/*
 * AVL tree implementation from libavl project.
 */

#include "yagl_avl.h"
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Creates and returns a new table
 * with comparison function |compare| using parameter |param|
 * and memory allocator |allocator|.
 * Returns |NULL| if memory allocation failed.
 */
struct yagl_avl_table *yagl_avl_create(yagl_avl_comparison_func *compare,
    void *param,
    struct yagl_libavl_allocator *allocator)
{
    struct yagl_avl_table *tree;

    assert(compare != NULL);

    if (allocator == NULL) {
        allocator = &yagl_avl_allocator_default;
    }

    tree = allocator->libavl_malloc(allocator, sizeof(*tree));
    if (tree == NULL) {
        return NULL;
    }

    tree->avl_root = NULL;
    tree->avl_compare = compare;
    tree->avl_param = param;
    tree->avl_alloc = allocator;
    tree->avl_count = 0;
    tree->avl_generation = 0;

    return tree;
}

/*
 * Search |tree| for an item matching |item|, and return it if found.
 * Otherwise return |NULL|.
 */
void *yagl_avl_find(const struct yagl_avl_table *tree, const void *item)
{
    const struct yagl_avl_node *p;

    assert(tree != NULL && item != NULL);
    for (p = tree->avl_root; p != NULL;) {
        int cmp = tree->avl_compare(item, p->avl_data, tree->avl_param);

        if (cmp < 0) {
            p = p->avl_link[0];
        } else if (cmp > 0) {
            p = p->avl_link[1];
        } else {
            return p->avl_data;
        }
    }

    return NULL;
}

/*
 * Inserts |item| into |tree| and returns a pointer to |item|'s address.
 * If a duplicate item is found in the tree,
 * returns a pointer to the duplicate without inserting |item|.
 * Returns |NULL| in case of memory allocation failure.
 */
void **yagl_avl_probe(struct yagl_avl_table *tree, void *item)
{
    struct yagl_avl_node *y, *z; /* Top node to update balance factor, and parent. */
    struct yagl_avl_node *p, *q; /* Iterator, and parent. */
    struct yagl_avl_node *n; /* Newly inserted node. */
    struct yagl_avl_node *w; /* New root of rebalanced subtree. */
    int dir; /* Direction to descend. */

    unsigned char da[YAGL_AVL_MAX_HEIGHT]; /* Cached comparison results. */
    int k = 0; /* Number of cached results. */

    assert(tree != NULL && item != NULL);

    z = (struct yagl_avl_node *) &tree->avl_root;
    y = tree->avl_root;
    dir = 0;
    for (q = z, p = y; p != NULL; q = p, p = p->avl_link[dir]) {
        int cmp = tree->avl_compare(item, p->avl_data, tree->avl_param);
        if (cmp == 0) {
            return &p->avl_data;
        }

        if (p->avl_balance != 0) {
            z = q, y = p, k = 0;
        }
        da[k++] = dir = cmp > 0;
    }

    n = q->avl_link[dir] = tree->avl_alloc->libavl_malloc(tree->avl_alloc,
        sizeof(*n));
    if (n == NULL) {
        return NULL;
    }

    tree->avl_count++;
    n->avl_data = item;
    n->avl_link[0] = n->avl_link[1] = NULL;
    n->avl_balance = 0;
    if (y == NULL) {
        return &n->avl_data;
    }

    for (p = y, k = 0; p != n; p = p->avl_link[da[k]], k++) {
        if (da[k] == 0) {
            p->avl_balance--;
        } else {
            p->avl_balance++;
        }
    }

