title: Double - IEEE 754 alternatives
body: <p>According to the following site:
  <a href="http://en.cppreference.com/w/cpp/language/types">http://en.cppreference.com/w/cpp/language/types</a></p>
  
  <p>"double - double precision floating point type. Usually IEEE-754 64 bit floating point type".</p>
  
  <p>It says "usually".  What other possible formats/standard could C++ <code>double</code> use?  What compiler uses an alternative to the IEEE format?  Or architecture?</p>