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。