Portability problems fixed by Gnulib module @code{ceil-ieee}:
@itemize
@item
+This function returns a positive zero for an argument between @minus{}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.