《汇编语言 基于x86处理器》第六章条件处理部分的代码

▶ 书中第六章的程序，使用了条件判断和跳转来实现一些功能

● 代码，查找数组首个非零值

 INCLUDE Irvine32.inc

 .data
 intArray SWORD  , , , , , , , -, , ,    ; 测试用的数组
 ;intArray SWORD  1, 0, 0, 0
 ;intArray SWORD  0, 0, 0, 0
 ;intArray SWORD  0, 0, 0, 1
 noneMsg  BYTE "Non-zero value not found", 

 .code
 main PROC
     mov   ebx, OFFSET intArray
     mov   ecx, LENGTHOF intArray

 L1:
     cmp   WORD PTR [ebx],      ; 与 0 作比较
     jnz   found                 ; 结果非零即找到了
     add   ebx, TYPE intArray
     loop  L1
     jmp   notFound

 found:
     movsx eax, WORD PTR [ebx]
     call  WriteInt
     jmp   quit

 notFound:
     mov   edx, OFFSET noneMsg
     call  WriteString

 quit:
     call  crlf
     call WaitMsg
 main ENDP

 END main

● 代码，简单的加密 / 解密

 INCLUDE Irvine32.inc
 KEY     =                        ; 用来异或的秘钥
 BUFMAX  = 

 .data
 sPrompt  BYTE   "Plain text:    ",
 sEncrypt BYTE   "Cipher text:   ",
 sDecrypt BYTE   "Decrypted:     ",
 buffer   BYTE   BUFMAX +       DUP()
 bufSize  DWORD  ?

 .code
 main PROC
     call    InputTheString          ; 输入

     call    TranslateBuffer         ; 加密并输出
     mov     edx,    OFFSET sEncrypt
     call    DisplayMessage

     call    TranslateBuffer         ; 解密并输出
     mov     edx,    OFFSET sDecrypt
     call    DisplayMessage

     call    WaitMsg
     exit
 main ENDP

 InputTheString PROC
     pushad                          ; 寄存器全压栈
     mov     edx,    OFFSET sPrompt
     call    WriteString
     mov     ecx,    BUFMAX
     mov     edx,    OFFSET buffer
     call    ReadString
     mov     bufSize,eax
     call    Crlf
     popad                           ; 寄存器全恢复，返回值在 buffer 里
     ret
 InputTheString ENDP

 DisplayMessage PROC
     pushad
     call    WriteString
     mov     edx,    OFFSET buffer
     call    WriteString
     call    Crlf
     call    Crlf
     popad
     ret
 DisplayMessage ENDP

 TranslateBuffer PROC
     pushad
     mov     ecx, bufSize
     mov     esi,
 L1:
     xor     buffer[esi], KEY    ; 用一个循环来逐字节异或
     inc     esi
     loop    L1

     popad
     ret
 TranslateBuffer ENDP
 END main

● 代码，表驱动选择

 INCLUDE Irvine32.inc
 .data
 CaseTable  BYTE   'A'           ; 驱动表，交替存储选项和分支
            DWORD   Process_A
            BYTE   'B'
            DWORD   Process_B
            BYTE   'C'
            DWORD   Process_C
            BYTE   'D'
            DWORD   Process_D
 NumberOfEntries = 

 prompt BYTE "Input A, B, C or D: ",
 msgA BYTE "Process_A",
 msgB BYTE "Process_B",
 msgC BYTE "Process_C",
 msgD BYTE "Process_D", 

 .code
 main PROC
     mov  edx, OFFSET prompt     ; 输入字符
     call WriteString
     call ReadChar
     mov  ebx, OFFSET CaseTable  ; ebx 指向表
     mov  ecx, NumberOfEntries
 L1:
     cmp  al, [ebx]              ; 是否匹配 ebx 指向的项
     jne  L2                     ; 否分支
     call NEAR PTR [ebx + ]     ; 是分支，调用对应的子过程（过程指针解引用，NEAR PTR）
     call WriteString            ; 显示相应的信息并退出循环
     call Crlf
     jmp  L3

 L2:
     add  ebx,                  ; 指向表中下一项
     loop L1

 L3:
     exit

     call WaitMsg
 main ENDP

 Process_A PROC
     mov  edx, OFFSET msgA
     ret
 Process_A ENDP

 Process_B PROC
     mov  edx, OFFSET msgB
     ret
 Process_B ENDP

 Process_C PROC
     mov  edx, OFFSET msgC
     ret
 Process_C ENDP

 Process_D PROC
     mov  edx, OFFSET msgD
     ret
 Process_D ENDP

 END main

● 代码，简单反汇编输出

 INCLUDE Irvine32.inc

 .data
 TRUE =
 FALSE =
 gradeAverage  WORD
 credits       WORD
 OkToRegister  BYTE ?

