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From: cottrell@nbs-vms.arpa (COTTRELL, JAMES)
Newsgroups: net.lang.c
Subject: PDP-11 as 68000 Cloner
Message-ID: <3418@brl-tgr.ARPA>
Date: Tue, 19-Nov-85 20:14:56 EST
Article-I.D.: brl-tgr.3418
Posted: Tue Nov 19 20:14:56 1985
Date-Received: Thu, 21-Nov-85 07:08:08 EST
Sender: news@brl-tgr.ARPA
Lines: 37

/*  >> = Me, > = Ron Natalie
> > Of course there are *some* differences. And of course the 68000 is a 
> > 32-bit machine (crammed onto a 16-bit bus) while the pdp is a 16-bit one.
> 
> And it has the bytes in the wrong order.

Great! Another Little Endian!
 
> > As far as relative code, the pdp is missing something. How do you
> > load the address of a variable relative to the PC? This way:
> > 
> > 		mov	pc,r0			; address of `here'
> > 	here:	add	#foobar-here,r0		; make relative
> > 
> Bad example, now what are you going to do with this loaded
> address?  PDP-11 instructions allow things like
> 
> 		tst	foobar(pc)
> 
> which is exactly equivalent to
> 		
> 		tst	foobar

Bad example, now what can I do with that loaded question? You see,
foobar just happens to be an array! What I need to do is get it's
address into a register so I can auto-{in,de}crement the bugger. Or
maybe I want to pass it's address as a parameter to
str{cpy,cat,cmp,mung}. Since this ain't no VAX, we can't double index as

		tst	foobar(pc)[r0]. 

And it's just a box of rain, I don't know who put it there
Believe if if you need it, or leave it if you dare

	jim		cottrell@nbs
*/
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