title: are 2^n exponent calculations really less efficient than bit-shifts?
body: <p>if I do:</p>
  
  <pre><code>int x = 4;
  pow(2, x);
  </code></pre>
  
  <p>Is that really that much less efficient than just doing:</p>
  
  <pre><code>1 &lt;&lt; 4
  </code></pre>
  
  <p>?</p>