-- Fernando Cacciola fernando_cacciola-at-movi-dot-com-dot-ar "Guillaume Melquiond" <[EMAIL PROTECTED]> escribió en el mensaje news:[EMAIL PROTECTED] > On Fri, 4 Jul 2003, Fernando Cacciola wrote: > > > Gabriel Dos Reis <[EMAIL PROTECTED]> wrote in message > > news:[EMAIL PROTECTED] > > > "jvd" <[EMAIL PROTECTED]> 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 _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
