GCD.ASM

.MODEL SMALL
.DATA
  M DW 20
  N DW 05
  RESULT DW ?

.CODE
  MOV AX,@DATA
  MOV DS,AX
  MOV AX,M
  MOV BX,N
 L1:
  CMP AX,BX
  JE L3
  JA L2
  SUB BX,AX
  JMP L1
 L2:
  SUB AX,BX
  JMP L1
 L3:
  MOV RESULT,AX
  MOV AH,4CH
  INT 21H
 END