.I x
and a magnitude less than the magnitude of
.IR y .
-
+.PP
If
.I x
or
.I y
is a NaN, a NaN is returned.
-
+.PP
If
.I x
is an infinity,
a domain error occurs, and
a NaN is returned.
-
+.PP
If
.I y
is zero,
a domain error occurs, and
a NaN is returned.
-
+.PP
If
.I x
is +0 (\-0), and
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
-
+.PP
The variant returning
.I double
also conforms to