RCL IND IND: a solution in search of a problem?

[Sylvain Cote]

(12-16-2014 06:54 PM)Ángel Martin Wrote:  Is the RCL IND IND an absurd concept, or would it be actually useful for anything? I must admit I can't come up with an example right now... also wonder if some similar structure is available in RPL models (so advanced they were, right?).

What say you?

I am late for my comments, but I have been thinking since you first mention it on how could this or a derivative be use in the real world.

A pratical use I could find with one of the derivative is an indirect indexed addressing that could be use to access vectors and matrices.

ex.: RCL IND 01 IDX X or RCL IND 01 IDX 02

Another more simpler alternative for the indirect indexed addressing is to implement recall arithmetics like the one in HP-42S with standard indirect access.

ex.: RC+ X then use RCL IND X

I have did a rapid search if you had already implemented the recall arithmetic but did not find it.

Here are some examples with direct indirect indexed addressing (it's becoming confusing here lol) and with alternate indirect indexed addressing using recall arithmetic.

First scenario ...

vector[5] -> R11=33, R12=44, R13=55, R14=66, R15=77
base address -> R01=11
index -> X=2

HP-41C RPN standard (the X<>Y is there to produce the same stack result as the 42S)
Stack before -> L=90 X=2 Y=92 Z=93 T=94
Operation -> [RCL 01] [X<>Y] [+] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=92 T=93

HP-42S RPN with arithmetic recall
Stack before -> L=90 X=2 Y=92 Z=93 T=94
Operation -> [RCL+ 01] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=92 T=93

Possible implementation ?

HP-41C RPN with arithmetic recall like the 42S
Stack before -> L=90 X=2 Y=92 Z=93 T=94
Operation -> [RC+ 01] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=92 T=93

HP-41C RPN with indirect indexed
Stack before -> L=90 X=2 Y=92 Z=93 T=94
Operation -> [RCL IND 01 IDX X]
Stack after -> L=90 X=55 Y=2 Z=92 T=93

Second scenario ...

vector[5] -> R11=33, R12=44, R13=55, R14=66, R15=77
base address -> R01=11
index -> R02=2

HP-41C RPN standard
Stack before -> L=90 X=91 Y=92 Z=93 T=94
Operation -> [RCL 01] [RCL 02] [+] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=91 T=92

HP-42S RPN with arithmetic recall
Stack before -> L=90 X=91 Y=92 Z=93 T=94
Operation -> [RCL 02] [RCL+ 01] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=91 T=92

Possible implementation ?

HP-41C RPN with arithmetic recall like the 42S
Stack before -> L=90 X=91 Y=92 Z=93 T=94
Operation -> [RCL 02] [RC+ 01] [RCL IND X]
Stack after -> L=2 X=55 Y=13 Z=91 T=92

HP-41C RPN with indirect indexed
Stack before -> L=90 X=91 Y=92 Z=93 T=94
Operation -> [RCL IND 01 IDX 02]
Stack after -> L=90 X=55 Y=91 Z=92 T=93

Best regards,

Sylvain