.model small                            ;.model directive is to specify len of our program
.386                                    ;80386 microprocessor directive library is installed           

.data                                   ;.data means we are using data segment register
MESS1 DB "Enter 1st 32 bit number: $"   ;message to be displayed on the screen to input 1st no.
MESS2 DB "Enter 2nd 32 bit number: $"   ;message to be displayed on the screen to input 2nd no.
MESS3 DB "          Difference is: $"   ;message to be displayed on the screen to display sum.

.code                                   ; .code means our program code follows here 
.startup                                ; now the program starts

MOV DX, OFFSET MESS1                    ;offset of mess1 passed in DX
CALL MSG                                ;procedure to display message
CALL REGS                               ;procedure to clear EBX,EDX
CALL NUMB                               ;procedure to input 32bit no.
PUSH EBX                                ;storing the number in stack
CALL LINE                               ;line break

;---------- SECOND NUMBER ------------

MOV DX, OFFSET MESS2                    ;offset of mess2 passed in DX
CALL MSG                                ;procedure to display message
CALL REGS                               ;procedure to clear EBX,EDX
CALL NUMB                               ;procedure to input 32bit no.
PUSH EBX                                ;storing the number in stack
CALL LINE                               ;line break

;---------- SUBTRACTION CODE ------------

MOV DX, OFFSET MESS3                    ;offset of mess3 passed in DX
CALL MSG                                ;procedure to display messagePOP EDX
POP EBX                                 ;retrive 2nd number
POP EDX                                 ;retrive 1st number
CMP EDX,EBX                             ;compare 1st & 2nd number
JAE JUMP9                               ;if EDX > EBX then jump
MOV ECX,EBX                             ;swaping of EDX & EBX
MOV EBX,EDX     
MOV DL,0C4H                             ;loading code for minus sign sign
MOV AH,02                               ;display the sign
INT 21H
MOV EDX,ECX
MOV ECX,00H                             ;clear ECX register
JUMP9:SUB EDX,EBX                       ;subtract two numbers
MOV EBX,EDX                             ;store the result in EBX
;---------- OUTPUT DIFFERENCE -----------------
JUMP8: MOV CL,28                        ;counter for nibble shift
MOV EBP,0F0000000H                      ;register for nibble selection
JUMP16: MOV EDX,EBX                     ;retrive difference
AND EDX,EBP                             ;select nibble
SHR EDX,CL                              ;shift nibble to LSB nibble location
CALL OUTPUT                             ;procedure to display sum
SHR EBP,4                               ;shift register contents for other nibble selection
SUB CL,4                                ;decrement counter
JNZ JUMP16                              ;check counter status

MOV EDX,EBX                             ;retrive difference
AND EDX,EBP                             ;select nibble
CALL OUTPUT                             ;procedure to display sum

;------------ THE END --------------

.exit                                   ;exit to DOS

LINE PROC NEAR
;---------- NEW LINE -------------
MOV DL,0AH
MOV AH,02
INT 21H
RET
LINE ENDP

MSG PROC NEAR
;---------- TYPE MESSAGE -------------
MOV AH,09H
INT 21h
RET
MSG ENDP

REGS PROC NEAR
MOV EBX,00H
MOV EDX,00H
RET
REGS ENDP

OUTPUT PROC NEAR
;---------- convert to ascii ---------
CMP DL,09                               
JBE JUMP10
ADD DL,07H
JUMP10: ADD DL,30H
MOV AH,02
INT 21H
RET
OUTPUT ENDP

NUMB PROC NEAR
;-------------- INPUT NUMBER -----------
MOV CX,7
JUMP0: MOV AH,01
INT 21H
SUB AL,30H
CMP AL,09
JBE JUMP1
SUB AL,07H
JUMP1: ADD BL,AL 
SHL EBX,4
LOOP JUMP0

MOV AH,01
INT 21H
SUB AL,30H
CMP AL,09
JBE JUMP2
SUB AL,07H
JUMP2: ADD BL,AL
RET
NUMB ENDP

end                                     ;end of program