emu8086，汇编程序：屏幕输入字符串,设置寄存器的值

题目：

代码：

data segment
MaxSize db 20
ActualSize db 0
InputString db 20 DUP(0)
Temp1 dw 0
Temp2 dw 0
Temp3 dw 0
LoopCnt dw 0
Num dw 0
Msg1_NoEqualSign DB 0DH,0AH,'The expression does not have any equal sign!',0DH,0AH,'$' 
Msg2_NotVaildReg DB 0DH,0AH,'Not a vaild register!',0DH,0AH,'$'
ends

stack segment
ends

code segment
start:
;1.输入字符串
MOV AX,data
MOV DS,AX 
LEA DI,MaxSize
MOV AH,0AH
int 21h                            
;2.先把输入的值（=号后面的内容）转为数值放到AX里

;2-1.寻找等于号
MOV CX,0
MOV AL,'='            
MOV AH,0
FindTheEqualSign: 
LEA BX,InputString
ADD BX,CX
MOV BL,[BX]
CMP AX,BX
JZ TheEqualSignFound;找到等于号 
INC CX
CMP CL,ActualSize
JZ TheEqualSignNotFound;输入的字符中没有等于号
JMP FindTheEqualSign

;2-1->1找到，等于号的下标存入AX
TheEqualSignFound:
MOV AX,CX
JMP StringToInt         
;2-1->0没找到，程序结束
TheEqualSignNotFound:
MOV AH,9
LEA DI,Msg1_NoEqualSign
INT 21H
JMP End
   
;3.从等于号往后直到末尾的十六进制字符转化为实际数值
StringToInt:
MOV CH,0
MOV CL,ActualSize
SUB CX,AX
DEC CX
INC AX;AX先指向=号后面第一个字符
LEA BX,InputString
ADD BX,AX;求出=号后第一个字符的偏移地址
MOV DX,0
MOV AX,0
ParseNum:
MOV AH,0
MOV AL,[BX]
CMP AL,'A'
JNAE ZeroToNine;输入是字符0~9
JAE AtoF;输入字符是A~F
ZeroToNine:
SUB AL,30H
JMP E1
AtoF:
SUB AL,'A'
ADD AL,10
JMP E1
E1:
MOV Temp1,AX;T1暂存此时AX
MOV Temp2,CX;T2暂存此时CX
DEC CX
MOV AX,4
MUL CX
MOV Temp3,AX;T3存入要移位的次数
MOV AX,Temp1
MOV CX,Temp3
SAL AX,CL
MOV DX,Num
ADD DX,AX
MOV Num,DX
MOV CX,Temp2
INC BX
LOOP ParseNum 

;解析字符串的前两个字符是AX~DX中哪个
SelectReg:
LEA BX,InputString
MOV AL,[BX]
CMP AL,'A'
JZ IsA
CMP AL,'B'
JZ IsB
CMP AL,'C'
JZ IsC
CMP AL,'D'
JZ IsD
JMP NotVailedReg


    
IsA:
INC BX
MOV AL,[BX]
CMP AL,'L'
JZ IsAL
CMP AL,'H'
JZ IsAH
CMP AL,'X'
JZ IsAX
JMP NotVailedReg

    IsAL:
    LEA BX,Num
    MOV AL,[BX];取Num低位放入AL
    JMP End
    IsAH:
    LEA BX,Num
    MOV AH,[BX];取Num低位放入AH
    JMP End
    IsAX:
    MOV AX,Num
    JMP End

IsB:
INC BX
MOV BL,[BX]
CMP BL,'L'
JZ IsBL
CMP BL,'H'
JZ IsBH
CMP BL,'X'
JZ IsBX
JMP NotVailedReg

    IsBL:
    LEA BX,Num
    
    MOV BL,[BX];取Num低位放入AL
    JMP End
    IsBH:
    LEA BX,Num
    
    MOV BH,[BX];取Num低位放入AH
    JMP End
    IsBX:
    MOV BX,Num
    JMP End

IsC:
INC BX
MOV CL,[BX]
CMP CL,'L'
JZ IsCL
CMP CL,'H'
JZ IsCH
CMP CL,'X'
JZ IsCX
JMP NotVailedReg

    IsCL:
    LEA BX,Num
    
    MOV CL,[BX];取Num低位放入CL
    JMP End
    IsCH:
    LEA BX,Num
    
    MOV CH,[BX];取Num低位放入CH
    JMP End
    IsCX:
    MOV CX,Num
    JMP End   
    
IsD:
INC BX
MOV DL,[BX]
CMP DL,'L'
JZ IsDL
CMP DL,'H'
JZ IsDH
CMP DL,'X'
JZ IsDX
JMP NotVailedReg

    IsDL:
    LEA BX,Num
    
    MOV DL,[BX];取Num低位放入DL
    JMP End
    IsDH:
    LEA BX,Num
    
    MOV DH,[BX];取Num低位放入DH
    JMP End
    IsDX:
    MOV DX,Num
    JMP End

NotVailedReg:
MOV AH,9
LEA DI,Msg2_NotVaildReg
INT 21H
JMP End

End:
ends

end start ; set entry point and stop the assembler.