// use that instead of the generic one.
	if specific, ok := matchesSpecificCurve(curve); ok {
		return specific.Add(x1, y1, x2, y2)
	}
	panicIfNotOnCurve(curve, x1, y1)
	panicIfNotOnCurve(curve, x2, y2)

	z1 := zForAffine(x1, y1)
	z2 := zForAffine(x2, y2)
	return curve.affineFromJacobian(curve.addJacobian(x1, y1, z1, x2, y2, z2))
}

//
// Deprecated: for ECDH, use the crypto/ecdh package. This function returns an
// encoding equivalent to that of PublicKey.Bytes in crypto/ecdh.
func Marshal(curve Curve, x, y *big.Int) []byte {
	panicIfNotOnCurve(curve, x, y)

	byteLen := (curve.Params().BitSize + 7) / 8

	ret := make([]byte, 1+2*byteLen)
	ret[0] = 4 // uncompressed point

	x.FillBytes(ret[1 : 1+byteLen])