isnan
=====

POSIX specification:
 http://www.opengroup.org/onlinepubs/9699919799/functions/isnan.html

Gnulib module: isnan

Portability problems fixed by Gnulib:

  * This macro is missing on some platforms: MSVC 9.

  * isnan was introduced with C99 and is thus commonly not present on pre-C99 systems.

  * isnan is not a macro on some platforms: IRIX 6.5, OSF/1 5.1 with gcc, Solaris 11 2010-11.

  * On IRIX 6.5 with cc, isnan does not recognize some NaNs.

  * On NetBSD/i386 and glibc/ia64, isnan does not recognize some forms of NaNs, such as pseudo-NaNs, pseudo-Infinities, and unnormalized numbers.

  * On i686 and X86-64, __builtin_isnanl (and thus isnan implementations based on it) in GCC 4.0 and later does not recognize pseudo-denormals as NaNs, and similarly for pseudo-zeroes, unnormalized numbers, and pseudo-denormals on ia64.

Portability problems not fixed by Gnulib: