.model     tiny
        .code
        .186                     
        org        100h         

start:
        mov        ax,cs         
        add        ax,1000h      
        mov        ds,ax         
                                
        push       0A000h       
        pop        es         
        mov        ax,13h        
        int        10h

        mov        di,320*200
        mov        cx,600h       
        rep        stosb         
                                 
        xor        si,si   
        mov        bp,10  
        jmp        init_food 

main_cycle:
        call delay
        mov        ah,1                
        int        16h
        jz         short no_keypress 
        xor        ah,ah             
        int        16h                 
        cmp        ah,48h             
        jne        short not_up
        mov        word ptr cs:move_direction,-320

not_up:
        cmp        ah,50h             
        jne        short not_down
        mov        word ptr cs:move_direction,320

not_down:
        cmp        ah,4Bh 
        jne        short not_left
        mov        word ptr cs:move_direction,-1

not_left:
        cmp        ah,4Dh   
        jne        short no_keypress
        mov        word ptr cs:move_direction,1

no_keypress:
        and        bp,bp     
        jnz        short advance_head  
        lodsw   
        xchg       bx,ax
        mov        byte ptr es:[bx],0 
        mov        bx,ax
        inc        bp

advance_head:
        dec        bp
        add        bx,word ptr cs:move_direction
        mov        al,es:[bx]  
        and        al,al            
        jz         short move_worm    
        cmp        al,0Dh     
        je         short grow_worm   
        mov        ax,3      
        int        10h     
        retn    

move_worm:
        mov        [di],bx    
        inc        di
        inc        di    
        mov        byte ptr es:[bx],09 
        cmp        byte ptr cs:eaten_food,1
        je         if_eaten_food 
        jmp        short main_cycle 

grow_worm:
        push       bx             
        mov        bx,word ptr cs:food_at 
        xor        ax,ax            
        call       draw_food          
        call       random           
        and        ax,3Fh          
        mov        bp,ax  
        mov        byte ptr cs:eaten_food,1 
        pop        bx              
        jmp        short move_worm  

if_eaten_food:          
        mov        byte ptr cs:eaten_food,0

init_food:                            
        push       bx                 

make_food:
        call       random      
        and        ax,0FFFEh        
        mov        bx,ax      
        xor        ax,ax
        cmp        word ptr es:[bx],ax
        jne        make_food 
        cmp        word ptr es:[bx+320],ax 
        jne        make_food           
        mov        word ptr cs:food_at,bx 
        mov        ax,0D0Dh     
        call       draw_food    
        pop        bx
        jmp        main_cycle

delay proc
        pusha
        mov ah, 0
        int 1ah
        mov bx,dx
        add bx, 1 
    d1:
        int 1ah
        cmp dx, bx
        jb d1
        popa
     ret
delay endp

draw_food:
        mov        es:[bx],ax
        mov        word ptr es:[bx+320],ax
        retn

random: mov        ax,word ptr cs:seed
        mov        dx,8E45h
        mul        dx
        inc        ax
        mov        cs:word ptr seed,ax
        retn

eaten_food         db            0
move_direction     dw            1   ;1 - left, -1 - right, 320 - down, -320 - up
seed:                                
food_at equ        seed+2           
        
end        start
    

        org        100h

start:
        mov        ax,cs
        add        ax,1000h
        mov        ds,ax

        push       0A000h
        pop        es
        mov        ax,13h
        int        10h

        mov        di,320*200
        mov        cx,600h
        rep        stosb

        xor        si,si
        mov        bp,10
        jmp        init_food

main_cycle:
        call delay
        mov        ah,1
        int        16h
        jz         short no_keypress
        xor        ah,ah
        int        16h
        cmp        ah,48h
        jne        short not_up
        mov        word [cs:move_direction],-320

not_up:
        cmp        ah,50h
        jne        short not_down
        mov        word [cs:move_direction],320

not_down:
        cmp        ah,4Bh
        jne        short not_left
        mov        word [cs:move_direction],-1

not_left:
        cmp        ah,4Dh
        jne        short no_keypress
        mov        word [cs:move_direction],1

no_keypress:
        and        bp,bp
        jnz        short advance_head
        lodsw
        xchg       bx,ax
        mov        byte [es:bx],0
        mov        bx,ax
        inc        bp

advance_head:
        dec        bp
        add        bx,word [cs:move_direction]
        mov        al,[es:bx]
        and        al,al
        jz         short move_worm
        cmp        al,0Dh
        je         short grow_worm
        mov        ax,3
        int        10h
        ret

move_worm:
        mov        [di],bx
        inc        di
        inc        di
        mov        byte [es:bx],09
        cmp        byte [cs:eaten_food],1
        je         if_eaten_food
        jmp        short main_cycle

grow_worm:
        push       bx
        mov        bx,word [cs:food_at]
        xor        ax,ax
        call       draw_food
        call       random
        and        ax,3Fh
        mov        bp,ax
        mov        byte [cs:eaten_food],1
        pop        bx
        jmp        short move_worm

if_eaten_food:
        mov        byte [cs:eaten_food],0

init_food:
        push       bx

make_food:
        call       random
        and        ax,0FFFEh
        mov        bx,ax
        xor        ax,ax
        cmp        word [es:bx],ax
        jne        make_food
        cmp        word [es:bx+320],ax
        jne        make_food
        mov        word [cs:food_at],bx
        mov        ax,0D0Dh
        call       draw_food
        pop        bx
        jmp        main_cycle

delay:
        pusha
        mov ah, 0
        int 1ah
        mov bx,dx
        add bx, 1
    d1:
        int 1ah
        cmp dx, bx
        jb d1
        popa
             ret


draw_food:
        mov        [es:bx],ax
        mov        word [es:bx+320],ax
        retn

random: mov        ax,word [cs:seed]
        mov        dx,8E45h
        mul        dx
        inc        ax
        mov        word [seed],ax
        ret

eaten_food         db            0
move_direction     dw            1   ;1 - left, -1 - right, 320 - down, -320 - up
seed:
food_at dw        seed+2