Path: utzoo!attcan!uunet!sdrc!scjones
From: scjones@sdrc.UUCP (Larry Jones)
Newsgroups: comp.lang.c
Subject: Re: Detecting overflow
Message-ID: <731@sdrc.UUCP>
Date: 21 May 89 14:25:21 GMT
References: <455@skye.ed.ac.uk> <723@tukki.jyu.fi> <1076@garcon.cso.uiuc.edu>
Organization: Structural Dynamics Research Corp., Cincinnati
Lines: 21

In article <1076@garcon.cso.uiuc.edu>, mcdaniel@uicsrd.csrd.uiuc.edu (Tim McDaniel) writes:
> Under pANS C, "(a*b)/b" cannot be optimized to "a".  However, if it's not
> pANS C-compliant, all bets are off.  (That's the reason for having a
> standard in the first place, so that at least SOME bets can be made.
> :-) [where a and b are both integers]

Sorry, but you're wrong -- pANS DOES allow the expression to be
optimized provided the optimized expression gives the same result
as the original expression in all cases where the result is well
defined.  If a and b are both integers, then the expression "a"
does give the same result as "(a*b)/b" except when "(a*b)/b"
overflows.  If it overflows, the results are undefined and
getting the "correct" answer without generating an overflow is
certainly an allowable response to undefined behavior.
----
Larry Jones                         UUCP: uunet!sdrc!scjones
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