checksum.h

00001 #ifdef __cplusplus
00002 extern "C" {
00003 #endif
00004 
00005 #ifndef _CHECKSUM_H_
00006 #define _CHECKSUM_H_
00007 
00008 // Visual Studio versions before 2010 don't have stdint.h, so we just error out.
00009 #if (defined _MSC_VER) && (_MSC_VER < 1600)
00010 #error "The C-MAVLink implementation requires Visual Studio 2010 or greater"
00011 #endif
00012 
00013 #include <stdint.h>
00014 
00015 /**
00016  *
00017  *  CALCULATE THE CHECKSUM
00018  *
00019  */
00020 
00021 #define X25_INIT_CRC 0xffff
00022 #define X25_VALIDATE_CRC 0xf0b8
00023 
00024 #ifndef HAVE_CRC_ACCUMULATE
00025 /**
00026  * @brief Accumulate the X.25 CRC by adding one char at a time.
00027  *
00028  * The checksum function adds the hash of one char at a time to the
00029  * 16 bit checksum (uint16_t).
00030  *
00031  * @param data new char to hash
00032  * @param crcAccum the already accumulated checksum
00033  **/
00034 static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
00035 {
00036         /*Accumulate one byte of data into the CRC*/
00037         uint8_t tmp;
00038 
00039         tmp = data ^ (uint8_t)(*crcAccum &0xff);
00040         tmp ^= (tmp<<4);
00041         *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
00042 }
00043 #endif
00044 
00045 
00046 /**
00047  * @brief Initiliaze the buffer for the X.25 CRC
00048  *
00049  * @param crcAccum the 16 bit X.25 CRC
00050  */
00051 static inline void crc_init(uint16_t* crcAccum)
00052 {
00053         *crcAccum = X25_INIT_CRC;
00054 }
00055 
00056 
00057 /**
00058  * @brief Calculates the X.25 checksum on a byte buffer
00059  *
00060  * @param  pBuffer buffer containing the byte array to hash
00061  * @param  length  length of the byte array
00062  * @return the checksum over the buffer bytes
00063  **/
00064 static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length)
00065 {
00066         uint16_t crcTmp;
00067         crc_init(&crcTmp);
00068     while (length--) {
00069                 crc_accumulate(*pBuffer++, &crcTmp);
00070         }
00071         return crcTmp;
00072 }
00073 
00074 
00075 /**
00076  * @brief Accumulate the X.25 CRC by adding an array of bytes
00077  *
00078  * The checksum function adds the hash of one char at a time to the
00079  * 16 bit checksum (uint16_t).
00080  *
00081  * @param data new bytes to hash
00082  * @param crcAccum the already accumulated checksum
00083  **/
00084 static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length)
00085 {
00086     const uint8_t *p = (const uint8_t *)pBuffer;
00087     while (length--) {
00088                 crc_accumulate(*p++, crcAccum);
00089         }
00090 }
00091 
00092 #endif /* _CHECKSUM_H_ */
00093 
00094 #ifdef __cplusplus
00095 }
00096 #endif
00097