--- Mer 1/4/09, Corinna Vinschen ha scritto:
> Da: Corinna Vinschen
> Oggetto: Re: complex number
> A: cygwin@cygwin.com
> Data: Mercoledì 1 Aprile 2009, 17:22
> 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);
> }
>
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.
> > 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
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=src
Regards
Marco
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