Why is expat extremely fast?

Hey guys,

I'm a student from the University of Luebeck in Germany. For my diploma
thesis I've just created a small xml parser of ca. 1000 lines of code and
compared its speed to the expat parser. My results are poor: my parser's
speed is only a half of expat's speed. I worked with an endless loop
performing switch and if structures. Sometimes a callback function requests
more buffer. Once the loop detects a final flag which is set to 1, it will
parse the rest of the input stream and exit. The parser works fine but is so
lame. What's the reason expat reaches such a great performance?
I've tried to understand the source code and failed :-) It's just confusing
me. There is so much functionality I do not perform... but my application is
still slower.

Is there any trick which makes expat so fast?

I've searched the internet for an answer, no one could help me. Could you?

Best regards and many thanks for your replies!