Four types of RPN
09-10-2014, 06:46 AM
Post: #21
 Thomas Klemm Senior Member Posts: 1,448 Joined: Dec 2013
RE: Four types of RPN
(09-10-2014 02:04 AM)htom trites Wrote:  It is more useful on a drop to stuff a 1 into t (assuming a constant size stack), rather than a 0 (1 being more used than 0 in computations), although echoing t is also useful.

In case of a constant stack size this is what probably happens behind the scene:
Code:
L = X X = Y ∘ X Y = Z Z = T

Thus T isn't changed at all.

Cheers
Thomas
09-11-2014, 10:19 AM (This post was last modified: 09-11-2014 11:40 AM by Marcus von Cube.)
Post: #22
 Marcus von Cube Senior Member Posts: 754 Joined: Dec 2013
RE: Four types of RPN
The HP 35 has limited memory and uses its T register for intermediate calculations in some transcendental functions. It makes sense to clear T after its "abuse" in order to avoid presenting garbage to the user. So as long as you don't use any transcendental functions, the behavior is "top copy", but top can be cleared on occasion.

Edit: I just read in another thread that only the trig functions are affected and that the HP 35 duplicates Z to T after such an operation.

Marcus von Cube
Wehrheim, Germany
http://www.mvcsys.de
http://wp34s.sf.net
http://mvcsys.de/doc/basic-compare.html
09-11-2014, 10:41 AM
Post: #23
 walter b On Vacation Posts: 1,957 Joined: Dec 2013
RE: Four types of RPN
Well, well, the claim was top copy versus
Quote:top is zeroed (HP-35 does this until T has a non-zero value)

Learning English together again ... (or: How shall I know what I meant until I read what I wrote?).

d:-/
09-11-2014, 01:30 PM (This post was last modified: 09-11-2014 01:56 PM by Thomas Klemm.)
Post: #24
 Thomas Klemm Senior Member Posts: 1,448 Joined: Dec 2013
RE: Four types of RPN
(09-11-2014 10:19 AM)Marcus von Cube Wrote:  The HP 35 has limited memory and uses its T register for intermediate calculations in some transcendental functions. It makes sense to clear T after its "abuse" in order to avoid presenting garbage to the user. So as long as you don't use any transcendental functions, the behavior is "top copy", but top can be cleared on occasion.

There's an instruction stack -> a that drops the X register from the stack and moves it to register a:

X → a
Y → X
Z → Y
T → Z

There's another instruction c -> stack that pushes register c to the stack. After executing this instruction the previous value of the T register is lost.

Z → T
Y → Z
X → Y
c → X

Thus the intermediate result during the calculations of transcendental functions is saved in the X register and not in the T register.

Quote:Edit: I just read in another thread that only the trig functions are affected and that the HP 35 duplicates Z to T after such an operation.

With the instruction stack -> a the T register is duplicated to the Z register.

Cheers
Thomas
09-11-2014, 05:09 PM
Post: #25
 axd1967 Junior Member Posts: 20 Joined: Sep 2014
RE: Four types of RPN
(09-11-2014 10:19 AM)Marcus von Cube Wrote:  The HP 35 has limited memory and uses its T register for intermediate calculations in some transcendental functions. It makes sense to clear T after its "abuse" in order to avoid presenting garbage to the user. So as long as you don't use any transcendental functions, the behavior is "top copy", but top can be cleared on occasion.

Edit: I just read in another thread that only the trig functions are affected and that the HP 35 duplicates Z to T after such an operation.

BTW - sounds like a waste of time/energy to clear the register: does a zero help the user more than a random value?

48SX; 42S; 15C; DM-15; DM-41; my public HP links
09-11-2014, 05:11 PM
Post: #26
 axd1967 Junior Member Posts: 20 Joined: Sep 2014
RE: Four types of RPN
(09-11-2014 10:19 AM)Marcus von Cube Wrote:  Edit: I just read in another thread that only the trig functions are affected and that the HP 35 duplicates Z to T after such an operation.

That other thread would be this one ? :-)

48SX; 42S; 15C; DM-15; DM-41; my public HP links
09-11-2014, 08:57 PM
Post: #27
 Marcus von Cube Senior Member Posts: 754 Joined: Dec 2013
RE: Four types of RPN
(09-11-2014 05:11 PM)axd1967 Wrote:  That other thread would be this one ? :-)

Of course...

Marcus von Cube
Wehrheim, Germany
http://www.mvcsys.de
http://wp34s.sf.net
http://mvcsys.de/doc/basic-compare.html
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