    if (y->avl_balance == -2) {
        struct yagl_avl_node *x = y->avl_link[0];
        if (x->avl_balance == -1) {
            w = x;
            y->avl_link[0] = x->avl_link[1];
            x->avl_link[1] = y;
            x->avl_balance = y->avl_balance = 0;
        } else {
            assert(x->avl_balance == 1);
            w = x->avl_link[1];
            x->avl_link[1] = w->avl_link[0];
            w->avl_link[0] = x;
            y->avl_link[0] = w->avl_link[1];
            w->avl_link[1] = y;
            if (w->avl_balance == -1) {
                x->avl_balance = 0, y->avl_balance = 1;
            } else if (w->avl_balance == 0) {
                x->avl_balance = y->avl_balance = 0;
            } else {
                x->avl_balance = -1, y->avl_balance = 0;
            }
            w->avl_balance = 0;
        }
    } else if (y->avl_balance == 2) {
        struct yagl_avl_node *x = y->avl_link[1];
        if (x->avl_balance == 1) {
            w = x;
            y->avl_link[1] = x->avl_link[0];
            x->avl_link[0] = y;
            x->avl_balance = y->avl_balance = 0;
        } else {
            assert(x->avl_balance == -1);
            w = x->avl_link[0];
            x->avl_link[0] = w->avl_link[1];
            w->avl_link[1] = x;
            y->avl_link[1] = w->avl_link[0];
            w->avl_link[0] = y;
            if (w->avl_balance == 1) {
                x->avl_balance = 0, y->avl_balance = -1;
            } else if (w->avl_balance == 0) {
                x->avl_balance = y->avl_balance = 0;
            } else {
                x->avl_balance = 1, y->avl_balance = 0;
            }
            w->avl_balance = 0;
        }
    } else {
        return &n->avl_data;
    }
    z->avl_link[y != z->avl_link[0]] = w;

    tree->avl_generation++;
    return &n->avl_data;
}

/*
 * Inserts |item| into |table|.
 * Returns |NULL| if |item| was successfully inserted
 * or if a memory allocation error occurred.
 * Otherwise, returns the duplicate item.
 */
void *yagl_avl_insert(struct yagl_avl_table *table, void *item)
{
    void **p = yagl_avl_probe(table, item);
    return p == NULL || *p == item ? NULL : *p;
}

/*
 * Inserts |item| into |table|, replacing any duplicate item.
 * Returns |NULL| if |item| was inserted without replacing a duplicate,
 * or if a memory allocation error occurred.
 * Otherwise, returns the item that was replaced.
 */
void *yagl_avl_replace(struct yagl_avl_table *table, void *item)
{
    void **p = yagl_avl_probe(table, item);
    if (p == NULL || *p == item) {
        return NULL;
    } else {
        void *r = *p;
        *p = item;
        return r;
    }
}

/*
 * Deletes from |tree| and returns an item matching |item|.
 * Returns a null pointer if no matching item found.
 */
void *yagl_avl_delete(struct yagl_avl_table *tree, const void *item)
{
    /* Stack of nodes. */
    struct yagl_avl_node *pa[YAGL_AVL_MAX_HEIGHT]; /* Nodes. */
    unsigned char da[YAGL_AVL_MAX_HEIGHT]; /* |avl_link[]| indexes. */
    int k; /* Stack pointer. */

    struct yagl_avl_node *p; /* Traverses tree to find node to delete. */
    int cmp; /* Result of comparison between |item| and |p|. */

    assert(tree != NULL && item != NULL);

    k = 0;
    p = (struct yagl_avl_node *) &tree->avl_root;
    for (cmp = -1; cmp != 0;
        cmp = tree->avl_compare(item, p->avl_data, tree->avl_param)) {
        int dir = cmp > 0;

        pa[k] = p;
        da[k++] = dir;

        p = p->avl_link[dir];
        if (p == NULL) {
            return NULL;
        }
    }
    item = p->avl_data;

    if (p->avl_link[1] == NULL) {
        pa[k - 1]->avl_link[da[k - 1]] = p->avl_link[0];
    } else {
        struct yagl_avl_node *r = p->avl_link[1];
        if (r->avl_link[0] == NULL) {
            r->avl_link[0] = p->avl_link[0];
            r->avl_balance = p->avl_balance;
            pa[k - 1]->avl_link[da[k - 1]] = r;
            da[k] = 1;
            pa[k++] = r;
        } else {
            struct yagl_avl_node *s;
            int j = k++;

            for (;;) {
                da[k] = 0;
                pa[k++] = r;
                s = r->avl_link[0];
                if (s->avl_link[0] == NULL) {
                    break;
                }

                r = s;
            }

            s->avl_link[0] = p->avl_link[0];
            r->avl_link[0] = s->avl_link[1];
            s->avl_link[1] = p->avl_link[1];
            s->avl_balance = p->avl_balance;

            pa[j - 1]->avl_link[da[j - 1]] = s;
            da[j] = 1;
            pa[j] = s;
        }
    }

    tree->avl_alloc->libavl_free(tree->avl_alloc, p);

    assert(k > 0);
    while (--k > 0) {
        struct yagl_avl_node *y = pa[k];

