我正在尝试完成我的微处理器课程的上一个实验练习，可以为此提供一些帮助。工作是用我自己的代码填充注释的空行。这是任务：
**Task 2. Test if the string is a palindrome**
Modify the previous program so, that it checks whether the string is a palindrome. Complement the following program. Add the missing instructions.
include "emu8086.inc"
; START-OF-PROGRAM
org 100h
jmp start
; Memory variables:
msg3 db 0ah,0dh,"The string is a palindrome.",0
msg2 db 0ah,0dh,"The string is NOT a palindrome.",0
msg1 db "Enter a string (max 128 characters): ",0
; the buffer to save the entered string
mystr db 128 dup (0),0
mystrREV db 128 dup (0),0
endl db 0dh,0ah,0
length db 0
start: lea SI, msg1 ; Message address
CALL PRINT_STRING ; Print message from [SI]
; String mystring: Read string here!
; String max. length
; Read string into [DI]
lea si,endl
call print_string
; count the number of characters in the buffer mystr into CX:
mov cl,0 ; start from 0
lea SI,mystr ; Point SI to mystr
tess: mov al,[SI],0 ; End of data?
cmp al,0 ; -“-
je seur ; Proceed to next step
inc cl ; Increment data counter
inc SI ; Increment data pointer
jmp tess ; Check next
; copy mystr into mystrREV in reverse order
seur: mov length,cl ; Store # of characters in length
; Result buffer address into DI
; Source buffer address id SI(decremented)
coop: ; Copy character from source
; Copy character to destination
; Decrement source pointer
; Increment result pointer
; Decrement counter
; Take next if not done
; print both buffers
lea si,mystr
call print_string ; Print mystr
lea si,endl
call print_string ; Print cr+lf
lea si,mystrREV
call print_string ; Print mystrREV
lea si,endl
call print_string ;print cr+lf
; compare strings. If equal => palindrome
mov cl,length ; # of characters in buffers
lea si,mystr ; address of first buffer
lea di,mystrREV ; address of second buffer
niis: cmp cl,0 ; test if end-of-comparison/buffer
; jump to ok, palindrome/empty buffer
; Source buffer address
; Result buffer address
; Are same, still chance?
; Nop, jump to print NOT-message and exit
: increment source pointer
; increment destination pointer
; decrement counter
jmp niis ; Try next
positive: lea SI,msg3 ; Yess, palindrome
call PRINT_STRING ; Print it
jmp bort ; and exit
negative: lea si,msg2 ; NOT a palindrome
call PRINT_STRING ; Print it and exit
bort: mov ax,4c00h ; code for return to ms-dos
int 21h ; call ms-dos terminate program
ret
; Macro definitions
DEFINE_GET_STRING
DEFINE_PRINT_STRING
DEFINE_PRINT_NUM
DEFINE_PRINT_NUM_UNS
end ;END-OF-PROGRAM
我的程序仅将输入字符串的第一个字母打印为反向字符串，并没有真正测试回文。这是我到目前为止所做的：
include "emu8086.inc"
; START-OF-PROGRAM
org 100h
jmp start
; Memory variables:
msg3 db 0ah,0dh,"The string is a palindrome.",0
msg2 db 0ah,0dh,"The string is NOT a palindrome.",0
msg1 db "Enter a string (max 128 characters): ",0
; The buffer to save the entered string
mystr db 128 dup (0),0
mystrREV db 128 dup (0),0
endl db 0dh,0ah,0
length db 0
start: lea SI, msg1 ; Message msg1 address
CALL PRINT_STRING ; Print message from [SI]
; *********************** My code starts *********************
lea di, mystr ; String mystring: Read string here!
mov dx, 128 ; String max. length
call get_string ; Read string into [DI]
; *********************** My code ends ***********************
lea si,endl ; String endl
call print_string ; Print endl
; count the number of characters in the buffer mystr into CX:
mov cl,0 ; start from 0
lea SI,mystr ; Point SI to mystr
tess: mov al,[SI],0 ; End of data?
cmp al,0 ; -"-
je seur ; Proceed to next step
inc cl ; Increment data counter
inc SI ; Increment data pointer
jmp tess ; Check next
; copy mystr into mystrREV in reverse order
seur: mov length,cl ; Store # of characters in length
; *********************** My code starts *********************
; Something goes wrong in this code block
lea di, mystrREV ; Result buffer address into DI
lea si, mystr ; Source buffer address id SI(decremented)
coop:mov al, [si] ; Copy character from source
mov [di], al ; Copy character to destination
dec si ; Decrement source pointer
inc di ; Increment result pointer
dec cl ; Decrement counter
cmp cl,0 ; Take next if not done
jne coop
; *********************** My code ends ***********************
; print both buffers
lea si,mystr
call print_string ; Print mystr
lea si,endl
call print_string ; Print cr+lf
lea si,mystrREV
call print_string ; Print mystrREV
lea si,endl ; CODE DOESN'T PRINT ENOUGH
call print_string ;print cr+lf
; compare strings. If equal => palindrome
mov cl,length ; # of characters in buffers
lea si,mystr ; address of first buffer
lea di,mystrREV ; address of second buffer
niis: cmp cl,0 ; test if end-of-comparison/buffer
; *********************** My code starts *********************
je positive ; jump to ok, palindrome/empty buffer
lea si,mystr ; Source buffer address
lea di,mystrREV ; Result buffer address
cmp di,si ; Are same, still chance?
