     The Patefield-Tandy algorithm is accurate to approximately 20 decimal places,
      so for types with greater precision we use:
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          A modified version of T1 which folds the calculation of <span class="emphasis"><em>atan(h)</em></span>
          into the T1 series (to avoid subtracting two values similar in magnitude),
          and then accelerates the resulting alternating series us