title: In Git, how do I diff to the first commit of my branch?
body: <p>I've made several commits to a local branch, but I'm not sure what the best way to diff what I currently have to my branch's starting state.  I know I can do something like <code>git diff HEAD HEAD~6</code> if there's been 6 commits to my branch, but I was hoping for something that was independent of the number of commits.</p>
  
  <p>Edit:
  I failed to mention this: I was hoping I wouldn't have to dig through the log to get the hash of the commit I branched from.  If I had 80 commits for example, this wouldn't be a fun task.</p>
  
  <p>Also, presume that the original branch I branched from has already had several changes.</p>