static ECPoint implShamirsTrickJsf(ECPoint P, BigInteger k, ECPoint Q, BigInteger l) { ECCurve curve = P.getCurve(); ECPoint infinity = curve.getInfinity(); // TODO conjugate co-Z addition (ZADDC) can return both of these ECPoint PaddQ = P.add(Q); ECPoint PsubQ = P.subtract(Q); ECPoint[] points = new ECPoint[]{ Q, PsubQ, P, PaddQ }; curve.normalizeAll(points); ECPoint[] table = new ECPoint[] { points[3].negate(), points[2].negate(), points[1].negate(), points[0].negate(), infinity, points[0], points[1], points[2], points[3] }; byte[] jsf = WNafUtil.generateJSF(k, l); ECPoint R = infinity; int i = jsf.length; while (--i >= 0) { int jsfi = jsf[i]; // NOTE: The shifting ensures the sign is extended correctly int kDigit = ((jsfi << 24) >> 28), lDigit = ((jsfi << 28) >> 28); int index = 4 + (kDigit * 3) + lDigit; R = R.twicePlus(table[index]); } return R; }
static ECPoint implShamirsTrickJsf(ECPoint P, BigInteger k, ECPoint Q, BigInteger l) { ECCurve curve = P.getCurve(); ECPoint infinity = curve.getInfinity(); // TODO conjugate co-Z addition (ZADDC) can return both of these ECPoint PaddQ = P.add(Q); ECPoint PsubQ = P.subtract(Q); ECPoint[] points = new ECPoint[]{ Q, PsubQ, P, PaddQ }; curve.normalizeAll(points); ECPoint[] table = new ECPoint[] { points[3].negate(), points[2].negate(), points[1].negate(), points[0].negate(), infinity, points[0], points[1], points[2], points[3] }; byte[] jsf = WNafUtil.generateJSF(k, l); ECPoint R = infinity; int i = jsf.length; while (--i >= 0) { int jsfi = jsf[i]; // NOTE: The shifting ensures the sign is extended correctly int kDigit = ((jsfi << 24) >> 28), lDigit = ((jsfi << 28) >> 28); int index = 4 + (kDigit * 3) + lDigit; R = R.twicePlus(table[index]); } return R; }