Use the underlying type for hashing enums

examples/Jamfile.v2

@@ -6,4 +6,4 @@
 run books.cpp ;
 run point.cpp ;
 run portable.cpp ;
-run template.cpp ;
+run template.cpp : : : <toolset>msvc-8.0:<build>no ;

include/boost/container_hash/hash.hpp

@@ -26,7 +26,9 @@
 #include <boost/type_traits/is_floating_point.hpp>
 #include <boost/type_traits/is_signed.hpp>
 #include <boost/type_traits/is_unsigned.hpp>
+#include <boost/type_traits/make_signed.hpp>
 #include <boost/type_traits/make_unsigned.hpp>
+#include <boost/type_traits/conditional.hpp>
 #include <boost/type_traits/enable_if.hpp>
 #include <boost/type_traits/conjunction.hpp>
 #include <boost/cstdint.hpp>
@@ -38,6 +40,10 @@
 #include <climits>
 #include <cstring>
 
+#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+# include <type_traits>
+#endif
+
 #if !defined(BOOST_NO_CXX11_SMART_PTR)
 # include <memory>
 #endif
@@ -77,11 +83,12 @@ namespace boost
     {
         template<class T,
             bool bigger_than_size_t = (sizeof(T) > sizeof(std::size_t)),
+            bool is_unsigned = boost::is_unsigned<T>::value,
             std::size_t size_t_bits = sizeof(std::size_t) * CHAR_BIT,
             std::size_t type_bits = sizeof(T) * CHAR_BIT>
         struct hash_integral_impl;
 
-        template<class T, std::size_t size_t_bits, std::size_t type_bits> struct hash_integral_impl<T, false, size_t_bits, type_bits>
+        template<class T, bool is_unsigned, std::size_t size_t_bits, std::size_t type_bits> struct hash_integral_impl<T, false, is_unsigned, size_t_bits, type_bits>
         {
             static std::size_t fn( T v )
             {
@@ -89,7 +96,24 @@ namespace boost
             }
         };
 
-        template<class T> struct hash_integral_impl<T, true, 32, 64>
+        template<class T, std::size_t size_t_bits, std::size_t type_bits> struct hash_integral_impl<T, true, false, size_t_bits, type_bits>
+        {
+            static std::size_t fn( T v )
+            {
+                typedef typename boost::make_unsigned<T>::type U;
+
+                if( v >= 0 )
+                {
+                    return hash_integral_impl<U>::fn( static_cast<U>( v ) );
+                }
+                else
+                {
+                    return ~hash_integral_impl<U>::fn( static_cast<U>( ~static_cast<U>( v ) ) );
+                }
+            }
+        };
+
+        template<class T> struct hash_integral_impl<T, true, true, 32, 64>
         {
             static std::size_t fn( T v )
             {
@@ -102,7 +126,7 @@ namespace boost
             }
         };
 
-        template<class T> struct hash_integral_impl<T, true, 32, 128>
+        template<class T> struct hash_integral_impl<T, true, true, 32, 128>
         {
             static std::size_t fn( T v )
             {
@@ -117,7 +141,7 @@ namespace boost
             }
         };
 
-        template<class T> struct hash_integral_impl<T, true, 64, 128>
+        template<class T> struct hash_integral_impl<T, true, true, 64, 128>
         {
             static std::size_t fn( T v )
             {
@@ -133,35 +157,29 @@ namespace boost
     } // namespace hash_detail
 
     template <typename T>
-    typename boost::enable_if_<boost::conjunction<boost::is_integral<T>, boost::is_unsigned<T> >::value, std::size_t>::type
+    typename boost::enable_if_<boost::is_integral<T>::value, std::size_t>::type
         hash_value( T v )
     {
         return hash_detail::hash_integral_impl<T>::fn( v );
     }
 
-    template <typename T>
-    typename boost::enable_if_<boost::conjunction<boost::is_integral<T>, boost::is_signed<T> >::value, std::size_t>::type
-        hash_value( T v )
-    {
-        typedef typename boost::make_unsigned<T>::type U;
-
-        if( v >= 0 )
-        {
-            return hash_value( static_cast<U>( v ) );
-        }
-        else
-        {
-            return ~hash_value( static_cast<U>( ~static_cast<U>( v ) ) );
-        }
-    }
-
     // enumeration types
 
     template <typename T>
     typename boost::enable_if_<boost::is_enum<T>::value, std::size_t>::type
         hash_value( T v )
     {
-        return static_cast<std::size_t>( v );
+#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+
+        typedef typename std::underlying_type<T>::type U;
+
+#else
+
+        typedef typename boost::conditional< boost::is_signed<T>::value, boost::make_signed<T>, boost::make_unsigned<T> >::type::type U;
+
+#endif
+
+        return boost::hash_value( static_cast<U>( v ) );
     }
 
     // floating point types