alignedallocator.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_ALIGNED_ALLOCATOR_HH
#define DUNE_ALIGNED_ALLOCATOR_HH

#include "mallocallocator.hh"
#include <cstdlib>
#include <type_traits>

namespace Dune
{

  template<class T, int Alignment = -1>
  class AlignedAllocator : public MallocAllocator<T> {

#if __APPLE__

    /*
     * macOS has pretty draconian restrictions on the
     * alignments that you may ask for: It has to be
     *
     * 1) a power of 2
     * 2) at least as large as sizeof(void*)
     *
     * So here is a little constexpr function that calculates just that
     * (together with the correct starting value for align fed in further down).
     */
    static constexpr int fixAlignment(int align)
    {
      return ((Alignment==-1) ? std::alignment_of<T>::value : Alignment) > align
        ? fixAlignment(align << 1) : align;
    }

#else

    /*
     * Non-Apple platforms we just have to check whether an explicit alignment was
     * restricted or fall back to the default alignment of T.
     */
    static constexpr int fixAlignment(int align)
    {
      return (Alignment==-1) ? std::alignment_of<T>::value : Alignment;
    }

#endif

  public:
    using pointer = typename MallocAllocator<T>::pointer;
    using size_type = typename MallocAllocator<T>::size_type;
    template <class U> struct rebind {
      typedef AlignedAllocator<U,Alignment> other;
    };

    static constexpr int alignment = fixAlignment(sizeof(void*));

    pointer allocate(size_type n, [[maybe_unused]] const void* hint = 0)
    {
      if (n > this->max_size())
        throw std::bad_alloc();

#if __APPLE__
      // Apple is also restrictive regarding the allocation size.
      // size must be at least the alignment size.
      size_type size = n * sizeof(T) >= alignment ? n * sizeof(T) : alignment;
#else
      size_type size = n * sizeof(T);
#endif

      /*
       * Everybody else gets the standard treatment.
       */
#if defined(_MSC_VER)
      pointer ret = static_cast<pointer>(_aligned_malloc(alignment, size));
#else
      pointer ret = static_cast<pointer>(std::aligned_alloc(alignment, size));
#endif
      if (!ret)
        throw std::bad_alloc();

      return ret;
    }

#if defined(_MSC_VER)
    void deallocate(pointer p, [[maybe_unused]] size_type n)
    {
        _aligned_free(p);
    }
#endif
  };

}

#endif // DUNE_ALIGNED_ALLOCATOR_HH