8086 program to Multiply two 8 bit numbers using add and shift method

03:05

ØØ Explanation :

· Consider that one byte is present in the AL register and another byte is present in the BL register.

· We have to multiply the byte in AL with the byte in BL.

· We will multiply the numbers using add and shift method. In this method, you add number with itself and rotate the other number each time and shift it by one bit to left alongwith carry. If carry is present add the two numbers.

· Initialise the count to 4 as we are scanning for 4 digits. Decrement counter each time the bits are added. The result is stored in AX. Display the result.

For example : AL = 11 H, BL = 10 H, Count = 4

Step I :

AX =		11
	+	11
		22 H

Rotate BL by one bit to left along with carry.

BL = 10 H		0	¬	0	0	0	1	0	0	0	0
		CY
BL =	0	0	0	1	0	0	0	0	0
	CY		2				0

Step II : Now decrement counter count = 3.

Check for carry, carry is not there so add number with itself.

AX =		22
	+	22
		44 H

Rotate BL to left,

BL =	0	¬	0	1	0	0	0	0	0	0
	CY			4				0

Carry is not there.

Decrement count, count=2

Step III : Add number with itself

AX =		44
	+	44
		88 H

Rotate BL to left,

BL =	0		1	0	0	0	0	0	0	0
	CY			8				0

Carry is not there.

Step IV : Decrement counter count = 1.

Add number with itself as carry is not there.

AX =		88
	+	88
		110 H

Rotate BL to left,

BL =	1		0	0	0	0	0	0	0	0
	CY			0				0

Carry is there.

Step V : Decrement counter = 0.

Carry is present.

\ add AX, BX

\		0110	i.e.		11 H
	+	0000		´	10 H
		0110 H			0110 H

ØØ Algorithm :

Step I : Initialise the data segment.

Step II : Get the first number.

Step III : Get the second number.

Step IV : Initialize count = 04.

Step V : number 1 = number 1 ´ 2.

Step VI : Shift multiplier to left alongwith carry.

Step VII : Check for carry, if present goto step VIII else goto step IX.

Step VIII : number 1 = number1 + shifted number 2.

Step IX : Decrement counter.

Step X : If not zero, goto step V.

Step XI : Display the result.

Step XII : Stop.

ØØ Flowchart : Refer flowchart 12.

.model small

.data

a db 11H

b db 10H

.code

mov ax, @data ; Initialize data section

mov ds, ax

mov al, a ; Load number1 in al

mov bl, b ; Load number2 in bl

mov ah, 0

mov dl, 04h ; initialize counter

ad: add ax, ax ; add numbers. Result in dx

rcl bl, 01

jnc skip

add ax, bx

skip: dec dl ; dec number

jnz ad

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

Flowchart 12

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

ØØ Result :

C:\programs>tasm shaddmul.asm

Assembling file: shaddmul.asm

Error messages: None

Warning messages: None

Passes: 1

Remaining memory: 438k

C:\programs>tlink shaddmul.obj

Warning: No stack

C:\programs>shaddmul

0110

C:\programs>

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