子程序递归的问题

[masmaster]

如下代码：是杨继文《80X86汇编语言程序设计教程》中关于子程序递归的代码。我觉得有问题，我原封不动抄上来，请大家指出哪错啦？

fact	proc
	push dx
	mov dx,ax
	cmp ax,0
	jz done
	dec ax
	call fact
	mul dx
	pop dx
	ret
done:	mov ax,1
	pop dx
	ret
fact	endp

[masmaster]

这本书给我的感觉， 错误确实不少！！！

[suchx]

This program looks strange, you can write your own fact program.

.MODEL SMALL
.STACK 1024H
CR=0DH
LF=0AH
.DATA
INMES  DB 'INPUT N : ','$'
CHRERR DB CR,LF,'0..9 EXPECTED.',CR,LF,'$'
RNGERR DB CR,LF,'RANGE CHECK ERROR .','$'
OUTMES DB CR,LF,'FACT= ','$'
HLTMES DB CR,LF,'PRESS ANY KEY TO HALT .','$'
BUFSIZE=6
BUF    DB BUFSIZE
       DB 0
       DB BUFSIZE DUP(0)
     N DW 0
     Y DW 0
BASE   DW 10
.CODE
_MAIN PROC NEAR
START:NOP
      MOV AX,@DATA
      MOV DS,AX
      MOV ES,AX
      CALL READ
      MOV CX,N
      CALL FACT
      MOV Y,AX
      CALL WRITE
      MOV AX,4C00H
      INT 21H
_MAIN ENDP
READ PROC NEAR
  RE1:LEA DX,INMES
      CALL DISPMES
      LEA DX,BUF
      MOV AH,0AH
      INT 21H
      CALL ATOD
      JC RE1
      MOV N,AX
      RET
READ ENDP
FACT PROC NEAR
      PUSH CX
      TEST CX,CX
      JZ F1
      DEC CX
      TEST CX,CX
      JZ F1
      CALL FACT
      POP CX
      MUL CX
      TEST DX,DX
      JZ F2
      LEA DX,RNGERR
      CALL DISPMES
      CALL HALT
      JMP SHORT F2
   F1:POP CX
      MOV AX,1
   F2:RET
FACT ENDP
WRITE PROC NEAR
       LEA DX,OUTMES
       CALL DISPMES
       MOV AX,Y
       CALL DTOA
       LEA DX,BUF[2]
       CALL DISPMES
       RET
WRITE ENDP
ATOD   PROC NEAR
       PUSH SI
       XOR AX,AX
       XOR DX,DX
       XOR BX,BX
       XOR CH,CH
       MOV CL,BUF[1]
       LEA SI,BUF[2]
   AT1:MUL BASE
       TEST DX,DX
       JZ AT2
       LEA DX,RNGERR
       CALL DISPMES
       JMP SHORT AT9
   AT2:MOV BL,[SI]
       CMP BL,'0'
       JB AT3
       CMP BL,'9'
       JA AT3
       JMP SHORT AT4
   AT3:LEA DX,CHRERR
       CALL DISPMES
       JMP SHORT AT9
   AT4:SUB BL,'0'
       ADD AX,BX
       JNO AT5
       LEA DX,RNGERR
       CALL DISPMES
       JMP SHORT AT9
   AT5:INC SI
       LOOP AT1
       CLC
       JMP SHORT AT8
   AT9:STC
   AT8:POP SI
       RET
ATOD   ENDP
DTOA   PROC NEAR
       PUSH SI
       PUSH DI
       XOR CX,CX
       LEA DI,BUF[2+BUFSIZE-1]
       MOV WORD PTR [DI],'$'
       DEC DI
   DT1:XOR DX,DX
       DIV BASE
       ADD DL,'0'
       MOV [DI],DL
       DEC DI
       INC CX
       TEST AX,AX
       JNZ DT1
       MOV SI,DI
       INC SI
       LEA DI,BUF[2]
       CLD
       REP MOVSB
       MOV BYTE PTR [DI],'$'
       POP DI
       POP SI
       RET
DTOA   ENDP
DISPMES PROC NEAR
       PUSH AX
       MOV AH,9
       INT 21H
       POP AX
       RET
DISPMES ENDP
HALT  PROC NEAR
       LEA DX,HLTMES
       CALL DISPMES
       MOV AH,1
       INT 21H
       MOV AX,4C00H
       INT 21H
HALT  ENDP
END START

[masmaster]

[Quote=引用 2 楼 suchx 的回复:]
This program looks strange, you can write your own fact program.
Assembly code

.MODEL SMALL
.STACK 1024H
CR=0DH
LF=0AH
.DATA
INMES DB 'INPUT N : ','$'
CHRERR DB CR,LF,'0..9 EXPECTED.',CR,LF……
[/Quote]

thanks