学习C++反汇编-表达式短路

作为"&&"和"||"操作符的操作数表达式，这些表达式在进行求值时，只要最终的结果已经可以确定是真或假，求值过程便告终止，这称之为短路求值（short-circuit evaluation）。这是这两个操作符的一个重要属性。

C++源代码：

#include<stdio.h>

int Accumulation(int number)
{
	number&&(number+=Accumulation(number-1));
	return number;
}

int main()
{
	int res=Accumulation(5);
	printf("%d\n",res);
}

生成的汇编代码：

int Accumulation(int number)
{
003A1660  push        ebp  
003A1661  mov         ebp,esp  
003A1663  sub         esp,0C0h  
003A1669  push        ebx  
003A166A  push        esi  
003A166B  push        edi  
003A166C  lea         edi,[ebp-0C0h]  
003A1672  mov         ecx,30h  
003A1677  mov         eax,0CCCCCCCCh  
003A167C  rep stos    dword ptr es:[edi]  
	number && (number += Accumulation(number - 1));
003A167E  cmp         dword ptr [number],0 把number值和0比较
003A1682  je          Accumulation+39h (03A1699h) 相等则跳出循环
003A1684  mov         eax,dword ptr [number]  
003A1687  sub         eax,1 减1  
003A168A  push        eax 压入栈作为参数
003A168B  call        Accumulation (03A1339h) 继续调用自己形成递归
003A1690  add         esp,4 
003A1693  add         eax,dword ptr [number]  
003A1696  mov         dword ptr [number],eax  
	return number;
003A1699  mov         eax,dword ptr [number]  
}

C++源代码：

#include<stdio.h>

int Accumulation(int number)
{
	(number==0)||(number+=Accumulation(number-1));
	return number;
}

int main()
{
	int res=Accumulation(5);
	printf("%d\n",res);
}

生成的汇编代码：

int Accumulation(int number)
{
00201660  push        ebp  
00201661  mov         ebp,esp  
00201663  sub         esp,0C0h  
00201669  push        ebx  
0020166A  push        esi  
0020166B  push        edi  
0020166C  lea         edi,[ebp-0C0h]  
00201672  mov         ecx,30h  
00201677  mov         eax,0CCCCCCCCh  
0020167C  rep stos    dword ptr es:[edi]  
	(number == 0) || (number += Accumulation(number - 1));
0020167E  cmp         dword ptr [number],0  
00201682  je          Accumulation+39h (0201699h)  
00201684  mov         eax,dword ptr [number]  
00201687  sub         eax,1  
0020168A  push        eax  
0020168B  call        Accumulation (0201339h)  
00201690  add         esp,4  
00201693  add         eax,dword ptr [number]  
00201696  mov         dword ptr [number],eax  
	return number;
00201699  mov         eax,dword ptr [number]  
}

||的情况和&&基本一样，就不再赘述了。