testBit' u [b] n | n > fromIntegral (7 - u) = error "index out of bounds"
                 | otherwise   = B.testBit b (fromIntegral $ 7 - n)
testBit' u [b] n | n > fromIntegral (7 - u) = error "index out of bounds"
                 | otherwise   = B.testBit b (fromIntegral $ 7 - n)
testBit' u [b] n | n > fromIntegral (7 - u) = error "index out of bounds"
                 | otherwise   = B.testBit b (fromIntegral $ 7 - n)