CRC算法的研究

    由于用AVR对DS18B20读取数据匹配需要效验，在家里研究CRC算法，借鉴网上的一些方法，我把它终于被研究出来了，编写成了一个C++类库希望对大家有所帮助。经过试验，成功！

直接调用CRC :: get(char* pData, int nLength, char bitWidth)就可返回CRCt

pData：需要效验的数组首地址

nLength:数组的宽度，单位（字节）

bitWidth:需要生成的CRC编码方式，7，8，16可选.

此函数基于IAR AVR设计 

__flash UINT crc16_REF[256]=
{              
  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 
};

class CRC
{
public:
  UINT get(char *pData, int nLength , char bitWidth = 8)
  {
    switch(bitWidth)
    {
    case 7:
      return getCRC8(pData , nLength);
    case 8:
      return getCRC8(pData , nLength);
    case 16:
      return getCRC16(pData , nLength);
    }
    return getCRC8(pData , nLength);
  }
  
  UINT getCRC7(char* pData,int nLength)
  {
    UINT i; 
    UINT crc = 0x0000; 
    while(nLength--) 
    { 
      for(i = 0x80; i != 0; i /= 2) 
      { 
        if((crc & 0x40) != 0) 
        {
          crc *= 2; 
          crc ^= 0x09;
        }    
        else 
        {
          crc *= 2; 
        }
        if((*pData & i) != 0) 
        {
          crc ^= 0x09;
        }
      } 
      pData++; 
    } 
    crc = crc & 0x7f;
    crc = crc << 1;
    crc = crc | 0x01;
    return(crc);
  }
  
  UINT getCRC8(char* pData, int nLength)
  {
    UINT crc,  j;
    crc = 0;
    for (j = 0; j < nLength; j++)
    {
      char x = *pData++;
      for (char i = 0 ; i < 8 ; i++)
      {  
        if (((crc & 0x01) ^ (x & 0x01)))
        {
          crc ^= 0x18;
          crc >>= 1;
          crc |= 0x80;
        }
        else
          crc >>= 1;
        x >>= 1;
      }
    }
    return crc;
  }
  
  UINT getCRC16(char* pData, int nLength)
  {
    UINT crc = 0x0000;    // 初始化
    unsigned char i;
    while(nLength--) 
    { 
      i = (unsigned char) (crc / 256);  
      crc <<= 8;  
      crc ^= crc16_REF[i ^ *pData]; 
      pData++; 
    } 
    return crc;  
}

};