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

;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

;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

;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

;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

;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