Path: utzoo!attcan!uunet!husc6!mailrus!uwmcsd1!vanvleck!uwvax!oddjob!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: Unnecessary parenthesis
Message-ID: <12281@mimsy.UUCP>
Date: 2 Jul 88 08:13:29 GMT
References: <326@marob.MASA.COM>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 42

In article <326@marob.MASA.COM> daveh@marob.MASA.COM (Dave Hammond) writes:
>Is different code produce by the compiler for "return n" and "return(n)" ?
>How about "if (x>1 && y<2)" and "if ((x>1) && (y<2))" ? Do unnecessary
>parenthesis generate more code ?

For these expressions, one would hope not.

On some machines, in certain expressions (including but not limited
to floating point arithmetic), `unnecessary' parentheses may cause
more code generation under dpANS rules:

	#define TWICE(x) ((x) + (x))
		...
		float p, q, r;
		...
		r = TWICE(p + q);

expands to

		r = ((p + q) + (p + q));

which might or might not be equivalent to

		r = p + p; r += q + q;

and if this cannot be determined, must be compiled as

		r = p + q; r += p + q;	/* more or less */

The important problem that is being solved is that

		a = (b + c) * d;

might give 0.0 where

		a = (b * d) + (c * d);

gives `floating point overflow'.  Whether this is an ideal solution
(or even a not-too-awful one) is another argument entirely....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris