From 94c037416577d196d7396a3365f8ff88ffac6e37 Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Sat, 19 May 2018 17:39:26 +0300
Subject: [PATCH 1/3] Fixed the union code generation: if the union contained a
 power of two number of items, the tag bit length was one higher than needed,
 causing incorrect serialization.

---
 .../libuavcan_dsdl_compiler/data_type_template.tmpl             | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/data_type_template.tmpl b/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/data_type_template.tmpl
index 2b0acbf8e9..3107426bf0 100644
--- a/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/data_type_template.tmpl
+++ b/libuavcan/dsdl_compiler/libuavcan_dsdl_compiler/data_type_template.tmpl
@@ -70,7 +70,7 @@ struct UAVCAN_EXPORT ${t.cpp_type_name}
         };
     };
 
-    typedef ::uavcan::IntegerSpec< ::uavcan::IntegerBitLen< ${len(fields)} >::Result,
+    typedef ::uavcan::IntegerSpec< ::uavcan::IntegerBitLen< ${len(fields)}U - 1U >::Result,
                                    ::uavcan::SignednessUnsigned, ::uavcan::CastModeTruncate > TagType;
 
         <!--(macro expand_enum_per_field)--> #! enum_name, enum_comparator

From 53e33d01f7f39a16048d04fe23d131bc6419d3b8 Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Sat, 19 May 2018 17:52:07 +0300
Subject: [PATCH 2/3] Unit test for the previous commit

---
 .../dsdl_test/dsdl_uavcan_compilability.cpp   | 33 +++++++++++++++++++
 .../dsdl_test/root_ns_a/UnionTest4.uavcan     |  6 ++++
 2 files changed, 39 insertions(+)
 create mode 100644 libuavcan/test/dsdl_test/root_ns_a/UnionTest4.uavcan

diff --git a/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp b/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
index 8fc57ac7fb..5643ade02d 100644
--- a/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
+++ b/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
@@ -22,6 +22,7 @@
 
 #include <root_ns_a/Deep.hpp>
 #include <root_ns_a/UnionTest.hpp>
+#include <root_ns_a/UnionTest4.hpp>
 
 template <typename T>
 static bool validateYaml(const T& obj, const std::string& reference)
@@ -200,6 +201,38 @@ TEST(Dsdl, Union)
 }
 
 
+
+TEST(Dsdl, UnionTagWidth)
+{
+    using root_ns_a::UnionTest4;
+
+    ASSERT_EQ(2, UnionTest4::MinBitLen);
+    ASSERT_EQ(8, UnionTest4::MaxBitLen);
+
+    UnionTest4 s;
+
+    {
+        uavcan::StaticTransferBuffer<100> buf;
+        uavcan::BitStream bs_wr(buf);
+        uavcan::ScalarCodec sc_wr(bs_wr);
+
+        ASSERT_EQ(1, UnionTest4::encode(s, sc_wr));
+        ASSERT_EQ("00000000", bs_wr.toString());
+    }
+
+    {
+        uavcan::StaticTransferBuffer<100> buf;
+        uavcan::BitStream bs_wr(buf);
+        uavcan::ScalarCodec sc_wr(bs_wr);
+
+        s.to<UnionTest4::Tag::third>() = 1U << 5U;   // 32, 0b100000
+
+        ASSERT_EQ(1, UnionTest4::encode(s, sc_wr));
+        ASSERT_EQ("10100000", bs_wr.toString());
+    }
+}
+
+
 TEST(Dsdl, ParamGetSetRequestUnion)
 {
     uavcan::protocol::param::GetSet::Request req;
diff --git a/libuavcan/test/dsdl_test/root_ns_a/UnionTest4.uavcan b/libuavcan/test/dsdl_test/root_ns_a/UnionTest4.uavcan
new file mode 100644
index 0000000000..05bfb5c98c
--- /dev/null
+++ b/libuavcan/test/dsdl_test/root_ns_a/UnionTest4.uavcan
@@ -0,0 +1,6 @@
+# A union of four items; tag 2 bits wide, total length 1 byte
+@union          # 2 bits
+Empty first     # Tag value 0
+uint5 second    # Tag value 1
+uint6 third     # Tag value 2
+int2  fourth    # Tag value 3

From e096e33bb61d18b7f0adeefb6cd1f0b6a82ce385 Mon Sep 17 00:00:00 2001
From: Pavel Kirienko <pavel.kirienko@gmail.com>
Date: Sat, 19 May 2018 17:57:40 +0300
Subject: [PATCH 3/3] Formatting fix

---
 libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp b/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
index 5643ade02d..079ab96e29 100644
--- a/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
+++ b/libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp
@@ -201,7 +201,6 @@ TEST(Dsdl, Union)
 }
 
 
-
 TEST(Dsdl, UnionTagWidth)
 {
     using root_ns_a::UnionTest4;