CRC25 - kuidas ? - Printerisõbralik versioon

Kood:

#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



/**

 * @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

Kood:

;===============================================================================

;#define X25_INIT_CRC 0xffff

;static inline void crc_init(uint16_t* crcAccum)

;{

;       *crcAccum = X25_INIT_CRC;

;}

;--------------------

;{

;       /*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);

;}

; ---- Arvuta CRC -------

;       crc_init(&crcTmp);



;       for (i = 0; i < length; i++){

;               crc_accumulate(*pTmp++, &crcTmp);

;       }

;



;FE  09  4E  01  01  00  00  00  00  00  02  03  51  04  03  1C  7F

test:            movlw    0xFF        ; crc_init(&crcTmp)

                movwf    TBLPTRLt

                movwf    TBLPTRHt

                movlw    .10

                movwf    t_count

                LFSR    .0,0x25    ; puhver

;       tmp=data ^ (uint8_t)(*crcAccum &0xff);

;       tmp^= (tmp<<4);

;       *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);

tst1:            movf    POSTINC0,W        ; loe databait puhvrist -> W

                xorwf    TBLPTRLt,W         ; databait XOR CRC LOW -> t1_count (tmp=data ^ (uint8_t)(*crcAccum &0xff);)

                movwf    t1_count

                movwf    t2_count    

                bcf        CARRY            ; tmp^= (tmp<<4)

                rlcf    t1_count,F

                rlcf    t1_count,F

                rlcf    t1_count,F

                rlcf    t1_count,W        ; = tmp

                xorwf    t2_count,W

                movwf    t1_count

;*crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4); 

                bcf        CARRY

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                rrcf    TBLPTRHt,F

                rrcf    TBLPTRLt,F

                movff    t1_count,t2_count

                bcf        CARRY

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,W

                xorwf    TBLPTRLt,F                



                movff    t1_count,t2_count

                bcf        CARRY

                rlcf    t2_count,F

                rlcf    t2_count,F

                rlcf    t2_count,W

                xorwf    TBLPTRLt,F                



                movff    t1_count,t2_count

                bcf        CARRY

                rrcf    t2_count,F

                rrcf    t2_count,F

                rrcf    t2_count,F

                rrcf    t2_count,W

                xorwf    TBLPTRLt,F                



                decfsz    t_count

                goto    tst1