title: Looking for something like fetch_add for atomic<double>
body: <p>I'm looking for some sort of an add-operation working on atomic doubles.
  Sadly:</p>
  
  <pre><code>myatomdouble += toadddouble;
  </code></pre>
  
  <p>isn't defined,</p>
  
  <pre><code>myatomdouble = myatomdouble + toadddouble;
  </code></pre>
  
  <p>gets screwed by multithreading and fetch_add is only available for integral types, but not for doubles. But something like fetch_add would be exactly what I need. :(</p>
  
  <p>and mutexing every attempt to modify the variable makes the program superslow, the code unreadable and destroys the idea of atomic.</p>
  
  <p>So is there any solution for this problem?</p>