        if (da[k] == 0) {
            y->avl_balance++;
            if (y->avl_balance == 1) {
                break;
            } else if (y->avl_balance == 2) {
                struct yagl_avl_node *x = y->avl_link[1];
                if (x->avl_balance == -1) {
                    struct yagl_avl_node *w;
                    assert(x->avl_balance == -1);
                    w = x->avl_link[0];
                    x->avl_link[0] = w->avl_link[1];
                    w->avl_link[1] = x;
                    y->avl_link[1] = w->avl_link[0];
                    w->avl_link[0] = y;
                    if (w->avl_balance == 1) {
                        x->avl_balance = 0, y->avl_balance = -1;
                    } else if (w->avl_balance == 0) {
                        x->avl_balance = y->avl_balance = 0;
                    } else {
                        x->avl_balance = 1, y->avl_balance = 0;
                    }
                    w->avl_balance = 0;
                    pa[k - 1]->avl_link[da[k - 1]] = w;
                } else {
                    y->avl_link[1] = x->avl_link[0];
                    x->avl_link[0] = y;
                    pa[k - 1]->avl_link[da[k - 1]] = x;
                    if (x->avl_balance == 0) {
                        x->avl_balance = -1;
                        y->avl_balance = 1;
                        break;
                    } else {
                        x->avl_balance = y->avl_balance = 0;
                    }
                }
            }
        } else {
            y->avl_balance--;
            if (y->avl_balance == -1) {
                break;
            } else if (y->avl_balance == -2) {
                struct yagl_avl_node *x = y->avl_link[0];
                if (x->avl_balance == 1) {
                    struct yagl_avl_node *w;
                    assert(x->avl_balance == 1);
                    w = x->avl_link[1];
                    x->avl_link[1] = w->avl_link[0];
                    w->avl_link[0] = x;
                    y->avl_link[0] = w->avl_link[1];
                    w->avl_link[1] = y;
                    if (w->avl_balance == -1) {
                        x->avl_balance = 0, y->avl_balance = 1;
                    } else if (w->avl_balance == 0) {
                        x->avl_balance = y->avl_balance = 0;
                    } else {
                        x->avl_balance = -1, y->avl_balance = 0;
                    }
                    w->avl_balance = 0;
                    pa[k - 1]->avl_link[da[k - 1]] = w;
                } else {
                    y->avl_link[0] = x->avl_link[1];
                    x->avl_link[1] = y;
                    pa[k - 1]->avl_link[da[k - 1]] = x;
                    if (x->avl_balance == 0) {
                        x->avl_balance = 1;
                        y->avl_balance = -1;
                        break;
                    } else {
                        x->avl_balance = y->avl_balance = 0;
                    }
                }
            }
        }
    }

    tree->avl_count--;
    tree->avl_generation++;
    return (void *) item;
}

/*
 * Refreshes the stack of parent pointers in |trav|
 * and updates its generation number.
 */
static void yagl_trav_refresh(struct yagl_avl_traverser *trav)
{
    assert(trav != NULL);

    trav->avl_generation = trav->avl_table->avl_generation;

    if (trav->avl_node != NULL) {
        yagl_avl_comparison_func *cmp = trav->avl_table->avl_compare;
        void *param = trav->avl_table->avl_param;
        struct yagl_avl_node *node = trav->avl_node;
        struct yagl_avl_node *i;

        trav->avl_height = 0;
        for (i = trav->avl_table->avl_root; i != node;) {
            assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
            assert(i != NULL);

            trav->avl_stack[trav->avl_height++] = i;
            i = i->avl_link[cmp(node->avl_data, i->avl_data, param) > 0];
        }
    }
}

/*
 * Initializes |trav| for use with |tree|
 * and selects the null node.
 */
void yagl_avl_t_init(struct yagl_avl_traverser *trav,
                     struct yagl_avl_table *tree)
{
    trav->avl_table = tree;
    trav->avl_node = NULL;
    trav->avl_height = 0;
    trav->avl_generation = tree->avl_generation;
}

