abled, which is much larger than the usual
      performance increases we see by turning on this flag. Hence, if the default
      performance is not sufficient, this flag is available, though it comes with
      its own problems.
    </p>
<p>
      This requires C++17 <code class="computeroutput"><span class="keyword">if</span> <span class="keyword">constexpr</span></code>.
    </p>
<h4>
<a name="math_toolkit.diff0.h4"></a>
      <span class="phrase"><a name="math_toolkit.diff0.references"></a></span><a cl