4. Prove the correctness of the following loop using the provided pre and post conditions, and provided loop invariant. Require: A and B are positive integers, x=A,y=B and p=0 1: while y=0 do 2:r:=ymod2 3: if r=0 then 4:x:=2x 5:y:=y div 2 6: end if 7: if r=1 then 8:p:=p+x 9:ynew=yold1 10: end if 11: end while Ensure: p=AB Loop invariant: I(n):xy+p=AB What does this loop compute