author | eosterlund |
Mon, 09 Oct 2017 14:39:59 +0200 | |
changeset 47609 | a1f68e415b48 |
parent 47216 | 71c04702a3d5 |
child 49364 | 601146c66cad |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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#ifndef SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP |
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#define SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP |
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#include "memory/allocation.hpp" |
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#include "metaprogramming/enableIf.hpp" |
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#include "metaprogramming/integralConstant.hpp" |
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#include "metaprogramming/isFloatingPoint.hpp" |
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#include "metaprogramming/isIntegral.hpp" |
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#include "metaprogramming/isRegisteredEnum.hpp" |
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#include "utilities/debug.hpp" |
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class PrimitiveConversions : public AllStatic { |
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public: |
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// Return a value of type T with the same representation as x. |
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// |
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// T and U must be of the same size. |
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// |
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// At least one of T or U must be an integral type. The other must |
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// be an integral, floating point, or pointer type. |
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template<typename T, typename U> static T cast(U x); |
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// Support thin wrappers over primitive types. |
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// If derived from TrueType, provides representational conversion |
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// from T to some other type. When true, must provide |
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// - Value: typedef for T. |
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// - Decayed: typedef for decayed type. |
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// - static Decayed decay(T x): return value of type Decayed with |
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// the same representation as x. |
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// - static T recover(Decayed x): return a value of type T with the |
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// same representation as x. |
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template<typename T> struct Translate : public FalseType {}; |
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private: |
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template<typename T, |
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typename U, |
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bool same_size = sizeof(T) == sizeof(U), |
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typename Enable = void> |
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struct Cast; |
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template<typename T, typename U> static T cast_using_union(U x); |
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}; |
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// Return an object of type T with the same value representation as x. |
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// |
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// T and U must be of the same size. It is expected that one of T and |
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// U is an integral type, and the other is an integral type, a |
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// (registered) enum type, or a floating point type |
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// |
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// This implementation uses the "union trick", which seems to be the |
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// best of a bad set of options. Though technically undefined |
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// behavior, it is widely and well supported, producing good code. In |
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// some cases, such as gcc, that support is explicitly documented. |
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// |
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// Using memcpy is the correct method, but some compilers produce |
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// wretched code for that method, even at maximal optimization levels. |
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// |
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// Using static_cast is only possible for integral and enum types, not |
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// for floating point types. And for integral and enum conversions, |
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// static_cast has unspecified or implementation-defined behavior for |
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// some cases. C++11 <type_traits> can be used to avoid most or all |
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// of those unspecified or implementation-defined issues, though that |
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// may require multi-step conversions. |
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// |
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// Using reinterpret_cast of references has undefined behavior for |
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// many cases, and there is much less empirical basis for its use, as |
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// compared to the union trick. |
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template<typename T, typename U> |
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inline T PrimitiveConversions::cast_using_union(U x) { |
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STATIC_ASSERT(sizeof(T) == sizeof(U)); |
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union { T t; U u; }; |
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u = x; |
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return t; |
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} |
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////////////////////////////////////////////////////////////////////////////// |
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// cast<T>(x) |
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// |
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// Cast<T, U, same_size, Enable> |
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// Give an informative error if the sizes differ. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast<T, U, false> VALUE_OBJ_CLASS_SPEC { |
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STATIC_ASSERT(sizeof(T) == sizeof(U)); |
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}; |
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// Conversion between integral types. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast< |
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T, U, true, |
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typename EnableIf<IsIntegral<T>::value && IsIntegral<U>::value>::type> |
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VALUE_OBJ_CLASS_SPEC |
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{ |
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T operator()(U x) const { return cast_using_union<T>(x); } |
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}; |
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// Convert an enum or floating point value to an integer value. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast< |
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T, U, true, |
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typename EnableIf<IsIntegral<T>::value && |
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(IsRegisteredEnum<U>::value || |
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IsFloatingPoint<U>::value)>::type> |
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VALUE_OBJ_CLASS_SPEC |
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{ |
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T operator()(U x) const { return cast_using_union<T>(x); } |
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}; |
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// Convert an integer to an enum or floating point value. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast< |
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T, U, true, |
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typename EnableIf<IsIntegral<U>::value && |
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(IsRegisteredEnum<T>::value || |
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IsFloatingPoint<T>::value)>::type> |
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VALUE_OBJ_CLASS_SPEC |
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{ |
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T operator()(U x) const { return cast_using_union<T>(x); } |
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}; |
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// Convert a pointer to an integral value. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast< |
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T, U*, true, |
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typename EnableIf<IsIntegral<T>::value>::type> |
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VALUE_OBJ_CLASS_SPEC |
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{ |
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T operator()(U* x) const { return reinterpret_cast<T>(x); } |
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}; |
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// Convert an integral value to a pointer. |
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template<typename T, typename U> |
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struct PrimitiveConversions::Cast< |
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T*, U, true, |
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typename EnableIf<IsIntegral<U>::value>::type> |
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VALUE_OBJ_CLASS_SPEC |
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{ |
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T* operator()(U x) const { return reinterpret_cast<T*>(x); } |
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}; |
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template<typename T, typename U> |
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inline T PrimitiveConversions::cast(U x) { |
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return Cast<T, U>()(x); |
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} |
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// jfloat and jdouble translation to integral types |
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template<> |
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struct PrimitiveConversions::Translate<jdouble> : public TrueType { |
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typedef double Value; |
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typedef int64_t Decayed; |
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static Decayed decay(Value x) { return PrimitiveConversions::cast<Decayed>(x); } |
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static Value recover(Decayed x) { return PrimitiveConversions::cast<Value>(x); } |
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}; |
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template<> |
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struct PrimitiveConversions::Translate<jfloat> : public TrueType { |
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typedef float Value; |
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typedef int32_t Decayed; |
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static Decayed decay(Value x) { return PrimitiveConversions::cast<Decayed>(x); } |
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static Value recover(Decayed x) { return PrimitiveConversions::cast<Value>(x); } |
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}; |
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#endif // SHARE_VM_METAPROGRAMMING_PRIMITIVECONVERSIONS_HPP |