CRC知识点总结-1

美信：crc8

1.按位进行运算

void Cal_Crc8(unsigned char num) {
	unsigned char i     = 0;
	unsigned char j     = 0;
	unsigned char temp  = 0; 	// 临时存储
	unsigned char romb  = 0;	//  rom一位

	crc8  = 0;
	for ( i = 0; i < num; i++) {
		for (j = 0; j < 8; j++) {
			romb = (dat[i]>>j) & 1;
			temp = (crc8 & 1) ^ romb;	
			crc8  = (crc8 & 0xf7) + ((crc8 & 0x08) ^ (temp << 3));
			crc8  = (crc8 & 0xef) + ((crc8 & 0x10) ^ (temp << 4));
			crc8  =  crc8 >> 1;
			crc8  = (crc8 & 0x7f) + (temp << 7);
		}
	}
}

2.按字节直接运算

unsigned char cal_table_low_first(unsigned char value)
{
    unsigned char i, crc;
 
    crc = value;
/* 同样需要计算8次 */
    for (i=8; i>0; --i)
    { 
        if (crc & 0x01)  /* 反序异或变成判断最低位是否为1 */
            /* 数据变成往右移位了 */
            /* 计算的多项式从0x31（0011 0001）变成了0x8C (1000 1100) */
/* 多项式值，原来的最高位变成了最低位，原来的最低位变成最高位，8位数据高低位交换一下位置 */
            crc = (crc >> 1) ^ 0x8C;
        else
            crc = (crc >> 1);
    }
 
    return crc;
}