base: Add a default output function for bitunion types.

This way printing bitunions with, for instance, DPRINTF actually prints
something useful. More specialized overloads will still allow printing
particular bitunion types in ways that might make more sense for that
particular type.

Change-Id: I92beb0ce07683ba8b318cf25aa73e0057e4a60ef
Reviewed-on: https://gem5-review.googlesource.com/9461
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/base/bitunion.hh

@@ -32,7 +32,9 @@
 #define __BASE_BITUNION_HH__
 
 #include <functional>
+#include <iostream>
 #include <type_traits>
+#include <typeinfo>
 
 #include "base/bitfield.hh"
 
@@ -414,4 +416,48 @@ namespace std
     };
 }
 
+
+namespace BitfieldBackend
+{
+namespace
+{
+    template<typename T>
+    std::ostream &
+    bitfieldBackendPrinter(std::ostream &os, const T &t)
+    {
+        os << t;
+        return os;
+    }
+
+    //Since BitUnions are generally numerical values and not character codes,
+    //these specializations attempt to ensure that they get cast to integers
+    //of the appropriate type before printing.
+    template <>
+    std::ostream &
+    bitfieldBackendPrinter(std::ostream &os, const char &t)
+    {
+        os << (const int)t;
+        return os;
+    }
+
+    template <>
+    std::ostream &
+    bitfieldBackendPrinter(std::ostream &os, const unsigned char &t)
+    {
+        os << (const unsigned int)t;
+        return os;
+    }
+}
+}
+
+//A default << operator which casts a bitunion to its underlying type and
+//passes it to BitfieldBackend::bitfieldBackendPrinter.
+template <typename T>
+std::ostream &
+operator << (std::ostream &os, const BitUnionType<T> &bu)
+{
+    return BitfieldBackend::bitfieldBackendPrinter(
+            os, (BitUnionBaseType<T>)bu);
+}
+
 #endif // __BASE_BITUNION_HH__

src/base/bituniontest.cc

@@ -270,3 +270,17 @@ TEST_F(BitUnionData, Templating)
     is64 = std::is_same<BitUnionBaseType<Dummy32>, uint64_t>::value;
     EXPECT_FALSE(is64);
 }
+
+TEST_F(BitUnionData, Output)
+{
+    sixtyFour = 1234567812345678;
+    std::stringstream ss;
+    ss << sixtyFour;
+    EXPECT_EQ(ss.str(), "1234567812345678");
+    ss.str("");
+
+    EmptyEight eight = 65;
+    ss << eight;
+    EXPECT_EQ(ss.str(), "65");
+    ss.str("");
+}