long reverseBits(long num, int b1, int b2) { // b1, b2 E [0, sizeof(long) - 1]
  if (b1 > b2) {b1 = b1 ^ b2; b2 = b1 ^ b2; b1 = b1 ^ b2;} // swap
  return (num & ~((1 << b1) | (1 << b2))) | ((num & (1 << b1)) << (b2 - b1)) | ((num & (1 << b2)) >> (b2 - b1));
}