John Maddock wrote:
Martin Bonner wrote:
----Original Message---- From: Johan Råde
template<class T> bool is_nan(T a) { return a != a; }
1. Do these implementations work an all platforms? I believe is_nan is vunerable to over-eager optimizers for built-in types.
If implemented that way, then yes: only compilers in strict IEEE mode and probably with optimisations turned off will do the right thing. It won't work at all on platforms with non-IEEE arithmetic :-(
Which I why I routed everything through fpclassify: try get it right once in one place and hopefully it doesn't turn into a maintenence problem :-)
Of course if the platform has native floating point classification macros then these should be used: they're likely to be much more efficient than "generic" solutions. Unfortunately I found several platforms with native macros that didn't actually do the right thing in all cases during testing of that code :-(
John.
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
John, You seem to have thought through these issues carefully. When will you submit the floating point properties library to Boost? I need it. Based on your document and input from Paul Giaconne I suggest the following interface: bool is_finite(); bool is_normal(); bool is_subnormal(); bool is_infinite(); bool is_plus_infinity(); bool is_minus_infinity(); bool is_nan(); bool is_quiet_nan(); bool is_signalling_nan(); The IEEE754 standard uses the term "denormal", but the draft for the next revision of the IEEE754 standard uses the term "subnormal", so "subnormal" is probably better. --Johan Råde