RE: [stella] Stack pointer. Some questions

["Paul Slocum" <paul-stella@xxxxxxxxxxxxxx>]

> Really? Can you give a practical example?

Mainly places where you're using X for some index, but you need to 
temporarily use it for a different index.  I use it in the RPG in the 
routine that decompresses the map, and I think I used it in the Marble 
Craze kernel.

> Unless your swapping out of X is really timing critical but you can spare 
> the cycles required to save/restore the stack. Or you've got a stack free 
> program. Or you have no scratch RAM available.

Yeah, saving two cycles in a kernel or a long loop can make a big 
difference.  And the overhead to save/restore the stack before/after the 
kernel or loop is insignificant.

Even if you don't have a stack-free program, if you use the trick in a 
top-level routine you don't need to save the stack.  Just set it back to 
$ff when finished.

-paul 

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