Sort linked list with size at most 16 and limited to numeric element value.

vb16sort.c

/* Concate lists in arr. No dummy head required for the list */
struct list_head *b16sort(struct list_head *arr[])
{
    struct list_head *begin = 0, *end = 0, *tmp = 0;
    int size = 0;
    for (int i = 0; i < 15; i++) {
        if (arr[i] != 0) {
            tmp = arr[i]->prev;
            if (size != 0) {
                end->next = arr[i];
                arr[i]->prev = end;
            }
            end = tmp;
            size += 1;
            if (size == 1)
                begin = arr[i];
        }
    }
    if (size != 0) {
        begin->prev = end;
        end->next = begin;
    }
    return begin;
}

void q_vbsort(struct list_head *head)
{
    struct list_head *arr[16], *itr, *safe;
    memset(arr, 0, sizeof(struct list_head *) * 16);
    list_for_each_safe (itr, safe, head) {
        INIT_LIST_HEAD(itr);
        element_t *entry = list_entry(itr, element_t, list);

        int value = atoi(entry->value);
        if (arr[value] != 0) {
            list_add(itr, arr[value]);
        } else {
            arr[value] = itr;
        }
    }
    list_add_tail(head, b16sort(arr));
}