这里的任何人都可以让我理解这个程序以及我将通过它获得什么输出？

Question

DATA SEGMENT
STRING1 DB 11H,22H,33H,44H,55H
MSG1    DB "FOUND$"
MSG2    DB "NOT FOUND$"
SE      DB 34H
DATA ENDS

PRINT MACRO MSG
    MOV AH, 09H
    LEA DX, MSG
    INT 21H
    INT 3
ENDM

CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START:
    MOV AX, DATA
    MOV DS, AX
    MOV AL, SE
    LEA SI, STRING1
    MOV CX, 04H

UP:
    MOV BL,[SI]
    CMP AL, BL
    JZ FO
    INC SI
    DEC CX
    JNZ UP

    PRINT MSG2
    JMP END1
FO:
    PRINT MSG1
END1:
    INT 3

CODE ENDS
END START

Answer 1

程序在序列11H，22H，33H，44H中搜索字节'34H'。

START部分执行以下操作：

• 将DS：SI设置为STRING1的地址。
• 为要搜索的字节设置AL。
• 将CX设置为在STRING1中搜索的字节数（4个字节）。

循环部分执行以下操作：

• 将DS：SI（从STRING1）加载到BL中
• 将其与要搜索的字节进行比较（在AL中）
• 如果字节相等（零标志= 1）则打印“发现”
• else（不相等）转到下一个字节（INC SI），递减计数器（CX）
• 如果计数器为零，则退出循环并打印“NOT FOUND”

---

打印宏：

MOV AH, 09H
INT 21H 

是打印的MS-DOS调用，直到“$”INT 3表示退出程序。

计数器CX设置为4是可疑的，但STRING1序列包含5个字节。没有真正调试程序我会说CX = 5会是正确的吗？

Answer 2

我的投票相当于memchr(s,c,n)，其中s在SI（每次迭代递增），c在BL（与从'SI得到的'物品被发现'退出条件得到的东西相比）和n在CX（如果在BL中则减少，如果数组元素等于http://man7.org/linux/man-pages/man3/memchr.3.html未找到，这是其他退出条件）加上友好输出（包含int21h调用的宏）。见33h

Answer 3

它在字节数组11H,22H,33H,44H,55H中搜索值

DATA SEGMENT
# Data where we will look up for value
STRING1 DB 11H,22H,33H,44H,55H
# message to be printed out
MSG1 DB "FOUND$"
# yet one message
MSG2 DB "NOT FOUND$"
# program will look up for this value
SE DB 33H

DATA ENDS

# this is PRINT macro- will be used later like a function
PRINT MACRO MSG
# 09H - is a function of interrupt 21h - print to console http://spike.scu.edu.au/~barry/interrupts.html
MOV AH, 09H
LEA DX, MSG
# print message using interrupt 21h
INT 21H
# I think it's exit - check it in the x86 interrupts table if you need
INT 3

ENDM # end of print macro

CODE SEGMENT

ASSUME CS:CODE, DS:DATA

START:

# this is the first line of code
MOV AX, DATA
MOV DS, AX
# copy value of SE (33h) to the AL register so later we can compare it
MOV AL, SE
LEA SI, STRING1

# save in CX length of the data to be looked up for value (actually num or iterations)
MOV CX, 04H

# the main loop starts here
UP:
# copy byte from buffer STRING1 to the BL register
MOV BL,[SI]
# check if AL==BL -> value found
CMP AL, BL

# if AL==BLjump to FO (will print FOUND)
JZ FO
# if not found, 
# move to next byte in STRING1
INC SI
# decrement loop constraint (loop should end before reaching end of string)
DEC CX
# if CX <> 0 loop again
JNZ UP
# if CX==0 print message NOT FOUND
PRINT MSG2
JMP END1
FO:
PRINT MSG1
END1:
INT 3
CODE ENDS

END START

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