查表法优化简单加解密

xx服务中需要对IP包进行简单的加解密，

以前有段时间也是用过简单加解密，

通过测试发现占用了大量的时间， 如果能够提高其执行效率，那么对提升xx服务性能将有很好的帮助

 

oprfile测试结果：

CPU: CPU with RTC device, speed 2800.22 MHz (estimated)

Counted RTC_INTERRUPTS events (RTC interrupts/sec (rounded up to power of two)) count 1024

vma      samples  %           app name                 symbol name

c01070c0 73441111 83.6575     vmlinux                  default_idle

c0121690 1086084   1.2372     vmlinux                  do_softirq

c0141d80 1078445   1.2285     vmlinux                  fget                                                                                                                                                                                                                                        

08053abe 635922    0.7244     iptun                    crypt       //加解密函数， 非常占cpu

原来算法：

 

void crypt(unsigned char *data, int length )

{

    for( int i = 0; i < length; i++ )

    {

          data[i] ^= '@';

    }

}

 

 

主要措施如下：

 

(1) 以前是函数形式，准备用宏进行替换

(2) 由于简单加解密的特殊性， 准备采用字典表的形式进行加解密

unsigned char 是00000000 ~ 11111111范围

 

主要过程如下：

//生成加密字典

 

//生成字典

unsigned char dictionary[256];

int length = sizeof(dictionary)/sizeof(dictionary[0]);

for (int i = 0; i < length; ++i)

{   dictionary[i] = i;

    dictionary[i] ^= '@';

}

 

//通过字典进行查找加密

unsigned char data[100];

for (int i = 0; i < 100; ++i)

{

    data[i]=dictionary[data[i]];   

}

 

测试代码：

//生成字典

    unsigned char dictionary[256];

    int length = sizeof(dictionary)/sizeof(dictionary[0]);

    for (int i = 0; i < length; ++i)

    {   dictionary[i] = i;

        dictionary[i] ^= '@';

    }

   

    unsigned char test1[10000];

    unsigned char test2[10000];

    memcpy(test2, test1, 10000);

  

  

    SYSTEMTIME sys;

    GetLocalTime( &sys );

    printf( "%4d/%02d/%02d %02d:%02d:%02d.%03d 星期%1d/n",sys.wYear,sys.wMonth,sys.wDay,sys.wHour,sys.wMinute, sys.wSecond,sys.wMilliseconds,sys.wDayOfWeek);

   

    for (int i = 0; i <1000000; ++i)

    {

        for(int i = 0; i < 10000; ++i)

        {

                      test1[i] ^= '@';

            }

      }

   

    GetLocalTime( &sys );

    printf( "%4d/%02d/%02d %02d:%02d:%02d.%03d 星期%1d/n",sys.wYear,sys.wMonth,sys.wDay,sys.wHour,sys.wMinute, sys.wSecond,sys.wMilliseconds,sys.wDayOfWeek);

   

   

     system("PAUSE");

   

   

   

    cout<<"Round Two"<<endl;

   

   

    GetLocalTime( &sys );

    printf( "%4d/%02d/%02d %02d:%02d:%02d.%03d 星期%1d/n",sys.wYear,sys.wMonth,sys.wDay,sys.wHour,sys.wMinute, sys.wSecond,sys.wMilliseconds,sys.wDayOfWeek);

   

    for (int i = 0;  i < 1000000; ++i)

    {

        for (int i = 0; i < 10000; ++i)

        {

            test2[i] = dictionary[test2[i]];

        }

    }

  

    GetLocalTime( &sys );

    printf( "%4d/%02d/%02d %02d:%02d:%02d.%03d 星期%1d/n",sys.wYear,sys.wMonth,sys.wDay,sys.wHour,sys.wMinute, sys.wSecond,sys.wMilliseconds,sys.wDayOfWeek);

  

 

测试结果如下：

 

 

 

以前的加解密耗时：1分零7秒，合67秒

 

查表法耗时： 24 + 17 = 41秒，

 

性能还是有较大的提升

 

 

里面有很多循环，如果用汇编写，效果会更好