请帮忙注释一下这个代码，电梯上行下行那里，我都不懂怎么就实现了电梯上下滚动，从当前层滚动到目标层

#include <reg51.h>  
#include <intrins.h>
unsigned char temp, key, keynum, current_num, end_num, offset, t, x;
void delay(int num)
{
    int m, n;
    for(m = 0; m < num; m++)
        for(n = 0; n < 100; n++)    
            ;
}
unsigned char table[]={
0x00, 0x66, 0x99, 0x81, 0x42, 0x24, 0x18, 0x00,//
0x08, 0x18, 0x38, 0x18, 0x18, 0x18, 0x3c, 0x00,//1
0x3c, 0x7e, 0x46, 0x0c, 0x18, 0x3e, 0x7e, 0x00,//2
0x3c, 0x66, 0x06, 0x3c, 0x06, 0x66, 0x3c, 0x00,//3
0x0c, 0x1c, 0x3c, 0x6c, 0x7e, 0x7e, 0x0c, 0x00,//4
0x7e, 0x7e, 0x70, 0x7c, 0x06, 0x7e, 0x7e, 0x00,//5
0x3c, 0x7e, 0x60, 0x7c, 0x66, 0x66, 0x3c, 0x00,//6
0x7e, 0x7e, 0x0c, 0x0c, 0x18, 0x18, 0x18, 0x00,//7
0x3c, 0x66, 0x66, 0x3c, 0x66, 0x66, 0x3c, 0x00,//8
0x3c, 0x66, 0x66, 0x3e, 0x06, 0x7e, 0x3c, 0x00};//9
unsigned char key_table[]={
0xee, 0xde, 0xbe, 0x7e,
0xed, 0xdd, 0xbd, 0x7d,
0xeb, 0xdb, 0xbb, 0x7b,
0xe7, 0xd7, 0xb7, 0x77};
void display_t0() interrupt 1
{   
    int i, j;
    TH0 = -4000/256;
    TL0 = -4000%256;
    P1 = 0xf0;
    if (P1 != 0xf0)
    {
    //  delay(100);
    //  if(P1!= 0xf0)
    //  {       
            temp = P1;
            P1 = 0x0f;
            key = temp|P1;
            for(i = 0; i < 16; i++)
            {
                if(key == key_table[i])
                {
                    keynum = i;
                    break;
                }
            }
    //  }
    }
    P2 = _crol_(P2 , 1);
    j = current_num * 8 + t + offset;
    P0 = ~table[j];                                                      
    if (current_num < keynum)
    {
        if( ++t == 8)
        {
            t = 0;
            if (++x == 4)
            {
                x = 0;
                if (++offset == 8)
                {
                    offset = 0;
                    current_num++;
                    end_num = current_num;
                }
            }
        }
    }

    else if (current_num > keynum )
    {
        if( ++t == 8)
        {
            t = 0;
            if  (++x == 4)
            {
                x = 0;
                if (--offset == -8)
                {
                    offset = 0;
                    current_num--;
                    end_num = current_num;
                }
            }
        }
    }   

    else
    {
        if( ++t == 8)
            t = 0;
    }
}         
void main()
{   
    TMOD = 0x01;
    TH0 = -4000/256;
    TL0 = -4000%256;
    TR0 = 1;
    ET0 = 1;
    EA = 1;
    EX0=1;
    EX1=1;
    IT0=1;
    IT1=1;
    PX0=1;
    P2 = 0x80;
    keynum = 1;
    current_num = 1;
    t = 0;
    x = 0;
    led = 1;
    BEEP = 1;
    while(1);
}

https://www.zhihu.com/question/413339019