简介

在数据储存或者数据传输过程经常需要对数据进行校验，以确保数据的准确性。本文介绍一些常用的CRC校验算法

和校验、异或校验

• 这两种校验方式在短数据传输过程应该是最常见的，实现过程很简单，这里不做过多的介绍

多项式与POLY

• CRC算法中必然会提到多项式，比如多项式“x8+x2+x+1”,即第8、2、1、0，bit为1。而POLY(生成项)计算中，最高位不参与，所以此多项式的POLY为0x07。
• 又如CRC-16-MODBUS，它的多项式为x16 + x15 + x2 + 1，所以此多项式的POLY为0x8005

CRC

• 实现CRC8，即实现了CRC4、CRC5、CRC6、CRC7以及CRC8-ITU、CRC8-ROHC等，不同的是它们的初值、多项式以及数据是否反转之间的配置不一样罢了,或者最终计算的结果异或某个值而已
• 同理实现CRC16，CRC32，即可实现大部分CRC算法的需求

算法

数据反转

/**
* @brief  数据反转(高低位调换的意思，将数据最高位调到最低位,次高位调到次低位)
* @note
* @param  data:数据
*		  bitLen:数据位数
* @retval Reverse Result
*
*/
unsigned int Reverse(unsigned int data, unsigned char bitLen)
{
	unsigned int i;
	unsigned int buf=0;
	for (i = 0; i<bitLen; i++) {
		buf <<= 1;
		if (data & 0x01) {
			buf |= 1;
		}
		data >>= 1;
	}

	return buf;
}

CRC8算法

/**
* @brief  CRC8 Calculate
* @note   
* @param  crcInit:		CRC初始值
*		  poly:			CRC多项式
*		  BlockStart:	数据段
*		  BlockLength:	数据长度(需要计算的长度)
*		  inRev:		输入数据是否反转 0:不反转 1:反转
*		  outRev:		输出数据是否反转 0:不反转 1:反转
* @retval CRC8 Calculate Result
*         
*/
unsigned char CRC8(unsigned char crcInit, unsigned char poly, unsigned char *BlockStart, unsigned char BlockLength, unsigned char inRev, unsigned char outRev)
{
	unsigned int i, j;
	unsigned char CRC_VAL = crcInit;
	unsigned char buf;

	for (j = 0; j<BlockLength; j++) {
		buf = *(BlockStart + j);

		if (inRev != 0) {
			buf = Reverse(buf,8);
		}

		CRC_VAL ^= buf;
		for (i = 0; i<8; i++) {
			if (CRC_VAL & 0x80) {
				CRC_VAL = (CRC_VAL << 1) ^ poly;
			}
			else {
				CRC_VAL <<= 1;
			}
		}
	}


	if (outRev != 0) {
		CRC_VAL = Reverse(CRC_VAL,8);
	}

	return 	CRC_VAL & 0xFF;

}

CRC16算法

/**
* @brief  CRC16 Calculate
* @note
* @param  crcInit:		CRC初始值
*		  poly:			CRC多项式
*		  BlockStart:	数据段
*		  BlockLength:	数据长度(需要计算的长度)
*		  inRev:		输入数据是否反转 0:不反转 1:反转
*		  outRev:		输出数据是否反转 0:不反转 1:反转
* @retval CRC16 Calculate Result
*
*/
unsigned short CRC16(unsigned short crcInit, unsigned short poly, unsigned char *BlockStart, unsigned char BlockLength, unsigned char inRev, unsigned char outRev)
{
	unsigned int i, j;
	unsigned short CRC_VAL = crcInit;
	unsigned char buf;

	for (j = 0; j<BlockLength; j++) {
		buf = *(BlockStart + j);

		if (inRev != 0) {
			buf = Reverse(buf,8);
		}

		CRC_VAL ^= ((unsigned short)buf << 8);
		for (i = 0; i<8; i++) {
			if (CRC_VAL & 0x8000) {
				CRC_VAL = (CRC_VAL << 1) ^ poly;
			}
			else {
				CRC_VAL <<= 1;
			}
		}
	}

	if (outRev != 0) {
		CRC_VAL = Reverse(CRC_VAL,16);
	}

	return 	CRC_VAL & 0xFFFF;

}

CRC32算法

/**
* @brief  CRC32 Calculate
* @note
* @param  crcInit:		CRC初始值
*		  poly:			CRC多项式
*		  BlockStart:	数据段
*		  BlockLength:	数据长度(需要计算的长度)
*		  inRev:		输入数据是否反转 0:不反转 1:反转
*		  outRev:		输出数据是否反转 0:不反转 1:反转
* @retval CRC32 Calculate Result
*
*/
unsigned int CRC32(unsigned int crcInit, unsigned int poly, unsigned char *BlockStart, unsigned char BlockLength, unsigned char inRev, unsigned char outRev)
{
	unsigned int i, j;
	unsigned int CRC_VAL = crcInit;
	unsigned char buf;

	for (j = 0; j<BlockLength; j++) {
		buf = *(BlockStart + j);

		if (inRev != 0) {
			buf = Reverse(buf, 8);
		}

		CRC_VAL ^= ((unsigned int)buf << 24);
		for (i = 0; i<8; i++) {
			if (CRC_VAL & 0x80000000) {
				CRC_VAL = (CRC_VAL << 1) ^ poly;
			}
			else {
				CRC_VAL <<= 1;
			}
		}
	}

	if (outRev != 0) {
		CRC_VAL = Reverse(CRC_VAL, 32);
	}

	return 	CRC_VAL & 0xFFFFFFFF;

}

测试代码与输出

int main(void)
{
	unsigned char test[] = { 0x01,0x03,0x00,0x00,0x00,0x01 };
	unsigned char crc8_result=0;
	unsigned short crc16_result=0;
	unsigned int  crc32_result = 0;

	//CRC8
	crc8_result = CRC8(0x00, 0x07, test, sizeof(test), 0, 0);
	//CRC16 MODBUS
	crc16_result = CRC16(0xFFFF, 0x8005, test, sizeof(test), 1, 1);
	//CRC-32/MPEG-2
	crc32_result = CRC32(0xFFFFFFFF,0x04C11DB7, test, sizeof(test), 0, 0);

	printf("CRC8 result  = 0x%02X\r\n", crc8_result);
	printf("CRC16 result = 0x%04X\r\n", crc16_result);
	printf("CRC32 result = 0x%08X\r\n", crc32_result);

	while (1);

	return 0;
}

输出
CRC8 result = 0x88
CRC16 result = 0x0A84
CRC32 result = 0xFE84042A

常见CRC参数模型