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Date: Wed, 1 Apr 2009 19:30:54 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: complex number
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On Apr  1 16:58, Marco Atzeri wrote:
> --- Mer 1/4/09, Corinna Vinschen  ha scritto:
> > > I was trying to understand why this code
> > > 
> > > #include <iostream>
> > > #include <complex>
> > > 
> > > int main()
> > > {
> > >   double a = 0;
> > >   double b = 1. / a;
> > >   a += 1;
> > >   std::cout << std::abs
> > (std::complex<double> (b, a)) << '\n';
> > >  }
> > > 
> > > produce Inf on most platform and NaN on cygwin.
> > 
> > That's the result of the newlib function which is defined
> > as
> > 
> >   double
> >   cabs(z)
> >   struct complex z;
> >   {
> >     return hypot(z.x, z.y);
> >   }
> > 
> 
> Hi Corinna,
> that is not correct as hypot( 0, Inf) 
> return Inf and not NaN.
> 
> There is a cabs backup implementation in libgcc that is probably
> the one used when system cabs is not available.

But cabs *is* exported by Cygwin and the function is the newlib
function.  I can't tell you why you see what you see.  I'm not
on good terms with this complex math thingy.  That's why I think
you should really discuss this on the newlib list :}


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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