base: Fix assigning between identical bitfields.

If two bitfields are of the same type, also implying that they have the same
first and last bit positions, the existing implementation would copy the
entire bitfield. That includes the __data member which is shared among all the
bitfields, effectively overwritting the entire bitunion.

This change also adjusts the write only signed bitfield assignment operator to
be like the unsigned version, using "using" instead of implementing it again
and calling down to the underlying implementation.

src/base/bitunion.hh

@@ -100,6 +100,12 @@ namespace BitfieldBackend
                 this->setBits(first, last, _data);
                 return _data;
             }
+
+            uint64_t
+            operator=(Bitfield<first, last> const & other)
+            {
+                return *this = (uint64_t)other;
+            }
         };
 
         //A class which specializes the above so that it can only be read
@@ -113,6 +119,9 @@ namespace BitfieldBackend
           private:
             uint64_t
             operator=(const uint64_t _data);
+
+            uint64_t
+            operator=(const Bitfield<first, last>& other);
         };
 
         //Similar to the above, but only allows writing.
@@ -150,6 +159,12 @@ namespace BitfieldBackend
                 this->setBits(first, last, _data);
                 return _data;
             }
+
+            int64_t
+            operator=(SignedBitfield<first, last> const & other)
+            {
+                return *this = (int64_t)other;
+            }
         };
 
         //A class which specializes the above so that it can only be read
@@ -163,6 +178,9 @@ namespace BitfieldBackend
           private:
             int64_t
             operator=(const int64_t _data);
+
+            int64_t
+            operator=(const SignedBitfield<first, last>& other);
         };
 
         //Similar to the above, but only allows writing.
@@ -173,11 +191,7 @@ namespace BitfieldBackend
             operator const int64_t () const;
 
           public:
-            int64_t operator=(const int64_t _data)
-            {
-                *((SignedBitfield<first, last> *)this) = _data;
-                return _data;
-            }
+            using SignedBitfield<first, last>::operator=;
         };
     };
 
@@ -215,6 +229,13 @@ namespace BitfieldBackend
             return _data;
         }
 
+        Type
+        operator=(BitUnionOperators const & other)
+        {
+            Base::__data = other;
+            return Base::__data;
+        }
+
         bool
         operator<(Base const & base) const
         {