/*
 * Initializes |trav| for |tree|
 * and selects and returns a pointer to its least-valued item.
 * Returns |NULL| if |tree| contains no nodes.
 */
void *yagl_avl_t_first(struct yagl_avl_traverser *trav,
                       struct yagl_avl_table *tree)
{
    struct yagl_avl_node *x;

    assert(tree != NULL && trav != NULL);

    trav->avl_table = tree;
    trav->avl_height = 0;
    trav->avl_generation = tree->avl_generation;

    x = tree->avl_root;
    if (x != NULL) {
        while (x->avl_link[0] != NULL) {
            assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
            trav->avl_stack[trav->avl_height++] = x;
            x = x->avl_link[0];
        }
    }
    trav->avl_node = x;

    return x != NULL ? x->avl_data : NULL;
}

/*
 * Initializes |trav| for |tree|
 * and selects and returns a pointer to its greatest-valued item.
 * Returns |NULL| if |tree| contains no nodes.
 */
void *yagl_avl_t_last(struct yagl_avl_traverser *trav,
                      struct yagl_avl_table *tree)
{
    struct yagl_avl_node *x;

    assert(tree != NULL && trav != NULL);

    trav->avl_table = tree;
    trav->avl_height = 0;
    trav->avl_generation = tree->avl_generation;

    x = tree->avl_root;
    if (x != NULL) {
        while (x->avl_link[1] != NULL) {
            assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
            trav->avl_stack[trav->avl_height++] = x;
            x = x->avl_link[1];
        }
    }
    trav->avl_node = x;

    return x != NULL ? x->avl_data : NULL;
}

/*
 * Searches for |item| in |tree|.
 * If found, initializes |trav| to the item found and returns the item
 * as well.
 * If there is no matching item, initializes |trav| to the null item
 * and returns |NULL|.
 */
void *yagl_avl_t_find(struct yagl_avl_traverser *trav,
                      struct yagl_avl_table *tree, void *item)
{
    struct yagl_avl_node *p, *q;

    assert(trav != NULL && tree != NULL && item != NULL);
    trav->avl_table = tree;
    trav->avl_height = 0;
    trav->avl_generation = tree->avl_generation;
    for (p = tree->avl_root; p != NULL; p = q) {
        int cmp = tree->avl_compare(item, p->avl_data, tree->avl_param);

        if (cmp < 0) {
            q = p->avl_link[0];
        } else if (cmp > 0) {
            q = p->avl_link[1];
        } else {
            trav->avl_node = p;
            return p->avl_data;
        }

        assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
        trav->avl_stack[trav->avl_height++] = p;
    }

    trav->avl_height = 0;
    trav->avl_node = NULL;
    return NULL;
}

/*
 * Attempts to insert |item| into |tree|.
 * If |item| is inserted successfully, it is returned and |trav| is
 * initialized to its location.
 * If a duplicate is found, it is returned and |trav| is initialized to
 * its location.  No replacement of the item occurs.
 * If a memory allocation failure occurs, |NULL| is returned and |trav|
 * is initialized to the null item.
 */
void
*yagl_avl_t_insert(struct yagl_avl_traverser *trav,
                   struct yagl_avl_table *tree, void *item)
{
    void **p;

    assert(trav != NULL && tree != NULL && item != NULL);

    p = yagl_avl_probe(tree, item);
    if (p != NULL) {
        trav->avl_table = tree;
        trav->avl_node = ((struct yagl_avl_node *) ((char *) p
            - offsetof(struct yagl_avl_node, avl_data)));
        trav->avl_generation = tree->avl_generation - 1;
        return *p;
    } else {
        yagl_avl_t_init(trav, tree);
        return NULL;
    }
}

/* Initializes |trav| to have the same current node as |src|. */
void *yagl_avl_t_copy(struct yagl_avl_traverser *trav,
                      const struct yagl_avl_traverser *src)
{
    assert(trav != NULL && src != NULL);

    if (trav != src) {
        trav->avl_table = src->avl_table;
        trav->avl_node = src->avl_node;
        trav->avl_generation = src->avl_generation;
        if (trav->avl_generation == trav->avl_table->avl_generation) {
            trav->avl_height = src->avl_height;
            memcpy(trav->avl_stack, (const void *) src->avl_stack,
                sizeof(*trav->avl_stack) * trav->avl_height);
        }
    }

    return trav->avl_node != NULL ? trav->avl_node->avl_data : NULL;
}

/*
 * Returns the next data item in inorder
 * within the tree being traversed with |trav|,
 * or if there are no more data items returns |NULL|.
 */
void *yagl_avl_t_next(struct yagl_avl_traverser *trav)
{
    struct yagl_avl_node *x;

    assert(trav != NULL);

