title: Test if a bitboard have only one bit set to 1
body: <p>I have a bitboard and I want to check in C if there is ONLY one bit set to 1.</p>
  
  <pre><code>#include &lt;stdint.h&gt;
  typedef uint64_t bboard;
  bboard b = 0x0000000000000010;
  if (only_one_bit_set_to_one (b)) // in this example expected true
    // do something...
  </code></pre>
  
  <p>Any idea to write the function <code>int only_one_bit_set_to_one (bboard b)</code>?</p>