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NNTP-Posting-Date: Fri, 02 Dec 2011 18:49:02 -0600
Message-ID: <4ED971FE.7646@mindspring.com>
Date: Fri, 02 Dec 2011 19:49:02 -0500
From: pete <pfiland@mindspring.com>
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Subject: Re: casting constant value from float to unsigned short - compiler bugs?
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.c:14254

pete wrote:
> 
> jacob navia wrote:
> >
> > Le 02/12/11 23:36, Quentin Pope a écrit :
> > > On Fri, 02 Dec 2011 10:34:22 +0100, jacob navia wrote:
> > >> Yes. The first one is that the range for unsigned short is zero to
> > >> USHORT_MAX. Your program has undefined behavior
> > >> since a negative value
> > >> will not go into an unsigned short, it is OUTSIDE its domain.
> > >
> > > Sorry, but this is nonsense.
> > > Negative numbers stored in unsigned integer
> > > types "wrap around" - there is NO overflow for unsigned types,
> > > but all arithmetic is done modulo USHORT_MAX+1.
> > > It is amazing that you are not
> > > aware of this as a compiler writer!
> >
> > The C standard specifies that when the
> >
> > <quote> (C Standard 6.3.1.4)
> >   If the value being converted is outside the range of values that can
> > be represented, the behavior is undefined.
> > <end quote>
> >
> > A negative value can't be represented in an UNsigned integer.
> >
> > By definition.
> 
> You got that all wrong.

Sorry about that.
I got that all wrong.
I hadn't read back far enough into thread 
to realise what you were talking about.

6.3.1.4 Real floating and integer
   1 When a finite value of real floating type 
     is converted to an integer type other than _Bool,
     the fractional part is discarded 
     (i.e., the value is truncated toward zero). 
     If the value of the integral part 
     cannot be represented by the integer type, 
     the behavior is undefined.)

-- 
pete