can actually do this. But if we imagine an HP with a DSNZ function, you could replace the original loop early exit:

Code:


...loop body...
DSZ 4
GTO 0
GTO 9 //exit loop
LBL 0
...rest of the loop body...

...with this:

Code:


...loop body...
DSNZ 4
GTO 9 //exit loop
...rest of the loop body...

It's not a super frequent occurrence, but it does come up for me now and then. I suspect in the case of TI, they figured they've got this unmerged INV prefix instruction already, so might as well make it have an effect on as many other instructions as makes sense. In the case of a calculator with merged steps, it's probably more difficult to argue for giving it space in the opcode table.