title: Number of unset bit left of most significant set bit?
body: <p>Assuming the 64bit integer <code>0x000000000000FFFF</code> which would be represented as </p>
  
  <pre><code>00000000 00000000  00000000 00000000
  00000000 00000000 &gt;11111111 11111111
  </code></pre>
  
  <p>How do I find the amount of unset bits to the left of the most significant set bit (the one marked with >) ?</p>