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

[Joel Rees]

On Sun, Jan 30, 2022 at 10:49 AM Joel Rees <joel.rees at gmail.com> wrote:
>
> On Sun, Jan 30, 2022 at 8:58 AM tim lindner <tlindner at macmess.org> wrote:
> >
> > On Fri, Jan 28, 2022 at 5:51 PM Don Barber <don at dgb3.net> wrote:
> > > However, I've already run across two bugs:
> >
> > <snip>
> >
> > It should be noted all of the programs from that book have been typed in at:
> >
> > https://github.com/jmatzen/leventhal-6809
>
> Cool. Since I'm interested, I'll check whether the bugs in question
> have been fixed.

After sidetracking on jmatzen's repository for gcc6809 and attending
some church meetings online, I finally checked, and the bugs mentioned
above are not yet fixed.

Here's the nitty-gritty:

-------- lines 95, 96 of MPBMUL.s --------

94:DECCTR:
95:  LEAU    -1,U        ; DECREMENT BYTE COUNT
96:  BNE    MULLUP        ; LOOP UNTIL MULTIPLICATION DONE

As Don noted, LEAU and LEAS do not set flags -- so that they can be
used in adjusting the stack(s) without interfering with the algorithm
flow.

As a simple fix, add one line:

94:DECCTR:
95:  LEAU    -1,U        ; DECREMENT BYTE COUNT
     CMPU #0
96:  BNE    MULLUP        ; LOOP UNTIL MULTIPLICATION DONE

-------- end lines 95, 96 of MPBMUL.s --------



-------- line 162 of MPBMUL.s --------

160:SETUP:
161:  LDX    ,S        ; GET SHIFT COUNT
162:  LEAX    -1,S        ; DECREMENT SHIFT COUNT BY 1
163:  STX    ,S
164:  BNE    SHFTST        ; CONTINUE UNLESS SHIFT COUNT EXHAUSTED

As a simple fix, add one line:

160:SETUP:
161:  LDX    ,S        ; GET SHIFT COUNT
162:  LEAX    -1,X        ; DECREMENT SHIFT COUNT BY 1
163:  STX    ,S
164:  BNE    SHFTST        ; CONTINUE UNLESS SHIFT COUNT EXHAUSTED

Note that both LEAX and STX set the Z flag, so that is not a problem here.

-------- end line 162 of MPBMUL.s --------




> > --
> > tim lindner
> >
> > "Proper User Policy apparently means Simon Says."
>
> LOL
>
> --
> Joel Rees
>
> http://reiisi.blogspot.jp/p/novels-i-am-writing.html



--
Joel Rees

http://reiisi.blogspot.jp/p/novels-i-am-writing.html