.SH RETURN VALUE
On success, these functions return the inverse hyperbolic sine of
.IR x .
-
+.PP
If
.I x
is a NaN, a NaN is returned.
-
+.PP
If
.I x
is +0 (\-0), +0 (\-0) is returned.
-
+.PP
If
.I x
is positive infinity (negative infinity),
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
-
+.PP
The variant returning
.I double
also conforms to