 .code
 main PROC
     mov OkToRegister,FALSE

     .IF gradeAverage >
        mov OkToRegister,TRUE
     .ELSEIF (gradeAverage > ) && (credits <= )
        mov OkToRegister,TRUE
     .ELSEIF (credits <= )
        mov OkToRegister,TRUE
     .ENDIF

     exit
 main ENDP

 END main

■ 反汇编后，

 _main@0:
 002E1005  jmp         main (02E1010h)
 002E100A  int
 002E100B  int
 002E100C  int
 002E100D  int
 002E100E  int
 002E100F  int
 --- D:\Code\assembler\project6\asm6\asm6\haha.asm ------------------------------

     mov OkToRegister,FALSE
 002E1010  mov         byte ptr [OkToRegister (02E4004h)],

     .IF gradeAverage >
 002E1017  cmp         word ptr [gradeAverage (02E4000h)],15Eh
 002E1020  jbe         @C0001 (02E102Bh)
        mov OkToRegister,TRUE
 002E1022  mov         byte ptr [OkToRegister (02E4004h)],
     .ELSEIF (gradeAverage > ) && (credits <= )
 002E1029  jmp         @C0001+2Fh (02E105Ah)
 @C0001:
 002E102B  cmp         word ptr [gradeAverage (02E4000h)],0FAh
 002E1034  jbe         @C0001+1Eh (02E1049h)
 002E1036  cmp         word ptr [credits (02E4002h)],10h
 002E103E  ja          @C0001+1Eh (02E1049h)
        mov OkToRegister,TRUE
 002E1040  mov         byte ptr [OkToRegister (02E4004h)],
     .ELSEIF (credits <= )
 002E1047  jmp         @C0001+2Fh (02E105Ah)
 @C0004:
 002E1049  cmp         word ptr [credits (02E4002h)],0Ch
 002E1051  ja          @C0001+2Fh (02E105Ah)
        mov OkToRegister,TRUE
 002E1053  mov         byte ptr [OkToRegister (02E4004h)],
     .ENDIF

     exit
 002E105A  push
 002E105C  call        _ExitProcess@4 (02E1075h)

● 代码，有限自动机判断输入的是否是一个合法的数字。注意每输入一个字符就进行状态跳转，而不是输入一行后回车才开始分析

 INCLUDE Irvine32.inc

 ENTER_KEY =               ; 回车键作为停止输入的标志
 .data
 InvalidInputMsg BYTE "Invalid input", , , 

 .code
 main PROC
     call    Clrscr

 StateA:
     call    Getnext         ; 读取下一个字符
     cmp     al,'+'          ; 前导 +，前往状态 B
     je      StateB
     cmp     al,'-'          ; 前导 -，前往状态 B
     je      StateB
     call    IsDigit         ; 数字，置 ZF = 1，前往状态 C
     jz      StateC
     call    DisplayErrorMsg ; 错误状态
     jmp     Quit

 StateB:
     call    Getnext
     call    IsDigit
     jz      StateC
     call    DisplayErrorMsg
     jmp    Quit

 StateC:
     call    Getnext
     call    IsDigit
     jz      StateC
     cmp     al, ENTER_KEY
     je      Quit
     call    DisplayErrorMsg
     jmp     Quit

 Quit:
     call    Crlf
     call    WaitMsg
     exit
 main ENDP

 Getnext PROC
      call ReadChar
      call WriteChar
      ret
 Getnext ENDP

 DisplayErrorMsg PROC
      push   edx
      mov    edx, OFFSET InvalidInputMsg
      call   WriteString
      pop    edx
      ret
 DisplayErrorMsg ENDP
 END main