case 15: return make(-1);
case 15: return valueOf(-1);
  private static BigInteger bitOp(int op, BigInteger x, BigInteger y)  {    switch (op)      {        case 0:  return ZERO;        case 1:  return x.and(y);        case 3:  return x;        case 5:  return y;        case 15: return make(-1);      }    BigInteger result = new BigInteger();    setBitOp(result, op, x, y);    return result.canonicalize();  }