public override ECPoint Twice() { if (this.IsInfinity) { return(this); } ECCurve curve = this.Curve; SecP521R1FieldElement Y1 = (SecP521R1FieldElement)this.RawYCoord; if (Y1.IsZero) { return(curve.Infinity); } SecP521R1FieldElement X1 = (SecP521R1FieldElement)this.RawXCoord, Z1 = (SecP521R1FieldElement)this.RawZCoords[0]; uint[] t1 = Nat.Create(17); uint[] t2 = Nat.Create(17); uint[] Y1Squared = Nat.Create(17); SecP521R1Field.Square(Y1.x, Y1Squared); uint[] T = Nat.Create(17); SecP521R1Field.Square(Y1Squared, T); bool Z1IsOne = Z1.IsOne; uint[] Z1Squared = Z1.x; if (!Z1IsOne) { Z1Squared = t2; SecP521R1Field.Square(Z1.x, Z1Squared); } SecP521R1Field.Subtract(X1.x, Z1Squared, t1); uint[] M = t2; SecP521R1Field.Add(X1.x, Z1Squared, M); SecP521R1Field.Multiply(M, t1, M); Nat.AddBothTo(17, M, M, M); SecP521R1Field.Reduce23(M); uint[] S = Y1Squared; SecP521R1Field.Multiply(Y1Squared, X1.x, S); Nat.ShiftUpBits(17, S, 2, 0); SecP521R1Field.Reduce23(S); Nat.ShiftUpBits(17, T, 3, 0, t1); SecP521R1Field.Reduce23(t1); SecP521R1FieldElement X3 = new SecP521R1FieldElement(T); SecP521R1Field.Square(M, X3.x); SecP521R1Field.Subtract(X3.x, S, X3.x); SecP521R1Field.Subtract(X3.x, S, X3.x); SecP521R1FieldElement Y3 = new SecP521R1FieldElement(S); SecP521R1Field.Subtract(S, X3.x, Y3.x); SecP521R1Field.Multiply(Y3.x, M, Y3.x); SecP521R1Field.Subtract(Y3.x, t1, Y3.x); SecP521R1FieldElement Z3 = new SecP521R1FieldElement(M); SecP521R1Field.Twice(Y1.x, Z3.x); if (!Z1IsOne) { SecP521R1Field.Multiply(Z3.x, Z1.x, Z3.x); } return(new SecP521R1Point(curve, X3, Y3, new ECFieldElement[] { Z3 }, IsCompressed)); }