 is thread safe even
          for user-defined types, also so that user defined types get the full precision
          of the constant, even when <code class="computeroutput"><span class="keyword">long</span>
          <span class="keyword">double</span></code> does not. So for example
          128-bit rational approximations will work with UDT's and do the right thing,
          even though <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span></code>
         