code: func (BitCurve *BitCurve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
  	z := new(big.Int).SetInt64(1)
  	return BitCurve.affineFromJacobian(BitCurve.addJacobian(x1, y1, z, x2, y2, z))
  }
docs: // Add returns the sum of (x1,y1) and (x2,y2)