like(NAN, qr/^NaN/, "NAN is Perl's NaN");
cmp_ok(NAN, '!=', NAN, "NAN != NAN");
ok(!(NAN == NAN), "NAN == NAN");
+ # we have a fallback copysign(), but it doesn't work for NaN
+ skip('no copysign', 2) unless $Config{d_copysign};
ok(!signbit(copysign(NAN, 1.0)), "signbit(copysign(NAN, 1.0)))");
ok(signbit(copysign(NAN, -1.0)), "signbit(copysign(NAN, -1.0)))");
}