alignedallocator.hh

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// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
// vi: set et ts=4 sw=4 sts=4:
#ifndef EWOMS_ALIGNED_ALLOCATOR_HH
#define EWOMS_ALIGNED_ALLOCATOR_HH

#include <cassert>
#include <cstdlib>
#include <memory>
#include <type_traits>
#include <utility>

namespace Opm {

namespace detail {

constexpr inline bool is_alignment(std::size_t value) noexcept
{
    return (value > 0) && ((value & (value - 1)) == 0);
}

template<std::size_t N>
struct is_alignment_constant
    : std::integral_constant<bool, (N > 0) && ((N & (N - 1)) == 0)>
{};

template<std::size_t A, std::size_t B>
struct min_size
    : std::integral_constant<std::size_t, (A < B) ? A : B>
{};

template<class T>
struct offset_object
{
    char offset;
    T object;
};

template<class T>
struct alignment_of
    : min_size<sizeof(T), sizeof(offset_object<T>) - sizeof(T)>::type
{};

template<std::size_t A, std::size_t B>
struct max_align
    : std::integral_constant<std::size_t,(A > B) ? A : B>
{};

template<class T>
struct max_count_of
    : std::integral_constant<std::size_t, ~static_cast<std::size_t>(0) / sizeof(T)>
{};

using std::addressof;

}

inline void* aligned_alloc(std::size_t alignment,
                           std::size_t size) noexcept
{
    assert(detail::is_alignment(alignment));
    if (alignment < sizeof(void*)) {
        alignment = sizeof(void*);
    }
    void* p;
    if (::posix_memalign(&p, alignment, size) != 0) {
        p = 0;
    }
    return p;
}

inline void aligned_free(void* ptr)
    noexcept
{
    ::free(ptr);
}

template<class T, std::size_t Alignment>
class aligned_allocator
{
    static_assert(detail::is_alignment_constant<Alignment>::value, "Alignment must be powers of two!");

public:
    using value_type = T;
    using pointer = T*;
    using const_pointer = const T*;
    using void_pointer = void*;
    using const_void_pointer = const void*;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    using reference = T&;
    using const_reference = const T&;

private:
    using MaxAlign = detail::max_align<Alignment, detail::alignment_of<value_type>::value>;

public:
    template<class U>
    struct rebind
    {
        using other = aligned_allocator<U, Alignment>;
    };

    aligned_allocator() noexcept = default;

    template<class U>
    aligned_allocator(const aligned_allocator<U,
                      Alignment>&) noexcept
    {}

    pointer address(reference value) const noexcept
    {
        return detail::addressof(value);
    }

    const_pointer address(const_reference value) const noexcept
    {
        return detail::addressof(value);
    }

    pointer allocate(size_type size,
                     const_void_pointer = 0)
    {
        void* p = aligned_alloc(MaxAlign::value,
                                sizeof(T) * size);
        if (!p && size > 0) {
            throw std::bad_alloc();
        }
        return static_cast<T*>(p);
    }

    void deallocate(pointer ptr, size_type)
    {
        aligned_free(ptr);
    }

    constexpr size_type max_size() const noexcept
    {
        return detail::max_count_of<T>::value;
    }

    template<class U, class... Args>
    void construct(U* ptr, Args&&... args)
    {
        void* p = ptr;
        ::new(p) U(std::forward<Args>(args)...);
    }

    template<class U>
    void construct(U* ptr)
    {
        void* p = ptr;
        ::new(p) U();
    }

    template<class U>
    void destroy(U* ptr)
    {
        (void)ptr;
        ptr->~U();
    }
};

template<std::size_t Alignment>
class aligned_allocator<void, Alignment>
{
    static_assert(detail::is_alignment_constant<Alignment>::value,
                  "The specified alignment is not a power of two!");

public:
    using value_type = void;
    using pointer = void*;
    using const_pointer = const void*;

    template<class U>
    struct rebind
    {
        using other = aligned_allocator<U, Alignment>;
    };
};

template<class T1, class T2, std::size_t Alignment>
inline bool operator==(const aligned_allocator<T1,
                       Alignment>&, const aligned_allocator<T2,
                       Alignment>&) noexcept
{
    return true;
}

template<class T1, class T2, std::size_t Alignment>
inline bool operator!=(const aligned_allocator<T1,
                       Alignment>&, const aligned_allocator<T2,
                       Alignment>&) noexcept
{
    return false;
}
}

#endif