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[this is perhaps a little simplistic to be of interest, but…]

I often want to perform two successive binary operations (i.e. operations with two operands/arguments) on the same input, leaving the two results in the two lower stack levels.

An example might be finding the quotient and remainder (DIV/MOD) of two integers, on calculators that don't have a combined operation such as e.g 41/SandMath QREM, 50g IDIV2, Prime iquorem(). That often requires the first operation to be a binary operation followed by one or more unary operations, e.g. ÷ IP, followed by the second binary operation, e.g. MOD.

My clumsy efforts are as follows; I've not yet considered using STO/RCL methods, which might be useful if stack preserving was a requirement.

This is for interactive use; of course a program could be simpler.

I'd be interested in hearing of quicker/easier/more elegant methods.

RPN (stack not preserved)

Code:

Y ENTER ENTER X ENTER

R↓ x<>y R↓

<first binary operation>

<successive unary operations>

ENTER R↓ R↓                    # dup first result to Z

<second binary operation>

if the RPN example has just a single first binary operation, with no successive unary operations, it's much simpler:

RPN (stack not preserved)

Code:

Y ENTER ENTER X

<first binary operation>

x<>y

LASTX

<second binary operation>

RPL (uses stack levels 1–4)

Code:

Y X DUP2

<first binary operation>

<successive unary operations>

3 ROLLD                        # move first result to level 3; alt: ROT ROT

<second binary operation>

if the RPL example has just a single first binary operation, with no successive unary operations, it's much simpler:

RPL (uses stack levels 1–4)

Code:

Y X

<first binary operation>

LASTARG

<second binary operation>

arg! I stupidly forgot that RPL LASTARG will restore both args, which makes the RPL case trivial; ah well.

Although, LASTARG will only work if there's just one operation.

e.g. in my example, on many calcs the quotient requires two operations: ÷ IP, and so LASTARG won't restore the original Y X.

The RPL example in the first post will allow successive unary operations after the first binary operation.

and there's a similar use of LASTX that can be used to simplify the RPN case, again if there's only the one binary operation. I'll edit that in too.

(02-23-2020 01:03 AM)cdmackay Wrote: [ -> ]I often want to perform two successive binary operations...
My clumsy efforts are as follows; I've not yet considered using STO/RCL methods, which might be useful if stack preserving was a requirement.

Sure! Check the attachment, there is my opinion about "Tricky-Genius-Programming-Style" - just as a practical engineer point of view...

So, with STO and RCL, with one flag and with lots of labels:

LBL A and LBL B: the two binary operation
LBL S: store the stack status
LBL T: store previous result
LBL R: restore the stack status

variable R: previous result
flag 0: set, if the stack X is the previous result

for the first running clear the flag 0

Code:

LBL A / LBL B

  XEQ S

  //do the binary operation on Y and X here; result in X

  SF 0 //it was an operation and the result is in X

  XEQ R //recover the stack

RTN

LBL S //store stack status

  FS0? //there is a result in X?

  XEQ T

  STO X

  x<>y

  STO Y

  x<>y

RTN

LBL T

  STO R

  Rdown

  CF0

RTN

LBL R //stack recovery

  RCL Y

  x<>y

  RCL X

  x<>y

RTN

Csaba

https://www.hpmuseum.org/forum/attachment.php?aid=8104

On the hp50g, I've done this several way depending on the desired operations. Sometimes I do things like (assuming two operands on the stack):
MAX LASTARG MIN
In other cases:
DUP2 "ops leaving single result" UNROT

I often need things like IDIV2 but that's so slow that IQUOT (or even / FLOOR) and MOD with LASTART or DUP2 are much faster.

hah! very good, I agree Wink

thanks for all the suggestions, will study. forgot about UNROT too.

I've been mostly doing this interactive, so hadn't even thought about performance e.g. IDIV2, good point thanks!

cdmackay

cdmackay

cdmackay

cdmackay

Csaba Tizedes

ttw

cdmackay