Path: utzoo!attcan!uunet!portal!cup.portal.com!chrisj
From: chrisj@cup.portal.com (Christopher T Jewell)
Newsgroups: comp.sys.m68k
Subject: Re: addq.w #n,sp and a pop quiz
Message-ID: <12562@cup.portal.com>
Date: 13 Dec 88 05:28:51 GMT
References: <5005@bsu-cs.UUCP> <5460@cbmvax.UUCP> <1100@ncar.ucar.edu> <670@auspex.UUCP> <1737@oakhill.UUCP>
Distribution: na
Organization: The Portal System (TM)
Lines: 18

In article <1737@oakhill.UUCP>, davet@oakhill.UUCP (David Trissel) writes:

>There is only one place in the instruction set where a data register is
>implicitly sign-extended. Where?

Aw come on!  Three cases at least:
1.	ADDA.W	Dn,Am		(also SUBA.W, CMPA.W, MOVEA.W)
2.	d8(xx,Dn.W) addressing	(xx IN {PC, An})
3.	MOVEM.W	 memory to dataregs

I suppose that you intended #3, since the values loaded INTO the DRegs are
actually sign-extended during loading; in the other two cases, the value
taken FROM a DReg is sign-extended, but the reg itself is unchanged.  (The
wording of the question in your pop-quiz was ambiguous, professor! :-) )

Christopher T. Jewell   chrisj@cup.portal.com   sun!cup.portal.com!chrisj
"Just because I tell only the truth doesn't mean I tell the only truth there
is."  Father McAleer in Brad Ferguson's "To Tell the Troof" (Jan '89 F&SF)