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Date: Wed, 1 Apr 2009 17:22:56 +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 14:48, Marco Atzeri wrote:
> 
> Dear All,
> 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);
  }

> I found that newlib have the function cabs (complex absolute)
> but in cygwin the prototypes is
> 
>     extern double cabs();

The math.h header is from newlib as well.  I don't know why the
math.h header is missing a normal prototype.  I *assume* that nobody
ever made the effort to convert these old functions (cabs is from 1994)
to the ANSI C style.  You should ask this question on the newlib list.

> so just a placeholder but not a useful function.
> There is any reason why cygwin is missing functional
> C99 complex functions ?

Sorry, it's all about newlib.


Corinna

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

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