public static GetWindowSize ( int bits ) : int | ||
bits | int | |
Результат | int |
public static int GetWindowSize(int bits) { return(WNafUtilities.GetWindowSize(bits, WNafUtilities.DEFAULT_WINDOW_SIZE_CUTOFFS)); }
/** * 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) { int minWidth = WNafUtilities.GetWindowSize(k.BitLength); WNafPreCompInfo info = WNafUtilities.Precompute(p, minWidth, true); ECPoint[] preComp = info.PreComp; ECPoint[] preCompNeg = info.PreCompNeg; int width = info.Width; 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 = 32 - Integers.NumberOfLeadingZeros(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; //Console.WriteLine("Optimized: 2^" + scale + " * " + n + " = " + i1 + " + " + i2); } 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); }
protected virtual int GetWindowSize(int bits) { return(WNafUtilities.GetWindowSize(bits)); }
protected virtual int GetWindowSize(int bits) => WNafUtilities.GetWindowSize(bits);