POSIX specification: http://www.opengroup.org/susv3xbd/float.h.html
Gnulib module: float
Portability problems fixed by Gnulib:
LDBL_* macros are incorrect on some platforms:
On OpenBSD 4.0 and BeOS, they are the same as the values of the
DBL_* macros, although ‘long double’ is a larger type than
‘double’.
Portability problems not fixed by Gnulib: