Gabriel Dos Reis <[EMAIL PROTECTED]> wrote: > "Joel de Guzman" <[EMAIL PROTECTED]> writes: > >> Fernando Cacciola <[EMAIL PROTECTED]> wrote: >>> Gabriel Dos Reis <[EMAIL PROTECTED]> wrote in >> >>>> Yes. It is an incorrect (unfortunately popular) >>>> implementation. >>>> >>> Right. We should say that more often. It is incorrect >>> however popular. >>> >>> Most compilers provide a non standard extension for this >>> purpose. >>> For instance, Borland uses _isnan. >>> In general, these extensions are found on <float>. >>> The best approach, IMO, is to have a boost::is_nan() with >>> compiler specific implementations. >> >> Hi, >> >> We have an is_nan(float) implementation (for quiet NaNs of course) >> that does just that. Right now, it supports most compilers on Win32 but it >> should be straight-forward to support others. Right now, it is tested on: >> >> g++2.95.3 (MinGW) >> g++3.1 (MinGW) >> Borland 5.5.1 >> Comeau 4.24 (Win32) >> Microsoft Visual C++ 6 >> Microsoft Visual C++ 7 >> Microsoft Visual C++ 7.1 >> Metrowerks CodeWarrior 7.2 >> >> The default implementation assumes IEEE754 floating point. It takes advantage >> of the fact that IEEE754 has a well defined binary layout for quiet NaNs. > > I'm not sure what you mean by that. IEEE-754 defines an *abstract* > binary model, not a concrete one. And the exact mapping to concrete > implementation is NOT defined. That is not what I call a well defined > binary layout.
Yes of course. What's important is that it defines the bits of what constitutes a NaN, b[0] .. b[N] and we can create a mapping from bits 0..N of the abstract binary model to the actual (concrete) binary layout of a platform/processor. > For example on HP boxes, the concrete binary layout of qNaNs and sNaNs > is flipped (in the leading bits) from those of SPARCs. Yes, both have > IEEE-754 conforming representations. There are many other variants. > (I learnt those when I tried to get compiler support for > numeric_limits<> in GCC). Those who are interested might want to have > a look at gcc/real.[hc]. Nice. Thanks for the tip. -- Joel de Guzman joel at boost-consulting.com http://www.boost-consulting.com http://spirit.sf.net _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
