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

[Robert Gault]

Here is a typical issue with the Leventhal book. He has   clra   clrb   std ,s 
The first two lines are two cycles each but it could be: 
  ldd #0   std ,s 
where ldd #0 is three cycles. 
He frequently does math operations on a stack item instead of a memory location without explaining why the more complex routine was chosen. 
I sugest entering some of the code in EDTASM and then running it in Zbug to see if the code works as claimed. 

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  On Sat, Jan 29, 2022 at 11:40 AM, michaelkline704 at gmail.com<michaelkline704 at gmail.com> wrote:   Good Point! I did that when I learned BASIC years ago. The cool thing about Adobe CC; you can usually make changes and resave the book. 
Michael

-----Original Message-----
From: Coco <coco-bounces at maltedmedia.com> On Behalf Of Robert Gault
Sent: 29 January 2022 10:21
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Subject: Re: [Coco] Errors in Leventhal's 6809 Subroutines book?

You will find that many of the examples in the subroutine book are far from optimal and there are others that are bad. The obvious way to learn programming is not to assume the routines are good but to actually test them say with EDTASM and try to improve on them. You will quickly find that there are much better, simpler, and more direct ways to write many of the routines. Regards p78 if you want to decrease a 16 bit number, you could just
  subd #1
RegB could be loaded from memory or from the stack. The point is to see what assumptions were made starting on p74.
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    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



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