Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!killer!ames!claris!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MPW Pascal Bug? Or am I wrong.
Message-ID: <12528@apple.Apple.COM>
Date: 20 Jun 88 18:55:45 GMT
References: <3203@polyslo.UUCP>
Reply-To: lsr@apple.apple.com.UUCP (Larry Rosenstein)
Organization: Advanced Technology Group, Apple Computer
Lines: 29

In article <3203@polyslo.UUCP> dorourke@polyslo.UUCP (David O'Rourke) writes:
>
>the wrong result, usually negative, in Z even though Z is a LONGINT.  Now is
>this what the compiler is suppose to do, or is it suppose to convert to the
>LONGINT.

The compiler is oprating correctly.  If you turn on overflow checking, then
you would get a runtime exception.  The reason that overflow checking is not
on all the time is that it expands the resulting code enormously.

One workaround is to coerce one value to a LONGINT so that the compiler uses
32-bit multiplication.  The only problem with that is that the
multiplication requires a library routine, since the 68000 doesn't have a
32-bit multiply.

A really nifty solution (used in MacApp) is to define the following
function:

FUNCTION IntMultiply(x,y: INTEGER): LONGINT; INLINE $301F, $C1DF, $2E80;

This takes the 2 integers and multiplies them using the 68000 multiply
instruction, yielding a longint.  It doesn't require a call to the Pascal
library, and is relatively fast.

-- 
		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 27-AJ  Cupertino, CA 95014
	    AppleLink:Rosenstein1    domain:lsr@Apple.COM
		UUCP:{sun,voder,nsc,decwrl}!apple!lsr