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/* SPDX-License-Identifier: GPL-2.0-or-later */
#pragma once
/** \file
* \ingroup bli
*
* An `Allocator` can allocate and deallocate memory. It is used by containers such as
* blender::Vector. The allocators defined in this file do not work with standard library
* containers such as std::vector.
*
* Every allocator has to implement two methods:
* void *allocate(size_t size, size_t alignment, const char *name);
* void deallocate(void *ptr);
*
* We don't use the std::allocator interface, because it does more than is really necessary for an
* allocator and has some other quirks. It mixes the concepts of allocation and construction. It is
* essentially forced to be a template, even though the allocator should not care about the type.
* Also see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2271.html#std_allocator. Some
* of these aspects have been improved in new versions of C++, so we might have to reevaluate the
* strategy later on.
*
* The allocator interface dictated by this file is very simplistic, but for now that is all we
* need. More complexity can be added when it seems necessary.
*/
#include <algorithm>
#include <stdlib.h>
#include "MEM_guardedalloc.h"
#include "BLI_math_base.h"
#include "BLI_utildefines.h"
namespace blender {
/**
* Use Blender's guarded allocator (aka MEM_*). This should always be used except there is a
* good reason not to use it.
*/
class GuardedAllocator {
public:
void *allocate(size_t size, size_t alignment, const char *name)
{
/* Should we use MEM_mallocN, when alignment is small? If yes, how small must alignment be? */
return MEM_mallocN_aligned(size, alignment, name);
}
void deallocate(void *ptr)
{
MEM_freeN(ptr);
}
};
/**
* This is a wrapper around malloc/free. Only use this when the GuardedAllocator cannot be
* used. This can be the case when the allocated memory might live longer than Blender's
* allocator. For example, when the memory is owned by a static variable.
*/
class RawAllocator {
private:
struct MemHead {
int offset;
};
public:
void *allocate(size_t size, size_t alignment, const char * /*name*/)
{
BLI_assert(is_power_of_2_i(int(alignment)));
void *ptr = malloc(size + alignment + sizeof(MemHead));
void *used_ptr = reinterpret_cast<void *>(
uintptr_t(POINTER_OFFSET(ptr, alignment + sizeof(MemHead))) & ~(uintptr_t(alignment) - 1));
int offset = int(intptr_t(used_ptr) - intptr_t(ptr));
BLI_assert(offset >= int(sizeof(MemHead)));
(static_cast<MemHead *>(used_ptr) - 1)->offset = offset;
return used_ptr;
}
void deallocate(void *ptr)
{
MemHead *head = static_cast<MemHead *>(ptr) - 1;
int offset = -head->offset;
void *actual_pointer = POINTER_OFFSET(ptr, offset);
free(actual_pointer);
}
};
} // namespace blender
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