Hello John, i tinkered a bit so that std::isnan+std::fpclassify now also work with the value NANS (numeric_limits::signaling_NaN). For this i used the coming types and functions (stdlib.h). gcc supports this. That's why i don't want to speak directly of a patch, since this still has to be adapted for other compilers. It all boils down to that anyway, so please treat this as a pattern. The functions returns the same values as the gcc-builtins. However, i cannot say at the moment whether these are actually correct. But i have the feeling that not all of them are correct, since the (bit)schemes differ in part. adjusted (boost/math/cstdfloat) cstdfloat_types.hpp: add BOOST_CSTDFLOAT_FLOAT128_HUGE_VAL cstdfloat_limits.hpp: add forward-declarations for nanq/nansq in numeric_limits: change has_signaling_NaN to true, correct ? change infinity change quiet_NaN change signaling_NaN cstdfloat_cmath.hpp: add in detail:: a lot of functions change #define BOOST_CSTDFLOAT_FLOAT128_NAN add #define BOOST_CSTDFLOAT_FLOAT128_NANS change nanq add nansq add in std:: a lot of usings and functions regards Gero