[Coco] Errors in Leventhal's 6809 Subroutines book?

[Don Barber]

Hi Michael, I tested both fixes I suggested in my original message at the start of this thread. As others have said there are more efficient techniques but those are the fixes to get Leventhal’s algorithms working as designed.

Sent from my iPhone

> On Jan 29, 2022, at 10:59 AM, michaelkline704 at gmail.com wrote:
> 
> If anyone comes up with a definitive/tested answer, I would like to know so that I can correct my copy of the book (if necessary). One of my desires is to learn ASM for the CoCo. 
> 
> Cheers!
> Michael
> 
> 
> -----Original Message-----
> From: Coco <coco-bounces at maltedmedia.com> On Behalf Of Robert Gault
> Sent: 29 January 2022 00:11
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>; robert.gault at att.net; lost <lost at l-w.ca>
> Subject: Re: [Coco] Errors in Leventhal's 6809 Subroutines book?
> 
> Sorry about that. My cellphone trashed the line feeds. Maybe this will work. 
>   ldx ,s    leax -1,s    stx ,s 
> Bad code might be 
>   ldx ,s    leax -1,x    stx ,s 
> Or depending on what is in regS 
>   leas -1,s 
> The comments suggest that regS is a pointer to a 16bit value so the second sequence should be the correct one.
> 
> Sent from AT&T Yahoo Mail on Android 
> 
>  On Sat, Jan 29, 2022 at 1:02 AM, robert.gault at att.net<robert.gault at att.net> wrote:   Right, I just looked up what I think are the lines in question.      ldx ,s      leax -1,s      stx ,s The instruction is legitimate but the sequence makes no sense to me. The second instruction removes the result of the first. The comments with the code suggest that regS points to a value which is to be decreased. In that case the code should be      ldx ,s     leax -1,x     stx ,sIf regS held a value instead of a pointer, then one should just use      leas -1,s Sent from my LG Mobile
> 
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