How to use

getLucas

method

in

org.spongycastle.math.ec.Tnaf

public static BigInteger[] getSi(int fieldSize, int curveA, BigInteger cofactor)
{
  byte mu = getMu(curveA);
  int shifts = getShiftsForCofactor(cofactor);
  int index = fieldSize + 3 - curveA;
  BigInteger[] ui = getLucas(mu, index, false);
  if (mu == 1)
  {
    ui[0] = ui[0].negate();
    ui[1] = ui[1].negate();
  }
  BigInteger dividend0 = ECConstants.ONE.add(ui[1]).shiftRight(shifts);
  BigInteger dividend1 = ECConstants.ONE.add(ui[0]).shiftRight(shifts).negate();
  return new BigInteger[] { dividend0, dividend1 };
}

BigInteger[] us = getLucas(mu, w, false);
BigInteger twoToW = ECConstants.ZERO.setBit(w);
BigInteger u1invert = us[1].modInverse(twoToW);

BigInteger[] us = getLucas(mu, w, false);
BigInteger twoToW = ECConstants.ZERO.setBit(w);
BigInteger u1invert = us[1].modInverse(twoToW);

BigInteger[] v = getLucas(mu, m, true);
BigInteger vm = v[1];

BigInteger[] v = getLucas(mu, m, true);
BigInteger vm = v[1];

/**
 * Computes the auxiliary values <code>s<sub>0</sub></code> and
 * <code>s<sub>1</sub></code> used for partial modular reduction. 
 * @param curve The elliptic curve for which to compute
 * <code>s<sub>0</sub></code> and <code>s<sub>1</sub></code>.
 * @throws IllegalArgumentException if <code>curve</code> is not a
 * Koblitz curve (Anomalous Binary Curve, ABC).
 */
public static BigInteger[] getSi(ECCurve.AbstractF2m curve)
{
  if (!curve.isKoblitz())
  {
    throw new IllegalArgumentException("si is defined for Koblitz curves only");
  }
  int m = curve.getFieldSize();
  int a = curve.getA().toBigInteger().intValue();
  byte mu = getMu(a);
  int shifts = getShiftsForCofactor(curve.getCofactor());
  int index = m + 3 - a;
  BigInteger[] ui = getLucas(mu, index, false);
  if (mu == 1)
  {
    ui[0] = ui[0].negate();
    ui[1] = ui[1].negate();
  }
  BigInteger dividend0 = ECConstants.ONE.add(ui[1]).shiftRight(shifts);
  BigInteger dividend1 = ECConstants.ONE.add(ui[0]).shiftRight(shifts).negate();
  return new BigInteger[] { dividend0, dividend1 };
}

int h = curve.getH().intValue();
int index = m + 3 - a;
BigInteger[] ui = getLucas(mu, index, false);