secp256k1EcmultConstXonly static method

Implementation

static int secp256k1EcmultConstXonly(
    Secp256k1Fe r, Secp256k1Fe n, Secp256k1Scalar q,
    {Secp256k1Fe? d, int knownOnCurve = 0}) {
  Secp256k1Fe g = Secp256k1Fe(), i = Secp256k1Fe();
  Secp256k1Ge p = Secp256k1Ge();
  Secp256k1Gej rj = Secp256k1Gej();

  /// Compute g = (n^3 + B*d^3).
  secp256k1FeSqr(g, n);
  secp256k1FeMul(g, g, n);
  if (d != null) {
    Secp256k1Fe b = Secp256k1Fe();
    _cond(secp256k1FeNormalizesToZero(d) == 0, "secp256k1EcmultConstXonly");
    secp256k1FeSqr(b, d);
    _cond(Secp256k1Const.secp256k1B <= 8, "secp256k1EcmultConstXonly");
    secp256k1FeMulInt(b, Secp256k1Const.secp256k1B);
    secp256k1FeMul(b, b, d);
    secp256k1FeAdd(g, b);
    if (knownOnCurve == 0) {
      Secp256k1Fe c = Secp256k1Fe();
      secp256k1FeMul(c, g, d);
      if (secp256k1FeIsSquareVar(c) == 0) return 0;
    }
  } else {
    secp256k1FeAddInt(g, Secp256k1Const.secp256k1B);
    if (knownOnCurve == 0) {
      /// g at this point equals x^3 + 7. Test if it is square.
      if (secp256k1FeIsSquareVar(g) == 0) return 0;
    }
  }
  secp256k1FeMul(p.x, g, n);
  secp256k1FeSqr(p.y, g);
  p.infinity = 0;

  /// Perform x-only EC multiplication of P with q.
  _cond(secp256k1ScalarIsZero(q) == 0, "secp256k1EcmultConstXonly");
  secp256k1ECmultConst(rj, p, q);
  _cond(secp256k1GejIsInfinity(rj) == 0, "secp256k1EcmultConstXonly");
  secp256k1FeSqr(i, rj.z);
  secp256k1FeMul(i, i, g);
  if (d != null) secp256k1FeMul(i, i, d);
  secp256k1FeInv(i, i);
  secp256k1FeMul(r, rj.x, i);

  return 1;
}