palindrome

//palindrome
data segment
string db "HEllo World$"
pal db 01h
data ends

extra segment
rev db ?
extra ends

code segment
assume cs:code,es:extra,ds:data
start: mov ax,data
       mov ds,ax

       mov ax,extra
       mov es,ax

       mov cx,0000H

       lea si,string
   up: mov al,[si]
       cmp al,'$'
       jz down
       inc cx
       inc si
       jnp up

down:  mov bx,cx
       dec si
       lea di,rev

up1:   std
       lodsb
       dec bx
       jnz up1
       lea si,string
       lea di,rev
       cld
       repe cmpsb
       cmp cx,0000H
       jz exit
       mov pal,00h

exit:  int 03h

data ends
end start