Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!ittatc!dcdwest!sdcsvax!sdcrdcf!hplabs!hpda!hpisoa2!hpitg!ttrdc!levy@ttrdc
From: levy@ttrdc
Newsgroups: net.lang.c
Subject: Re: Infinite Loops
Message-ID: <854@ttrdc>
Date: Wed, 30-Apr-86 04:50:00 EDT
Article-I.D.: ttrdc.854
Posted: Wed Apr 30 04:50:00 1986
Date-Received: Tue, 13-May-86 01:16:55 EDT
References: <8200004@ztivax>
Lines: 69

In article <140@toram.UUCP>, roe@toram.UUCP writes:
>In article <577@ur-helheim.UUCP> badri@ur-helheim.UUCP (Badri Lokanathan) writes:
>>My question is the following: is there any reason (other
>>than personal preferance) why one would prefer to use any particular form?
>>I personally prefer the while(1) form since it seems to make better reading.
>>Even better, I sometimes define TRUE to be 1 and then use while(TRUE).
>Unless you have a very unique optimizer, it is usually better to use the
>for(;;) form rather than the while(1) form.  Reason is:  while(1) is
>ALWAYS evaluated (ie. : is 1 TRUE? if so, continue) before each iteration,
>whereas for(;;) compiles as a simple branch or jump instruction with no
>test and no conditional branch.
>				Roe Peterson

What very unique optimizer?  Here's what I get (SysV 3B20, cc -S [note no -O]):

$ cat > while1.c
main()	/* while1.c */
{
	register int a=0;
	while (1) a++;
}
^D$ cc -S while1.c
$ cat while1.s
	.file	"while1.c"
	.data
	.text
	.align	4
	.def	main;	.val	main;	.scl	2;	.type	044;	.endef
	.globl	main
main:
	save	&.R1
	addw2	&.F1,%sp
	movw	&0,%r8
.L14:
	addw2	&1,%r8
	jmp	.L14
	^^^^^^^^^^^^
.L13:
.L12:
	ret	&.R1
	.set	.R1,1
	.set	.F1,0
	.def	main;	.val	.;	.scl	-1;	.endef
	.data
$ cc -c while1.s
$ dis while1.o
		****   DISASSEMBLER  ****


disassembly for while1.o

section	.text
main()
	   0:  7a10                          save    &0x1,&0x0
	   2:  346c 0000 0000 000b           addw2   &0x00000,%sp
	   a:  1508                          movw    &0x0,%r8
	   c:  1118                          addw2   &0x1,%r8
	   e:  9002                          br      -0x2 <c>
					     ^^^^^^^^^^^^^^^^
	  10:  7b10                          ret     &0x1
	  12:  dede                          nop     
-- 
 -------------------------------    Disclaimer:  The views contained herein are
|       dan levy | yvel nad      |  my own and are not at all those of my em-
|         an engihacker @        |  ployer or the administrator of any computer
| at&t computer systems division |  upon which I may hack.
|        skokie, illinois        |
 --------------------------------   Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa,
						vax135}!ttrdc!levy