Diff: MAVlink/include/checksum.h

Revision:

0:826c6171fc1b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MAVlink/include/checksum.h	Wed Jun 20 14:57:48 2012 +0000
@@ -0,0 +1,95 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef _CHECKSUM_H_
+#define _CHECKSUM_H_
+
+#include "inttypes.h"
+
+
+/**
+ *
+ *  CALCULATE THE CHECKSUM
+ *
+ */
+
+#define X25_INIT_CRC 0xffff
+#define X25_VALIDATE_CRC 0xf0b8
+
+/**
+ * @brief Accumulate the X.25 CRC by adding one char at a time.
+ *
+ * The checksum function adds the hash of one char at a time to the
+ * 16 bit checksum (uint16_t).
+ *
+ * @param data new char to hash
+ * @param crcAccum the already accumulated checksum
+ **/
+static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
+{
+        /*Accumulate one byte of data into the CRC*/
+        uint8_t tmp;
+
+        tmp=data ^ (uint8_t)(*crcAccum &0xff);
+        tmp^= (tmp<<4);
+        *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
+}
+
+/**
+ * @brief Initiliaze the buffer for the X.25 CRC
+ *
+ * @param crcAccum the 16 bit X.25 CRC
+ */
+static inline void crc_init(uint16_t* crcAccum)
+{
+        *crcAccum = X25_INIT_CRC;
+}
+
+
+/**
+ * @brief Calculates the X.25 checksum on a byte buffer
+ *
+ * @param  pBuffer buffer containing the byte array to hash
+ * @param  length  length of the byte array
+ * @return the checksum over the buffer bytes
+ **/
+static inline uint16_t crc_calculate(uint8_t* pBuffer, int length)
+{
+
+        // For a "message" of length bytes contained in the unsigned char array
+        // pointed to by pBuffer, calculate the CRC
+        // crcCalculate(unsigned char* pBuffer, int length, unsigned short* checkConst) < not needed
+
+        uint16_t crcTmp;
+        //uint16_t tmp;
+        uint8_t* pTmp;
+		int i;
+
+        pTmp=pBuffer;
+        
+
+        /* init crcTmp */
+        crc_init(&crcTmp);
+
+        for (i = 0; i < length; i++){
+                crc_accumulate(*pTmp++, &crcTmp);
+        }
+
+        /* This is currently not needed, as only the checksum over payload should be computed
+        tmp = crcTmp;
+        crcAccumulate((unsigned char)(~crcTmp & 0xff),&tmp);
+        crcAccumulate((unsigned char)((~crcTmp>>8)&0xff),&tmp);
+        *checkConst = tmp;
+        */
+        return(crcTmp);
+}
+
+
+
+
+#endif /* _CHECKSUM_H_ */
+
+#ifdef __cplusplus
+}
+#endif