请教一下，下面的这段代码是做什么的？求最大范围?如果是求最大范围前两行不就行了吗

第一行已经是x1、x2的最大值了，第三行又是什么意思呢？

               double x1_ = Math.Max(x1, x2);
                double x1__ = Math.Min(x1, x2);
                double x11 = Math.Max(x1_, x2);
                double x12 = Math.Min(x1__, x2);
                int n = 1000000;
                double h = (x11 - x12) / n;


                for (int j = 0; j < n; j++)
                {
                    x12 = x12 + h;
                    double A, B;
                    double A1 = 0, B1 = 0;
                    if (x1 <= x12)
                    {
                        if (x12 <= x2 && x12 <= x3)
                        {
                            A = (y3 - y1) / (x3 - x1) * (x12 - x1) + y1;
                            B = (y2 - y1) / (x2 - x1) * (x12 - x1) + y1;
                            A1 = Math.Max(A, B);
                            B1 = Math.Min(A, B);
                        }
                    else if (x12 > x2 || x12 > x3)
                    {
                        if (x2 < x3)
                        {
                            A = (y3 - y1) / (x3 - x1) * (x12 - x1) + y1;
                            B = (y3 - y2) / (x3 - x2) * (x12 - x2) + y2;
                            A1 = Math.Max(A, B);
                            B1 = Math.Min(A, B);
                         }
                         else
                         {
                            A = (y2 - y1) / (x2 - x1) * (x12 - x1) + y1;
                            B = (y3 - y2) / (x3 - x2) * (x12 - x2) + y2;
                            A1 = Math.Max(A, B);
                            B1 = Math.Min(A, B);
                          }
                     }
                    }
                    if (x2 <= x12)
                    {
                        if (x12 <= x1 && x12 <= x3)
                        {
                            A = (y3 - y2) / (x3 - x2) * (x12 - x2) + y2;
                            B = (y1 - y2) / (x1 - x2) * (x12 - x2) + y2;
                            A1 = Math.Max(A, B);
                            B1 = Math.Min(A, B);
                        }
                        else if (x12 > x1 || x12 > x3)
                        {
                            if (x1 < x3)
                            {
                                A = (y3 - y2) / (x3 - x2) * (x12 - x2) + y2;
                                B = (y3 - y1) / (x3 - x1) * (x12 - x1) + y1;
                                A1 = Math.Max(A, B);
                                B1 = Math.Min(A, B);
                            }
                            else
                            {
                                A = (y1 - y2) / (x1 - x2) * (x12 - x2) + y2;
                                B = (y3 - y1) / (x3 - x1) * (x12 - x1) + y1;
                                A1 = Math.Max(A, B);
                                B1 = Math.Min(A, B);
                            }
                        }
                    }
                    if (x3 <= x12)
                    {
                        if (x12 <= x2 && x12 <= x3)
                        {
                            A = (y1 - y3) / (x1 - x3) * (x12 - x3) + y3;
                            B = (y2 - y3) / (x2 - x3) * (x12 - x3) + y3;
                            A1 = Math.Max(A, B);
                            B1 = Math.Min(A, B);
                        }
                        else if (x12 > x2 || x12 > x3)
                        {
                            if (x2 < x3)
                            {
                                A = (y1 - y3) / (x1 - x3) * (x12 - x3) + y3;
                                B = (y1 - y2) / (x1 - x2) * (x12 - x2) + y2;
                                A1 = Math.Max(A, B);
                                B1 = Math.Min(A, B);
                            }
                            else
                            {
                                A = (y2 - y3) / (x2 - x3) * (x12 - x3) + y3;
                                B = (y1 - y2) / (x1 - x2) * (x12 - x2) + y2;
                                A1 = Math.Max(A, B);
                                B1 = Math.Min(A, B);
                            }
                        }
                    }