flight/libraries/mavlink/v1.0/checksum.h

   1 #ifdef __cplusplus
   2 extern "C" {
   3 #endif
   4
   5 #ifndef _CHECKSUM_H_
   6 #define _CHECKSUM_H_
   7
   8
   9 /**
  10  *
  11  *  CALCULATE THE CHECKSUM
  12  *
  13  */
  14
  15 #define X25_INIT_CRC     0xffff
  16 #define X25_VALIDATE_CRC 0xf0b8
  17
  18 /**
  19  * @brief Accumulate the X.25 CRC by adding one char at a time.
  20  *
  21  * The checksum function adds the hash of one char at a time to the
  22  * 16 bit checksum (uint16_t).
  23  *
  24  * @param data new char to hash
  25  * @param crcAccum the already accumulated checksum
  26  **/
  27 static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
  28 {
  29     /*Accumulate one byte of data into the CRC*/
  30     uint8_t tmp;
  31
  32     tmp  = data ^ (uint8_t)(*crcAccum & 0xff);
  33     tmp ^= (tmp << 4);
  34     *crcAccum = (*crcAccum >> 8) ^ (tmp << 8) ^ (tmp << 3) ^ (tmp >> 4);
  35 }
  36
  37 /**
  38  * @brief Initiliaze the buffer for the X.25 CRC
  39  *
  40  * @param crcAccum the 16 bit X.25 CRC
  41  */
  42 static inline void crc_init(uint16_t *crcAccum)
  43 {
  44     *crcAccum = X25_INIT_CRC;
  45 }
  46
  47
  48 /**
  49  * @brief Calculates the X.25 checksum on a byte buffer
  50  *
  51  * @param  pBuffer buffer containing the byte array to hash
  52  * @param  length  length of the byte array
  53  * @return the checksum over the buffer bytes
  54  **/
  55 static inline uint16_t crc_calculate(const uint8_t *pBuffer, uint16_t length)
  56 {
  57     uint16_t crcTmp;
  58
  59     crc_init(&crcTmp);
  60     while (length--) {
  61         crc_accumulate(*pBuffer++, &crcTmp);
  62     }
  63     return crcTmp;
  64 }
  65
  66 /**
  67  * @brief Accumulate the X.25 CRC by adding an array of bytes
  68  *
  69  * The checksum function adds the hash of one char at a time to the
  70  * 16 bit checksum (uint16_t).
  71  *
  72  * @param data new bytes to hash
  73  * @param crcAccum the already accumulated checksum
  74  **/
  75 static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint8_t length)
  76 {
  77     const uint8_t *p = (const uint8_t *)pBuffer;
  78
  79     while (length--) {
  80         crc_accumulate(*p++, crcAccum);
  81     }
  82 }
  83
  84
  85 #endif /* _CHECKSUM_H_ */
  86
  87 #ifdef __cplusplus
  88 }
  89 #endif