File content as of revision 36:1bbd2fb7d2c8:

#ifdef __cplusplus
extern "C" {
#endif

#ifndef _CHECKSUM_H_
#define _CHECKSUM_H_

#include "inttypes.h"


/**
 *
 *  CALCULATE THE CHECKSUM
 *
 */

#define X25_INIT_CRC 0xffff
#define X25_VALIDATE_CRC 0xf0b8

/**
 *
 * Additionnal seed for crc calculation in MavLink 1.0 
 *
 */

#define MAVLINK_MESSAGE_CRCS {50, 124, 137, 0, 237, 217, 104, 119, 0, 0, 0, 89, 0, 0, 0, 0, 0, 0, 0, 0, 214, 159, 220, 168, 24, 23, 170, 144, 67, 115, 39, 246, 185, 104, 237, 244, 222, 212, 9, 254, 230, 28, 28, 132, 221, 232, 11, 153, 41, 39, 214, 223, 141, 33, 15, 3, 100, 24, 239, 238, 30, 200, 183, 0, 130, 0, 148, 21, 0, 52, 124, 0, 0, 0, 20, 0, 152, 143, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 231, 183, 63, 54, 0, 0, 0, 0, 0, 0, 0, 175, 102, 158, 208, 56, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 204, 49, 170, 44, 83, 46, 0}

/**
 * @brief Accumulate the X.25 CRC by adding one char at a time.
 *
 * The checksum function adds the hash of one char at a time to the
 * 16 bit checksum (uint16_t).
 *
 * @param data new char to hash
 * @param crcAccum the already accumulated checksum
 **/
static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
{
        /*Accumulate one byte of data into the CRC*/
        uint8_t tmp;

        tmp=data ^ (uint8_t)(*crcAccum &0xff);
        tmp^= (tmp<<4);
        *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
}

/**
 * @brief Initiliaze the buffer for the X.25 CRC
 *
 * @param crcAccum the 16 bit X.25 CRC
 */
static inline void crc_init(uint16_t* crcAccum)
{
        *crcAccum = X25_INIT_CRC;
}


/**
 * @brief Calculates the X.25 checksum on a byte buffer
 *
 * @param  pBuffer buffer containing the byte array to hash
 * @param  length  length of the byte array
 * @return the checksum over the buffer bytes
 **/
static inline uint16_t crc_calculate(uint8_t* pBuffer, int length)
{

        // For a "message" of length bytes contained in the unsigned char array
        // pointed to by pBuffer, calculate the CRC
        // crcCalculate(unsigned char* pBuffer, int length, unsigned short* checkConst) < not needed

        uint16_t crcTmp;
        //uint16_t tmp;
        uint8_t* pTmp;
		int i;

        pTmp=pBuffer;
        

        /* init crcTmp */
        crc_init(&crcTmp);

        for (i = 0; i < length; i++){
                crc_accumulate(*pTmp++, &crcTmp);
        }

        /* This is currently not needed, as only the checksum over payload should be computed
        tmp = crcTmp;
        crcAccumulate((unsigned char)(~crcTmp & 0xff),&tmp);
        crcAccumulate((unsigned char)((~crcTmp>>8)&0xff),&tmp);
        *checkConst = tmp;
        */
        return(crcTmp);
}




#endif /* _CHECKSUM_H_ */

#ifdef __cplusplus
}
#endif