Hi!
Thanks for the link. But even if I check the length
like I would do in a software normalize function
I wonder how I should handle length == 0 in the
shader… I mean for example I calculate some
direction vector for a light source or for eye
position and do some lighting calculation based
on this direction vector.
But if I am not able to calculate this direction
vector because he is just zero how should I proceed?
I guess this would require a lot of extra code
for checking and handling this edge case that
might slow down the whole shader? 
But on the other side it could happen quite often
if my light source touches an object’s triangle
or vertex.