calculate sum of 2 numbers.asm

; this sample gets two numbers from the user,
; then it calculates the sum of these numbers,
; and prints it out.

name "calc"

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; these maros are copied from emu8086.inc ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; this macro prints a string that is given as a parameter, example:
; PRINTN 'hello world!'
; the same as PRINT, but new line is automatically added.
PRINTN   MACRO   sdat
LOCAL   next_char, s_dcl, printed, skip_dcl

PUSH    AX      ; store registers...
PUSH    SI      ;

JMP     skip_dcl        ; skip declaration.
        s_dcl DB sdat, 0Dh,0Ah, 0

skip_dcl:
        LEA     SI, s_dcl
        
next_char:      
        MOV     AL, CS:[SI]
        CMP     AL, 0
        JZ      printed
        INC     SI
        MOV     AH, 0Eh ; teletype function.
        INT     10h
        JMP     next_char
printed:

POP     SI      ; re-store registers...
POP     AX      ;
ENDM

; this macro prints a char in AL and advances
; the current cursor position:
PUTC    MACRO   char
        PUSH    AX
        MOV     AL, char
        MOV     AH, 0Eh
        INT     10h     
        POP     AX
ENDM
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;




org     100h







jmp     start   ; skip data.
   
msg1  db 0Dh,0Ah, 'input numbers in this range: [-32768..32767]', 0Dh,0Ah
      db 0Dh,0Ah, 'enter first number: $'

msg2  db 0Dh,0Ah, 'enter second number: $'

msg3  db 0Dh,0Ah, 'the sum is: $'

; declaration of variable:
num  dw ?

start:


; print first message
mov dx, offset msg1
mov ah, 9
int 21h


call    scan_num

; keep first number:
mov     num, cx


; print second message
mov dx, offset msg2
mov ah, 9
int 21h


call    scan_num


; add numbers:
add     num, cx
jo      overflow


; print the result:
mov dx, offset msg3
mov ah, 9
int 21h


mov     ax, num
call    print_num

jmp     exit

; process overlow error:
overflow:
   
   printn 'we have overflow!'


exit:

; wait for any key press:
mov ah, 0
int 16h

ret   ; return control to operating system.






;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; these functions are copied from emu8086.inc ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


; gets the multi-digit SIGNED number from the keyboard,
; and stores the result in CX register:
SCAN_NUM        PROC    NEAR
        PUSH    DX
        PUSH    AX
        PUSH    SI
        
        MOV     CX, 0

        ; reset flag:
        MOV     CS:make_minus, 0

next_digit:

        ; get char from keyboard
        ; into AL:
        MOV     AH, 00h
        INT     16h
        ; and print it:
        MOV     AH, 0Eh
        INT     10h

        ; check for MINUS:
        CMP     AL, '-'
        JE      set_minus

        ; check for ENTER key:
        CMP     AL, 0Dh  ; carriage return?
        JNE     not_cr
        JMP     stop_input
not_cr:


        CMP     AL, 8                   ; 'BACKSPACE' pressed?
        JNE     backspace_checked
        MOV     DX, 0                   ; remove last digit by
        MOV     AX, CX                  ; division:
        DIV     CS:ten                  ; AX = DX:AX / 10 (DX-rem).
        MOV     CX, AX
        PUTC    ' '                     ; clear position.
        PUTC    8                       ; backspace again.
        JMP     next_digit
backspace_checked:


        ; allow only digits:
        CMP     AL, '0'
        JAE     ok_AE_0
        JMP     remove_not_digit
ok_AE_0:        
        CMP     AL, '9'
        JBE     ok_digit
remove_not_digit:       
        PUTC    8       ; backspace.
        PUTC    ' '     ; clear last entered not digit.
        PUTC    8       ; backspace again.        
        JMP     next_digit ; wait for next input.       
ok_digit:


        ; multiply CX by 10 (first time the result is zero)
        PUSH    AX
        MOV     AX, CX
        MUL     CS:ten                  ; DX:AX = AX*10
        MOV     CX, AX
        POP     AX

        ; check if the number is too big
        ; (result should be 16 bits)
        CMP     DX, 0
        JNE     too_big

        ; convert from ASCII code:
        SUB     AL, 30h

        ; add AL to CX:
        MOV     AH, 0
        MOV     DX, CX      ; backup, in case the result will be too big.
        ADD     CX, AX
        JC      too_big2    ; jump if the number is too big.

        JMP     next_digit

set_minus:
        MOV     CS:make_minus, 1
        JMP     next_digit

too_big2:
        MOV     CX, DX      ; restore the backuped value before add.
        MOV     DX, 0       ; DX was zero before backup!
too_big:
        MOV     AX, CX
        DIV     CS:ten  ; reverse last DX:AX = AX*10, make AX = DX:AX / 10
        MOV     CX, AX
        PUTC    8       ; backspace.
        PUTC    ' '     ; clear last entered digit.
        PUTC    8       ; backspace again.        
        JMP     next_digit ; wait for Enter/Backspace.
        
        
stop_input:
        ; check flag:
        CMP     CS:make_minus, 0
        JE      not_minus
        NEG     CX
not_minus:

        POP     SI
        POP     AX
        POP     DX
        RET
make_minus      DB      ?       ; used as a flag.
SCAN_NUM        ENDP





; this procedure prints number in AX,
; used with PRINT_NUM_UNS to print signed numbers:
PRINT_NUM       PROC    NEAR
        PUSH    DX
        PUSH    AX

        CMP     AX, 0
        JNZ     not_zero

        PUTC    '0'
        JMP     printed

not_zero:
        ; the check SIGN of AX,
        ; make absolute if it's negative:
        CMP     AX, 0
        JNS     positive
        NEG     AX

        PUTC    '-'

positive:
        CALL    PRINT_NUM_UNS
printed:
        POP     AX
        POP     DX
        RET
PRINT_NUM       ENDP



; this procedure prints out an unsigned
; number in AX (not just a single digit)
; allowed values are from 0 to 65535 (FFFF)
PRINT_NUM_UNS   PROC    NEAR
        PUSH    AX
        PUSH    BX
        PUSH    CX
        PUSH    DX

        ; flag to prevent printing zeros before number:
        MOV     CX, 1

        ; (result of "/ 10000" is always less or equal to 9).
        MOV     BX, 10000       ; 2710h - divider.

        ; AX is zero?
        CMP     AX, 0
        JZ      print_zero

begin_print:

        ; check divider (if zero go to end_print):
        CMP     BX,0
        JZ      end_print

        ; avoid printing zeros before number:
        CMP     CX, 0
        JE      calc
        ; if AX<BX then result of DIV will be zero:
        CMP     AX, BX
        JB      skip
calc:
        MOV     CX, 0   ; set flag.

        MOV     DX, 0
        DIV     BX      ; AX = DX:AX / BX   (DX=remainder).

        ; print last digit
        ; AH is always ZERO, so it's ignored
        ADD     AL, 30h    ; convert to ASCII code.
        PUTC    AL


        MOV     AX, DX  ; get remainder from last div.

skip:
        ; calculate BX=BX/10
        PUSH    AX
        MOV     DX, 0
        MOV     AX, BX
        DIV     CS:ten  ; AX = DX:AX / 10   (DX=remainder).
        MOV     BX, AX
        POP     AX

        JMP     begin_print
        
print_zero:
        PUTC    '0'
        
end_print:

        POP     DX
        POP     CX
        POP     BX
        POP     AX
        RET
PRINT_NUM_UNS   ENDP



ten             DW      10      ; used as multiplier/divider by SCAN_NUM & PRINT_NUM_UNS.