import Data.Array (Array, listArray, (!))
import Data.Bits (shiftL, (.&.))

ladder :: [Int] -> [Int] -> [Int]
ladder a b = [fibArr ! (ai + 1) .&. ((1 `shiftL` bi) - 1) | (ai, bi) <- zip a b]
  where
    maxA       = maximum a
    globalMask = (1 `shiftL` maximum b) - 1
    fibs       = 0 : 1 : zipWith (\x y -> (x + y) .&. globalMask) fibs (tail fibs)
    fibArr     = listArray (0, maxA + 1) (take (maxA + 2) fibs) :: Array Int Int