printNumber.asm

; Author: Daniel Aguilar S.
; IS:     8086 Assembly.
; Desc:   Prints a positive or negative number.

org 100h

mov al, 11010101b               ; Number to be displayed. (8 bits)

print           proc
                mov bx, 0AH     ; Initialize divisor by 10
                mov cx, 0H      ; Clean CX
                mov dx, 0H      ; Clean DX
                
.isNegative:
                mov dx, ax      ; Move number to DX to check if its negative
                shr dx, 7H      ; Shift 7 bits to the right (leaves the most significant bit)
                cmp dx, 1H      ; Check if DX equals to 1 (negative)
                je .negative    ; If DX is equal to 1 add a "-" and apply two's complement to AX
                jmp .split      ; Otherwise (positive) make normal split and convert
                
.negative:
                push 0C0H       ; Push character "-", ASCII code - mask(48) = 192
                inc cx          ; Increment to track the number of characters
                
                mov ah, 0FFH    ; Put high 8 bits of ax in 255 to apply two's complement correctly
                neg ax          ; Apply two's complement to AX and continue to split and convert

.split:          
                mov dx, 0H      ; Clean DX 
                div bx          ; Divide AX by BX
                push dx         ; Push DX reminder to stack
                inc cx          ; Increment to track the number of characters
                cmp ax, 0H      ; Check if its possible to keep dividing
                jne .split      ; Loop again if AX is not 0

.convert:
                pop dx          ; Pop from stack to dx
                add dx, 30H     ; Apply mask and convert to ASCII
                mov ah, 02H
                int 21h         ; Call OS to print character
                loop .convert   ; Loop until cx (counter) is zero.                                          
               
print           endp

ret                             ; Return control to OS