Why is post-check more optimized than a Repeat loop, though?

I think I remember mentioning why this is in a previous post somewhere... ah yes, here it is:

Quote from: ScoutDavid on December 31, 2010, 05:22:09 pm

Quote from: Runer112 on December 31, 2010, 05:20:38 pm

Speaking of optimizing control structures, any chance for Do...While loops?

I'd like Switch cases more than Do...While loops, but I don't really know how the second works.

Do...While loops are a lot like While...End loops, except that the check to advance to another iteration of the loop is at the end instead of the beginning. This turns out to be more optimized. Whereas a While...End loop has two jumps, one to exit the loop if the condition is false and one to jump back to the beginning, a Do...While combines the two into one jump that jumps back to the beginning if the condition is true.

I don't know how good that explanation was, but perhaps this pseudocode will help clarify it. Numbers in brackets indicate the number of bytes the real code takes:

While...End loop		Do...While loop
Code: [Select] ;While [x] Loop condition [2] Check if loop condition is true or false [3] Exit the loop if false ;Loop contents ;End [3] Jump back to the beginning of the loop		Code: [Select] ;Do ;[0] Start of the loop, takes no actual code ;Loop contents ;While [x] Loop condition [2] Check if loop condition is true or false [3] Jump back to the beginning of the loop if true

---

I like leaving the last Return in because it helps code readability, and it makes it easier to add new subroutines after it. It doesn't actually affect the compiled code, right?

I agree that it improves readability, but because Axe automatically adds a return to the end of programs it's redundant and a waste of 1 byte. You can always improve readability while maintaining optimization by keeping the final Return, but commenting it out.

Quote from: Deep Thought on March 01, 2011, 09:26:00 am

Why is post-check more optimized than a Repeat loop, though?

I think I remember mentioning why this is in a previous post somewhere... ah yes, here it is:

Oh, right, I keep thinking Repeat is the same as in BASIC (post-checking).

Quote from: Deep Thought on March 01, 2011, 09:26:00 am

I like leaving the last Return in because it helps code readability, and it makes it easier to add new subroutines after it. It doesn't actually affect the compiled code, right?

I agree that it improves readability, but because Axe automatically adds a return to the end of programs it's redundant and a waste of 1 byte. You can always improve readability while maintaining optimization by keeping the final Return, but commenting it out.

Axe actually checks if there's already a Return at the end. If there is, it isn't added.

Quote from: Deep Thought on February 28, 2011, 10:55:41 pm

Quote from: ztrumpet on February 28, 2011, 09:50:07 pm

Looks great!  Are you going to keep the ship on the screen?

What do you mean?

Are you going to make it so the player's sprite cannot go off the screen?

Yeah, definitely. Runer112's code takes care of that, and I think I'll use it for ASHMUPK. That part of it should be fairly easy to understand.

I swear Quigibo mentioned he optimized the Return...

Maybe it was just a feature request. I'll check.

I swear Quigibo mentioned he optimized the Return...

Maybe it was just a feature request. I'll check.

It was available at one time, but I removed this feature for some reason because there was a case where this behavior was not desired.  I can't seem to remember what it was though... if I can't think of anything, I'll add it back in.

I believe it was removed because of something to do with subprograms and memory leaks o.O