Allocator

/*  This file is part of the Vc library. {{{
Copyright © 2014 Matthias Kretz <kretz@kde.org>

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}}}*/

#ifndef VC_ALLOCATOR_H_
#define VC_ALLOCATOR_H_

#include <new>
#include <cstddef>
#include <cstdlib>
#include <utility>

#include "global.h"
#include "common/macros.h"

/**
 * \ingroup Utilities
 *
 * Convenience macro to set the default allocator for a given \p Type to
 * Vc::Allocator.
 *
 * \param Type Your type that you want to use with STL containers.
 *
 * \note You have to use this macro in the global namespace.
 */
#ifdef Vc_MSVC
#define Vc_DECLARE_ALLOCATOR(Type)                                                   \
namespace std                                                                        \
{                                                                                    \
template <> class allocator<Type> : public ::Vc::Allocator<Type>                     \
{                                                                                    \
public:                                                                              \
    template <typename U> struct rebind {                                            \
        typedef ::std::allocator<U> other;                                           \
    };                                                                               \
    /* MSVC brokenness: the following function is optional - just doesn't compile    \
     * without it */                                                                 \
    const allocator &select_on_container_copy_construction() const { return *this; } \
};                                                                                   \
}
#else
#define Vc_DECLARE_ALLOCATOR(Type)                                                   \
namespace std                                                                        \
{                                                                                    \
template <> class allocator<Type> : public ::Vc::Allocator<Type>                     \
{                                                                                    \
public:                                                                              \
    template <typename U> struct rebind {                                            \
        typedef ::std::allocator<U> other;                                           \
    };                                                                               \
};                                                                                   \
}
#endif

namespace Vc_VERSIONED_NAMESPACE
{
    using std::size_t;
    using std::ptrdiff_t;

    /**
     * \headerfile Allocator <Vc/Allocator>
     * An allocator that uses global new and supports over-aligned types, as per [C++11 20.6.9].
     *
     * Meant as a simple replacement for the allocator defined in the C++ Standard.
     * Allocation is done using the global new/delete operators. But if the alignment property of \p
     * T is larger than the size of a pointer, the allocate function allocates slightly more memory
     * to adjust the pointer for correct alignment.
     *
     * If the \p T does not require over-alignment no additional memory will be allocated.
     *
     * \tparam T The type of objects to allocate.
     *
     * Example:
     * \code
     * struct Data {
     *   Vc::float_v x, y, z;
     * };
     *
     * void fun()
     * {
     *   std::vector<Data> dat0; // this will use std::allocator<Data>, which probably ignores the
     *                           // alignment requirements for Data. Thus any access to dat0 may
     *                           // crash your program.
     *
     *   std::vector<Data, Vc::Allocator<Data> > dat1; // now std::vector will get correctly aligned
     *                           // memory. Accesses to dat1 are safe.
     *   ...
     * \endcode
     *
     * %Vc ships a macro to conveniently tell STL to use Vc::Allocator per default for a given type:
     * \code
     * struct Data {
     *   Vc::float_v x, y, z;
     * };
     * Vc_DECLARE_ALLOCATOR(Data)
     *
     * void fun()
     * {
     *   std::vector<Data> dat0; // good now
     *   ...
     * \endcode
     *
     * \ingroup Utilities
     */
    template<typename T> class Allocator
    {
    private:
        enum Constants {
#ifdef Vc_HAVE_STD_MAX_ALIGN_T
            NaturalAlignment = alignof(std::max_align_t),
#elif defined(Vc_HAVE_MAX_ALIGN_T)
            NaturalAlignment = alignof(::max_align_t),
#else
            NaturalAlignment = sizeof(void *) > alignof(long double) ? sizeof(void *) :
                (alignof(long double) > alignof(long long) ? alignof(long double) : alignof(long long)),
#endif
#if defined Vc_IMPL_AVX
            SimdAlignment = 32,
#elif defined Vc_IMPL_SSE
            SimdAlignment = 16,
#else
            SimdAlignment = 1,
#endif
            Alignment = alignof(T) > SimdAlignment ? alignof(T) : SimdAlignment,
            /* The number of extra bytes allocated must be large enough to put a pointer right
             * before the adjusted address. This pointer stores the original address, which is
             * required to call ::operator delete in deallocate.
             *
             * The address we get from ::operator new is a multiple of NaturalAlignment:
             *   p = N * NaturalAlignment
             *
             * Since all alignments are powers of two, Alignment is a multiple of NaturalAlignment:
             *   Alignment = k * NaturalAlignment
             *
             * two cases:
             * 1. If p is already aligned to Alignment then allocate will return p + Alignment. In
             *    this case there are Alignment Bytes available to store a pointer.
             * 2. If p is not aligned then p + (k - (N modulo k)) * NaturalAlignment will be
             *    returned. Since NaturalAlignment >= sizeof(void*) the pointer fits.
             */
            ExtraBytes = Alignment > NaturalAlignment ? Alignment : 0,
            AlignmentMask = Alignment - 1
        };
    public:
        typedef size_t    size_type;
        typedef ptrdiff_t difference_type;
        typedef T*        pointer;
        typedef const T*  const_pointer;
        typedef T&        reference;
        typedef const T&  const_reference;
        typedef T         value_type;

