Using C99 signaling NaNs provided by mathlib (_WANT_SNAN)
If you want to use signaling NaNs, you must indicate this to the compiler by defining the macro
_WANT_SNAN in your application.
This macro must be defined before you include
any standard C headers. If your application is comprised of two
or more translation units, either all or none of them must define
That is, the definition must be consistent for any given application.
You must also use the relevant command-line option when you compile your
source code. This is associated with the predefined macro