/*

 * 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

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 */

#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