fun2比fun3稍快点

运行环境：WinXP VS2005(VC8)

 核心代码:

 #include <iostream>

 using namespace std ;

 #include <time.h>


 #define WAN (10000)

 const int iNum = WAN*WAN*3;



 void fun2(int* p)

 {

     for( int i = 0 ; i < iNum ; i+= 4  )

     {

         p[i] = i;

         p[i+1] = i+1;

         p[i+2] = i+2;

         p[i+3] = i+3 ;

     }

 }


 void fun3(int* p)

 {

     for( int i = 0 ; i < iNum ; i+= 8 )

     {

         p[i] = i;

         p[i+1] = i+1;

         p[i+2] = i+2;

         p[i+3] = i+3 ;

         p[i+4] = i+4 ;

         p[i+5] = i+5 ;

         p[i+6] = i+6 ;

         p[i+7] = i+7 ;


     }

 }


 测试程序一：

 void main()

 {

     int * p = new int[iNum];

     int x1 = time(NULL);

     fun2(p);

     int x2 = time(NULL);

     fun3(p);

     int x3 = time(NULL);

     cout << (long)(x2-x1) << "秒 " << (long)(x3-x2) << "秒";

     delete [] p ;

 }

 五次的运行结果：

 4,3

 3,3

 3,3

 4,2

 3,3


 测试程序三（fun3在前，fun2在后):

 2,3

 2,4

 2,3

 3,3

 2,3


 总的来说fun3 比fun2快，但平均不到1秒。