operator + method

ECPoint operator +(ECPoint other)

Point addition

Implementation

ECPoint operator +(ECPoint other) {
  if (isInfinity) return other;
  if (other.isInfinity) return this;

  if (x == other.x && y != other.y) {
    return ECPoint.infinity;
  }

  BigInt lambda;
  if (x == other.x && y == other.y) {
    // Point doubling
    lambda =
        ((BigInt.from(3) * x * x + ECDSACurve.a) *
            _modInverse(BigInt.from(2) * y, ECDSACurve.p)) %
        ECDSACurve.p;
  } else {
    // Point addition
    lambda =
        ((other.y - y) * _modInverse(other.x - x, ECDSACurve.p)) %
        ECDSACurve.p;
  }

  final x3 = (lambda * lambda - x - other.x) % ECDSACurve.p;
  final y3 = (lambda * (x - x3) - y) % ECDSACurve.p;

  return ECPoint(x3, y3);
}