title: Combining MD5 hash values
body: <p>When calculating a single MD5 checksum on a large file, what technique is generally used to combine the various MD5 values into a single value?  Do you just add them together?  I'm not really interested in any particular language, library or API which will do this; rather I'm just interested in the technique behind it.  Can someone explain how it is done?</p>
  
  <p>Given the following algorithm in pseudo-code:</p>
  
  <pre><code>MD5Digest X
  for each file segment F
     MD5Digest Y = CalculateMD5(F)
     Combine(X,Y)
  </code></pre>
  
  <p>But what exactly would <code>Combine</code> do?  Does it add the two MD5 digests together, or what?</p>