title: log base 2 and nan
body: <p>I use the code below to calculate log base 2.</p>
  
  <pre><code>Math.log(x)/Math.log(2);
  </code></pre>
  
  <p>With this function, i get nan if x=4/5.</p>
  
  <p>With calc, excel this problem don't exist.</p>
  
  <p>How to avoid to get nan and get the real value?</p>