void main(){
struct POINT a;
a.x = 2;
a.y = 3;
a = doublePoint(a);
printf("x:%d y:%d\n", a.x, a.y);
}
ECPoint ECCurve::addPoint(ECPoint &p, ECPoint &q)
{
BigInteger rx;
BigInteger ry;
BigInteger px = p.getX();
BigInteger py = p.getY();
BigInteger qx = q.getX();
BigInteger qy = q.getY();
// Px == Qx && Py == Qy
if (p == q) {
return doublePoint(p);
}
// Px == Qx && Py != Qy
if (px == qx) {
return ECPoint();
}
if (p.isPointAtInfinity()) {
return q;
}
if (q.isPointAtInfinity()) {
return p;
}
// s = (py - qy)/(px - qx)
BigInteger rise = (py - qy) % _p;
BigInteger run = (px - qx) % _p;
BigInteger s = (run.invm(_p) * rise) % _p;
// rx = s^2 - px - qx
rx = (s*s - px - qx) % _p;
// ry = -py + s(px - rx)
ry = (s * (px - rx) - py) % _p;
return ECPoint(rx, ry);
}
