Add routines that will implement 77-bit messages for MSK144. Initial tests will use a (128,90) code.

lib/crc13.cpp

@@ -0,0 +1,31 @@
+#include <boost/crc.hpp>
+#include <boost/config.hpp>
+
+extern "C"
+{
+   short crc13 (unsigned char const * data, int length);
+   bool crc13_check (unsigned char const * data, int length);
+}
+
+#define POLY 0x15D7
+
+#ifdef BOOST_NO_CXX11_CONSTEXPR
+#define TRUNCATED_POLYNOMIAL POLY
+#else
+namespace
+{
+  unsigned long constexpr TRUNCATED_POLYNOMIAL = POLY;
+}
+#endif
+
+// assumes CRC is last 13 bits of the data and is set to zero
+// caller should assign the returned CRC into the message in big endian byte order
+short crc13 (unsigned char const * data, int length)
+{
+    return boost::augmented_crc<13, TRUNCATED_POLYNOMIAL> (data, length);
+}
+
+bool crc13_check (unsigned char const * data, int length)
+{
+   return !boost::augmented_crc<13, TRUNCATED_POLYNOMIAL> (data, length);
+}