From owner-freebsd-audit  Thu May 16 12: 7: 0 2002
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From: Bill Fenner <fenner@research.att.com>
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To: obrien@FreeBSD.ORG
Subject: Re: moused(8): char signed-ness problem with gcc 3.1
Cc: knu@iDaemons.org, audit@FreeBSD.ORG, current@FreeBSD.ORG
References:  <200205160346.UAA27116@windsor.research.att.com> <86k7q48h2w.wl@archon.local.idaemons.org> <20020516114247.A67791@dragon.nuxi.com>
Date: Thu, 16 May 2002 12:06:49 -0700
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>Specifically what is the problem?  Given the program below, take the
>ISO-C spec and explain the problem.  Or even w/o the spec -- I haven't
>been reading this thread.

> > int
> > main()
> > {
> >    unsigned char i = 127;
> >    char j;
> > 
> >    printf("%d\n", ((char)(i << 1)));

This prints -2, which is correct -- (signed char)254 is -2.

> >    j = ((char)(i << 1)) / 2;
> >    printf("%d\n", j);

This prints 127, which is incorrect.  -2 / 2 is -1.

> >    j = ((char)(i << 1));
> >    printf("%d\n", j / 2);

This breaks down the previous expression into two halves, and
results in the correct answer of -1.  However, there should
be no difference between
((char)(i << 1)) / 2
and
char j = ((char)(i << 1); j / 2

  Bill

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