+Portability problems fixed by Gnulib module @code{modf-ieee}:
+@itemize
+@item
+This function has problems with a NaN argument on some platforms:
+NetBSD 5.1, Cygwin.
+@item
+This function has problems with infinite arguments on some platforms:
+FreeBSD 6.4, OpenBSD 4.9, IRIX 6.5, OSF/1 5.1.
+@end itemize
+