Do you have the book, Elements of Computer Systems ?
Have you read the previous chapters ?
If so there's lots of info to get you going and help describe what it is specifically you need help with...
What have you tried so far ?
Have you built all the previous chips ?
Will need a bit more info than just "so how do you do it with 5 control bits?"...
I know this might be very annoying, but this forum works on the principle that the question asker needs to put in a bit of effort (and show that effort) before they get any help. I've been in your shoes, I know it can be frustrating, but we are giving you our time (well I am, I don't know if anyone else is paid on this forum) so help us to help you. The more info you give us the more helpful we can be..
Sorry if this was not quite what you're expecting (also if greater minds than mine feel that I'm being unreasonable please jump in)
I've moved your post to its own thread -- you were hijacking the prior thread with something completely unrelated, which only serves to cause confusion. I'm trying to change the title to something more meaningful (such as "Need help with custom ALU design"), but it doesn't seem to be taking -- may just have to wait for the update to work its way through the system.