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From: pjh@mccc.UUCP (Pete Holsberg)
Newsgroups: comp.lang.c
Subject: Re: Another silly question
Message-ID: <761@mccc.UUCP>
Date: 23 May 89 16:32:17 GMT
References: <17812@cup.portal.com> <607@kl-cs.UUCP> <749@mccc.UUCP> <17635@mimsy.UUCP> <756@mccc.UUCP> <25711@amdcad.AMD.COM>
Reply-To: pjh@mccc.UUCP (Pete Holsberg)
Organization: The College On The Other Side of U. S. Route 1
Lines: 35

In article <25711@amdcad.AMD.COM> tim@amd.com (Tim Olson) writes:
=However, if instead you wrote them like:
=
=	int a[MAX];			int a[MAX];
=	int i;				int *p;
=	for (i=0; i<MAX; ++i)		for (p=&a[0]; p<&a[MAX]; ++p)
=		a[i] = 0;			*p=0;
=
=Then you indeed might get different assembly language generated.  The
=second pointer version has had a "loop induction" optimization performed
=by hand. On some compiler/machine combinations, this will run faster,
=because the scaling operation and base/offset addition have been
=eliminated; on others it may run slower, because a specific addressing
=mode cannot be used.

Tim,
	Here's the actual code.  I think you've hit the nail on the head.

#define IMAX 10
#define LOOP 10000

main()
{
	int a[IMAX];
	register int * p;
	int v=0;
	
	while (v++ < LOOP)
		for (p=a; p < &a[IMAX];)
			*p++=v;
}

-- 
Pete Holsberg, Mercer County Community College, Trenton, NJ 08690  
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