I have put together optimized implementations of the following functions: template<class T> int fpclassify(T x); template<class T> bool isfinite(T x); template<class T> bool isinf(T x); template<class T> bool isnan(T x); template<class T> bool isnormal(T x); template<class T> bool signbit(T x); template<class T> T copysign(T x, T y); template<class T> T changesign(T x); Here T is required to be float, double or long double. -------------------- The code has been tested with Windows / VC7.1 / i386 Mac / GCC 4.0 / powerpc Linux / GCC 3.3 / i386, amd64, ia64, powerpc, mips, hppa The code should work with most platforms that support the IEEE754 standard. -------------------- Many of these functions have also been implemented by John Maddock. The difference is that my implementation is optimized for speed. Here are some timing numbers on VC 7.1: float Råde Maddock Native fpclassify 8 57 - isfinite 5 57 - isnormal 6 59 - isinf 5 57 - isnan 6 57 - double Råde Maddock Native fpclassify 13 52 29 isfinite 11 56 17 isnormal 14 56 - isinf 10 52 - isnan 4 52 19 The times are in clock cycles for a single call, based on an average of 10,000,000 calls with random input. -------------------- The code is available in the vault, at "Home/Math - Numerics/fpclassify.zip". Many thanks to Håkan Ardö who tested the code on Linux and Olivier Verdie who tested the code on Mac. --Johan Råde