title: How to use and verify quad precision in gfortran?
body: <p>I am trying to use quad precision in gfortran, but it seems like the <code>real*16</code> does not work. After some fishing around, I have found that it may be implemented as <code>real*10</code>. Is <code>real*10</code> <em>actually</em> quad precision?</p>
  
  <p>How can I test the precision of my code? Is there a standard simple algorithm for testing precision? For example, when I want to figure out what computer zero is, I continue to divide by 2.0 until I reach 0.0. Keeping track of the values lets me know when the computer 'thinks' that my non-zero number is zero - giving me computer zero.</p>
  
  <p>Is there a good way of figuring out the precision with a type of algorithm like I described?</p>