67 lines
1.5 KiB
NASM
67 lines
1.5 KiB
NASM
; 实验七-3: 字符串查找程序 - 使用REP SCASB
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; 功能: 在字符串中查找特定字符
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DATAS SEGMENT
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TARGET_STRING DB 'Hello, Assembly Language!', 0 ; 目标字符串
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SEARCH_CHAR DB 'A' ; 要查找的字符
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CHAR_FOUND DB 'Character Found!', 0DH, 0AH, '$'
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CHAR_NOT_FOUND DB 'Character Not Found!', 0DH, 0AH, '$'
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POSITION DB 'Position: ', 0 ; 位置信息
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DATAS ENDS
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STACKS SEGMENT
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DB 64 DUP(?)
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STACKS ENDS
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CODES SEGMENT
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ASSUME CS:CODES, DS:DATAS, SS:STACKS
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START:
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MOV AX, DATAS
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MOV DS, AX
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MOV ES, AX ; SCASB使用ES:DI
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LEA DI, TARGET_STRING ; DI指向目标字符串
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MOV AL, SEARCH_CHAR ; AL=要查找的字符
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; 计算字符串长度
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MOV CX, 0
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COUNT_LOOP:
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CMP BYTE PTR [DI + CX], 0
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JE COUNT_DONE
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INC CX
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JMP COUNT_LOOP
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COUNT_DONE:
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; 使用REP SCASB查找字符
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; SCASB将AL与[ES:DI]比较，不等则继续，相等则停止
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REP SCASB
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; 检查查找结果
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; 如果CX=0且ZF=0，说明没找到
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; 如果ZF=1，说明找到了
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JZ FOUND
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; 未找到的情况
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LEA DX, CHAR_NOT_FOUND
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JMP DISPLAY
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FOUND:
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; 计算位置：原长度 - 剩余长度 = 找到的位置
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MOV AX, 0
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SUB AX, CX ; AX = 原长度 - CX
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DEC AX ; 位置从1开始计数
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ADD AX, 1
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LEA DX, CHAR_FOUND
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DISPLAY:
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MOV AH, 09H
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INT 21H
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; 程序结束
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MOV AH, 4CH
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INT 21H
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CODES ENDS
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END START |