Rein-Peter de Boer wrote:

I'm trying to grasp the inner workings of the dct32 function. I can understand the matrixing stuff of the butterflies, but i don't understand the shifts (<<1) before or after a calculation.

A left shift, of course, is equivalent to multiplication by 2.

A couple of the links on this page might be helpful:

http://www.fe.uni-lj.si/~arpadb/interests.html

The dct32 function is essentially an unrolled implementation of Hou's fast DCT algorithm.