Swapping Registers on HP calculators

[Valentin Albillo]

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Hi, n1msr,

(03-30-2024 10:06 AM)n1msr Wrote:  Thank you very much for taking t he time to reply in such detail.

You're welcome, I lean heavily on the verbose side. And excuse me for not replying sooner, I've been extremely busy creating and posting this to meet the April, 1st deadline.

Quote:I learned a lot from the post you made previously and it cleared the confusion I had about USER mode and the User RCL A for matrices.

I'm glad you did find my post useful. The HP-15C is a wonderful calc which packs tons of advanced functionalities in a small frame and thus it can be somewhat complicated for beginners or for owners who haven't used it for a long while. Myself, I don't usually remember how to deal with complex matrices as per the Owner's Handbook's instructions so I wrote my own routines.

Quote:In fact, I used registers (I had to) on the HP-67 and HP-41CX. My attempt on the 15c using matrices (which now works) was purely an exercise. However, I did learn a lot, thanks to you and others who replied.

Congratulations on making your program work using the matrix approach. And much as I loved it when I bought it new circa 1977, the HP-67 doesn't hold a candle to the HP-15C in terms of sheer power and functionality. But that red LED display, that sturdy built, that card reader ...

Quote:You might not be surprised to know that the 15c program is longer (more steps) than the HP-67 and HP-41CX programs :-) As I said, I needed to try it. I hadn't used matrices on the 15c for about 40 years, so I have had a bit of a re-learning curve to climb :-) Plus some RTFM

Good. Reading The Fantastic Manual is always a great idea. I do re-read it from time to time, it's always quite enjoyable and one usually discovers some features here and there which were passed by in earlier readings.

As for an efficient way to exchange two arbitrary registers, say Ra and Rb, these nine HP-15C steps will accomplish the task. It would be much easier if the HP-15C had a second indexing register J (as is the case with the HP35s) but as we only have RI, a little juggling is needed to load RI with a and b as needed to perform the required indirect RCL, X<> and STO operations. The procedure is highly symmetrical:

To swap Ra with Rb, where initially a is in RI and b is in stack X:

  RCL (i) 
  X<>Y 
  X<> I 
  X<>Y 
  X<> (i) 
  X<>Y 
  X<> I 
  X<>Y
  STO (i)

At the end Ra and Rb have been exchanged and additionally Rb is in stack X, b is in stack Y and a is in RI.

Quote:Thanks again for taking the time to reply. Much appreciated.

Again, you're welcome.

Regards.
V.