gen_crc16_table.c

根据不同的生成多项

#include <stdio.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>


#define CRC16POLY 0x8005
#define CRC16POLY_REV 0xa001
#define CRC_CCITT0 0x1021
#define CRC_CCITT0_REV 0x8408

#define FCS(crcnum, c) (((crcnum) << 8) ^ crc16_table[(((crcnum) >> 8) ^ (c)) & 0xff])
#define FCS_REV(crcnum, c) (((crcnum) >> 8) ^ crc16_table[((crcnum) ^ (c)) & 0xff])

#define REVERSE 1 

unsigned short crc16_table[256];
void init_crc16_table(unsigned short genpoly)
{
	unsigned short ccnum = 0;
    	unsigned short i, j, k;

	for(i=0; i<256; i++)
    	{
		ccnum = 0;

#if REVERSE
		k = (i << 1);
		for(j=8;j>0;j--)
		{
			k >>= 1;
		  	if((k ^ ccnum) & 0x0001)
				ccnum = (ccnum >> 1) ^ genpoly;
			else
				ccnum >>= 1;
		}
		
#else
		k = (i << 8);
    	
		for(j=8;j>0;j--)
		{
    			if((k^ccnum) & 0x8000)
    				ccnum = (ccnum <<= 1) ^ genpoly;
    		   	else
    				ccnum <<= 1;
    			
			k <<= 1;
		}
    		
#endif
		crc16_table[i] =  ccnum;
	}
}


unsigned short Trid_CRC16_Gen(unsigned char *buf, int len)
{
	unsigned short oldcrc16;
	unsigned short crc16;
	unsigned short oldcrc;
	unsigned int charcnt;
	char c, t;
	
	//oldcrc16 = 0x0000; //初值为0
	crc16 = 0xffff;
	//crc16 = 0x0000;
	charcnt = 0;
/*	
	while(len--) 
	{
		t = (oldcrc16 >> 8) & 0xFF; //要移出的字节的值
		//oldcrc = crc16_table[t]; //根据移出的字节的值查表
		c = buf[charcnt]; //新移进来的字节值
		oldcrc16 <<= 8;
		//printf("\n0x%x\n", t ^ c);
		//printf("\n0x%x\n", oldcrc16);
		oldcrc16 ^= crc16_table[(t ^ c) & 0xff]; 
		charcnt++;
	}
	crc16 = oldcrc16;
*/
	while(len--)
	{
		c = buf[charcnt++]; 
#if REVERSE
		crc16 = FCS_REV(crc16, c);
#else
		crc16 = FCS(crc16, c);
#endif
	}		

	return ~crc16;
}

void main()
{
	int i;
	unsigned char data = 0x10;
	unsigned char j=0;
	//int fd;

	//fd = open("table.txt", O_CREAT | O_RDWR);
	//if(fd == -1)
	//{
	//	printf("open file error!!\n");
	//	exit(-1);
	//}

	FILE *fp;

	fp = fopen("table.txt", "w+");

	if(fp == NULL)
	{
		printf("error\n");
		exit(-1);
	}

	init_crc16_table(CRC_CCITT0_REV);
	
	for(i=0; i<256; i++)
	{
		//fprintf(fp, "0x%x, ", crc16_table[i]);
		printf("0x%04x ", crc16_table[i]);
		
		if((i % 8) == 7)
			//fprintf(fp, "\n");
			printf("\n");
	}

	printf("\n\n0x%04x\n\n", Trid_CRC16_Gen(&data, 1));

	for(i=0; i<256; i++)
	{
		printf("0x%04x ", Trid_CRC16_Gen(&j, 1));
		
		if((i%8) == 7)
			printf("\n");
		j++;
	}
	
	fclose(fp);

}