    if (trav->avl_generation != trav->avl_table->avl_generation) {
        yagl_trav_refresh(trav);
    }

    x = trav->avl_node;
    if (x == NULL) {
        return yagl_avl_t_first(trav, trav->avl_table);
    } else if (x->avl_link[1] != NULL) {
        assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
        trav->avl_stack[trav->avl_height++] = x;
        x = x->avl_link[1];

        while (x->avl_link[0] != NULL) {
            assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
            trav->avl_stack[trav->avl_height++] = x;
            x = x->avl_link[0];
        }
    } else {
        struct yagl_avl_node *y;

        do {
            if (trav->avl_height == 0) {
                trav->avl_node = NULL;
                return NULL;
            }

            y = x;
            x = trav->avl_stack[--trav->avl_height];
        } while (y == x->avl_link[1]);
    }
    trav->avl_node = x;

    return x->avl_data;
}

/*
 * Returns the previous data item in inorder
 * within the tree being traversed with |trav|,
 * or if there are no more data items returns |NULL|.
 */
void *yagl_avl_t_prev(struct yagl_avl_traverser *trav)
{
    struct yagl_avl_node *x;

    assert(trav != NULL);

    if (trav->avl_generation != trav->avl_table->avl_generation) {
        yagl_trav_refresh(trav);
    }

    x = trav->avl_node;
    if (x == NULL) {
        return yagl_avl_t_last(trav, trav->avl_table);
    } else if (x->avl_link[0] != NULL) {
        assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
        trav->avl_stack[trav->avl_height++] = x;
        x = x->avl_link[0];

        while (x->avl_link[1] != NULL) {
            assert(trav->avl_height < YAGL_AVL_MAX_HEIGHT);
            trav->avl_stack[trav->avl_height++] = x;
            x = x->avl_link[1];
        }
    } else {
        struct yagl_avl_node *y;

        do {
            if (trav->avl_height == 0) {
                trav->avl_node = NULL;
                return NULL;
            }

            y = x;
            x = trav->avl_stack[--trav->avl_height];
        } while (y == x->avl_link[0]);
    }
    trav->avl_node = x;

    return x->avl_data;
}

/* Returns |trav|'s current item. */
void *yagl_avl_t_cur(struct yagl_avl_traverser *trav)
{
    assert(trav != NULL);

    return trav->avl_node != NULL ? trav->avl_node->avl_data : NULL;
}

/*
 * Replaces the current item in |trav| by |new| and returns the item replaced.
 * |trav| must not have the null item selected.
 * The new item must not upset the ordering of the tree.
 */
void *yagl_avl_t_replace(struct yagl_avl_traverser *trav, void *new)
{
    void *old;

    assert(trav != NULL && trav->avl_node != NULL && new != NULL);
    old = trav->avl_node->avl_data;
    trav->avl_node->avl_data = new;
    return old;
}

/*
 * Destroys |new| with |avl_destroy (new, destroy)|,
 * first setting right links of nodes in |stack| within |new|
 * to null pointers to avoid touching uninitialized data.
 */
static void yagl_copy_error_recovery(struct yagl_avl_node **stack, int height,
    struct yagl_avl_table *new, yagl_avl_item_func *destroy)
{
    assert(stack != NULL && height >= 0 && new != NULL);

    for (; height > 2; height -= 2) {
        stack[height - 1]->avl_link[1] = NULL;
    }
    yagl_avl_destroy(new, destroy);
}

/*
 * Copies |org| to a newly created tree, which is returned.
 * If |copy != NULL|, each data item in |org| is first passed to |copy|,
 * and the return values are inserted into the tree,
 * with |NULL| return values taken as indications of failure.
 * On failure, destroys the partially created new tree,
 * applying |destroy|, if non-null, to each item in the new tree so far,
 * and returns |NULL|.
 * If |allocator != NULL|, it is used for allocation in the new tree.
 * Otherwise, the same allocator used for |org| is used.
 */
struct yagl_avl_table *yagl_avl_copy(const struct yagl_avl_table *org,
    yagl_avl_copy_func *copy,
    yagl_avl_item_func *destroy,
    struct yagl_libavl_allocator *allocator)
{
    struct yagl_avl_node *stack[2 * (YAGL_AVL_MAX_HEIGHT + 1)];
    int height = 0;

    struct yagl_avl_table *new;
    const struct yagl_avl_node *x;
    struct yagl_avl_node *y;

