title: What's the disadvantage of mt_rand?
body: <p>What's the definition of bias in:</p>
  
  <blockquote>
    <p>The distribution of <a href="http://php.net/manual/en/function.mt-rand.php">mt_rand()</a> return values is biased towards even numbers on 64-bit builds of PHP when max is beyond 2^32.</p>
  </blockquote>
  
  <p>If it's the kind of bias stated in <a href="http://en.wikipedia.org/wiki/Rounding#Alternating_tie-breaking">alternate tie-breaking rules for rounding</a>, I don't think it really matters (since the bias is not really visible).</p>
  
  <p>Besides <code>mt_rand()</code> is <a href="http://php.net/manual/en/function.mt-rand.php">claimed</a> to be four times faster than <code>rand()</code>, just by adding three chars in front!</p>
  
  <p>Assuming <code>mt_rand</code> is available, what's the disadvantage of using it?</p>