Re: A83:'ret'

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Re: A83:'ret'


On the other hand, it's possible that you could have perfectly bug-free code
and still want to save/restore the stack pointer.  A oft-used example is a
"boss-key".  If you want a certain key to be able to exit instantaneously
from any point in the program, it's a whole lot easier just to restore the
stack and quit than to bother with making sure that you're not in the middle
of any calls or have any registers pushed.

-Dan Englender

----- Original Message -----
From: "David Phillips" <david@acz.org>
To: <assembly-83@lists.ticalc.org>
Sent: Monday, January 29, 2001 7:30 PM
Subject: Re: A83:'ret'


>
> As several people suggested, you can save the stack pointer at the
beginning
> of your program and restore it at the end as a sort of "safety net" in
case
> you screw things up.  However, this is generally not good practice and
> should be avoided if at all possible.  A well written program will never
> need to manually restore the stack.  Usually having a corrupt stack is a
> sign of a bug.  Think about it: why are you randomly pushing values that
you
> aren't going to pop off?  Or why are you calling a routine that you are
not
> going to return from?  When writing complex routines that use a lot of
> registers that also involve some complex logic, it sometimes be tricky to
> make sure you don't mess up the stack, but that doesn't mean you should
let
> it become corrupted.  It's still a bug.
>
> About the only time you would need to clear the stack is for error
handling.
> But on a calculator, you don't really need to be bailing out of routines
due
> to random errors, simply because they don't exist.  In general programming
> (such as games), there are only a couple things that I can think of that
> would force you to abort the program.  The first would be not finding a
> required variable, such as graphics or levels.  In this case, you would
> probably do the detection at the start of the program, and it would be
> trivial to exit without corrupting the stack.  The other instance would be
> needing to allocate variables, either for more memory or to save a high
> score.  Again, these are going to happen at some fixed point in the
program,
> and not just at any random time.  For something like C++'s exception
> handling, saving and restoring the stack could be genuinely useful.  But
as
> I said before, you don't really need that on a calculator.  Using it for
any
> other purpose is just going to make it harder on yourself, because you're
> using very poor coding methods and introducing very difficult to find bugs
> into your program.
>
> > If you use al lot of 'push' and 'pop' during a program, your calculator
> can
> > easily crash when trying to exit the program with the usual 'ret'(i'm
> > writing for ION btw, but i don't think that has an influence)
> > Is there a way of avoiding crashes or do you just have count how many
> times
> > you pushed a register and then pop it as many times? (and that's not so
> > easy! So i hope there is another way...)
>
>
>
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