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Fernando Cacciola
fernando_cacciola-at-movi-dot-com-dot-ar
"Guillaume Melquiond" <gmelquio_at_[hidden]> escribió en el mensaje news:Pine.LNX.4.44.0307050538540.31315-100000_at_goldorak...
> On Fri, 4 Jul 2003, Fernando Cacciola wrote:
>
> > Gabriel Dos Reis <gdr_at_[hidden]> wrote in message
> > news:m31xx6i7tm.fsf_at_uniton.integrable-solutions.net...
> > > "jvd" <vygis_d_at_[hidden]> writes:
> > >
> > > | Dear boosters,
> > > |
> > > | seems like this code
> > > |
> > > |     template< typename T >
> > > |     bool is_nan( const T& v )
> > > |     {
> > > |         return std::numeric_limits<T>::has_quiet_NaN && (v != v);
> > > |     }
> > > |
> > > | does not work correctly on some machines.
> > >
> > > Yes.  It is an incorrect (unfortunately popular) implementation.
> > >
> > Right. We should say that more often. It is incorrect however popular.
>
> Yes, it is incorrect for C++. But it's something we can hope to see one
> day. For example, in the LIA-1 annex I about C langage bindings, it is
> written that != is a binding for IEEE-754 ?<> operator (unordered
> compare). In the C9X annex F.8.3 about relational operators, it is written
> that the optimization "x != x -> false" is not allowed since "The
> statement x != x is true if x is a NaN". And so on.
>
Yes of course... but we will have to wait until the LIA-1 bindings
make into C++.
But not too long I hope.
> > Most compilers provide a non standard extension for this purpose.
> > For instance, Borland uses _isnan.
> > In general, these extensions are found on <float>.
>
> In fact, since it is not specified by the C++ standard, isnan comes from
> the C headers and is supposed to be found in <math.h>.
>
Right.. I was actually thinking on the C header but wrote it incorrectly.
I meant <cfloat>.
> > The best approach, IMO, is to have a boost::is_nan() with compiler specific
> > implementations.
>
> Yes, and there also were discussions on this mailing-list about a
> <boost/fenv.hpp> header. But unless somebody finds the time to tackle this
> whole problem...
>
Thanks to Gabriel we may have an is_nan() right now.
Is there anything else that the interval library uses which might be better
packed as a compiler-platform specific routine?
Fernando Cacciola