Path: utzoo!attcan!uunet!cs.utexas.edu!sdd.hp.com!samsung!think!snorkelwacker!spdcc!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: () ignored in some expressions
Message-ID: <16426@haddock.ima.isc.com>
Date: 10 Apr 90 18:56:48 GMT
References: <48079@lanl.gov> <101287@convex.convex.com> <18833@duke.cs.duke.edu>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Cambridge, MA 02138-5302
Lines: 12

In article <18833@duke.cs.duke.edu> drh@duke.cs.edu writes:
>I often what to do things like increase an integer by 50%.  This can
>be done as follows:    i = (i*3)/2;   If an optimizing compiler can
>ignore the parenthesis, then it will [reduce this to a no-op]

Yeah, right.  And it will change "(x+1)*(x+1)" to "x + 1*x + 1", which isn't
what I wanted!  Horrors!

Seriously, folks, this is *not* what K&R 1 said.  "i = (i*3)/2" has always
been safe from this type of optimization.

Karl W. Z. Heuer (karl@ima.ima.isc.com or harvard!ima!karl), The Walking Lint