*-----------------------------------------------------------
* Title      : Ceasar chipher
* Written by : Manuel V?gele, Simon W?rner (Team 1)
* Date       : 12.05.2015
* Description: This program encrypts a string using ROT3
*-----------------------------------------------------------
    ORG    $3000
START:                  ; This is where the program starts - obviously

* Put program code here
    
    ; Load string address
    move.l  #input, A0
    move.l  #output, A1
    
LOOP:
    ; Load char to register
    move.b  (A0), D0
    
    ; If end of string is reached end loop
    cmp.b   #0, D0
    beq     LOOP_END
    
    ; Apply the encryption key
    add.b   #key, D0
    
    ; Make the char lower case
    move.b  D0, D1
    or.b    #casebit, D1

    ; Check if char is greater than 'z'
    cmp.b   #z, D1
    ble     WRITE_CHAR
    
    ; Cycle to A after Z
    sub.b   #alphabetLength, D0
    
WRITE_CHAR:
    ; Write the encrypted char to the output string
    move.b  D0, (A1)
    
    ; Move pointers to next char
    add.l   #1, A0
    add.l   #1, A1
    bra     LOOP

LOOP_END:

    ; Add '\0' at output string end
    move.b  #0, (A1)

    SIMHALT             ; halt simulator

* Put variables and constants here

input           dc.b    'Zykluszeit',0
output          ds.b    11

key             EQU     3

z               EQU     'z'
casebit         EQU     $20
alphabetLength  EQU     26


    END    START        ; last line of source




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