Function _rpmalloc_aligned_allocate

source/extern/rpmalloc.c:2293–2409

}

static void*
_rpmalloc_aligned_allocate(heap_t* heap, size_t alignment, size_t size) {
	if (alignment <= SMALL_GRANULARITY)
		return _rpmalloc_allocate(heap, size);

#if ENABLE_VALIDATE_ARGS
	if ((size + alignment) < size) {
		errno = EINVAL;
		return 0;
	}
	if (alignment & (alignment - 1)) {
		errno = EINVAL;
		return 0;
	}
#endif

	if ((alignment <= SPAN_HEADER_SIZE) && ((size + SPAN_HEADER_SIZE) < _memory_medium_size_limit)) {
		// If alignment is less or equal to span header size (which is power of two),
		// and size aligned to span header size multiples is less than size + alignment,
		// then use natural alignment of blocks to provide alignment
		size_t multiple_size = size ? (size + (SPAN_HEADER_SIZE - 1)) & ~(uintptr_t)(SPAN_HEADER_SIZE - 1) : SPAN_HEADER_SIZE;
		rpmalloc_assert(!(multiple_size % SPAN_HEADER_SIZE), "Failed alignment calculation");
		if (multiple_size <= (size + alignment))
			return _rpmalloc_allocate(heap, multiple_size);
	}

	void* ptr = 0;
	size_t align_mask = alignment - 1;
	if (alignment <= _memory_page_size) {
		ptr = _rpmalloc_allocate(heap, size + alignment);
		if ((uintptr_t)ptr & align_mask) {
			ptr = (void*)(((uintptr_t)ptr & ~(uintptr_t)align_mask) + alignment);
			//Mark as having aligned blocks
			span_t* span = (span_t*)((uintptr_t)ptr & _memory_span_mask);
			span->flags |= SPAN_FLAG_ALIGNED_BLOCKS;
		}
		return ptr;
	}

	// Fallback to mapping new pages for this request. Since pointers passed
	// to rpfree must be able to reach the start of the span by bitmasking of
	// the address with the span size, the returned aligned pointer from this
	// function must be with a span size of the start of the mapped area.
	// In worst case this requires us to loop and map pages until we get a
	// suitable memory address. It also means we can never align to span size
	// or greater, since the span header will push alignment more than one
	// span size away from span start (thus causing pointer mask to give us
	// an invalid span start on free)
	if (alignment & align_mask) {
		errno = EINVAL;
		return 0;
	}
	if (alignment >= _memory_span_size) {
		errno = EINVAL;
		return 0;
	}

	size_t extra_pages = alignment / _memory_page_size;