CRC16-CCITT 的算法

http://djb69.blog.163.com/blog/static/6776323420100158391490/

 

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#include 

#define CRC_CCITT 0x1021    //CRC-CCITT多项式
using namespace std;

unsigned int crc_ta_8[256]={ /* CRC 字节余式表 */
    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
    0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
    0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
    0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
    0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
    0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
    0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
    0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
    0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
    0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
    0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
    0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
    0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
    0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
    0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
    0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
    0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
    0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
};

unsigned int crc_ta_4[16]={ /* CRC 半字节余式表 */
    0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
    0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
};

 

/**CRC算法一，适用于程序空间苛刻但CRC计算速度要求不高的微控制系统
算法概要说明：计算本位后的CRC 码等于上一位CRC 码乘以2 后除
以多项式，所得的余数再加上本位值除以多项式所得的余数
*/
/*函数名称：crc_cal_by_bit;按位计算CRC
  函数参数：unsigned char* ptr;指向发送缓冲区的首字节
            unsigned char len;要发送的总字节数
  函数返回值：unsigned int
  多项式采用CRC-CCITT 0x1021
*/
unsigned int crc_cal_by_bit(unsigned char* ptr, unsigned char len)
{
    unsigned int crc = 0;
    while(len-- != 0)
    {
        for(unsigned char i = 0x80; i != 0; i /= 2)
        {
            crc *= 2;
            if((crc&0x10000) !=0) //上一位CRC乘 2后，若首位是1，则除以 0x11021
                crc ^= 0x11021;

            if((*ptr&i) != 0)    //如果本位是1，那么CRC = 上一位的CRC + 本位/CRC_CCITT
                crc ^= CRC_CCITT;
        }
        ptr++;
    }
    return crc;
}

/**CRC算法二，适用于程序空间较大且CRC计算速度要求较高的计算机或微控制系统
算法概要说明：计算本字节后的CRC 码等于上一字节余式CRC码的低8位左移8位后，
再加上上一字节CRC 右移8 位（也既取高8 位）和本字节之和后所求得的CRC码
*/
/*函数名称：crc_cal_by_byte;按字节计算CRC
  函数参数：unsigned char* ptr:指向发送缓冲区的首字节
            unsigned char len:要发送的总字节数
  函数返回值：unsigned int
  多项式采用CRC-CCITT 0x1021
*/
unsigned int crc_cal_by_byte(unsigned char* ptr, unsigned char len)
{
    unsigned short crc = 0;

    while(len-- != 0)
    {
        unsigned int high = (unsigned int)(crc/256); //取CRC高8位
        crc <<= 8;
        crc ^= crc_ta_8[high^*ptr];
        ptr++;
    }

    return crc;
}

/**CRC算法三，适用于程序空间不太大且CRC计算速度又不可以太慢的微控制系统*/
/*函数名称：crc_cal_by_halfbyte:按半字节计算CRC
  函数参数：unsigned char* ptr:指向发送缓冲区的首字节
            unsigned char len:要发送的总字节数
  函数返回值：unsigned int
  多项式采用CRC-CCITT  0x1021
*/
unsigned int crc_cal_by_halfbyte(unsigned char* ptr, unsigned char len)
{
    unsigned short crc = 0;

    while(len-- != 0)
    {
        unsigned char high = (unsigned char)(crc/4096); //暂存CRC的高4位
        crc <<= 4;
        crc ^= crc_ta_4[high^(*ptr/16)];

        high = (unsigned char)(crc/4096);
        crc <<= 4;
        crc ^= crc_ta_4[high^(*ptr&0x0f)];

        ptr++;
    }

    return crc;
}

//unsigned short 最大是65535
int main()
{
    unsigned char ptr[] = {0xa0, 0xa0, 0xa0};
    cout << crc_cal_by_bit(ptr, 3) << '\n';
    cout << crc_cal_by_halfbyte(ptr, 3) << '\n';
    cout << crc_cal_by_byte(ptr, 3) << '\n';
}