Why does NaN - NaN == 0.0 with the Intel C++ Compiler?

Question

It is well-known that NaNs propagate in arithmetic, but I couldn\'t find any demonstrations, so I wrote a small test:

#include 
#include 

        

Answer 1

The default floating point handling in Intel C++ compiler is /fp:fast, which handles NaN's unsafely (which also results in NaN == NaN being true for example). Try specifying /fp:strict or /fp:precise and see if that helps.