Update hash_value for pointers to handle the case when uintptr_t is larger than size_t

include/boost/container_hash/hash.hpp

@@ -163,6 +163,20 @@ namespace boost
     typename boost::enable_if_<boost::is_enum<T>::value, std::size_t>::type
         hash_value( T v )
     {
+        // This should in principle return the equivalent of
+        //
+        // boost::hash_value( to_underlying(v) );
+        //
+        // However, the C++03 implementation of underlying_type,
+        //
+        // conditional<is_signed<T>, make_signed<T>, make_unsigned<T>>::type::type
+        //
+        // generates a legitimate -Wconversion warning in is_signed,
+        // because -1 is not a valid enum value when all the enumerators
+        // are nonnegative.
+        //
+        // So the legacy implementation will have to do for now.
+
         return static_cast<std::size_t>( v );
     }
 
@@ -330,12 +344,11 @@ namespace boost
 
     // pointer types
 
-    // Implementation by Alberto Barbati and Dave Harris.
+    // `x + (x >> 3)` adjustment by Alberto Barbati and Dave Harris.
     template <class T> std::size_t hash_value( T* const& v )
     {
-        std::size_t x = static_cast<std::size_t>(
-           reinterpret_cast<boost::uintptr_t>(v));
-        return x + (x >> 3);
+        boost::uintptr_t x = reinterpret_cast<boost::uintptr_t>( v );
+        return boost::hash_value( x + (x >> 3) );
     }
 
     // array types