Xref: utzoo comp.unix.wizards:16680 comp.lang.c:19188
Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!oliveb!sun!david@sun.com
From: david@sun.com (there IS no ``average'' SubGenius)
Newsgroups: comp.unix.wizards,comp.lang.c
Subject: Re: Optimal for loop on the 68020.
Message-ID: <108192@sun.Eng.Sun.COM>
Date: 6 Jun 89 03:21:49 GMT
References: <11993@well.UUCP>
Sender: david@sun.Eng.Sun.COM
Lines: 54

The Sun 680x0 compiler has been able to generate dbcc loops for a long
time.  However, the loop has to be written in a particular form.
Here are some examples compiled with the SunOS 3.5 cc:

1.
	register short s;
	for (s = 127; s != -1; s--) ;

	moveq	#127,d7
LY00001:
	dbra	d7,LY00001

2a.
	register int i;
	for (i = 127; i != -1; i--) ;

	moveq	#127,d6
LY00003:
	subql	#1,d6
	moveq	#-1,d7
	cmpl	d7,d6
	jne	LY00003

(Oops!)

2b.
	register int i;
	i = 127;
	while (--i != -1) ;

	moveq	#127,d6
L20:
	dbra	d6,L20
	clrw	d6
	subql	#1,d6
	jcc	L20

3.
	extern int x;
	register short s;
	s = 127;
	while (x >= 0 && --s != -1) ;

	moveq	#127,d7
L15:
	tstl	_x
	dblt	d7,L15


P.S. Sun users might want to look at the PR_LOOP macros in
<pixrect/pr_impl_util.h>.

-- 
David DiGiacomo, Sun Microsystems, Mt. View, CA  sun!david david@sun.com