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From: rind@popvax.uucp (747707@d.rind)
Newsgroups: comp.lang.pascal
Subject: Re: Is this not a bug?
Message-ID: <5777@husc6.harvard.edu>
Date: 21 Feb 91 13:32:05 GMT
References: <1991Feb20.170152.5401@ux1.cso.uiuc.edu>
Sender: news@husc6.harvard.edu
Organization: Health Sciences Computing Facility, Harvard University
Lines: 22

In article <1991Feb20.170152.5401@ux1.cso.uiuc.edu>
 mead@uxh.cso.uiuc.edu (Alan David Mead) writes:
>I finally tracked down a problem with an application writen in
>TP5.5:  Since my values are all positive, I used words instead of
>integers.  The ABS() function, however, does not operate as (I)
>expected with word parameters.  This code demonstrates.  While I
>can imagine how the value is produced by ABS(), I think the manual's
>description is deceptive.  What does the net think?
[Code deleted.]

I don't see this as a bug.  It's not ABS that's not functioning as you
expect.  Any other function would have behaved the same way.  When
you took the difference of two WORD variables inside a function call,
the result was a WORD.  Since a WORD is unsigned, it could never
go negative, and so the difference had to be a number between
0 and 65535.  The function call ABS(w2-w1) is equivalent to creating
a third word variable w3 and doing w3 := w2-w1 followed by ABS(w3).
I can't see the point in ever taking the absolute value of a WORD
type variable, but perhaps someone else has some thoughts on this.

David Rind
rind@popvax.harvard.edu