Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!agate!shelby!neon!kaufman
From: kaufman@Neon.Stanford.EDU (Marc T. Kaufman)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Increment (Was Re: Pascal deficiency)?
Message-ID: <1990Dec18.001753.3756@Neon.Stanford.EDU>
Date: 18 Dec 90 00:17:53 GMT
References: <1990Dec17.160242.5095@phri.nyu.edu> <1990Dec17.172613.7941@cs.umn.edu> <ewright.661465844@convex.convex.com>
Organization: Computer Science Department, Stanford University
Lines: 30

In article <ewright.661465844@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <1990Dec17.172613.7941@cs.umn.edu> sec@cs.umn.edu (Stephen E. Collins) writes:

>Actually, this would have to be

->x++:         LOAD  X
->             INC   X
->             STORE X

>Unless you have an instruction to increment variables in memory!

Well, since we ARE in a Mac group, lets just look at the code MPW C generates
for just such constructs:

	i = i+1;
	MOVE.L     i,D2
	ADDQ.L     #$1,D2
	MOVE.L     D2,i

	i++;
	MOVE.L     i,D2
	ADDQ.L     #$1,i

	++i;
	ADDQ.L     #$1,i

Behold.  The 68K does, indeed, have an instruction to increment variables in
memory.

Marc Kaufman (kaufman@Neon.stanford.edu)