;This code was written specifically for the A86 assembler although it may
;work with others such as TASM
.MODEL SMALL
.STACK 200H
.CODE

MAIN:
        CALL SETUP_INTS
        JMP OVERDATA1
;************************ DATA ****************************

PROMPT1         DB      18, 53, 45, 47, 52, 0, 230, 198 
                       ; L   o   g   i   n   :  [sp] [0]
PROMPT2         DB      211, 208, 22, 39, 57, 57, 61, 53, 56, 42, 0, 230, 198
                       ;[cr] [lf]  P   a   s   s   w   o   r   d   :  [sp] [0]
PASSWORD        DB 17 DUP (?)
LOGIN           DB 17 DUP (?)
SUCCESS         DB 211, 208, 57, 59, 41, 41, 43, 57, 57, 198
GENERAL1 DW 0
SPECIFIC1 DW 0

;********************* END OF DATA ************************

OVERDATA1:

;************************ CODE ****************************

        MOV SI, OFFSET PROMPT1
        MOV DH, 58
        MOV CX, 8
        CALL CHANGE_DATA        ;Add 58 to 8 chars at at prompt1 data
        CALL PRINT_MESSAGE      ;Then print it

        MOV DI, OFFSET LOGIN
        XOR DH, DH              ;DX = 0 = echo the char (not asterisk)
        CALL GET_INPUT          ;Get input & put in LOGIN

        MOV WORD PTR [GENERAL1], OFFSET USERS    ;Compare data at users (each user slot)
        MOV WORD PTR [SPECIFIC1], OFFSET LOGIN   ;with a single LOGIN data area
        CALL FIND_USER     ;See if it's a user, if so, return security # in AL
        PUSH SI            ;When done, push SI b/c this last accessed security byte
                           ;and it was INC so it now is in line with password for
                           ;successfully identified user

PRE_GET_PASS:
        MOV SI, OFFSET PROMPT2
        MOV DH, 58
        MOV CX, 13
        CALL CHANGE_DATA       ;Add 58 to 13 chars at prompt2
        CALL PRINT_MESSAGE     ;Print message

        MOV DI, OFFSET PASSWORD
        CALL GET_INPUT            ;Get password from user into PASSWORD

        POP SI     ;SI was pushed after it id'd the user now it points to password (after correct login name)
        MOV CX, 16  ;Password needs to have 121 added to each of its 16 chars
        MOV DH, 121
        MOV DI, OFFSET PASSWORD
        CALL CHANGE_DATA    ;Now add 121 to the chars
        CALL COMPARE_PASSWORD

        MOV AX, 840H     ;(7C00H + 200H + 3*200H + 100H) / 10H = 850H
        MOV DS, AX       ;THIS IS THE NASM VERSION SO 100H ISN'T ADDED
                         ; TO THE OFFSETS => 950H
        MOV ES, AX
        ;MOV SS, AX
        JMP CONTINUE_OS  ;If password and login correct, it will make it to
                         ;this stage....

;************************ PROCEDURES *************************

CHANGE_DATA:
        PUSH SI
CYCLE_OF_CD:
        MOV AL, BYTE PTR [ES:SI]
        ADD AL, DH
        MOV [ES:SI], AL 
        INC SI
        LOOP CYCLE_OF_CD
        POP SI
        RET
        ;***************

PRINT_MESSAGE:
        MOV AH, 0EH
        MOV BH, 0
        PUSH SI
MESSAGE_LP2:
        LODSB
        CMP AL, 0
        JZ GO_BACK2
        INT 10H
        JMP MESSAGE_LP2
GO_BACK2:
        POP SI
        RET
        ;***************

GET_INPUT:
        MOV CX, 16
        MOV BH, 0
THE_CYCLE1:
        XOR AH, AH
        INT 16H

        CMP AL, 8
        JZ DO_BACKSPACE

        CMP AL, 13
        JZ GO_BACK1

        STOSB

        CMP DH, 0
        JNZ ECHO_AST

ECHOED_AST:
        MOV AH, 0EH
        INT 10H
        LOOP THE_CYCLE1      
GO_BACK1:   RET
ECHO_AST:
        MOV AL, 42
        JMP ECHOED_AST
DO_BACKSPACE:
        CMP DI, OFFSET PASSWORD
        JZ THE_CYCLE1
        CMP DI, OFFSET LOGIN
        JZ THE_CYCLE1
        DEC DI
        MOV BYTE [ES:DI], 0
        MOV AH, 0EH
        INT 10H
        XOR AL, AL
        INT 10H
        MOV AL, 8
        INC CX
        INC CX
        JMP ECHOED_AST   ;'ECHOED_AST' is used for two return locations
        ;***************

FIND_USER:
        MOV CX, 30
OUTER_CYCLE:
        PUSH CX
        MOV SI, WORD PTR [GENERAL1]
        MOV AX, 30
        SUB AX, CX
        MOV DX, 33
        MUL DX
        ADD SI, AX
        MOV DI, WORD PTR [SPECIFIC1]
        MOV CX, 16
        
