Rearrange loop, clear stack, revise comments

[pamoroso]

This patch just tweaks the code a bit to make the flow more clear and fix a potential issue with not properly clearing the stack when exiting the program.

I moved the instructions that update the inner loop control registers closer to the check for termination, cleared PSW left on the stack when jumping to the program exit, and revised the comments.

[vbmacher]

Thanks @pamoroso !

[pamoroso]

You're welcome!