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From: dan@digi-g.UUCP (Dan Messinger)
Newsgroups: net.micro.68k
Subject: Re: Why no INC or DEC
Message-ID: <473@digi-g.UUCP>
Date: Wed, 23-Jan-85 11:08:03 EST
Article-I.D.: digi-g.473
Posted: Wed Jan 23 11:08:03 1985
Date-Received: Mon, 4-Feb-85 04:42:41 EST
References: <242@talcott.UUCP>
Reply-To: dan@digi-g.UUCP (dan)
Distribution: net
Organization: Digigraphic Systems Corp., Mpls, MN
Lines: 15
Summary: 

In article <242@talcott.UUCP> gjk@talcott.UUCP (Greg Kuperberg) writes:
>Why doesn't the 68000 have increment or decrement instructions?  I know
>that the 68000 was designed (at least to some degree) with the spirit of
>RISC, but INC and DEC are actually quite simple, and useful, instructions.

Have you noticed the ADDQ and SUBQ instructions?  These are single word
instructions that do a quick add/subtract of a 1 to 8 constant.  The
constant is kept in a 3 bit field that most other instructions use
to specify a register.  A special INC/DEC by 1 instruction could use
no less code space, and probably execute no faster.  So (in my opinion),
the 68000 has instructions superior to INC/DEC.

Dan Messinger
Digigraphic Systems Corp.
ihnp4!umn-cs!digi-g!dan