How to compile new PHP runtime function

Hi all, I'm interested in how I could write functions in C (I presume), and then compile them for use in PHP. In other words, I'd like to write functions that would be just as much a part of PHP as, say, mysql_fetch_object(). I assume that all the PHP functions are just functions written in C, and then compiled into a module appropriate for the desired Web server platform. Also, once I do such a thing, how would I get such functions included into PHP itself? Similarly, is any work being done on creating 3rd party freeware add-on libraries to PHP? As a programmer, I can see the desirability of such libraries as an alternative to script libraries, for reasons of both speed and security. Thanks, Chris