Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdcad!ames!ll-xn!husc6!bbn!rochester!PT.CS.CMU.EDU!IUS1.CS.CMU.EDU!edw
From: edw@IUS1.CS.CMU.EDU (Eddie Wyatt)
Newsgroups: comp.unix.questions
Subject: Re: Wierd Compilers
Message-ID: <300@PT.CS.CMU.EDU>
Date: Wed, 4-Nov-87 09:24:46 EST
Article-I.D.: PT.300
Posted: Wed Nov  4 09:24:46 1987
Date-Received: Sat, 7-Nov-87 11:06:11 EST
References: <367@white.gcm> <18964@amdcad.AMD.COM> <44177@beno.seismo.CSS.GOV>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 36
Keywords: Sun

In article <44177@beno.seismo.CSS.GOV>, rick@seismo.CSS.GOV (Rick Adams) writes:
> Even a mediocre compiler should be able to recognize that
> 	a++;
> is equivalent to
> 	++a;
> if there is no assignment, etc.
> 
> There is really no excuse for not making this trivial optimization. You should
> not have to depend on the user doing it.
> 
> --rick

But they are not equivalent in the context they where used  (refering back
to the original article).

i = 10

#1 while (i--) ;
#2 while (--i) ;

In number one the operation is executed 10 times.  In number two the
operation is executed 9 times.  This is because the value of
"--" applied to a var is not ignored.  #2 can be made totally equivalent to
#1 as follows:

i++;
while (--i) { /* my junk */ }

Which is what I do. 


-- 
That one looks Jewish -- And that one's a coon -- Who let all this riff raff
into the room -- There's one smoking a joint -- and Anoter with spots -- If
I had my way -- I'd have all of you shot ... Pink Floyd, "In the Flesh"
Eddie Wyatt 				e-mail: edw@ius1.cs.cmu.edu