[Coco] Optimizing 6809 Assembly Code: Part 2 – Speedup Storing Data – Unrolling Loops

[Dave Philipsen]

Here's a little trick you could add to your blog.  I think I posted an 
example of this before.  I don't know that it necessarily optimizes for 
speed but it saves space. When printing a string or any kind of calling 
a subroutine which requires a string, instead of pointing to the string 
and then calling the subroutine like this:

ldx   #strptr         point to the string
jsr   prtstr          print the string
lda   #??             continue with the rest of the program

You can do this:

jsr   prtstr          call the print string subroutine which pulls the 
address of the string from the
fcs   /text string/   program counter which was just pushed to the stack
lda   #?? continue with the rest of the program

The prtstr routine can change the program counter as it is saved on the 
stack so that when the routine returns, it returns to the point just 
past the end of the string. This optimizes for size by eliminating the 
need to load the pointer each time you print. It also reduces complexity 
because you don't need to assign a label to the string.




On 9/15/2017 9:44 PM, Glen Hewlett wrote:
> Hi Again,
>
> I just posted Part 2 of my series of blogs about optimizing 6809 assembly language programs.
>
> https://nowhereman999.wordpress.com/2017/09/15/optimizing-6809-assembly-code-part-2-speedup-storing-data-unrolling-loops/ <https://nowhereman999.wordpress.com/2017/09/15/optimizing-6809-assembly-code-part-2-speedup-storing-data-unrolling-loops/>
>
> Cheers,
> Glen
>