+Portability problems fixed by Gnulib module @code{ceil-ieee}:
+@itemize
+@item
+This function returns a positive zero for an argument between -1 and 0
+on some platforms:
+AIX 7.1, OSF/1 5.1.
+@item
+This function returns a positive zero for a minus zero argument
+on some platforms:
+OSF/1 5.1.
+@end itemize
+