汇编语言-009（表驱动选择、条件控制流伪指令、逻辑移位SHL,SHR 算术移位SAL,SAR）

1：表驱动选择，用查表来代替多路选择结构的一种方法

.386
.model flat,stdcallinclude Irvine32.inc.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
CaseTable BYTE 'A'             ;查询值DWORD Process_A      ;过程地址
EntrySize = ($ - CaseTable)BYTE 'B'             ;查询值DWORD Process_B      ;过程地址BYTE 'C'             ;查询值DWORD Process_C      ;过程地址BYTE 'D'             ;查询值DWORD Process_D      ;过程地址
NumberOfEntries = ($ - CaseTable) / EntrySize
prompt BYTE "Press capital A,B,C or D",0msgA BYTE "Process_A",0
msgB BYTE "Process_B",0
msgC BYTE "Process_C",0
msgD BYTE "Process_D",0.code
main PROCmov edx,OFFSET promptcall WriteStringcall ReadCharmov ebx ,OFFSET CaseTablemov ecx,NumberOfEntries
L1:cmp al,[ebx]jne L2call NEAR PTR [ebx+1]call WriteStringcall Crlfjmp L3
L2:add ebx,EntrySizeloop L1
L3:exit
main ENDPProcess_A PROCmov edx,OFFSET msgAret
Process_A ENDPProcess_B PROCmov edx,OFFSET msgBret
Process_B ENDPProcess_C PROCmov edx,OFFSET msgCret
Process_C ENDPProcess_D PROCmov edx,OFFSET msgDret
Process_D ENDPEND main

2：条件控制流伪指令，在汇编器预处理时生成ASM代码，可在反汇编窗口查看

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
val1 DWORD 10
result DWORD ?.code
main PROCmov eax,6.IF eax > val1mov result,1.ENDIFINVOKE ExitProcess,0
main ENDP
END main

3：条件控制流伪指令，例子应用 ||

.386
.model flat,stdcallinclude Irvine32.inc.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.code
main PROCINVOKE ExitProcess,0
main ENDPSetCursorPosition PROC
.data
BadXCoordMsg BYTE "X-Coordinate out of range!",0Dh,0Ah,0
BadYCoordMsg BYTE "Y-Coordinate out of range!",0Dh,0Ah,0.code.IF (dl < 0 )||( dl > 79)mov edx,OFFSET BadXCoordMsgcall WriteStringjmp quit.ENDIF.IF(dh < 0 )||(dh > 24)mov edx,OFFSET BadYCoordMsgcall WriteStringjmp quit.ENDIFcall Gotoxy
quit:retSetCursorPosition ENDPEND main

4：条件控制流伪指令，例子应用 &&

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
TRUE = 1
FALSE = 0
gradeAverage WORD 275  ;要检查的数值
credits  WORD 12       ;要检查的数值
OkToRegister BYTE ? .code
main PROCmov OkToRegister,FALSE.IF gradeAverage > 350mov OkToRegister,TRUE.ELSEIF (gradeAverage > 250) && (credits <= 16)mov OkToRegister,TRUE.ELSEIF (credits <= 12)mov OkToRegister,TRUE.ENDIFINVOKE ExitProcess,0
main ENDP
END main

5：条件控制流伪指令，.REPEAT .UNTIL和 .WHILE循环的使用

.386
.model flat,stdcallinclude Irvine32.inc.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.code
main PROCmov eax,0.WHILE eax<10inc eaxcall WriteDeccall Crlf.ENDWmov eax,0.REPEATinc eaxcall WriteDeccall Crlf.UNTIL eax == 10INVOKE ExitProcess,0
main ENDP
END main

6： .WHILE 循环内包含 .IF语句的使用

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
X DWORD 0
op1 DWORD 2 ;被检测的数据
op2 DWORD 4 ;被检测的数据
op3 DWORD 5 ;被检测的数据.code
main PROCmov eax,op1mov ebx,op2mov ecx,op3.WHILE eax < ebxinc eax.IF eax == ecxmov X,2.ELSEmov X,3.ENDIF.ENDWINVOKE ExitProcess,0
main ENDP
END main

7：若DX的无符号数小于等于CX就跳转若AX的有符号数大于CX就跳转

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.code
main PROCINVOKE ExitProcess,0
main ENDPproc_1 PROCcmp dx,cxjbe L1ret
L1:ret
proc_1 ENDPproc_2 PROCcmp ax,cxjg L2ret
L2:ret
proc_2 ENDPEND main

8：清除AL的位0和位1，若目的操作数等于0，跳转到L3，否则跳转到L4

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.code
main PROCmov al,5and al,0FChjnz L4
L3:mov ecx,0jmp quit
L4:mov ecx,1
quit:INVOKE ExitProcess,0
main ENDP
END main

9：奇偶性检查，使用字节XOR的方式对数组所占的字节空间进行奇偶性检查，判断是偶校验还是奇校验

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
bList1 BYTE 1,2,3,4,5,6,7,8,9,10   ;奇校验的
bList2 BYTE 1,2,3,4,5,6,7,8,9,2    ;偶校验的.code
main PROCmov ebx,OFFSET bList1mov ecx,SIZEOF bList1call myCheckmov ebx,OFFSET bList2mov ecx,SIZEOF bList2call myCheckINVOKE ExitProcess,0
main ENDPmyCheck PROCdec ecxmov dl,[ebx]
L1:pushfdinc ebxpopfdxor dl,[ebx]loop L1lahf     ;加载8位标志位到AHmov dl,ah ;保存到DLand dl,4  ;与位运算后，只保留奇偶位了cmp dl,0jne L2mov eax,0ret
L2:mov eax,1ret
myCheck ENDPEND main

10：逻辑移位SHL,SHR 算术移位SAL,SAR

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.code
main PROC;左移mov bl,8Fh ;BL = 10001111bshl bl,1   ;CF = 1 ,BL = 00011110bmov al,10000000bshl al,2   ;CF = 0,AL=00000000b;右移mov al,0D0h   ;AL = 11010000bshr al,1      ;AL = 01101000b  CF = 0mov al,00000010b   shr al,2      ;AL = 00000000b , CF =1;算术左移mov bl,8Fh ;BL = 10001111bsal bl,1   ;CF = 1 ,BL = 00011110bmov al,10000000bsal al,2   ;CF = 0,AL=00000000b;算术右移mov al,0F0h   ;AL = 11110000b (-16)sar al,1      ;AL = 11111000b (-8) CF = 0;AXt符号扩展到EAXmov ax,-128   ;EAX = ????FF80hshl eax,16    ;EAX = FF800000hsar eax,16    ;EAX = FFFFFF80hINVOKE ExitProcess,0
main ENDP
END main