lib/main/MAVLink/checksum.h

   1 #ifdef __cplusplus
   2 extern "C" {
   3 #endif
   4
   5 #ifndef _CHECKSUM_H_
   6 #define _CHECKSUM_H_
   7
   8 // Visual Studio versions before 2010 don't have stdint.h, so we just error out.
   9 #if (defined _MSC_VER) && (_MSC_VER < 1600)
  10 #error "The C-MAVLink implementation requires Visual Studio 2010 or greater"
  11 #endif
  12
  13 #include <stdint.h>
  14
  15 /**
  16  *
  17  *  CALCULATE THE CHECKSUM
  18  *
  19  */
  20
  21 #define X25_INIT_CRC 0xffff
  22 #define X25_VALIDATE_CRC 0xf0b8
  23
  24 #ifndef HAVE_CRC_ACCUMULATE
  25 /**
  26  * @brief Accumulate the X.25 CRC by adding one char at a time.
  27  *
  28  * The checksum function adds the hash of one char at a time to the
  29  * 16 bit checksum (uint16_t).
  30  *
  31  * @param data new char to hash
  32  * @param crcAccum the already accumulated checksum
  33  **/
  34 static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
  35 {
  36         /*Accumulate one byte of data into the CRC*/
  37         uint8_t tmp;
  38
  39         tmp = data ^ (uint8_t)(*crcAccum &0xff);
  40         tmp ^= (tmp<<4);
  41         *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
  42 }
  43 #endif
  44
  45
  46 /**
  47  * @brief Initiliaze the buffer for the X.25 CRC
  48  *
  49  * @param crcAccum the 16 bit X.25 CRC
  50  */
  51 static inline void crc_init(uint16_t* crcAccum)
  52 {
  53         *crcAccum = X25_INIT_CRC;
  54 }
  55
  56
  57 /**
  58  * @brief Calculates the X.25 checksum on a byte buffer
  59  *
  60  * @param  pBuffer buffer containing the byte array to hash
  61  * @param  length  length of the byte array
  62  * @return the checksum over the buffer bytes
  63  **/
  64 static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length)
  65 {
  66         uint16_t crcTmp;
  67         crc_init(&crcTmp);
  68         while (length--) {
  69                 crc_accumulate(*pBuffer++, &crcTmp);
  70         }
  71         return crcTmp;
  72 }
  73
  74
  75 /**
  76  * @brief Accumulate the X.25 CRC by adding an array of bytes
  77  *
  78  * The checksum function adds the hash of one char at a time to the
  79  * 16 bit checksum (uint16_t).
  80  *
  81  * @param data new bytes to hash
  82  * @param crcAccum the already accumulated checksum
  83  **/
  84 static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length)
  85 {
  86         const uint8_t *p = (const uint8_t *)pBuffer;
  87         while (length--) {
  88                 crc_accumulate(*p++, crcAccum);
  89         }
  90 }
  91
  92 #endif /* _CHECKSUM_H_ */
  93
  94 #ifdef __cplusplus
  95 }
  96 #endif