        template<typename U> struct rebind { typedef Allocator<U> other; };

        Allocator() throw() { }
        Allocator(const Allocator&) throw() { }
        template<typename U> Allocator(const Allocator<U>&) throw() { }

        pointer address(reference x) const { return &x; }
        const_pointer address(const_reference x) const { return &x; }

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

            char *p = static_cast<char *>(::operator new(n * sizeof(T) + ExtraBytes));
            if (ExtraBytes > 0) {
                char *const pp = p;
                p += ExtraBytes;
                const char *null = 0;
                p -= ((p - null) & AlignmentMask); // equivalent to p &= ~AlignmentMask;
                reinterpret_cast<char **>(p)[-1] = pp;
            }
            return reinterpret_cast<pointer>(p);
        }

        void deallocate(pointer p, size_type)
        {
            if (ExtraBytes > 0) {
                p = reinterpret_cast<pointer *>(p)[-1];
            }
            ::operator delete(p);
        }

        size_type max_size() const throw() { return size_t(-1) / sizeof(T); }

#ifdef Vc_MSVC
        // MSVC brokenness: the following function is optional - just doesn't compile without it
        const Allocator &select_on_container_copy_construction() const { return *this; }

        // MSVC also requires a function that neither C++98 nor C++11 mention
        // but it doesn't support variadic templates... otherwise the Vc_CXX11 clause would be nice
        void construct(pointer p) { ::new(p) T(); }

        // we still need the C++98 version:
        void construct(pointer p, const T& val) { ::new(p) T(val); }
        void destroy(pointer p) { p->~T(); }
#else
        template<typename U, typename... Args> void construct(U* p, Args&&... args)
        {
            ::new(p) U(std::forward<Args>(args)...);
        }
        template<typename U> void destroy(U* p) { p->~U(); }
#endif
    };

    template<typename T> inline bool operator==(const Allocator<T>&, const Allocator<T>&) { return true;  }
    template<typename T> inline bool operator!=(const Allocator<T>&, const Allocator<T>&) { return false; }

}

#include "vector.h"
namespace std
{
    template<typename T> class allocator<Vc::Vector<T> > : public ::Vc::Allocator<Vc::Vector<T> >
    {
    public:
        template<typename U> struct rebind { typedef ::std::allocator<U> other; };
#ifdef Vc_MSVC
        // MSVC brokenness: the following function is optional - just doesn't compile without it
        const allocator &select_on_container_copy_construction() const { return *this; }
#endif
    };
    template <typename T>
    class allocator<Vc::Mask<T>> : public ::Vc::Allocator<Vc::Mask<T>>
    {
    public:
        template<typename U> struct rebind { typedef ::std::allocator<U> other; };
#ifdef Vc_MSVC
        // MSVC brokenness: the following function is optional - just doesn't compile without it
        const allocator &select_on_container_copy_construction() const { return *this; }
#endif
    };
    template <typename T, std::size_t N, typename V, std::size_t M>
    class allocator<Vc::SimdArray<T, N, V, M>> : public ::Vc::Allocator<Vc::SimdArray<T, N, V, M>>
    {
    public:
        template<typename U> struct rebind { typedef ::std::allocator<U> other; };
#ifdef Vc_MSVC
        // MSVC brokenness: the following function is optional - just doesn't compile without it
        const allocator &select_on_container_copy_construction() const { return *this; }
#endif
    };
    template <typename T, std::size_t N, typename V, std::size_t M>
    class allocator<Vc::SimdMaskArray<T, N, V, M>> : public ::Vc::Allocator<Vc::SimdMaskArray<T, N, V, M>>
    {
    public:
        template<typename U> struct rebind { typedef ::std::allocator<U> other; };
#ifdef Vc_MSVC
        // MSVC brokenness: the following function is optional - just doesn't compile without it
        const allocator &select_on_container_copy_construction() const { return *this; }
#endif
    };
}

#endif // VC_ALLOCATOR_H_

// vim: ft=cpp et sw=4 sts=4