public int Evaluate(UInt128 n) { this.n = n; var sum = 0; sqrtn = (long)IntegerMath.FloorSquareRoot(n); kmax = (int)IntegerMath.FloorLog(n, 2); imax = (long)IntegerMath.FloorPower(n, 1, 5) * C1 / C2; xmax = DownToOdd(imax != 0 ? Xi(imax) : sqrtn); xmed = DownToOdd(Math.Min((long)(IntegerMath.FloorPower(n, 2, 7) * C3 / C4), xmax)); var dmax = (long)IntegerMath.Min(n / IntegerMath.Square((UInt128)xmed) + 1, n); mobius = new MobiusOddRangeAdditive((xmax + 2) | 1, threads); divisors = new DivisorOddRangeAdditive((dmax + 2) | 1, threads); xi = new long[imax + 1]; mx = new long[imax + 1]; // Initialize xi. for (var i = 1; i <= imax; i++) { xi[i] = Xi(i); } values = new sbyte[mobiusBatchSize >> 1]; m = new int[mobiusBatchSize >> 1]; m0 = 0; dsums = new ulong[divisorBatchSize >> 1]; d1 = d2 = 1; // Process small x values. for (var x = (long)1; x <= xmed; x += mobiusBatchSize) { var xfirst = x; var xlast = Math.Min(xmed, xfirst + mobiusBatchSize - 2); m0 = mobius.GetValuesAndSums(xfirst, xlast + 2, values, m, m0); sum += Pi2Small(xfirst, xlast); UpdateMx(xfirst, xlast); } // Process medium x values. #if true for (var x = xmed + 2; x <= xmax; x += mobiusBatchSize) { var xfirst = x; var xlast = Math.Min(xmax, xfirst + mobiusBatchSize - 2); m0 = mobius.GetValuesAndSums(xfirst, xlast + 2, values, m, m0); sum += Pi2Medium(xfirst, xlast); UpdateMx(xfirst, xlast); } #else for (var x = xmax; x > xmed; x -= mobiusBatchSize) { var xlast = x; var xfirst = Math.Max(xmed + 2, xlast - mobiusBatchSize + 2); m0 = mobius.GetValuesAndSums(xfirst, xlast + 2, values, m, m0); sum += Pi2Medium(xfirst, xlast); UpdateMx(xfirst, xlast); } #endif // Process large x values. sum += Pi2Large(); // Adjust for final parity of F2. sum -= IntegerMath.Mertens(kmax); // Compute final result. sum &= 3; Debug.Assert((sum & 1) == 0); sum >>= 1; return((sum + (n >= 2 ? 1 : 0)) % 2); }