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);
}