jne negative ; Nop, jump to print NOT-message and exit
inc si ; increment source pointer
inc di ; increment destination pointer
dec cl ; decrement counter
; *********************** My code ends ***********************
jmp niis ; Try next
positive: lea si,msg3 ; Yess, palindrome
call PRINT_STRING ; Print it
jmp bort ; and exit
negative: lea si,msg2 ; NOT a palindrome
call PRINT_STRING ; Print it and exit
bort: mov ax,4c00h ; code for return to ms-dos
int 21h ; call ms-dos terminate program
ret
; Macro definitions
DEFINE_GET_STRING
DEFINE_PRINT_STRING
DEFINE_PRINT_NUM
DEFINE_PRINT_NUM_UNS
end ;END-OF-PROGRAM
我的结果：
Enter a string (max 128 characters): abba
abba
a
The string is NOT a palindrome.
预期结果：
Enter a string (max 128 characters): innostunutsonni
innostunutsonni
innostunutsonni
The string is a palindrome.
我们正在使用名为emu8086的旧仿真器软件，该软件在线提供了一些文档。任何帮助将不胜感激！谢谢。
您将SI设置为指向mystr的第一个字节，并在复制此字节后递减SI，这会将SI从缓冲区中移出。 SI应该指向mystr开头的最后一个字符。代替
; Something goes wrong in this code block
lea di, mystrREV ; Result buffer address into DI
lea si, mystr ; Source buffer address id SI(decremented)
coop:mov al, [si] ; Copy character from source
mov [di], al ; Copy character to destination
dec si ; Decrement source pointer
尝试一下：
lea di, mystrREV ; Result buffer address into DI
lea si, mystr ; Source buffer address id SI(decremented)
movzx cx,[length] ; Let cx be the size of mystr.
add si,cx ; Let si point behind mystr.
dec si ; Let si point to the last character of mystr.
coop:mov al, [si] ; Copy character from source
mov [di], al ; Copy character to destination
dec si ; Decrement source pointer
指令LEA]要求（或至少允许）第二个操作数放在方括号中，例如LEA DI，[mystrREV]，您应该习惯这种语法。
tess: mov al,[SI],0 ; End of data?指令看起来很奇怪，您确定它不会触发错误吗？
与其在SO上发布图像，不如从控制台复制并粘贴文本，所以它包含在您的问题中，即使imgur.com停止存在它也保持可见。
发布源文本是不够的，应该附带有关其组装和链接方式的信息。
; *********************** My code starts ********************* ; Something goes wrong in this code block lea di, mystrREV ; Result buffer address into DI lea si, mystr ; Source buffer address id SI(decremented) coop: mov al, [si] ; Copy character from source mov [di], al ; Copy character to destination dec si ; Decrement source pointer inc di ; Increment result pointer dec cl ; Decrement counter cmp cl,0 ; Take next if not done jne coop ; *********************** My code ends **********************
您应该已经在注释“ ;;源缓冲区地址ID SI（decremented）”中使用了提示。
为了向后遍历源字符串-这就是'减少'的含义-您需要将源指针SI初始化为字符串的末尾。这意味着您需要计算StartOfString + LengthOfString-1。
; *********************** My code starts *********************
lea di, mystrREV ; Result buffer address into DI
lea bx, mystr ; Source buffer address id SI(decremented)
add bl, cl
adc bh, 0
lea si, [bx-1]
coop:
mov al, [si] ; Copy character from source
mov [di], al ; Copy character to destination
dec si ; Decrement source pointer
inc di ; Increment result pointer
dec cl ; Decrement counter
jne coop ; Take next if not done
; *********************** My code ends **********************
请注意，您不需要该cmp cl,0指令，因为前面的dec cl指令已经设置了必要的标志。
; compare strings. If equal => palindrome mov cl,length ; # of characters in buffers lea si,mystr ; address of first buffer lea di,mystrREV ; address of second buffer niis: cmp cl,0 ; test if end-of-comparison/buffer ; *********************** My code starts ********************* je positive ; jump to ok, palindrome/empty buffer lea si,mystr ; Source buffer address lea di,mystrREV ; Result buffer address cmp di,si ; Are same, still chance? jne negative ; Nop, jump to print NOT-message and exit inc si ; increment source pointer inc di ; increment destination pointer dec cl ; decrement counter ; *********************** My code ends ***********************
您用于比较字符串的代码根本不进行比较！他们的评论令人误解。
您不再需要SI和DI中的地址。您需要获取此寄存器指向的字符，然后进行比较：
; *********************** My code starts *********************
je positive
mov al, [si] ; Source buffer address <<<<< misleading comment
mov dl, [di] ; Result buffer address <<<<< misleading comment
cmp al, dl ; Are same, still chance?
jne negative