"I have a wandlike slot reader wich provides the bitstream"

What do you mean by that?

If you mean that it produces a '1' while it is sensing "white" and '0' for "black" (or vice-versa), you have a very long way to go indeed to decode that!
You need to work out the speed of the "swipe", so that you can decide whether you have a "thick" or a "thin" bar or space. This is the really trick bit; I think it's probably best left to dedicated devices?

But if you already know that you've read thick/thin bar/space, you just need to google for "barcode symbology"

Last time I looked at this was ~20 years ago; back then, HP (now Agilent) used to have a lot of good info on the subject - and suitable devices to help you!