    assert(org != NULL);
    new = yagl_avl_create(org->avl_compare, org->avl_param,
        allocator != NULL ? allocator : org->avl_alloc);
    if (new == NULL) {
        return NULL;
    }
    new->avl_count = org->avl_count;
    if (new->avl_count == 0) {
        return new;
    }

    x = (const struct yagl_avl_node *) &org->avl_root;
    y = (struct yagl_avl_node *) &new->avl_root;
    for (;;) {
        while (x->avl_link[0] != NULL) {
            assert(height < 2 * (YAGL_AVL_MAX_HEIGHT + 1));

            y->avl_link[0] = new->avl_alloc->libavl_malloc(new->avl_alloc,
                sizeof(*y->avl_link[0]));
            if (y->avl_link[0] == NULL) {
                if (y != (struct yagl_avl_node *) &new->avl_root) {
                    y->avl_data = NULL;
                    y->avl_link[1] = NULL;
                }

                yagl_copy_error_recovery(stack, height, new, destroy);
                return NULL;
            }

            stack[height++] = (struct yagl_avl_node *) x;
            stack[height++] = y;
            x = x->avl_link[0];
            y = y->avl_link[0];
        }
        y->avl_link[0] = NULL;

        for (;;) {
            y->avl_balance = x->avl_balance;
            if (copy == NULL) {
                y->avl_data = x->avl_data;
            } else {
                y->avl_data = copy(x->avl_data, org->avl_param);
                if (y->avl_data == NULL) {
                    y->avl_link[1] = NULL;
                    yagl_copy_error_recovery(stack, height, new, destroy);
                    return NULL;
                }
            }

            if (x->avl_link[1] != NULL) {
                y->avl_link[1] = new->avl_alloc->libavl_malloc(new->avl_alloc,
                    sizeof(*y->avl_link[1]));
                if (y->avl_link[1] == NULL) {
                    yagl_copy_error_recovery(stack, height, new, destroy);
                    return NULL;
                }

                x = x->avl_link[1];
                y = y->avl_link[1];
                break;
            } else {
                y->avl_link[1] = NULL;
            }

            if (height <= 2) {
                return new;
            }

            y = stack[--height];
            x = stack[--height];
        }
    }
}

/*
 * Frees storage allocated for |tree|.
 * If |destroy != NULL|, applies it to each data item in inorder.
 */
void yagl_avl_destroy(struct yagl_avl_table *tree, yagl_avl_item_func *destroy)
{
    struct yagl_avl_node *p, *q;

    assert(tree != NULL);

    for (p = tree->avl_root; p != NULL; p = q) {
        if (p->avl_link[0] == NULL) {
            q = p->avl_link[1];
            if (destroy != NULL && p->avl_data != NULL) {
                destroy(p->avl_data, tree->avl_param);
            }
            tree->avl_alloc->libavl_free(tree->avl_alloc, p);
        } else {
            q = p->avl_link[0];
            p->avl_link[0] = q->avl_link[1];
            q->avl_link[1] = p;
        }
    }

    tree->avl_alloc->libavl_free(tree->avl_alloc, tree);
}

/*
 * Allocates |size| bytes of space using |malloc()|.
 * Returns a null pointer if allocation fails.
 */
void *yagl_avl_malloc(struct yagl_libavl_allocator *allocator, size_t size)
{
    assert(allocator != NULL && size > 0);
    return g_malloc(size);
}

/* Frees |block|. */
void yagl_avl_free(struct yagl_libavl_allocator *allocator, void *block)
{
    assert(allocator != NULL && block != NULL);
    g_free(block);
}

/* Default memory allocator that uses |g_malloc()| and |g_free()|. */
struct yagl_libavl_allocator yagl_avl_allocator_default = {
    yagl_avl_malloc, yagl_avl_free
};

#undef NDEBUG
#include <assert.h>

/* Asserts that |avl_insert()| succeeds at inserting |item| into |table|. */
void (yagl_avl_assert_insert)(struct yagl_avl_table *table, void *item)
{
    void **p = yagl_avl_probe(table, item);
    assert(p != NULL && *p == item);
}

/*
 * Asserts that |avl_delete()| really removes |item| from |table|,
 * and returns the removed item.
 */
void *(yagl_avl_assert_delete)(struct yagl_avl_table *table, void *item)
{
    void *p = yagl_avl_delete(table, item);
    assert(p != NULL);
    return p;
}