Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!usc!srhqla!demott!kdq
From: kdq@demott.COM (Kevin D. Quitt)
Newsgroups: comp.lang.c
Subject: Re: Is something wrong with the compiler ?
Message-ID: <645@demott.COM>
Date: 2 Oct 90 21:42:05 GMT
References: <1895@tuvie>
Reply-To: kdq@demott.COM (Kevin D. Quitt)
Organization: DeMott Electronics Co., Van Nuys CA
Lines: 27

In article <1895@tuvie> hp@vmars.tuwien.ac.at (Peter Holzer) writes:
>
>Expression:					Value:
>(a = ~0)					(int) ~0
>(unsigned)(a = ~0)				(unsigned) ~0
>((unsigned)(a = ~0) >> 1)			(unsigned) MAXINT
>(int)((unsigned)(a = ~0) >> 1)			(int) MAXINT
>a = (int)((unsigned)(a = ~0) >> 1)		(int) MAXINT
>
>Anything wrong with my reasoning?

    Yes.  Undefined order or assignment means undefined.  It is
perfectly legitimate for the (a = ~0) assignment to actually take place
after the a = (int)((unsigned)(a = ~0) >> 1) assignment.  That's what
undefined order means. 

    I agree that a proper compiler "knows" that the former is
unnecessary, and can/will be optimized away, but a compiler that isn't
that smart *isn't* broken (according to the spec).

-- 
 _
Kevin D. Quitt         demott!kdq   kdq@demott.com
DeMott Electronics Co. 14707 Keswick St.   Van Nuys, CA 91405-1266
VOICE (818) 988-4975   FAX (818) 997-1190  MODEM (818) 997-4496 PEP last

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