Cyclic redundancy check （Cyclic Redundancy Check, CRC） It is a kind of channel coding technology that generates short fixed digit check code according to data such as network packets or computer files , It is mainly used to detect or verify the possible errors after data transmission or saving . It uses the principle of division and remainder to detect errors .
This paper implements CRC16 Of C Language verification algorithm , It adopts the method of looking up tables .CRC Polynomials are x16+x15+x2+1(0x8005),CRC The initial value of 0xFFFF, yes modbus Of CRC Check algorithm .

1 crc.c

#include "crc16.h"

/* CRC16  The remainder table  */
static uint16_t crctalbeabs[] = {
     
	0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401, 
	0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400 
};


/*! *  work   can : CRC16 check  * param1:  Pointer to the data to be verified  * param2:  The length of the data to be verified  * retval:  Check the value obtained ,uint16_t  type  * *  say   bright :  This time CRC Check to look-up table method , The polynomial is  x16+x15+x2+1(0x8005),CRC The initial value of 0xFFFF */
uint16_t Crc16(uint8_t *ptr, uint32_t len) 
{
    
	uint16_t crc = 0xffff; 
	uint32_t i;
	uint8_t ch;
 
	for (i = 0; i < len; i++) {
    
		ch = *ptr++;
		crc = crctalbeabs[(ch ^ crc) & 15] ^ (crc >> 4);
		crc = crctalbeabs[((ch >> 4) ^ crc) & 15] ^ (crc >> 4);
	} 
	
	return crc;
}

2 crc.h

#ifndef _CRC_H_
#define _CRC_H_

#include <stdint.h>

uint16_t Crc16(uint8_t *ptr, uint32_t len);

#define HIG_UINT16(a) ( ((a)>>8) & 0xFF )
#define LOW_UINT16(a) ( (a) & 0xFF )

#define HIG_UINT8(a) ( ((a)>>4) & 0x0F )
#define LOW_UINT8(a) ( (a) & 0x0F )

#endif /* crc.h */