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From: alan@oscvax.UUCP (Alan Rooks)
Newsgroups: net.micro.68k,net.lang.c
Subject: Re: Question of Ignorance
Message-ID: <355@oscvax.UUCP>
Date: Sat, 11-May-85 19:59:03 EDT
Article-I.D.: oscvax.355
Posted: Sat May 11 19:59:03 1985
Date-Received: Sun, 12-May-85 02:35:59 EDT
References: <198@unccvax.UUCP>
Reply-To: alan@oscvax.UUCP (Alan Rooks)
Organization: Ontario Science Centre, Toronto
Lines: 15
Xref: utcs net.micro.68k:737 net.lang.c:5094
Summary: 


David Anthony was wondering why Alcyon Corp's C compiler scales constants in:

if (ptr == CONSTANT) ...

Maybe Alcyon's justification for this is that (they think) it is equivalent to:

if (ptr - CONSTANT == 0) ...

which is generally true in comparisons, but not with pointers. So when they
subtract the constant from the pointer, they have to scale it, as per
K&R page 189. The funny thing is, they don't generate code with a subtraction
and a compare against zero (and it would be a shame if they did) ...

Alan Rooks, Ontario Science Centre