Question

MASM Assembly Language x86 Processor. Must use windows32 framework

Write a non-recursive algorithm to find the greatest common divisor of two positive numbers.

. • Your program should read the two positive integers using dialog boxes. If they are not positive, a message box should be displayed with an appropriate message.

• Your program needs to have a procedure that takes two positive integers as parameters.

• You need to follow cdecl protocol for parameter passing.

• Display the valid result returned from your procedure using a message box

Answer 1

.586
.MODEL FLAT
INCLUDE io.h
.STACK 4096

.DATA
long DWORD ?
wide DWORD ?
prompt1 BYTE "Enter First Number?", 0
string BYTE 30 DUP (?)
prompt2 BYTE "Enter 2nd Number", 0
string BYTE 30 DUP (?)
prompt3 BYTE "greatest common divisor of two number is", 0
failure BYTE "Entered number is negative number", 0

.CODE
MAIN PROC
MOV AX, @DATA ; initialize DS
MOV DS, AX

LEA DX, prompt1 ; load and display the string in prompt1
MOV AH, 9
INT 21H

CALL CheckDec ; call the procedure for checking posive number

PUSH AX ; push reg AX onto the STACK

LEA DX, prompt2 ; load and display the string in prompt2

MOV AH, 9
INT 21H

CALL CheckDec ; call the procedure CheckDec

MOV BX, AX ; set BX=AX

POP AX ; pop a value from STACK into AX reg

@REPEAT: ; jump label
XOR DX, DX ; clear DX reg
DIV BX ; set AX=DX:AX\BX , AX=DX:AX%BX

CMP DX, 0 ;compare DX with 0
JE @END_LOOP ; jump to label END_LOOP if CX=0

MOV AX, BX ; set AX=BX
MOV BX, DX ; set BX=DX
JMP @LOOP ; jump to label REPEAT

@END_LOOP: ; jump label

LEA DX, prompt3 ; load and display the string PROMPT_3
MOV AH, 9
INT 21H

MOV AX, BX ; set AX=BX

CALL OutDecimal ; call the procedure OutDecimal

MOV AH, 4CH ; return control to DOS
INT 21H
MAIN ENDP

CheckDec PROC
; this procedureis used to read a number in decimal form
PUSH BX ; push BX reg onto the STACK
PUSH CX ; push CX reg onto the STACK
PUSH DX ; push DX reg onto the STACK

JMP @READ

@READ:
XOR BX, BX ; clear the BX reg
XOR CX, CX ; clear the CX reg
XOR DX, DX ; clear the DX reg

MOV AH, 1 ; set input function
INT 21H ; read a character

CMP AL, "-" ; compare AL with "-"
JE @MINUS ; jump to label MINUS if input no.="-"

@MINUS: ; jump label
LEA DX, failure ;display given no is negative number

AND AX, 000FH ; convert ascii code into decimal code

PUSH AX ; push AX onto the STACK

MOV AX, 10 ; set AX=10
MUL BX ; set AX=AX*BX
MOV BX, AX ; set BX=AX

POP AX ; pop a value from STACK into AX reg

ADD BX, AX ; set BX=AX+BX
JS @ERROR ; jump to label ERROR if SF=1

@ERROR:

MOV AH, 2 ; set output function
MOV DL, 7H ; set DL=7H
INT 21H ; print a character

XOR CH, CH ; clear CH

@CLEAR:
MOV DL, 8H ; set DL=8H
INT 21H ; print a character

MOV DL, 20H ; set DL=' '
INT 21H ; print a character

MOV DL, 8H ; set DL=8H
INT 21H ; print a character
LOOP @CLEAR ; jump to label CLEAR if CX!=0

JMP @READ ; jump to label READ

@END_INPUT: ; jump label

CMP CH, 1 ; compare CH with 1   
JNE @EXIT ; jump to label EXIT if CH!=1
NEG BX ; negate BX

@EXIT: ; jump label

MOV AX, BX ; set AX=BX

POP DX ; pop a value from STACK into DX reg
POP CX ; pop a value from STACK into CX reg
POP BX ; pop a value from STACK into BX reg

RET ; return control to the calling procedure
CheckDec ENDP
  
OutDecimal PROC
; this procedure is used to display a decimal number
PUSH BX ; push BX onto the STACK
PUSH CX ; push CX onto the STACK
PUSH DX ; push DX onto the STACK

CMP AX, 0 ;compare AX with 0
JGE @START ; jump to label START if AX>=0 i.e positive

PUSH AX ; push AX onto the STACK

@START: ; jump label

XOR CX, CX ; clear CX
MOV BX, 10 ; set BX=10

@OUTPUT: ; loop label
XOR DX, DX ; clear DX
DIV BX ; divide AX by BX
PUSH DX ; push DX onto the STACK
INC CX ; increment CX
OR AX, AX ; take OR of Ax with AX for conditioning
JNE @OUTPUT ; jump to label OUTPUT if ZF=0 i.e conditioning

MOV AH, 2 ; set output function

@DISPLAY: ; loop label
POP DX ; pop a value from STACK to DX reg
OR DL, 30H ; convert decimal into ascii code
INT 21H ; print a character
LOOP @DISPLAY ; jump to label DISPLAY if CX!=0

POP DX ; pop a value from STACK into DX reg
POP CX ; pop a value from STACK into CX reg
POP BX ; pop a value from STACK into BX reg

RET ; return control to the calling procedure
OutDecimal ENDP

END MAIN