This here is a design for a 4-bit ALU that (theoretically) could be built in a normal alpha minecraft world, meaning that I limited myself to only building with dust, torches, levers and solid blocks. It's slower than molasses, but it has 11 functions (Add, Subtract, XOR, XNOR, OR, NOR, AND, NAND, Implies, Nimplies, Left shift) Credit to mattbatwings's excellent series "Let's Make a Redstone Computer!" for the original design, which I then modified to remove every component that did not comply with my restrictions (mostly subbing out comparators for bulkier block-built logic gates)
by Stella314159