ll.c

// I'm assuming these are 8 bytes for the moment because C doesn't have generic functions.
struct list {
    int capacity;
    int start_i;
    int end_i;
}

struct list *allocate(int size) {
    int list_size = size * sizeof(void *);
    struct list *stuff = malloc(list_size + sizeof(struct list));
    stuff -> capacity = size;
    return stuff;
}

void *pop_beginning(struct list *l) {
    void *first_item = l+sizeof(struct list)+ (sizeof(void *) * l -> start_i);
    l -> start_i++;
    return first_item;
}

void *pop_end(struct list *l) {
    // assume they're not popping too far
    void *last_item = l+sizeof(struct list) + (sizeof(void *) * l -> start_i);
    l -> end_i--;
    return last_item;
}

int push_beginning(struct list *l, void *object) {
    if (l -> start_i == 0) {
        // reallocate the list from the beginning
    }
    *(l + sizeof(struct list) + (l -> start_i-- * sizeof(void *))) = object;
    return 1;
}

int push_end(struct list *l, void *object) {
    if (l -> end_i == capacity) {
        // realloc
    }
    *(l + sizeof(struct list) + (l -> end_i++ * sizeof(void *))) = object;
    return 0;
}