Geografic-Information-System/lib/vector/dglib/avl.c

/* Produced by texiweb from libavl.w on 2002/02/09 at 01:45. */

/* libavl - library for manipulation of binary trees.
   Copyright (C) 1998-2002 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   See the GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

   The author may be contacted at <blp@gnu.org> on the Internet, or
   as Ben Pfaff, 12167 Airport Rd, DeWitt MI 48820, USA through more
   mundane means.
 */

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "avl.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 avl_table *avl_create(avl_comparison_func * compare, void *param,
			     struct libavl_allocator *allocator)
{
    struct avl_table *tree;

    assert(compare != NULL);

    if (allocator == NULL)
	allocator = &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 *avl_find(const struct avl_table *tree, const void *item)
{
    const struct 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			/* |cmp == 0| */
	    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 **avl_probe(struct avl_table *tree, void *item)
{
    struct avl_node *y, *z;	/* Top node to update balance factor, and parent. */
    struct avl_node *p, *q;	/* Iterator, and parent. */
    struct avl_node *n;		/* Newly inserted node. */
    struct avl_node *w;		/* New root of rebalanced subtree. */
    int dir;			/* Direction to descend. */

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

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

    z = (struct 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 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		/* |w->avl_balance == +1| */
		x->avl_balance = -1, y->avl_balance = 0;
	    w->avl_balance = 0;
	}
    }
    else if (y->avl_balance == +2) {
	struct 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		/* |w->avl_balance == -1| */
		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 *avl_insert(struct avl_table *table, void *item)
{
    void **p = 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 *avl_replace(struct avl_table *table, void *item)
{
    void **p = 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 *avl_delete(struct avl_table *tree, const void *item)
{
    /* Stack of nodes. */
    struct avl_node *pa[AVL_MAX_HEIGHT];	/* Nodes. */
    unsigned char da[AVL_MAX_HEIGHT];	/* |avl_link[]| indexes. */
    int k;			/* Stack pointer. */

    struct 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 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 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 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 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 avl_node *x = y->avl_link[1];

		if (x->avl_balance == -1) {
		    struct 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	/* |w->avl_balance == -1| */
			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 avl_node *x = y->avl_link[0];

		if (x->avl_balance == +1) {
		    struct 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	/* |w->avl_balance == +1| */
			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 trav_refresh(struct avl_traverser *trav)
{
    assert(trav != NULL);

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

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

	trav->avl_height = 0;
	for (i = trav->avl_table->avl_root; i != node;) {
	    assert(trav->avl_height < 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 avl_t_init(struct avl_traverser *trav, struct 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 *avl_t_first(struct avl_traverser *trav, struct avl_table *tree)
{
    struct 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 < 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 *avl_t_last(struct avl_traverser *trav, struct avl_table *tree)
{
    struct 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 < 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 *avl_t_find(struct avl_traverser *trav, struct avl_table *tree,
		 void *item)
{
    struct 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 {			/* |cmp == 0| */

	    trav->avl_node = p;
	    return p->avl_data;
	}

	assert(trav->avl_height < 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 *avl_t_insert(struct avl_traverser *trav, struct avl_table *tree,
		   void *item)
{
    void **p;

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

    p = avl_probe(tree, item);
    if (p != NULL) {
	trav->avl_table = tree;
	trav->avl_node = ((struct avl_node *)
			  ((char *)p - offsetof(struct avl_node, avl_data)));

	trav->avl_generation = tree->avl_generation - 1;
	return *p;
    }
    else {
	avl_t_init(trav, tree);
	return NULL;
    }
}

/* Initializes |trav| to have the same current node as |src|. */
void *avl_t_copy(struct avl_traverser *trav, const struct 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 *avl_t_next(struct avl_traverser *trav)
{
    struct avl_node *x;

    assert(trav != NULL);

    if (trav->avl_generation != trav->avl_table->avl_generation)
	trav_refresh(trav);

    x = trav->avl_node;
    if (x == NULL) {
	return avl_t_first(trav, trav->avl_table);
    }
    else if (x->avl_link[1] != NULL) {
	assert(trav->avl_height < 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 < AVL_MAX_HEIGHT);
	    trav->avl_stack[trav->avl_height++] = x;
	    x = x->avl_link[0];
	}
    }
    else {
	struct 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 *avl_t_prev(struct avl_traverser *trav)
{
    struct avl_node *x;

    assert(trav != NULL);

    if (trav->avl_generation != trav->avl_table->avl_generation)
	trav_refresh(trav);

    x = trav->avl_node;
    if (x == NULL) {
	return avl_t_last(trav, trav->avl_table);
    }
    else if (x->avl_link[0] != NULL) {
	assert(trav->avl_height < 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 < AVL_MAX_HEIGHT);
	    trav->avl_stack[trav->avl_height++] = x;
	    x = x->avl_link[1];
	}
    }
    else {
	struct 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 *avl_t_cur(struct 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 *avl_t_replace(struct avl_traverser *trav, void *new)
{
    struct avl_node *old;

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

static void
copy_error_recovery(struct avl_node **stack, int height,
		    struct avl_table *new, avl_item_func * destroy)
{
    assert(stack != NULL && height >= 0 && new != NULL);

    for (; height > 2; height -= 2)
	stack[height - 1]->avl_link[1] = NULL;
    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 avl_table *avl_copy(const struct avl_table *org, avl_copy_func * copy,
			   avl_item_func * destroy,
			   struct libavl_allocator *allocator)
{
    struct avl_node *stack[2 * (AVL_MAX_HEIGHT + 1)];
    int height = 0;

    struct avl_table *new;
    const struct avl_node *x;
    struct avl_node *y;

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

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

	    stack[height++] = (struct 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;
		    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) {
		    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 avl_destroy(struct avl_table *tree, avl_item_func * destroy)
{
    struct 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 *avl_malloc(struct libavl_allocator *allocator, size_t size)
{
    assert(allocator != NULL && size > 0);
    return malloc(size);
}

/* Frees |block|. */
void avl_free(struct libavl_allocator *allocator, void *block)
{
    assert(allocator != NULL && block != NULL);
    free(block);
}

/* Default memory allocator that uses |malloc()| and |free()|. */
struct libavl_allocator avl_allocator_default = {
    avl_malloc,
    avl_free
};

/* Asserts that |avl_insert()| succeeds at inserting |item| into |table|. */
void (avl_assert_insert) (struct avl_table * table, void *item)
{
    void **p = avl_probe(table, item);

    assert(p != NULL && *p == item);
}

/* Asserts that |avl_delete()| really removes |item| from |table|,
   and returns the removed item. */
void *(avl_assert_delete) (struct avl_table * table, void *item)
{
    void *p = avl_delete(table, item);

    assert(p != NULL);
    return p;
}