Program to find GCD of two numbers

MY_DATA SEGMENT                 NUM1 DW 000AH                 NUM2 DW 0004H                 GCD DW ? MY_DATA ENDS CODE SEGMENT                 ASSUME CS:CODE, DS:DATA                 START:                 MOV AX, DATA                 MOV DS, AX                 ; INITIALISATION OF DATA SEGMENT                                 MOV AX, NUM1                 ; MOVE FIRST NUMBER TO AX                 MOV BX, NUM2                 ; MOVE SECOND NUMBER TO BX                                 UP:                 CMP AX, BX                 JE EXIT                 ; IF EQUAL THEN NO POINT IN FINDING GCD                 JB EXCG                 ; IF FIRST NUMBER IS SMALLER PUT IT BX                 ; MEANING SMALL NUMBER MUST STAY IN BX                                 UP1:                 MOV DX, 0000H                 ; INITIALISE DX                 DIV BX                 ; DIVIDE (BIGGER NUMBER)/(SMALLER NUMBER)                 CMP DX, 0                 ; SEE IF REMAINDER IS ZERO OR NOT                 JE EXIT                 ; IF ZERO VOILA YOU HAVE FOUND THE GCD IN THE SMALLER NUMBER                 MOV AX, DX                 ; IF NON ZERO MOVE REMAINDER TO AX                 JMP UP                 EXCG:                 XCHG AX, BX                 ; EXCHANGE CONTENTS OF AX AND BX                 JMP UP1                                 EXIT:                 MOV GCD, BX                 ; STORE RESULT IN GCD                                 ; WRITE THESE TWO LINES IF YOU ARE TESTING IN TASM                 MOV AH, 4CH                 INT 21H                 ; THE ABOVE TWO LINES ARE OBVIOUSLY THE EXIT INTERRUPT                 ; USED IN TASM CODE ENDS END START

Understanding the program What I did was basically divide the larger number with the smaller number. If we get remainder 0 then the smaller number is our GCD for the two given number. If we don’t get a zero remainder we transfer the remainder to AX and then again repeat the process till we get that zero remainder. In short I perform the same procedure we use mathematically to find the Greatest Common Denominator.