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95 lines
2.1 KiB
95 lines
2.1 KiB
#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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