--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/metaprogramming/primitiveConversions.hpp Wed Aug 23 14:01:17 2017 +0200
@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP
+#define SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP
+
+#include "memory/allocation.hpp"
+#include "metaprogramming/enableIf.hpp"
+#include "metaprogramming/integralConstant.hpp"
+#include "metaprogramming/isFloatingPoint.hpp"
+#include "metaprogramming/isIntegral.hpp"
+#include "metaprogramming/isRegisteredEnum.hpp"
+#include "utilities/debug.hpp"
+
+class PrimitiveConversions : public AllStatic {
+public:
+ // Return a value of type T with the same representation as x.
+ //
+ // T and U must be of the same size.
+ //
+ // At least one of T or U must be an integral type. The other must
+ // be an integral, floating point, or pointer type.
+ template<typename T, typename U> static T cast(U x);
+
+ // Support thin wrappers over primitive types.
+ // If derived from TrueType, provides representational conversion
+ // from T to some other type. When true, must provide
+ // - Value: typedef for T.
+ // - Decayed: typedef for decayed type.
+ // - static Decayed decay(T x): return value of type Decayed with
+ // the same representation as x.
+ // - static T recover(Decayed x): return a value of type T with the
+ // same representation as x.
+ template<typename T> struct Translate : public FalseType {};
+
+private:
+
+ template<typename T,
+ typename U,
+ bool same_size = sizeof(T) == sizeof(U),
+ typename Enable = void>
+ struct Cast;
+
+ template<typename T, typename U> static T cast_using_union(U x);
+};
+
+// Return an object of type T with the same value representation as x.
+//
+// T and U must be of the same size. It is expected that one of T and
+// U is an integral type, and the other is an integral type, a
+// (registered) enum type, or a floating point type
+//
+// This implementation uses the "union trick", which seems to be the
+// best of a bad set of options. Though technically undefined
+// behavior, it is widely and well supported, producing good code. In
+// some cases, such as gcc, that support is explicitly documented.
+//
+// Using memcpy is the correct method, but some compilers produce
+// wretched code for that method, even at maximal optimization levels.
+//
+// Using static_cast is only possible for integral and enum types, not
+// for floating point types. And for integral and enum conversions,
+// static_cast has unspecified or implementation-defined behavior for
+// some cases. C++11 <type_traits> can be used to avoid most or all
+// of those unspecified or implementation-defined issues, though that
+// may require multi-step conversions.
+//
+// Using reinterpret_cast of references has undefined behavior for
+// many cases, and there is much less empirical basis for its use, as
+// compared to the union trick.
+template<typename T, typename U>
+inline T PrimitiveConversions::cast_using_union(U x) {
+ STATIC_ASSERT(sizeof(T) == sizeof(U));
+ union { T t; U u; };
+ u = x;
+ return t;
+}
+
+//////////////////////////////////////////////////////////////////////////////
+// cast<T>(x)
+//
+// Cast<T, U, same_size, Enable>
+
+// Give an informative error if the sizes differ.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<T, U, false> VALUE_OBJ_CLASS_SPEC {
+ STATIC_ASSERT(sizeof(T) == sizeof(U));
+};
+
+// Conversion between integral types.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<
+ T, U, true,
+ typename EnableIf<IsIntegral<T>::value && IsIntegral<U>::value>::type>
+ VALUE_OBJ_CLASS_SPEC
+{
+ T operator()(U x) const { return cast_using_union<T>(x); }
+};
+
+// Convert an enum or floating point value to an integer value.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<
+ T, U, true,
+ typename EnableIf<IsIntegral<T>::value &&
+ (IsRegisteredEnum<U>::value ||
+ IsFloatingPoint<U>::value)>::type>
+ VALUE_OBJ_CLASS_SPEC
+{
+ T operator()(U x) const { return cast_using_union<T>(x); }
+};
+
+// Convert an integer to an enum or floating point value.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<
+ T, U, true,
+ typename EnableIf<IsIntegral<U>::value &&
+ (IsRegisteredEnum<T>::value ||
+ IsFloatingPoint<T>::value)>::type>
+ VALUE_OBJ_CLASS_SPEC
+{
+ T operator()(U x) const { return cast_using_union<T>(x); }
+};
+
+// Convert a pointer to an integral value.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<
+ T, U*, true,
+ typename EnableIf<IsIntegral<T>::value>::type>
+ VALUE_OBJ_CLASS_SPEC
+{
+ T operator()(U* x) const { return reinterpret_cast<T>(x); }
+};
+
+// Convert an integral value to a pointer.
+template<typename T, typename U>
+struct PrimitiveConversions::Cast<
+ T*, U, true,
+ typename EnableIf<IsIntegral<U>::value>::type>
+ VALUE_OBJ_CLASS_SPEC
+{
+ T* operator()(U x) const { return reinterpret_cast<T*>(x); }
+};
+
+template<typename T, typename U>
+inline T PrimitiveConversions::cast(U x) {
+ return Cast<T, U>()(x);
+}
+
+#endif // SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP