static int[] oneStepPt_l = {
  0, -1,
  -1, -1,
  -1, 0,
  -1, 1,
  0, 1,
  1, 1,
  1, 0,
  1, -1
};

static Pt oneStepPt(Pt p) {
  int i = mod(iround(Math.atan2(p.x, p.y)*8/2/pi()), 8);
  ret new Pt(oneStepPt_l[i*2], oneStepPt_l[i*2+1]);
}