title: A way to turn boost::posix_time::ptime into an __int64
body: <p>Does anyone know if there is a good way to turn a <code>boost::posix_time::ptime</code> into an <code>__int64</code> value.  (I have compiled the microsecond version, not the nanosecond version).</p>
  
  <p>I need to do this somehow as I am looking to store the resulting <code>__int64</code> in a <code>union</code> type which uses the raw data for a high-performance application.  Some type of Memento functionality like this would be highly useful for me.  I'd like to avoid casts, if possible, but will resort to them if I need to.</p>