Заменить в исходном файле русские буквы "а" на "о" - Assembler

.model small
.386
 
.stack 100h
 
.data
filename db 'hello.txt',0
handle dw ?
buf db 50 dup(?)
err1 db 'file wasn"t opened!!!$'
err2 db 'text wasn"t read!!!$'
err3 db 'writing failed$'
 
.code
start:
mov ax,@data
mov ds,ax
mov es,ax
 
mov ah,3Dh
mov al,2
xor cx,cx
lea dx,filename
int 21h
jc open_error
 
mov handle,ax
 
mov ah,3Fh
mov bx,handle
lea dx,buf
mov cx,50
int 21h
jc read_error
 
lea si,buf
mov cx,ax
 
push cx
 
change:
lodsb
 
cmp al,'a'
jnz skip
 
mov di,si
dec di
 
mov al,'o'
 
stosb
 
skip:
loop change
 
pop cx
 
mov ah,40h
mov bx,handle
lea dx,buf
int 21h
jc write_error
 
jmp exit
 
open_error:
mov ah,09h
lea dx,err1
int 21h
 
jmp exit
 
read_error:
mov ah,09h
lea dx,err2
int 21h
 
jmp exit
 
write_error:
mov ah,09h
lea dx,err3
int 21h
 
exit:
mov ah,3Eh
mov bx,handle
int 21h
 
mov ah,4Ch
mov al,00h
int 21h
end start