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Date: Wed, 1 Apr 2009 16:58:38 +0000 (GMT)
From: Marco Atzeri <marco_atzeri AT yahoo DOT it>
Subject: Re: complex number
To: cygwin AT cygwin DOT com
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--- Mer 1/4/09, Corinna Vinschen  ha scritto:

> Da: Corinna Vinschen=20
> Oggetto: Re: complex number
> A: cygwin AT cygwin DOT com
> Data: Mercoled=EC 1 Aprile 2009, 17:22
> On Apr=A0 1 14:48, Marco Atzeri
> wrote:
> >=20
> > Dear All,
> > I was trying to understand why this code
> >=20
> > #include <iostream>
> > #include <complex>
> >=20
> > int main()
> > {
> >=A0=A0=A0double a =3D 0;
> >=A0=A0=A0double b =3D 1. / a;
> >=A0=A0=A0a +=3D 1;
> >=A0=A0=A0std::cout << std::abs
> (std::complex<double> (b, a)) << '\n';
> >=A0 }
> >=20
> > produce Inf on most platform and NaN on cygwin.
>=20
> That's the result of the newlib function which is defined
> as
>=20
> =A0 double
> =A0 cabs(z)
> =A0 struct complex z;
> =A0 {
> =A0 =A0 return hypot(z.x, z.y);
> =A0 }
>=20

Hi Corinna,
that is not correct as hypot( 0, Inf)=20
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.


> > I found that newlib have the function cabs (complex
> absolute)
> > but in cygwin the prototypes is
> >=20
> >=A0 =A0=A0=A0extern double cabs();
>=20
> The math.h header is from newlib as well.=A0 I don't
> know why the
> math.h header is missing a normal prototype.=A0 I
> *assume* that nobody
> ever made the effort to convert these old functions (cabs
> is from 1994)
> to the ANSI C style.=A0 You should ask this question on
> the newlib list.
>=20
> > so just a placeholder but not a useful function.
> > There is any reason why cygwin is missing functional
> > C99 complex functions ?
>=20
> Sorry, it's all about newlib.
>=20
>=20
> Corinna

Ok,
I will follow up on newlib,
I was not sure it is a newlib issue or cygwin specific,
as newlib have cabs function and for linux also
the expected header:

http://sourceware.org/cgi-bin/cvsweb.cgi/src/newlib/libc/sys/linux/include/=
cmathcalls.h?cvsroot=3Dsrc

Regards
Marco





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