aligned_allocator.h

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/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * STL allocator for aligned memory
 */

#ifndef ALIGNED_ALLOCATOR
#define ALIGNED_ALLOCATOR

#include "lib/bits.h"   // round_up
#include "lib/sysdep/arch/x86_x64/cache.h"
#include "lib/sysdep/rtl.h" // rtl_AllocateAligned


/**
 * stateless STL allocator that aligns elements to the L1 cache line size.
 *
 * note: the alignment is hard-coded to avoid any allocator state.
 * this avoids portability problems, which is important since allocators
 * are rather poorly specified.
 *
 * references:
 * http://www.tantalon.com/pete/customallocators.ppt
 * http://www.flipcode.com/archives/Aligned_Block_Allocation.shtml
 * http://www.josuttis.com/cppcode/allocator.html
 *
 * derived from code that bears the following copyright notice:
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 **/
template<class T>
class AlignedAllocator
{
public:
    // type definitions
    typedef T        value_type;
    typedef T*       pointer;
    typedef const T* const_pointer;
    typedef T&       reference;
    typedef const T& const_reference;
    typedef std::size_t    size_type;
    typedef std::ptrdiff_t difference_type;

    // rebind allocator to type U
    template <class U>
    struct rebind
    {
        typedef AlignedAllocator<U> other;
    };

    pointer address(reference value) const
    {
        return &value;
    }

    const_pointer address(const_reference value) const
    {
        return &value;
    }

    NOTHROW_DEFINE AlignedAllocator()
    {
    }

    NOTHROW_DEFINE AlignedAllocator(const AlignedAllocator&)
    {
    }

    template <class U>
    NOTHROW_DEFINE AlignedAllocator (const AlignedAllocator<U>&)
    {
    }

    NOTHROW_DEFINE ~AlignedAllocator()
    {
    }

    NOTHROW_DEFINE size_type max_size() const
    {
        // maximum number of *elements* that can be allocated
        return std::numeric_limits<std::size_t>::max() / sizeof(T);
    }

    // allocate uninitialized storage
    pointer allocate(size_type numElements)
    {
        const size_type alignment = x86_x64::Caches(x86_x64::L1D)->entrySize;
        const size_type elementSize = round_up(sizeof(T), alignment);
        const size_type size = numElements * elementSize;
        pointer p = (pointer)rtl_AllocateAligned(size, alignment);
        return p;
    }

    // deallocate storage of elements that have been destroyed
    void deallocate(pointer p, size_type UNUSED(num))
    {
        rtl_FreeAligned((void*)p);
    }

    void construct(pointer p, const T& value)
    {
        new((void*)p) T(value);
    }

    void destroy(pointer p)
    {
        p->~T();
        UNUSED2(p); // otherwise, warning is raised for reasons unknown
    }
};

// indicate that all specializations of this allocator are interchangeable
template <class T1, class T2>
NOTHROW_DEFINE bool operator==(const AlignedAllocator<T1>&, const AlignedAllocator<T2>&)
{
    return true;
}

template <class T1, class T2>
NOTHROW_DEFINE bool operator!=(const AlignedAllocator<T1>&, const AlignedAllocator<T2>&)
{
    return false;
}

#endif  // #ifndef ALIGNED_ALLOCATOR