C语言CRC-16 MAXIM格式校验函数

C语言CRC-16 MAXIM格式校验函数

CRC-16校验产生2个字节长度的数据校验码,通过计算得到的校验码和获得的校验码比较,用于验证获得的数据的正确性。基本的CRC-16校验算法实现,参考: C语言标准CRC-16校验函数。

不同厂家通过对输入数据前处理和输出数据后处理的方式不同,又产生了不同的厂家校验函数,这里介绍MAXIM格式的CRC-16校验函数。MAXIM格式对输入数据,按照单个字节进行位反序。对于输出的校验码,进行整体位反序, 然后异或0xFFFF。

生成多项式为x^16 + x^15 + x^2 + 1

正向算法

正向算法是符合标准CRC-16的计算理论,从左向右计算,也即计算过程中移位时,向左移出。几种正向算法的实现如下:

CRC-16 MAXIM格式校验函数一(8位输入数据格式,64位装载计算):

#include 
#include 
uint16_t PY_CRC_16_MAXIM(uint8_t *di, uint32_t len)
{
    uint32_t crc_poly = 0x00018005;  //X^16+X^15+X^2+1 total 17 effective bits. Computed total data shall be compensated 16-bit '0' before CRC computing.

	uint8_t *datain;
	uint64_t cdata = 0; //Computed total data
    uint32_t data_t = 0; //Process data of CRC computing

	uint16_t index_t = 63;  ///bit shifting index for initial '1' searching
	uint16_t index = 63;    //bit shifting index for CRC computing
	uint8_t rec = 0; //bit number needed to be compensated for next CRC computing

    uint32_t cn=(len+2)/6;
    uint32_t cr=(len+2)%6;

	uint32_t j;

	datain = malloc(len+2);
	for(j=0;j<len;j++)
	{
		datain[j] = 0;
		for(uint8_t m=0; m<=7; m++)
		{
			datain[j] |= ( ( di[j]>>(7-m) ) & 1 ) << m;
		}
	}
        datain[len] = 0; datain[len+1] = 0;//Compensate 16-bit '0' for input data

    if(len<=6)   //Mount data for only one segment
     {
    	 for(j=0;j<=(len+1);j++)
    	 {
    		 cdata = (cdata<<8);
    		 cdata = cdata|datain[j];
    	 }
    	 cn = 1;
     }
    else
     {
    	 if(cr==0)
    	 {
    		 cr = 6;
    	 }
         else if(cr==1)
         {
             cr = 7;

         }
         else if(cr==2)
         {
             cr = 8;

         }
    	 else
    	 {
    		 cn++;
    	 }

    	 for(j=0;j<cr;j++)
    	 {
    		 cdata = (cdata<<8);
    		 cdata = cdata|datain[j];
    	 }
     }

     do
     {
 		cn--;

 		while(index_t>0)
 		{
 			if( (cdata>>index_t)&1 )
 			{
 				index = index_t;
 				index_t = 0;

 				data_t |= (cdata>>(index-16));
 				{
 					data_t = data_t ^ crc_poly;
 				}

 	            while((index!=0x5555)&&(index!=0xaaaa))
 	            {

	 	    		for(uint8_t n=1;n<17;n++)
	 	    		{
	 	    			if ((data_t>>(16-n))&1) {rec = n;break;}
	 	    			if (n==16) rec=17;
	 	    		}

 	    			if((index-16)<rec)
 	    			{
 	    				data_t = data_t<<(index-16);
 	    				data_t |=  (uint32_t)((cdata<<(64-(index-16)))>>(64-(index-16)));
 	    				index = 0x5555;
 	    			}
 	    			else
 	    			{
 	        			for(uint8_t i=1;i<=rec;i++)
 	        			{
 	        				data_t = (data_t<<1)|((cdata>>(index-16-i))&1) ;
 	        			}

 	        			if(rec!= 17)
 	        			{
 	        				data_t = data_t ^ crc_poly;
 	        				index -= rec;
 	        			}
 	        			else
 	        			{
 	        				data_t = 0;
 	        				index_t = index-16-1;
 	        				index = 0xaaaa;

 	        			}

 	    			}

 	            }
 				if(index==0x5555) break;
 			}
 			else
 			{
 				index_t--;
 				if(index_t<16) break;
 			}
         }

 		if(cn>0) //next segment
 		{
  			cdata = data_t&0x00ffff;

 			for(uint8_t k=0;k<6;k++)
 			{
 	    		 cdata = (cdata<<8);
 	    		 cdata = cdata|datain[j++];

 			}

 	    	data_t = 0;
 	 		index_t = 63;  ///bit shifting index for initial '1' searching
 	 		index = 63;    //bit shifting index for CRC computing
 	 		rec = 0; //bit number needed to be compensated for next CRC computing
 		}

     }
     while(cn>0);

     free(datain);

     uint16_t i_data_t = 0;

     for(uint8_t n=0; n<=15; n++)
     {
    	 i_data_t |=  ( ( data_t>>(15-n) ) & 1 ) << n;
     }

     return i_data_t ^ 0xFFFF;
}

CRC-16 MAXIM格式校验函数二(8位输入数据格式):

uint16_t PY_CRC_16_S_MAXIM(uint8_t *di, uint32_t len)
{
    uint16_t crc_poly = 0x8005;  //X^16+X^15+X^2+1 total 16 effective bits without X^16. Computed total data shall be compensated 16-bit '0' before CRC computing.

