Question

Assembly Language Programming

create an .asm [assembly language program file, using Microsoft Visual Studio or equivalent Windows32 integrated development environment (IDE)] program into one that inputs two positive integers, and outputs their greatest common divisor, by implementing the following pseudo-code:

input num1 and num2
(assume num1 > 0 and num2 > 0)

gcd := num1
remainder := num2
repeat
    numerator := gcd
    gcd := remainder
    remainder := numerator % gcd
until (remainder == 0)

output gcd

The following 3 windows are an example interaction of the complete program (output in Bold, input in Italics):

a: 24
b: 54
gcd: 6

Please leave notes. This is not a java or c++ program, meaning the file has to be saved as .asm and run as an assembly file. (not .cpp or .java). You can, but don't have to, trace execution using debugger.

Answer 1

.MODEL SMALL 
        .STACK 100H 
        .DATA 
                d1 dw 16 d2 dw 24 
        .CODE 
                MAIN PROC FAR 
                        MOV AX, 
        @DATA 
                MOV DS, 
        AX 

;initialize ax and bx 
        mov bx, 
        d2 
                mov ax, 
        d1 

;find gcd of two numbers 
        call gcd 

;load the gcd in ax 
        mov ax, 
        cx 

;print the value 
        CALL PRINT 

;interrupt to exit
        MOV AH, 
        4CH INT 21H 

        MAIN ENDP 
                GCD PROC 

;if
        bx is 0 cmp bx, 0 jne continue

;then gcd is ax 
        mov cx, 
        ax 
                ret 

        continue: 

;else gcd(b, a % b) 
        xor dx, 
        dx 

;divide ax by bx 
        div bx 

;initialize ax as bx 
        mov ax, 
        bx 

;and 
bx as ax % bx 
        mov bx, 
        dx 

;recursively call gcd 
        call GCD 
                ret 
                        GCD ENDP 
                                PRINT PROC 

;initilize count 
        mov cx, 
        0 mov dx, 0 label1: 

;if
        ax is zero 
                cmp ax, 
                0 je print1 


;initialize bx to 10 mov bx, 10 

;extract the last digit 
        div bx 

;push it in the stack 
        push dx 

;increment the count 
        inc cx 

;set dx to 0 
        xor dx, 
        dx 
                jmp label1 
                        print1: 

;check if count 
;is greater than zero 
        cmp cx, 
        0 je exit

;pop the top of stack 
        pop dx 

;add 48 so that it 
;represents the ASCII 
;value of digits 
        add dx, 
        48 

;interrupt to print a 
;character 
        mov ah, 
        02h int 21h 

;decrease the count 
        dec cx 
                jmp print1 
                        exit : ret 
                                        PRINT ENDP 
                                                END MAIN