code: void get_distance_features(final Context ctx,
                                 List<Integer> features)
      {
          if (!use_distance)
          {
              return;
          }
  
          int dist = 8;
          if (ctx.S0 >= 0 && ctx.S1 >= 0)
          {
              dist = math.binned_1_2_3_4_5_6_10[ctx.S0 - ctx.S1];
              if (dist == 10)
              {
                  dist = 7;
              }
          }
          features.add(dist + kDistanceInFeaturespace);
      }
docs: 获取距离特征
  @param ctx 当前特征
  @param features 输出特征