/*
 *  Copyright 2017 NVIDIA Corporation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/*! \file alignment.h
 *  \brief Type-alignment utilities.
 */

#pragma once

#include <thrust/detail/config.h>

#include <thrust/detail/type_traits.h> // For `integral_constant`.

#include <cstddef> // For `std::size_t` and `std::max_align_t`.
#include <type_traits> // For `std::alignment_of`.

THRUST_NAMESPACE_BEGIN

namespace detail
{

/// \p alignment_of provides the member constant `value` which is equal to the
/// alignment requirement of the type `T`, as if obtained by a C++11 `alignof`
/// expression.
///
/// It is an implementation of C++11's \p std::alignment_of.
template <typename T>
using alignment_of = std::alignment_of<T>;

/// \p aligned_type provides the nested type `type`, which is a trivial
/// type whose alignment requirement is a divisor of `Align`.
///
/// The behavior is undefined if `Align` is not a power of 2.
template <std::size_t Align>
struct aligned_type;

#if (THRUST_HOST_COMPILER == THRUST_HOST_COMPILER_GCC) && (THRUST_GCC_VERSION >= 40800)
// C++11 implementation, excluding GCC 4.7, which doesn't have `alignas`.
template <std::size_t Align>
struct aligned_type
{
  struct alignas(Align) type
  {};
};
#elif (THRUST_HOST_COMPILER == THRUST_HOST_COMPILER_MSVC) \
  || ((THRUST_HOST_COMPILER == THRUST_HOST_COMPILER_GCC) && (THRUST_GCC_VERSION < 40600))
// C++03 implementation for MSVC and GCC <= 4.5.
//
// We have to implement `aligned_type` with specializations for MSVC
// and GCC 4.2.x and older because they require literals as arguments to
// their alignment attribute.

#  if (THRUST_HOST_COMPILER == THRUST_HOST_COMPILER_MSVC)
// MSVC implementation.
#    define THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(X) \
      template <>                                        \
      struct aligned_type<X>                             \
      {                                                  \
        __declspec(align(X)) struct type                 \
        {};                                              \
      };                                                 \
      /**/
#  else
// GCC <= 4.2 implementation.
#    define THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(X) \
      template <>                                        \
      struct aligned_type<X>                             \
      {                                                  \
        struct type                                      \
        {                                                \
        } __attribute__((aligned(X)));                   \
      };                                                 \
      /**/
#  endif

THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(1);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(2);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(4);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(8);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(16);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(32);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(64);
THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION(128);

#  undef THRUST_DEFINE_ALIGNED_TYPE_SPECIALIZATION
#else
// C++03 implementation for GCC > 4.5, Clang, PGI, ICPC, and xlC.
template <std::size_t Align>
struct aligned_type
{
  struct type
  {
  } __attribute__((aligned(Align)));
};
#endif

/// \p aligned_storage provides the nested type `type`, which is a trivial type
/// suitable for use as uninitialized storage for any object whose size is at
/// most `Len` bytes and whose alignment requirement is a divisor of `Align`.
///
/// It is an implementation of C++11's \p std::max_align_t.
#if (THRUST_HOST_COMPILER == THRUST_HOST_COMPILER_GCC) && (THRUST_GCC_VERSION >= 40900)

// GCC 4.7 and 4.8 don't have `std::max_align_t`.
using max_align_t = std::max_align_t;
#else
union max_align_t
{
  // These cannot be private because C++03 POD types cannot have private
  // data members.
  char c;
  short s;
  int i;
  long l;
  float f;
  double d;
  long long ll;
  long double ld;
  void* p;
};
#endif

/// \p aligned_reinterpret_cast `reinterpret_cast`s \p u of type \p U to `void*`
/// and then `reinterpret_cast`s the result to \p T. The indirection through
/// `void*` suppresses compiler warnings when the alignment requirement of \p *u
/// is less than the alignment requirement of \p *t. The caller of
/// \p aligned_reinterpret_cast is responsible for ensuring that the alignment
/// requirements are actually satisified.
template <typename T, typename U>
THRUST_HOST_DEVICE T aligned_reinterpret_cast(U u)
{
  return reinterpret_cast<T>(reinterpret_cast<void*>(u));
}

THRUST_HOST_DEVICE inline std::size_t aligned_storage_size(std::size_t n, std::size_t align)
{
  return ((n + align - 1) / align) * align;
}

} // end namespace detail

THRUST_NAMESPACE_END
