I wrote this code to draw a shape using video ram. Whenever i call fixarray it seems to go into an infinite loop.Could you please help? I posted a big chunk of code so anyone can regenerate it and figure out what's causing the problem.
Data_segment_name segment para
hhead dw ? ;head
h dw 12 dup (?) ;array
hlength dw ? ;array length
htail dw ? ;array tail
Data_segment_name ends
Stack_segment_name segment para stack
dw 16 dup(0) ;define your stack segment
Stack_segment_name ends
Code_segment_name segment
Main_prog proc far
assume SS:Stack_segment_name,CS:Code_segment_name,DS:Data_segment_name
mov AX,Data_segment_name ;load the starting address of the data
mov DS,AX ; segment into DS reg.
call cls
call drawh
call movehu
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov ax,4c00h ; exit program
int 21h
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
fixharr proc near
;fix array positions
mov cx,hlength-1 ;i.e (don't need old tail)
fixarr:
mov si,cx
add si,si ;scale si to 2
mov ax,h[si-2]
mov h[si],ax
loop fixarr
mov ax,hhead
mov h[0],ax
ret
fixharr endp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
drawh proc near ;draw array
push ax
push cx
mov di,160*9+20*2
mov hhead,di
mov si,0
mov h[si],di ;save head position
inc si
mov hlength,si ;length = si+1 i.e. h[0]=position length=1
mov ax,0b800h
mov es,ax
mov ax, 1f2ah ;draw head
std
stosw
mov cx,2
label1:
;draw array
mov h[si],di ;save body position (si is already incremented)
mov htail,di
inc si ;to be ready for next insertion
mov hlength,si
mov ax,0b800h
mov es,ax
mov ax, 112ah
std
stosw
loop label1
pop cx
pop ax
ret
drawh endp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
movehu proc near
mov ax,hhead ;remove old head
mov di,hhead
mov ax,0b800h
mov es,ax
mov ax,112ah
stosw
mov ax,hhead ;draw new head (without deleting old head)
sub ax,160
mov hhead,ax
mov di,hhead
mov ax,0b800h
mov es,ax
mov ax,1f2ah
stosw
;delete tail
mov di,htail
mov ax,0b800h
mov es,ax
mov ax,002ah
cld
stosw
mov htail,di
;fix array positions
call fixharr
ret
movehu endp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
cls proc near
mov ax,0b800h
mov es,ax
mov ax,0720h
mov di,0
mov cx,2000
rep stosw
ret
cls endp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Code_segment_name ends
end Main_prog
See, this is why MCVE is important.
Now we know that you declared hlength as a variable in memory and not as a constant. For a constant, you can do mov cx, hlength-1 but for a variable that doesn't do what you think. Rewriting in "bracket syntax" that is mov cx, [hlength-1], which loads a word from memory at address hlength-1. It does not load a word from address hlength subsequently decrementing it. To achieve this (since this is what you really want) you should do:
mov cx, hlength
dec cx
(or equivalent)
PS: We have told you the problem is probably with the length even without seeing your full code. Learn to use a debugger.