INNER_CYCLE:
        LODSB
        CMP AL, BYTE PTR [ES:DI]
        JNZ NO_GOOD_CHAR
        INC DI
        LOOP INNER_CYCLE

        POP CX
        JMP FOUND_ONE
NO_GOOD_CHAR:
        POP CX
        CMP CX, 0
        JZ NOT_FOUND
        LOOP OUTER_CYCLE
        JMP REBOOT       
NOT_FOUND:
        JMP REBOOT      
FOUND_ONE:
;        CMP CX, 28
;        JZ ITS_DAN
;BACK_FROM_ITSDAN:
        MOV AH, 1
        LODSB
        RET
;DAN_MESSAGE   DB  13,10,"You SUCK!",0
;ITS_DAN:
;        MOV SI, OFFSET DAN_MESSAGE
;        CALL PRINT_MESSAGE
;        JMP BACK_FROM_ITSDAN
        ;***************

COMPARE_PASSWORD:

        MOV CX, 16
COMPARING:
        MOV AL, BYTE PTR [ES:DI]
        CMP BYTE PTR [ES:SI], AL
        JNZ GOTO_REBOOT
        INC SI
        INC DI
        LOOP COMPARING
        RET
GOTO_REBOOT:
        JMP REBOOT
                  
        ;***************

;****************** END OF PROCEDURES *********************

;********************* INTERRUPTS *************************

        ;************* SETUP ******************
SETUP_INTS:
        PUSH DS
        XOR AX, AX
        MOV DS, AX

        MOV AX, OFFSET INT2100
        MOV BX, OFFSET MAIN
        SUB AX, BX
        ADD AX, 7E00H      ;7C00H+512  AKA  7C00H+200H
        
        MOV WORD [DS:132], AX        ;OFFSET INT2100
        XOR AX, AX
        MOV WORD [DS:134], AX    ;SEG INT2100

        MOV AX, OFFSET INT2E
        SUB AX, BX
        ADD AX, 7E00H

        MOV WORD [DS:184], AX
        XOR AX, AX
        MOV WORD [DS:186], AX

        POP AX
        MOV DS, AX
        RET

        ;*********** ACTUAL INTERRUPTS ************

;Test interrupt for now...
INT2100:
        MOV AX, 4C00H
        IRET
        ;************
INT2E:              
        CMP AH, 0
        JZ CONV_HEX
;CONV_BUFFER     DB      4 DUP (?)
                ;DB      "H",0
CONV_HEX:  ;!!!!!!! DS:DI > Buffer for chars, AH = 0, DX = word to convert !!!
        MOV CX, 15
        MOV AX, 0F000H              ;
        ;MOV DI, OFFSET CONV_BUFFER
CONV_HEX_CYCLE1:
        CMP DX, AX                  ;
        JAE SUBTRACT1
        SUB AX, 1000H               ;
        LOOP CONV_HEX_CYCLE1
SUBTRACT1: CALL SUBTRACT
        MOV AX, 0F00H               ;
        MOV CX, 15
CONV_HEX_CYCLE2:
        CMP DX, AX                  ;
        JAE SUBTRACT2
        SUB AX, 100H                ;
        LOOP CONV_HEX_CYCLE2
SUBTRACT2: CALL SUBTRACT
        MOV AX, 0F0H                ;
        MOV CX, 15
CONV_HEX_CYCLE3:
        CMP DX, AX                  ;
        JAE SUBTRACT3
        SUB AX, 10H                 ;
        LOOP CONV_HEX_CYCLE3
SUBTRACT3: CALL SUBTRACT
        MOV AX, 0FH                 ;
        MOV CX, 15
CONV_HEX_CYCLE4:
        CMP DX, AX                  ;
        JAE SUBTRACT4
        DEC AX                      ;
        LOOP CONV_HEX_CYCLE4
SUBTRACT4: CALL SUBTRACT
        IRET

SUBTRACT:
        SUB DX, AX                  ;
        PUSH DX                     ;
        MOV DL, CL                  ;
        ADD DL, 48                  ;
        CMP DL, 57                  ;
        JA DO_A_LETTER
BACK_FROM_LETTER:
        MOV AL, DL                  ;ADDED
        STOSB
        POP DX                      ;
        RET
DO_A_LETTER:
        ADD DL, 7                   ;
        JMP BACK_FROM_LETTER
        ;***************

;****************** END OF INTERRUPTS *********************

;*********************** DATA2 *****************************
REBOOT:         DB      0EAH, 0, 0, 0FFH, 0FFH        
THE_SPACE       DB      542 DUP (?)
USERS           DB      "root", 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1
                DB      16 dup (135)   ;become nulls when added to 121
AFTER_THAT      DB      479 DUP (?)
CONTINUE_OS:

END MAIN