POSIX specification: http://www.opengroup.org/susv3xbd/math.h.html
Gnulib module: math
Portability problems fixed by Gnulib:
NAN is not defined on some platforms:
OpenBSD 4.0, AIX 5.1, IRIX 6.5, OSF/1 5.1.
NAN is not exposed outside of C99 compilation on some
platforms:
glibc.
NAN and HUGE_VAL expand to a function address
rather than a floating point constant on some platforms:
Solaris 10.
Portability problems not fixed by Gnulib:
NAN is not a compile time constant with some compilers:
OSF/1 with Compaq (ex-DEC) C 6.4.