 return 0 if its arguments
   compare as equal, a positive integer if the first is greater,
   and a negative integer if the first is smaller (see below for a
   complete specification).  For example, <a href="Pervasives.html#VALcompare"><code class="code">compare</code></a> is
   a suitable comparison function, provided there are no floating-point
   NaN values in the data.  After calling <code class="code"><span class="constructor">Array</span>.sort</code>, the
   array is sorted in place in increasing or