I have seen [this topic here](https://stackoverflow.com/questions/295579/fastest-way-to-determine-if-an-integers-square-root-is-an-integer) about John Carmack's magical way to calculate square root, which refers to this article: <http://www.codemaestro.com/reviews/9>. This surprised me a lot, I just didn't ever realized that calculating sqrt could be so faster. 

I was just wondering what other examples of "magic" exist out there that computer games use to run faster.

**UPDATE**:
John Carmack is not the author of the magic code. [This article](http://www.beyond3d.com/content/articles/8/) tells more. Thanks @moocha.