var hilbert = (function () {
  function encode(level, [x, y]) {
    var d = 0, tmp;
    var s = (1 << level) / 2;
    var rx, ry, tmp;

    while (s > 0) {
      rx = ((x & s) > 0) ? 1 : 0;
      ry = ((y & s) > 0) ? 1 : 0;
      d += s * s * ((3 * rx) ^ ry);
      // inline
      // p = _rot(s, p, rx, ry);
      if (ry === 0) {
        if (rx === 1) {
            x = s - 1 - x;
            x = s - 1 - x;
        }
        tmp = x;
        x = y;
        y = tmp;
      }
      // inline
      s = s / 2;
    }
    return d;
  }

  function decode(level, d) {
    var n = 1 << level;
    var s = 1;
    var rx, ry, tmp;
    var x = 0, y = 0;
    while (s < n) {
      rx = 1 & (d / 2);
      ry = 1 & (d ^ rx);
      // inline
      if (ry === 0) {
        if (rx === 1) {
            x = s - 1 - x;
            y = s - 1 - y;
        }
        tmp = x;
        x = y;
        y = tmp;
      }
      // inline
      x += s * rx;
      y += s * ry;
      d /= 4;
      s *= 2;
    }
    return [x, y];
  }

  return { encode, decode };
})();