Check that n & (n - 1) is non-zero for non-power-of-two numbers

bits.hs

import Data.Bits ((.&.))
import Test.QuickCheck (Property, (==>))

prop_bits :: Int -> Property
prop_bits n = n > 0 ==> intToBool (n .&. (n - 1)) == not (isPowerOfTwo n)

intToBool 0 = False
intToBool _ = True

isPowerOfTwo :: Int -> Bool
isPowerOfTwo x = fromIntegral (truncate l2) == l2
    where l2 = log xf / log 2
          xf = fromIntegral x