Guillaume Melquiond <[EMAIL PROTECTED]> writes: | 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.
You seem to forget that C99 does not consider Signalling NaNs -- which are other missing parts of C99. For those NaNs, the comparaison might just trap. Please, be careful when quoting. -- Gaby _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
