This function is missing on some platforms:
FreeBSD 5.2.1, OpenBSD 3.8, AIX 5.1, IRIX 6.5, OSF/1 4.0, Solaris 9, Interix 3.5.
@item
+This function is not declared on some platforms:
+OSF/1 5.1.
+@item
This functions returns a wrong result for x = 1/2 - 2^-54 on some platforms:
NetBSD 3.0, AIX 7.1.
@end itemize