	uint32_t clen = len+2;
	uint8_t cdata[clen] ;
	for(uint32_t j=0;j<len;j++)
	{
		cdata[j] = 0;

		for(uint8_t m=0; m<=7; m++)
		{
			cdata[j] |= ( ( di[j]>>(7-m) ) & 1 ) << m;
		}
	}
	cdata[len]=0; cdata[len+1]=0;

	uint16_t data_t = (((uint16_t)cdata[0]) << 8) + cdata[1]; //CRC register

    for (uint32_t i = 2; i < clen; i++)
    {
        for (uint8_t j = 0; j <= 7; j++)
        {
            if(data_t&0x8000)
            	data_t = ( (data_t<<1) | ( (cdata[i]>>(7-j))&0x01) ) ^ crc_poly;
            else
            	data_t = ( (data_t<<1) | ( (cdata[i]>>(7-j))&0x01) ) ;
        }
    }

    uint16_t i_data_t = 0;

    for(uint8_t n=0; n<=15; n++)
    {
   	 i_data_t |=  ( ( data_t>>(15-n) ) & 1 ) << n;
    }

    return i_data_t ^ 0xFFFF;
}

CRC-16 MAXIM格式校验函数三(16位输入数据格式):

uint16_t PY_CRC_16_T16_MAXIM(uint16_t *di, uint32_t len)
{
	uint16_t crc_poly = 0x8005;  //X^16+X^15+X^2+1 total 16 effective bits without X^16. 
	uint16_t data_t = 0; //CRC register

	uint16_t cdata[len];
	for(uint32_t j=0;j<len;j++)
	{
		cdata[j] = 0;
		for(uint8_t m=0; m<=7; m++)
		{
			cdata[j] |= ( ( ( (di[j]>>8)>>(7-m) ) & 1 ) << m ) | ( ( ( ( (di[j]&0x00ff)>>(7-m) ) & 1 ) << m ) <<8 );
		}

	}

    for(uint32_t i = 0; i < len; i++)
    {
    	data_t ^= cdata[i]; //16-bit data

        for (uint8_t j = 0; j < 16; j++)
        {
            if (data_t & 0x8000)
            	data_t = (data_t << 1) ^ crc_poly;
            else
            	data_t <<= 1;
        }
    }

    uint16_t i_data_t = 0;

    for(uint8_t n=0; n<=15; n++)
    {
   	 i_data_t |=  ( ( data_t>>(15-n) ) & 1 ) << n;
    }

    return i_data_t ^ 0xFFFF;
}

CRC-16 MAXIM格式校验函数四(8位输入数据格式):

uint16_t PY_CRC_16_T8_MAXIM(uint8_t *di, uint32_t len)
{
	uint16_t crc_poly = 0x8005;  //X^16+X^15+X^2+1 total 16 effective bits without X^16. 
	uint16_t data_t = 0; //CRC register

	uint8_t cdata[len];
	for(uint32_t j=0;j<len;j++)
	{
		cdata[j] = 0;
		for(uint8_t m=0; m<=7; m++)
		{
			cdata[j] |= ( ( di[j]>>(7-m) ) & 1 ) << m;
		}
	}

    for(uint32_t i = 0; i < len; i++)
    {
    	data_t ^= cdata[i]<<8; //8-bit data

        for (uint8_t j = 0; j < 8; j++)
        {
            if (data_t & 0x8000)
            	data_t = (data_t << 1) ^ crc_poly;
            else
            	data_t <<= 1;

        }
    }

    uint16_t i_data_t = 0;

    for(uint8_t n=0; n<=15; n++)
    {
   	 i_data_t |=  ( ( data_t>>(15-n) ) & 1 ) << n;
    }

    return i_data_t ^ 0xFFFF;
}

反向算法

反向算法是从由右向左计算,也即计算过程中移位时,向右移出。而计算过程中的输入数据高优先计算位和校验参数的对齐关系不变。因此把一个字节放在CRC计算寄存器的最低字节时,对于MAXIM格式,最右侧最低位实际上是高优先计算位,而校验参数要相应倒序,从而计算位置对照关系不变。

CRC-16 MAXIM格式校验函数五(反向算法,8位输入数据格式):

uint16_t PY_CRC_16_T8_MAXIM_i(uint8_t *di, uint32_t len)
{
	uint16_t crc_poly = 0xA001; //Bit sequence inversion of 0x8005
	uint16_t data_t = 0; //CRC register

    for(uint32_t i = 0; i < len; i++)
    {
    	data_t ^= di[i]; //8-bit data

        for (uint8_t j = 0; j < 8; j++)
        {
            if (data_t & 0x0001)
            	data_t = (data_t >> 1) ^ crc_poly;
            else
            	data_t >>= 1;
        }
    }

    return data_t ^ 0xFFFF;
}

算法验证

5种算法结果相同:
C语言CRC-16 MAXIM格式校验函数_第1张图片
通过在线CRC工具对照验证成功:
C语言CRC-16 MAXIM格式校验函数_第2张图片
–End–

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