cxxrtl: Fix value::shl

tests/cxxrtl/test_value.cc

@@ -0,0 +1,15 @@
+#include <cassert>
+#include <cstdint>
+
+#include "cxxrtl/cxxrtl.h"
+
+int main()
+{
+    {
+        // shl exceeding Bits should be masked
+        cxxrtl::value<6> a(1u);
+        cxxrtl::value<6> b(8u);
+        cxxrtl::value<6> c = a.shl(b);
+        assert(c.get<uint64_t>() == 0);
+    }
+}