How do you reverse a string in assembly language?

program:

assume cs:code,ds:data

code segment

mov ax,data

mov ds,ax

mov cl,count

mov si,offset str1

mov di,0003h

back:mov al,[si]

xchg [di],al

mov [si],al

inc si

dec di

dec cl

jnz back

hlt

code ends

data segment

str1 db 01h,02h,03h,04h

count equ 02h

data ends

end

result:

input: str1 (ds:0000h) = 01h,02h,03h,04h

output: str1 (ds:0000h) = 04h,03h,02h,01h