Question

我需要一些指向此任务的帮助：程序将返回字符串中字母序列“the”的总出现次数。 [注意：我们正在寻找字母“the”而不仅仅是“the”这个词。例如，你也可以计算“那里”或“然后”中的“the”。所以我应该首先看看它是否为't'，然后如果下一个char是'h'和'e'之后，如果这样增加总数。我的代码需要帮助。我无法弄清楚我的逻辑。有关如何做到这一点的任何建议将有助于我。到目前为止，这是我尚未完成的代码，我的主要问题是，即使第一个字符显然是“w”，我的跳转都被执行，但它执行就像是“t”：

#include "stdafx.h"
#include <iostream>

using namespace std;


int main(int argc, char* argv[])
{
//  your properly formatted assembly language data here
char Decl[] = "We hold these truths to be self-evident, that "
              "all men are created equal, that they are "
              "endowed by their Creator with certain "
              "unalienable Rights, that among these are "
              "Life, Liberty and the pursuit of Happiness. "
              "That to secure these rights, Governments are "
              "instituted among Men, deriving their just "
              "powers from the consent of the governed, "
              "That whenever any Form of Government becomes "
              "destructive of these ends, it is the Right of "
              "the People to alter or to abolish it, and to "
              "institute new Government, laying its foundation "
              "on such principles and organizing its powers in "
              "such form, as to them shall seem most likely to "
              "effect their Safety and Happiness. Prudence, "
              "indeed, will dictate that Governments long "
              "established should not be changed for light and "
              "transient causes; and accordingly all epxerience "
              "hath shewn, that mankind are more disposed to "
              "suffer, while evils are sufferable, than to "
              "right themselves by abolishing the forms to "
              "which they are accustomed. But when a long train "
              "of abuses and usurpations, pursuing invariably "
              "the same Object evinces a design to reduce them "
              "under absolute Despotism, it is their right, "
              "it is their duty, to throw off such Government "
              "and to provide new Guards for their future "
              "security. Such has been the patient sufferance "
              "of these Colonies; and such is now the "
              "necessity which constrains them to alter their "
              "former Systems of Government. The history of "
              "the present King of Great Britain is a history "
              "of repeated injuries and usurpations, all "
              "having in direct object the establishment of "
              "an absolute Tyranny over these States. To "
              "prove this, let Facts be submitted to a "
              "candid world. Entered by Thomas Arnol ";

unsigned short int total = 0;

     __asm {
//  your syntatically correct assembly language code here
//  column alignment markers below (to guide you)
//      |       |               |
        cld                     ;set left to right scan
        lea     edi, Decl       ;load offset of string
        mov     ecx, 1649       ;length of string +1
        mov     al, 't'         ;load first character into al to be scanned
more1:
repne   scasb                   ;scan byte by byte
        cmp     ecx, 0          ;see if end of string
        je      skip1           ;dont do any more processing
        jmp     case2

skip1:  cmp     ecx, 0 
        ja      more1

case2:  mov     ebx, ecx        ;how many characters left?
        not     ebx             ;form positive index to string
        add     ebx, 1649       ;and point to letter
        cmp     Decl[ebx+1], 'h'    ;compare next letter
        je      case3
        jmp     more1

case3:  mov     ebx, ecx
        not     ebx
        add     ebx, 1649
        cmp     Decl[ebx+2], 'e'
        je      final1
        jmp     more1

final1: inc     total

    }
    return(0);
}

Answer 1

在第一场比赛（执行scasb之后），执行以下跳转：

jmp     case2  ; meaning the string is not over
...
je      case3  ; meaning the second char is 'h'
...
je      final1   ; meaning the third character is 'e'

然后退出该功能。匹配时没有外循环。如果您有匹配项，则不执行jmp more1行 - 仅当't'之后的第三个字符不是'e'时才会执行。

说真的，你甚至在调试代码吗？一个简单的步骤将在一瞬间揭示出这一点。 Visual Studio，e。 G。这样做，并在Watch窗口中显示寄存器和带有寄存器的表达式。

编辑：计算ebx以获取第二个和第三个字符的逻辑是完全无关的。您已经有一个指向字符串中正确位置的注册表 - 这是edi之后的scasb。而不是

case2:  mov     ebx, ecx        ;how many characters left?
    not     ebx             ;form positive index to string
    add     ebx, 1649       ;and point to letter
    cmp     Decl[ebx+1], 'h'    ;compare next letter

你可以做到

case2: cmp [edi], 'h'

以后

cmp [edi+1], 'e'

使用字符串操作的汇编语言

1 个答案: