lib/main/MAVLink/checksum.h

   1 #pragma once
   2
   3 #if defined(MAVLINK_USE_CXX_NAMESPACE)
   4 namespace mavlink {
   5 #elif defined(__cplusplus)
   6 extern "C" {
   7 #endif
   8
   9 // Visual Studio versions before 2010 don't have stdint.h, so we just error out.
  10 #if (defined _MSC_VER) && (_MSC_VER < 1600)
  11 #error "The C-MAVLink implementation requires Visual Studio 2010 or greater"
  12 #endif
  13
  14 #include <stdint.h>
  15
  16 /**
  17  *
  18  *  CALCULATE THE CHECKSUM
  19  *
  20  */
  21
  22 #define X25_INIT_CRC 0xffff
  23 #define X25_VALIDATE_CRC 0xf0b8
  24
  25 #ifndef HAVE_CRC_ACCUMULATE
  26 /**
  27  * @brief Accumulate the CRC16_MCRF4XX checksum by adding one char at a time.
  28  *
  29  * The checksum function adds the hash of one char at a time to the
  30  * 16 bit checksum (uint16_t).
  31  *
  32  * @param data new char to hash
  33  * @param crcAccum the already accumulated checksum
  34  **/
  35 static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
  36 {
  37         /*Accumulate one byte of data into the CRC*/
  38         uint8_t tmp;
  39
  40         tmp = data ^ (uint8_t)(*crcAccum &0xff);
  41         tmp ^= (tmp<<4);
  42         *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
  43 }
  44 #endif
  45
  46
  47 /**
  48  * @brief Initiliaze the buffer for the MCRF4XX CRC16
  49  *
  50  * @param crcAccum the 16 bit MCRF4XX CRC16
  51  */
  52 static inline void crc_init(uint16_t* crcAccum)
  53 {
  54         *crcAccum = X25_INIT_CRC;
  55 }
  56
  57
  58 /**
  59  * @brief Calculates the CRC16_MCRF4XX checksum on a byte buffer
  60  *
  61  * @param  pBuffer buffer containing the byte array to hash
  62  * @param  length  length of the byte array
  63  * @return the checksum over the buffer bytes
  64  **/
  65 static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length)
  66 {
  67         uint16_t crcTmp;
  68         crc_init(&crcTmp);
  69         while (length--) {
  70                 crc_accumulate(*pBuffer++, &crcTmp);
  71         }
  72         return crcTmp;
  73 }
  74
  75
  76 /**
  77  * @brief Accumulate the MCRF4XX CRC16 by adding an array of bytes
  78  *
  79  * The checksum function adds the hash of one char at a time to the
  80  * 16 bit checksum (uint16_t).
  81  *
  82  * @param data new bytes to hash
  83  * @param crcAccum the already accumulated checksum
  84  **/
  85 static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length)
  86 {
  87         const uint8_t *p = (const uint8_t *)pBuffer;
  88         while (length--) {
  89                 crc_accumulate(*p++, crcAccum);
  90         }
  91 }
  92
  93 #if defined(MAVLINK_USE_CXX_NAMESPACE) || defined(__cplusplus)
  94 }
  95 #endif