Find 1’s complement of a number

 

Algorithm for finding 1’s Complement

 

Step I : Initialize the data memory.

Step II : Load the number in AX.

Step III : Initialize counter = 16.

Step IV : Rotate number by 1 bit position to left with carry.

Step V : Complement carry.

Step VI : Decrement counter.

Step VII : Check if count = 0. If yes, go to step VIII else goto Step IV.

Step VIII : Rotate number by 1 bit position to left with carry to restore original carry back.

Step IX : Display 1’s complement.

Step X : Stop.

Program Code 1’s complement of a number:

.model small

.data

a dw 1234H

.code

mov ax, @data           ; Initialize data section

mov ds, ax

mov ax, a               ; Load number1 in ax

mov cx, 16              ; Load CX with count

up : rcl ax, 1          ; Rotate ax by 1bit to left with carry

cmc                     ; find 1's complement of bit

loop up                 ; check if all bits complemented, if not goto up

rcl ax, 1               ; return carry back to original position

mov ch, 04h             ; Count of digits to be displayed

mov cl, 04h             ; Count to roll by 4 bits

mov bx, ax              ; Result in reg bx

l2: rol bx, cl          ; roll bl so that msb comes to lsb

mov dl, bl              ; load dl with data to be displayed

and dl, 0fH             ; get only lsb

cmp dl, 09              ; check if digit is 0-9 or letter A-F

jbe l4

add dl, 07              ; if letter add 37H else only add 30H

l4: add dl, 30H

mov ah, 02              ; Function 2 under INT 21H

; (Display character)

int 21H

dec ch                  ; Decrement Count

jnz l2

mov ah, 4cH             ; Terminate Program

int 21H

end