fenv.h
======

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fenv.h.html

Gnulib module: fenv

Portability problems fixed by Gnulib:

  * This header file is missing on some platforms: FreeBSD 5.2.1, NetBSD 5.0, OpenBSD 3.8, AIX 5.1, IRIX 6.5, Cygwin 1.7.7, MSVC 9.

Portability problems not fixed by Gnulib:

  * On MSVC, the values of the rounding direction macros have changed: In MSVC 14, FE_UPWARD is 0x100 and FE_DOWNWARD is 0x200, whereas in MSVC 14.30, it's the opposite.