protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k) { int num = Math.Max(2, Math.Min(16, GetWindowSize(k.BitLength))); WNafPreCompInfo wNafPreCompInfo = WNafUtilities.Precompute(p, num, includeNegated: true); ECPoint[] preComp = wNafPreCompInfo.PreComp; ECPoint[] preCompNeg = wNafPreCompInfo.PreCompNeg; int[] array = WNafUtilities.GenerateCompactWindowNaf(num, k); ECPoint eCPoint = p.Curve.Infinity; int num2 = array.Length; if (num2 > 1) { int num3 = array[--num2]; int num4 = num3 >> 16; int num5 = num3 & 0xFFFF; int num6 = Math.Abs(num4); ECPoint[] array2 = (num4 < 0) ? preCompNeg : preComp; if (num6 << 2 < 1 << num) { int num7 = LongArray.BitLengths[num6]; int num8 = num - num7; int num9 = num6 ^ (1 << num7 - 1); int num10 = (1 << num - 1) - 1; int num11 = (num9 << num8) + 1; eCPoint = array2[num10 >> 1].Add(array2[num11 >> 1]); num5 -= num8; } else { eCPoint = array2[num6 >> 1]; } eCPoint = eCPoint.TimesPow2(num5); } while (num2 > 0) { int num12 = array[--num2]; int num13 = num12 >> 16; int e = num12 & 0xFFFF; int num14 = Math.Abs(num13); ECPoint[] array3 = (num13 < 0) ? preCompNeg : preComp; ECPoint b = array3[num14 >> 1]; eCPoint = eCPoint.TwicePlus(b); eCPoint = eCPoint.TimesPow2(e); } return(eCPoint); }
/** * Multiplies <code>this</code> by an integer <code>k</code> using the * Window NAF method. * @param k The integer by which <code>this</code> is multiplied. * @return A new <code>ECPoint</code> which equals <code>this</code> * multiplied by <code>k</code>. */ protected override ECPoint MultiplyPositive(ECPoint p, BigInteger k) { // Clamp the window width in the range [2, 16] int width = System.Math.Max(2, System.Math.Min(16, GetWindowSize(k.BitLength))); WNafPreCompInfo wnafPreCompInfo = WNafUtilities.Precompute(p, width, true); ECPoint[] preComp = wnafPreCompInfo.PreComp; ECPoint[] preCompNeg = wnafPreCompInfo.PreCompNeg; int[] wnaf = WNafUtilities.GenerateCompactWindowNaf(width, k); ECPoint R = p.Curve.Infinity; int i = wnaf.Length; /* * NOTE: We try to optimize the first window using the precomputed points to substitute an * addition for 2 or more doublings. */ if (i > 1) { int wi = wnaf[--i]; int digit = wi >> 16, zeroes = wi & 0xFFFF; int n = System.Math.Abs(digit); ECPoint[] table = digit < 0 ? preCompNeg : preComp; // Optimization can only be used for values in the lower half of the table if ((n << 2) < (1 << width)) { int highest = LongArray.BitLengths[n]; // TODO Get addition/doubling cost ratio from curve and compare to 'scale' to see if worth substituting? int scale = width - highest; int lowBits = n ^ (1 << (highest - 1)); int i1 = ((1 << (width - 1)) - 1); int i2 = (lowBits << scale) + 1; R = table[i1 >> 1].Add(table[i2 >> 1]); zeroes -= scale; } else { R = table[n >> 1]; } R = R.TimesPow2(zeroes); } while (i > 0) { int wi = wnaf[--i]; int digit = wi >> 16, zeroes = wi & 0xFFFF; int n = System.Math.Abs(digit); ECPoint[] table = digit < 0 ? preCompNeg : preComp; ECPoint r = table[n >> 1]; R = R.TwicePlus(r); R = R.TimesPow2(zeroes); } return(R); }