int isll_rm_tail(isll *l)

isll.c

// Slow -> O(n). Return 1 if a node was removed, 0 otherwise. Untested :P
int isll_rm_tail(isll *l)
{
    if (l->head == NULL)
    {
        return 0;
    }
    if (l->head == l->tail)
    {
        return isll_rm_next(l, NULL);
    }
    isllnode *node = l->head;
    while (node->next != l->tail)
    {
        node = node->next;
    }
    return isll_rm_next(l, node);
}