Function rt_smem_alloc

src/mem.c:271–389

* @brief Allocate a block of memory with a minimum of 'size' bytes. * * @param m the small memory management object. * * @param size is the minimum size of the requested block in bytes. * * @return the pointer to allocated memory or NULL if no free memory was found. */

 * @return the pointer to allocated memory or NULL if no free memory was found.
 */
void *rt_smem_alloc(rt_smem_t m, rt_size_t size)
{
    rt_size_t ptr, ptr2;
    struct rt_small_mem_item *mem, *mem2;
    struct rt_small_mem *small_mem;

    if (size == 0)
        return RT_NULL;

    RT_ASSERT(m != RT_NULL);
    RT_ASSERT(rt_object_get_type(&m->parent) == RT_Object_Class_Memory);
    RT_ASSERT(rt_object_is_systemobject(&m->parent));

    small_mem = (struct rt_small_mem *)m;
    /* alignment size */
    size = RT_ALIGN(size, RT_ALIGN_SIZE);

    /* every data block must be at least MIN_SIZE_ALIGNED long */
    if (size < MIN_SIZE_ALIGNED)
        size = MIN_SIZE_ALIGNED;

    if (size > small_mem->mem_size_aligned)
    {
        LOG_D("no memory");

        return RT_NULL;
    }

    for (ptr = (rt_uint8_t *)small_mem->lfree - small_mem->heap_ptr;
         ptr <= small_mem->mem_size_aligned - size;
         ptr = ((struct rt_small_mem_item *)&small_mem->heap_ptr[ptr])->next)
    {
        mem = (struct rt_small_mem_item *)&small_mem->heap_ptr[ptr];

        if ((!MEM_ISUSED(mem)) && (mem->next - (ptr + SIZEOF_STRUCT_MEM)) >= size)
        {
            /* mem is not used and at least perfect fit is possible:
             * mem->next - (ptr + SIZEOF_STRUCT_MEM) gives us the 'user data size' of mem */

            if (mem->next - (ptr + SIZEOF_STRUCT_MEM) >=
                (size + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED))
            {
                /* (in addition to the above, we test if another struct rt_small_mem_item (SIZEOF_STRUCT_MEM) containing
                 * at least MIN_SIZE_ALIGNED of data also fits in the 'user data space' of 'mem')
                 * -> split large block, create empty remainder,
                 * remainder must be large enough to contain MIN_SIZE_ALIGNED data: if
                 * mem->next - (ptr + (2*SIZEOF_STRUCT_MEM)) == size,
                 * struct rt_small_mem_item would fit in but no data between mem2 and mem2->next
                 * @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty
                 *       region that couldn't hold data, but when mem->next gets freed,
                 *       the 2 regions would be combined, resulting in more free memory
                 */
                ptr2 = ptr + SIZEOF_STRUCT_MEM + size;

                /* create mem2 struct */
                mem2       = (struct rt_small_mem_item *)&small_mem->heap_ptr[ptr2];
                mem2->pool_ptr = MEM_FREED(small_mem);
                mem2->next = mem->next;