c++ 反汇编 循环结构

debug

• do···while

23:     int nSum = 0;
00A572AE C7 45 F8 00 00 00 00 mov         dword ptr [nSum],0
    24:     int nIndex = 0;
00A572B5 C7 45 EC 00 00 00 00 mov         dword ptr [nIndex],0
    25:     do
    26:     {
    27:         nSum += nIndex;
00A572BC 8B 45 F8             mov         eax,dword ptr [nSum]
00A572BF 03 45 EC             add         eax,dword ptr [nIndex]
00A572C2 89 45 F8             mov         dword ptr [nSum],eax
    28:         nIndex++;
00A572C5 8B 45 EC             mov         eax,dword ptr [nIndex]
00A572C8 83 C0 01             add         eax,1
00A572CB 89 45 EC             mov         dword ptr [nIndex],eax
    29:     } while(nIndex <= nCount);
00A572CE 8B 45 EC             mov         eax,dword ptr [nIndex]
00A572D1 3B 45 08             cmp         eax,dword ptr [nCount]//先执行循环体，后判断
00A572D4 7E E6                jle         LoopDO+2Ch (0A572BCh)
    30:     return nSum;
00A572D6 8B 45 F8             mov         eax,dword ptr [nSum]  

• while

34:     int nSum = 0;
00A5738E C7 45 F8 00 00 00 00 mov         dword ptr [nSum],0
    35:     int nIndex = 0;
00A57395 C7 45 EC 00 00 00 00 mov         dword ptr [nIndex],0
    36:     while (nIndex <= nCount)
00A5739C 8B 45 EC             mov         eax,dword ptr [nIndex]
00A5739F 3B 45 08             cmp         eax,dword ptr [nCount]  //先判断，后循环
00A573A2 7F 14                jg          LoopWhile+48h (0A573B8h)
    37:     {
    38:         nSum += nIndex;
00A573A4 8B 45 F8             mov         eax,dword ptr [nSum]
00A573A7 03 45 EC             add         eax,dword ptr [nIndex]
00A573AA 89 45 F8             mov         dword ptr [nSum],eax
    39:         nIndex++;
00A573AD 8B 45 EC             mov         eax,dword ptr [nIndex]
00A573B0 83 C0 01             add         eax,1
00A573B3 89 45 EC             mov         dword ptr [nIndex],eax
    40:     }
00A573B6 EB E4                jmp         LoopWhile+2Ch (0A5739Ch)
    41:     return nSum;
00A573B8 8B 45 F8             mov         eax,dword ptr [nSum]  

• for

46:     int nSum = 0;
00A5731E C7 45 F8 00 00 00 00 mov         dword ptr [nSum],0
    47:     for (int nIndex = 0; nIndex <= nCount; ++nIndex)
00A57325 C7 45 EC 00 00 00 00 mov         dword ptr [ebp-14h],0  //先初始化计数器变量
00A5732C EB 09                jmp         LoopFor+37h (0A57337h)
00A5732E 8B 45 EC             mov         eax,dword ptr [ebp-14h]
00A57331 83 C0 01             add         eax,1  //步长
00A57334 89 45 EC             mov         dword ptr [ebp-14h],eax
00A57337 8B 45 EC             mov         eax,dword ptr [ebp-14h]
00A5733A 3B 45 08             cmp         eax,dword ptr [nCount]  //判断循环条件
00A5733D 7F 0B                jg          LoopFor+4Ah (0A5734Ah)
    48:     {
    49:         nSum += nIndex;
00A5733F 8B 45 F8             mov         eax,dword ptr [nSum]
00A57342 03 45 EC             add         eax,dword ptr [ebp-14h]
00A57345 89 45 F8             mov         dword ptr [nSum],eax
    50:     }
00A57348 EB E4                jmp         LoopFor+2Eh (0A5732Eh)
    51:     return nSum;
00A5734A 8B 45 F8             mov         eax,dword ptr [nSum]

---

release

int GoToDo(int nCount)
{
int nSum = 0;
int nIndex = 0;
GOTO_DO:
nSum += nIndex;
nIndex++;
if (nIndex <= nCount)
{
goto GOTO_DO;
}
return nSum;
}

printf("%d \r\n", GoToDo(5));

00D01143  | 33C9            | xor ecx,ecx              | looptype.cpp:83
00D01145  | 33C0            | xor eax,eax              |
00D01147  | 03C8            | add ecx,eax              |
00D01149  | 40              | inc eax                  |
00D0114A  | 83F8 05         | cmp eax,0x5              |
00D0114D  | 7E F8           | jle looptype.D01147      |
00D0114F  | 51              | push ecx                 |
00D01150  | 68 9401D400     | push looptype.D40194     | D40194:"%d \r\n"
00D01155  | E8 76000000     | call <looptype.printf>   |
00D0115A  | 83C4 08         | add esp,0x8              |

int LoopDO(int nCount)
{

int nSum = 0;
int nIndex = 0;
do
{
nSum += nIndex;
nIndex++;
} while(nIndex <= nCount);
return nSum;
}

printf("%d \r\n", LoopDO(5));

00D0115D  | 33C9            | xor ecx,ecx              | looptype.cpp:84
00D0115F  | 33C0            | xor eax,eax              |
00D01161  | 03C8            | add ecx,eax              |
00D01163  | 40              | inc eax                  |
00D01164  | 83F8 05         | cmp eax,0x5              |
00D01167  | 7E F8           | jle looptype.D01161      |
00D01169  | 51              | push ecx                 |
00D0116A  | 68 9401D400     | push looptype.D40194     | D40194:"%d \r\n"
00D0116F  | E8 5C000000     | call <looptype.printf>   |

// 强度降低
void DoRate(int argc)
{
int t = 0;
int i = 0;
while (t < argc)
{
t = i * 99;
i++;
}
printf("%d", t);

}

00D011A6  | 8B55 08         | mov edx,dword ptr ss:[eb | looptype.cpp:88
00D011A9  | 83C4 08         | add esp,0x8              | looptype.cpp:87
00D011AC  | 33C9            | xor ecx,ecx              |
00D011AE  | 85D2            | test edx,edx             |//while优化为do···while结构，添加一个判断
00D011B0  | 7E 0B           | jle looptype.D011BD      |
00D011B2  | 33C0            | xor eax,eax              |
00D011B4  | 8BC8            | mov ecx,eax              |
00D011B6  | 83C0 63         | add eax,0x63             |循环体， *99优化为+99
00D011B9  | 3BCA            | cmp ecx,edx              |
00D011BB  | 7C F7           | jl looptype.D011B4       |
00D011BD  | 51              | push ecx                 |
00D011BE  | 68 9001D400     | push looptype.D40190     | D40190:"%d"
00D011C3  | E8 08000000     | call <looptype.printf>   |
00D011C8  | 83C4 08         | add esp,0x8              |