mirror of https://github.com/ArduPilot/ardupilot
96 lines
2.1 KiB
C
96 lines
2.1 KiB
C
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#ifdef __cplusplus
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extern "C" {
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#endif
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#ifndef _CHECKSUM_H_
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#define _CHECKSUM_H_
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#include "inttypes.h"
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/**
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*
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* CALCULATE THE CHECKSUM
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*
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*/
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#define X25_INIT_CRC 0xffff
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#define X25_VALIDATE_CRC 0xf0b8
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/**
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* @brief Accumulate the X.25 CRC by adding one char at a time.
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*
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* The checksum function adds the hash of one char at a time to the
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* 16 bit checksum (uint16_t).
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*
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* @param data new char to hash
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* @param crcAccum the already accumulated checksum
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**/
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static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
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{
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/*Accumulate one byte of data into the CRC*/
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uint8_t tmp;
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tmp=data ^ (uint8_t)(*crcAccum &0xff);
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tmp^= (tmp<<4);
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*crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
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}
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/**
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* @brief Initiliaze the buffer for the X.25 CRC
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*
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* @param crcAccum the 16 bit X.25 CRC
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*/
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static inline void crc_init(uint16_t* crcAccum)
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{
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*crcAccum = X25_INIT_CRC;
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}
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/**
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* @brief Calculates the X.25 checksum on a byte buffer
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*
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* @param pBuffer buffer containing the byte array to hash
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* @param length length of the byte array
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* @return the checksum over the buffer bytes
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**/
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static inline uint16_t crc_calculate(uint8_t* pBuffer, int length)
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{
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// For a "message" of length bytes contained in the unsigned char array
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// pointed to by pBuffer, calculate the CRC
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// crcCalculate(unsigned char* pBuffer, int length, unsigned short* checkConst) < not needed
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uint16_t crcTmp;
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//uint16_t tmp;
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uint8_t* pTmp;
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int i;
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pTmp=pBuffer;
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/* init crcTmp */
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crc_init(&crcTmp);
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for (i = 0; i < length; i++){
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crc_accumulate(*pTmp++, &crcTmp);
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}
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/* This is currently not needed, as only the checksum over payload should be computed
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tmp = crcTmp;
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crcAccumulate((unsigned char)(~crcTmp & 0xff),&tmp);
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crcAccumulate((unsigned char)((~crcTmp>>8)&0xff),&tmp);
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*checkConst = tmp;
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*/
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return(crcTmp);
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}
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#endif /* _CHECKSUM_H_ */
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#ifdef __cplusplus
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}
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#endif
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