Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site redwood.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!godot!harvard!seismo!hao!hplabs!hpda!fortune!rhino!redwood!rpw3
From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.micro.68k
Subject: Re: Why no INC or DEC
Message-ID: <136@redwood.UUCP>
Date: Tue, 22-Jan-85 07:54:32 EST
Article-I.D.: redwood.136
Posted: Tue Jan 22 07:54:32 1985
Date-Received: Thu, 24-Jan-85 19:20:42 EST
References: <242@talcott.UUCP>
Organization: [Consultant], Foster City, CA
Lines: 21

+---------------
| 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.
| 			Greg Kuperberg |      harvard!talcott!gjk
+---------------

It DOES! They're just not called that. Try looking at ADDQ and SUBQ (add and
subtract "quick"). These are opcodes that can increment/decrement from one
to eight. The constant (1-8) is buried in the op code. Much more useful than
just INC and DEC, especially for stepping address pointers to bigger things
than bytes. They work with any destination: data reg, address reg, memory;
with byte, word, or long (except no byte adds to address regs).


Rob Warnock
Systems Architecture Consultant

UUCP:	{ihnp4,ucbvax!dual}!fortune!redwood!rpw3
DDD:	(415)572-2607
USPS:	510 Trinidad Lane, Foster City, CA  94404