MPLab 32bit Multiplication

32-bit Binary Multiplication

1. Define the model and architecture for the assembly code

.model small 
.stack 100H 
.386          ; specifies that the program will use instructions of the 80386 processor (32-bit instructions).

2. Define your data in the data section ( here you can define various data items: variables, constants, strings, arrays)

.data          ; .data directive indicates the beginning of data section 

; DATA1 and DATA2 are 32-bit variables initialized to 0. 
DATA1 dd 00000000H         
DATA2 dd 00000000H

; PROD1 and PROD2 32-bit uninitialized variables.
PROD1 dd ?           
PROD2 dd ?

;define strings that will be displayed as messages to the user while executing the program.
msg db 10,13,"Enter the First Number: $"
msg1 db 10,13,"Enter the Second Number: $"
msg2 db 10,13,"The Product (in Hexadecimal) is: $"

3. Define your instruction in the code section (here you write the assembly instructions that perform computations, control program flow, and interact with data variables and memory)

.code        ; .code directive indicates the beginning of code section 
.startup     ;  the entry point of the program

; Using DOS interrupt 21H to display the message.
MOV AH,09         
MOV DX,OFFSET msg        
INT 21H  

; Read the First Number and store it into DATA1
MOV EBX, 0     ;sets the value of the EBX register to zero
MOV CX, 8       ;sets the value of the CX register to 8  (CX is used as a loop counter)
; Using Loop
AGAIN: 
             ; Using DOS interrupt 21H to read a character
             MOV AH, 01 
             INT 21H
             
             ;compares the value in the AL register (the character just read) with the character 'A'.
             CMP AL,'A'      
            
             ; If the character in AL is greater than or equal to 'A', program jumps to Label L5. 
             JGE L5      

             ; Otherwise it subtracts 30H from the ASCII value of the character.  To convert numeric character('0' to '9') to the numerical value (0 to 9) 
             SUB AL,30H      
             
             ;After subtraction program jumps to Label L6
             JMP L6

             ;If the character in AL is an upper case letter, it subtracts 37H from the ASCII value of the character
             L5: SUB AL,37H

             ;shift the contents of the EBX register left by 4 bits.
             L6: SHL EBX,4

             ;Add the value in AL (which has been adjusted to be a numerical value) to the low byte (BL) of the EBX register.
             ADD BL,AL
             
             ;This is a loop instruction that decrements the CX register and jumps back to the label AGAIN if CX is not zero. 
             LOOP AGAIN

; EBX contents are moved to DATA1
MOV DATA1, EBX

;Read the Second Number and store it into DATA2
MOV AH,09
MOV DX, OFFSET msg1
INT 21H

MOV EBX, 0
MOV CX, 8

AGAIN1: 
             MOV AH,01 
             INT 21H
             CMP AL,'A'
             JGE L7
             SUB AL, 30H
             JMP L8
             L7: SUB AL, 37H
             L8: SHL EBX, 4
             ADD BL,AL
             LOOP AGAIN1
MOV DATA2, EBX

; Multiply DATA1 and DATA2 and store the 64-bit result in PROD1 and PROD2.
MOV EBX,0
MOV EDX,0
MOV EAX,0
MOV EAX,DATA1
MOV EBX,DATA2
MUL EBX     ; multiplies the values in the EAX and EBX registers and stores the 64-bit result in the EDX:EAX register pair

MOV PROD1,EDX      ; moves the high 32 bits of the result (from the EDX register) into the memory location labeled as PROD1.
MOV PROD2,EAX      ; moves the low 32 bits of the result (from the EAX register) into the memory location labeled as PROD2.

Display the product

MOV AH,09 MOV DX,OFFSET msg2 INT 21H

Higher 32-bits of the product

MOV EBX, PROD1 MOV CX, 8 AGAIN2: ROL EBX, 4 MOV DL,BL AND DL, 0FH CMP DL, 9 JBE L1 ADD DL, 37H MOV AH, 02 INT 21H JMP L2 L1: ADD DL,30H MOV AH,02 INT 21H L2: LOOP AGAIN2

Lower 32-bits of the Product

MOV EBX, PROD2 MOV CX, 8 AGAIN3: ROL EBX, 4 MOV DL,BL AND DL, 0FH ; to o/p the result CMP DL,9 JBE L3 ADD DL,37H MOV AH,02 INT 21H JMP L4 L3: ADD DL,30H MOV AH,02 INT 21H L4: LOOP AGAIN3

END