$ uname -sr && cat t.cpp && nice gmake t && ./t
HP-UX B.11.23
#include <cassert>
#include <iostream>
#include <limits>
#include <sstream>
int main ()
{
std::ostringstream os;
os << std::numeric_limits<double>::quiet_NaN () << " == "
<< std::numeric_limits<long double>::quiet_NaN () << '\n'
<< -std::numeric_limits<double>::quiet_NaN () << " == "
<< -std::numeric_limits<long double>::quiet_NaN ();
std::cout << os.str () << '\n';
assert (os.str () == "nan == nan\n-nan == -nan");
}