And yet another post.
I want to describe two very nasty 6502 programming tricks, if you
promise to never ever use them and if so, that you don't claim that I
told you.
Ok, here's one I found by myself, it's utilized a lot in the Alpha demo.
Let's say you're in Subroutine1 which would end like this:
...
JSR Subroutine2
RTS
If you are totally aware what you are doing, you might consider to save
a Byte and some Cycles, by just doing:
...
JMP Subroutine2
instead. (Remember: Don't ever do this - and I didn't tell you!)
Here's the next, which I found in Starmaster:
Imagine you're doing a fast loop, where you'd need three variables, not
just X and Y.
Now you could use a temporary variable or push and pop the third value
to the stack.
But if you need to be faster, consider doing this to temporarily store
the variable away:
TXS
and get it back with
TSX
of course. This is way faster than PLA / PHA,
BUT KEEP IN MIND THESE RULES:
- Don't do this within a subroutine!
- Don't do any JSRs or other stack handling between TXS and TSX!
- Don't forget to restore the Stack to $FF after the loop!
(If you construct your loop in a way, that X ends with $FF, this
would cost just an additional TXS after the loop)
(And again: Remember: Don't ever do this - and I didn't tell you!)
Greetings,
Manuel
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