Prelim code to describe MAVLink messages

Makefile

@@ -9,7 +9,7 @@ CXXFLAGS += --std=c++14 -I include
 LDFLAGS += -lboost_system -lboost_thread -lboost_date_time -lboost_program_options -lboost_chrono
 LDFLAGS += -lpthread -lrt
 
-ALL += xml-describe
+ALL += xml-describe xml-mavlink-info xml-mavlink
 
 .PHONY: all clean distclean gitignore
 NOT_MISSING := all clean distclean gitignore

include/mavlink/checksum.h

@@ -0,0 +1,95 @@
+#pragma once
+
+#if defined(MAVLINK_USE_CXX_NAMESPACE)
+namespace mavlink {
+#elif defined(__cplusplus)
+extern "C" {
+#endif
+
+// Visual Studio versions before 2010 don't have stdint.h, so we just error out.
+#if (defined _MSC_VER) && (_MSC_VER < 1600)
+#error "The C-MAVLink implementation requires Visual Studio 2010 or greater"
+#endif
+
+#include <stdint.h>
+
+/**
+ *
+ *  CALCULATE THE CHECKSUM
+ *
+ */
+
+#define X25_INIT_CRC 0xffff
+#define X25_VALIDATE_CRC 0xf0b8
+
+#ifndef HAVE_CRC_ACCUMULATE
+/**
+ * @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);
+}
+#endif
+
+
+/**
+ * @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(const uint8_t* pBuffer, uint16_t length)
+{
+        uint16_t crcTmp;
+        crc_init(&crcTmp);
+	while (length--) {
+                crc_accumulate(*pBuffer++, &crcTmp);
+        }
+        return crcTmp;
+}
+
+
+/**
+ * @brief Accumulate the X.25 CRC by adding an array of bytes
+ *
+ * The checksum function adds the hash of one char at a time to the
+ * 16 bit checksum (uint16_t).
+ *
+ * @param data new bytes to hash
+ * @param crcAccum the already accumulated checksum
+ **/
+static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length)
+{
+	const uint8_t *p = (const uint8_t *)pBuffer;
+	while (length--) {
+                crc_accumulate(*p++, crcAccum);
+        }
+}
+
+#if defined(MAVLINK_USE_CXX_NAMESPACE) || defined(__cplusplus)
+}
+#endif