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From: franco@iuvax.cs.indiana.edu
Newsgroups: comp.sys.atari.st
Subject: Re: question of the day
Message-ID: <36500013@iuvax>
Date: Fri, 9-Oct-87 09:20:00 EDT
Article-I.D.: iuvax.36500013
Posted: Fri Oct  9 09:20:00 1987
Date-Received: Sun, 11-Oct-87 13:57:56 EDT
Organization: Indiana University CSCI, Bloomington
Lines: 28
Nf-ID: #N:iuvax:36500013:000:1033
Nf-From: iuvax.cs.indiana.edu!franco    Oct  9 08:20:00 1987


A few days ago I requested info on the following code which I thought should
replicate the bottom line until the end of readable memory:

		movea.l	#go,a0
	go:	move.w	(a0)+,(a0)

First, some people were concerned that I was about to release some devious
software.  No, I am teaching an assembly language course using the atari
and am merely interested in giving my students a straight story.

Second, the most reasonable suggestion was that a0 in (a0)+ gets updated
after the instruction "move.w (a0)+,(a0)" is executed.  However, I tried
the following code segment:

		movea.l	#go1,a0
		movea.l	#go2,a1
	go1:	move.w	(a0)+,(a1)+
	go2:

and the result was the same (normal termination with no damage when executed
outside of RAID and expected stomping over everything when executed in RAID).

We are so interested in understanding the behavior of this program that
I have been authorised to award a bust of Abraham Lincoln made from steel
to the first person that clears up the mystery.

Please email to franco@iuvax.cs.indiana.edu