This is posted again and again, and I re-read it <i>every</i> time.<p>I'm also reminded of this:<p><pre><code> You can't make your code run faster,
you can only make it do less work.
</code></pre>
I usually put links to previous discussions because I find value in the comments by HN users, but I'm not going to do that this time. You can search if you want to find previous discussions - there have been many, and some contain some real gems.
See also, The Treacherous Optimization:<p><a href="http://ridiculousfish.com/blog/posts/old-age-and-treachery.html" rel="nofollow">http://ridiculousfish.com/blog/posts/old-age-and-treachery.h...</a>