HilbertCurve

ll convHilbert(int x, int y, int pow, int rotate) {
   if (!pow) return 0;
   int hpow = 1 << (pow - 1);
   int seg = (x < hpow) ? ((y < hpow) ? 0 : 3) : ((y < hpow) ? 1 : 2);
   seg = (seg + rotate) & 3;
   const int rotateDelta[4] = {3, 0, 0, 1};
   int nx = x & (x ^ hpow), ny = y & (y ^ hpow);
   int nrot = (rotate + rotateDelta[seg]) & 3;
   ll subSquareSize = (ll) 1 << (2 * pow - 2);
   ll ans = seg * subSquareSize;
   ll add = convHilbert(nx, ny, pow - 1, nrot);
   ans += (seg == 1 || seg == 2) ? add : (subSquareSize - add - 1);
   return ans;
}