;Ben Weir
;CIS 35
;Assignment 2
        .model small
        .stack 100h
        .data
pass1   db 'CRAMP'
pass2   db 'PRINT'
pass3   db 'DANCE'
usrpass db 0ah dup (0)
wrongmsg db 0ah, 0dh, 'Invalid Password, Access Denied!$'
rightmsg db 0ah, 0dh, 'Password Valid, Access Permitted!$'
prompt  db 0ah, 0dh, 'Enter the Password: $'

        .code
        mov ax, @data
        mov ds, ax
        mov es, ax              ;set up DS, ES

        lea dx, prompt
        mov ah, 9h
        int 21h                 ;prompt user for password

        lea si, usrpass
        mov cx, 0ah
        call readstring         ;get password

        cmp ax, 5
        jnz wrong               ;make sure the password is 5 long

        lea si, pass1
        call comparestr
        cmp cx, 0               ;test first password
        jz right

        lea si, pass2
        call comparestr
        cmp cx, 0               ;test second password
        jz right

        lea si, pass3
        call comparestr
        cmp cx, 0               ;test third password
        jz right

wrong:
        lea dx, wrongmsg
        jmp displaymsg
right:
        lea dx, rightmsg
displaymsg:
        mov ah, 9h              ;show whether they got it right or not
        int 21h
done:
        mov ax, 4c00h           ;terminate program
        int 21h

comparestr proc near
;enter with si: pointer to string to compare to user entered string
;returns    cx: 0 if strings match, >0 if they don't match
        push di
        lea di, usrpass
        mov cx, 6
        repz cmpsb
        pop di
        ret
comparestr endp

readstring proc near
;enter with cx: number of characters to read
;           si: offset of place to store string
;returns    ax: number of chars entered
        push cx
        push si
        mov bx, si              ;save starting address
newchar:
        mov ah, 8               ;char input without echo
        int 21h
        cmp al, 0dh
        jz stringdone           ;exit if they press enter
        cmp al, 8
        jz backspace            ;don't add the character if it's BS
        mov dl, al
        mov ah, 2
        int 21h                 ;show character
        mov [si], al
        inc si
        loop newchar
        jmp stringdone
backspace:
        cmp si, bx               ;don't want to backspace
        jle nomorebs             ;past start of string
        dec si
        mov byte ptr [si], 0
        mov ah, 2
        mov dl, 8
        int 21h
        mov dl, 20h             ;erase character with ' ' and another BS
        int 21h
        mov dl, 8
        int 21h
nomorebs:
        cmp cx, 0
        jnz newchar
stringdone:
        mov ax, si
        sub ax, bx
        pop si
        pop cx
        ret
readstring endp

        end