Problem 1 (section 10.7)
Encoding and Decoding string using XLAT instruction
//Code
Title secret message
.Model small
.stack 100h
.data
; ;ABCDEFGHIJKLMNOPQRSTUVWXYZ
code_key db 65 dup(' '), 'XQPOGHZBCADEIJUVFMNKLRSTWY'
db 37 dup(' ')
; ;ABCDEFGHIJKLMNOPQRSTUVWXYZ
decode_key db 65 dup(' '), 'JHIKLQEFMNTURSDCBVWXOPYAZG'
db 37 dup(' ')
coded db 80 dup('$')
; XQPO$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$4
prompt db 'Enter a message to be encoded', 0dh, 0ah, '$'
crlf db 0dh, 0ah, '$'
.code
main proc
mov ax, @data
mov ds, ax
mov ah, 9
lea dx, prompt
int 21h
mov ah, 1
lea bx, code_key
lea di, coded
while_:
int 21h
cmp al, 0dh
je endwhile
xlat
mov [di], al
inc di
jmp while_
endwhile:
mov ah, 9
lea dx, crlf
int 21h
lea dx, coded
int 21h
lea dx, crlf
int 21h
mov ah, 2
lea bx, decode_key
lea si, coded
while1:
mov al, [si]
cmp al, '$'
je endwhile1
xlat
mov dl, al
int 21h
inc si
jmp while1
endwhile1:
mov ax, 4ch
int 21h
main endp
end main
Problem 2
Change the encode key and decode key in problem 1 to create a decoded message with the letters replaced by 3 letters ahead.
Example A becomes D, B becomes E, etc
//Code To be done by students
Problem 3
Change the code in problem 2 to encode both capital and small letters
//Code To be done by students