Signature CRC extension

libuavcan/include/uavcan/internal/data_type.hpp

@@ -32,6 +32,13 @@ class DataTypeSignatureCRC
     uint64_t crc_;
 
 public:
+    static DataTypeSignatureCRC extend(uint64_t crc)
+    {
+        DataTypeSignatureCRC ret;
+        ret.crc_ = crc ^ 0xFFFFFFFFFFFFFFFF;
+        return ret;
+    }
+
     DataTypeSignatureCRC() : crc_(0xFFFFFFFFFFFFFFFF) { }
 
     void add(uint8_t byte)

libuavcan/test/data_type.cpp

@@ -19,3 +19,19 @@ TEST(DataTypeSignatureCRC, Correctness)
 
     ASSERT_EQ(0x62EC59E3F1A4F00A, crc.get());
 }
+
+
+TEST(DataTypeSignatureCRC, Extension)
+{
+    uavcan::DataTypeSignatureCRC crc1;
+
+    crc1.add('1');
+    crc1.add('2');
+    crc1.add('3');
+
+    uavcan::DataTypeSignatureCRC crc2 = uavcan::DataTypeSignatureCRC::extend(crc1.get());
+
+    crc2.add(reinterpret_cast<const uint8_t*>("456789"), 6);
+
+    ASSERT_EQ(0x62EC59E3F1A4F00A, crc2.get());
+}