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学 Win32 汇编[22] - 逻辑运算指令: AND、OR、XOR、NOT、TEST

 
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AND: 逻辑与



;该指令会置 CF=OF=0; 其结果影响 SF、ZF、PF
;指令格式:
AND r/m, r/m/i

; Test22_1.asm - 使用 AND 运算将一个数的第二、四位清零 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .code main proc   mov al, 00001111b   and al, 11110101b   PrintHex al ;05 - 00000101b   ret main endp end main
; Test22_2.asm - 使用 AND 运算将字母转大写 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .data   szText db 'Delphi', 0 .code main proc   lea esi, szText   mov ecx, lengthof szText - 1 @@: and byte ptr [esi], 11011111b ;大写字母和小写字母只有第五位不同   inc esi   loop @B   PrintString szText ;DELPHI   ret main endp end main


OR: 逻辑或



;该指令会置 CF=OF=0; 其结果影响 SF、ZF、PF
;指令格式:
OR r/m, r/m/i

; Test22_3.asm - 使用 OR 运算确保一个数的第二、四位是 1 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .code main proc   mov al, 11110001b   or al, 00001010b   PrintHex al ;FB - 11111011b   ret main endp end main
; Test22_4.asm - 使用 OR 运算将字母转小写 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .data   szText db 'Delphi', 0 .code main proc   lea esi, szText   mov ecx, lengthof szText - 1 @@: or byte ptr [esi], 00100000b ;大写字母和小写字母只有第五位不同   inc esi   loop @B   PrintString szText ;delphi   ret main endp end main


XOR: 逻辑异或



;该指令会置 CF=OF=0; 其结果影响 SF、ZF、PF
;指令格式:
XOR r/m, r/m/i

; Test22_5.asm - 两次和一个相同的数 XOR 恢复到原来的数 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .code main proc   mov eax, 12345   xor eax, 88888888   PrintDec eax  ;88892929   xor eax, 88888888   PrintDec eax  ;12345   ret main endp end main
; Test22_6.asm - 使用 XOR 加密与解密字符串 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .data   szText db 'Hello World!', 0 .code main proc ;加密   lea esi, szText   mov ecx, lengthof szText - 1 @@: xor byte ptr [esi], 123 ;使用 123 做密码   inc esi   loop @B   PrintString szText  ;显示乱码   ;解密   lea esi, szText   mov ecx, lengthof szText - 1 @@: xor byte ptr [esi], 123   inc esi   loop @B   PrintString szText  ;Hello World!   ret main endp end main


NOT: 逻辑取反



;该指令不影响 EFlags
;指令格式:
NOT r/m

; Test22_7.asm - 使用 NOT 加密与解密字符串 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .data   szText db 'Hello World!', 0 .code main proc ;加密   lea esi, szText   mov ecx, lengthof szText - 1 @@: not byte ptr [esi]   inc esi   loop @B   PrintString szText ;显示乱码   ;解密   lea esi, szText   mov ecx, lengthof szText - 1 @@: not byte ptr [esi]   inc esi   loop @B   PrintString szText ;Hello World!   ret main endp end main


TEST: 测试逻辑与



;该指令会置 CF=OF=0; 其结果影响 SF、ZF、PF
;指令格式:
TEST r/m, r/m/i

;TEST 同 AND, 但它不修改运算数, 只改变标志寄存器; 也就是尝试 AND 的结果
;常用到它对 ZF 的影响(结果为0时ZF=1)
;TEST 之后常常跟着条件跳转指令 JZ、JNZ

; Test22_8.asm - 观察 TEST 之后的零标志位(ZF) .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .code main proc ;判断字母 A 二进制(01000001)的其最后一位是否是 0, 如果是 0 那么 ZF=1   mov al, 'A'   test al, 00000001b   lahf   PrintHex ah ;02 - 00000010b (ZF=0)   ;判断字母 B 二进制(01000010)的其最后一位是否是 0, 如果是 0 那么 ZF=1   mov al, 'B'   test al, 00000001b   lahf   PrintHex ah ;46 - 01000110b (ZF=1)   ;判断 ecx 是否为空   mov ecx, 1   test ecx, ecx   lahf   PrintHex ah ;06 - 00000010b (ZF=0, 不为空)     xor ecx, ecx   test ecx, ecx   lahf   PrintHex ah ;06 - 01000110b (ZF=1, 为空)   ret main endp end main
; Test22_9.asm - 判断字符串中每个字符的二进制位的最后一位是 1 还是 0 .386 .model flat, stdcall include windows.inc include kernel32.inc include masm32.inc include debug.inc includelib kernel32.lib includelib masm32.lib includelib debug.lib .data   szText db 'Delphi', 0 .code main proc ;清空两个寄存器用于计数   xor eax, eax   xor edx, edx     lea esi, szText        ;字符串地址   mov ecx, lengthof szText - 1 ;字符串长度 L1: test byte ptr [esi], 00000001b ;循环测试每个字符的最后一位是 1 还是 0   jz L2 ;如果是 0 则跳到 L2 给 edx+1   inc eax ;反之给 eax+1   jmp L3 L2: inc edx L3: inc esi   loop L1     PrintDec eax ;2 - 这是最后一位是 1 的字符的个数: e、i   PrintDec edx ;4 - 这是最后一位是 0 的字符的个数: D、l、p、h   ret main endp end main
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