em></span> is zero and the payload <span class="emphasis"><em>x</em></span>
        is nonzero, then it is a signaling NaN.
      </p>
<p>
        Although there has been theoretical interest in the ability of a signaling
        NaN to raise an exception, for example to prevent use of an uninitialised
        variable, in practice there appears to be no useful application of signaling
        NaNs for most current processors. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf" targe