convertNBytesLen :: [Word8] -> Int32
convertNBytesLen = foldr accum 0
  where accum bs a = 256 * a + fromIntegral bs


bsToDouble :: S.ByteString -> Int -> Double
bsToDouble bs n = if intV >= 0
                   then fromIntegral intV / 2147483647
                   else - (fromIntegral intV / (-2147483648))
  where intV = convertNBytesLen (S.unpack bs) `shift` (32 - 8 * n)