Geografic-Information-System/imagery/i.segment/pavl.c

/* Produced by texiweb from libavl.w. */

/* libavl - library for manipulation of binary trees.
   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004 Free Software
   Foundation, Inc.

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

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

/* Nov 2016, Markus Metz
 * from libavl-2.0.3
 * added safety checks and speed optimizations
 */

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include "pavl.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 pavl_table *pavl_create(pavl_comparison_func * compare,
			       struct libavl_allocator *allocator)
{
    struct pavl_table *tree;

    assert(compare != NULL);

    if (allocator == NULL)
	allocator = &pavl_allocator_default;

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

    tree->pavl_root = NULL;
    tree->pavl_compare = compare;
    tree->pavl_alloc = allocator;
    tree->pavl_count = 0;

    return tree;
}

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

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

    p = tree->pavl_root;
    while (p != NULL) {
	int cmp = tree->pavl_compare(item, p->pavl_data);

	if (cmp == 0)
	    return p->pavl_data;

	p = p->pavl_link[cmp > 0];
    }

    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 **pavl_probe(struct pavl_table *tree, void *item)
{
    struct pavl_node *y;	/* Top node to update balance factor, and parent. */
    struct pavl_node *p, *q;	/* Iterator, and parent. */
    struct pavl_node *n;	/* Newly inserted node. */
    struct pavl_node *w;	/* New root of rebalanced subtree. */
    int dir;			/* Direction to descend. */

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

    y = p = tree->pavl_root;
    q = NULL;
    dir = 0;
    while (p != NULL) {
	int cmp = tree->pavl_compare(item, p->pavl_data);

	if (cmp == 0)
	    return &p->pavl_data;

	dir = cmp > 0;

	if (p->pavl_balance != 0)
	    y = p;

	q = p, p = p->pavl_link[dir];
    }

    n = tree->pavl_alloc->libavl_malloc(sizeof *p);
    if (n == NULL)
	return NULL;

    tree->pavl_count++;
    n->pavl_link[0] = n->pavl_link[1] = NULL;
    n->pavl_parent = q;
    n->pavl_data = item;
    n->pavl_balance = 0;
    if (q == NULL) {
	tree->pavl_root = n;

	return &n->pavl_data;
    }
    q->pavl_link[dir] = n;

    p = n;
    while (p != y) {
	q = p->pavl_parent;
	/*
	   dir = q->pavl_link[0] != p;
	   if (dir == 0)
	   q->pavl_balance--;
	   else
	   q->pavl_balance++;
	 */
	if (q->pavl_link[0] != p)
	    q->pavl_balance++;
	else
	    q->pavl_balance--;

	p = q;
    }

    if (y->pavl_balance == -2) {
	struct pavl_node *x = y->pavl_link[0];

	if (x->pavl_balance == -1) {
	    w = x;
	    y->pavl_link[0] = x->pavl_link[1];
	    x->pavl_link[1] = y;
	    x->pavl_balance = y->pavl_balance = 0;
	    x->pavl_parent = y->pavl_parent;
	    y->pavl_parent = x;
	    if (y->pavl_link[0] != NULL)
		y->pavl_link[0]->pavl_parent = y;
	}
	else {
	    assert(x->pavl_balance == +1);
	    w = x->pavl_link[1];
	    x->pavl_link[1] = w->pavl_link[0];
	    w->pavl_link[0] = x;
	    y->pavl_link[0] = w->pavl_link[1];
	    w->pavl_link[1] = y;
	    if (w->pavl_balance == -1)
		x->pavl_balance = 0, y->pavl_balance = +1;
	    else if (w->pavl_balance == 0)
		x->pavl_balance = y->pavl_balance = 0;
	    else		/* |w->pavl_balance == +1| */
		x->pavl_balance = -1, y->pavl_balance = 0;
	    w->pavl_balance = 0;
	    w->pavl_parent = y->pavl_parent;
	    x->pavl_parent = y->pavl_parent = w;
	    if (x->pavl_link[1] != NULL)
		x->pavl_link[1]->pavl_parent = x;
	    if (y->pavl_link[0] != NULL)
		y->pavl_link[0]->pavl_parent = y;
	}
    }
    else if (y->pavl_balance == +2) {
	struct pavl_node *x = y->pavl_link[1];

	if (x->pavl_balance == +1) {
	    w = x;
	    y->pavl_link[1] = x->pavl_link[0];
	    x->pavl_link[0] = y;
	    x->pavl_balance = y->pavl_balance = 0;
	    x->pavl_parent = y->pavl_parent;
	    y->pavl_parent = x;
	    if (y->pavl_link[1] != NULL)
		y->pavl_link[1]->pavl_parent = y;
	}
	else {
	    assert(x->pavl_balance == -1);
	    w = x->pavl_link[0];
	    x->pavl_link[0] = w->pavl_link[1];
	    w->pavl_link[1] = x;
	    y->pavl_link[1] = w->pavl_link[0];
	    w->pavl_link[0] = y;
	    if (w->pavl_balance == +1)
		x->pavl_balance = 0, y->pavl_balance = -1;
	    else if (w->pavl_balance == 0)
		x->pavl_balance = y->pavl_balance = 0;
	    else		/* |w->pavl_balance == -1| */
		x->pavl_balance = +1, y->pavl_balance = 0;
	    w->pavl_balance = 0;
	    w->pavl_parent = y->pavl_parent;
	    x->pavl_parent = y->pavl_parent = w;
	    if (x->pavl_link[0] != NULL)
		x->pavl_link[0]->pavl_parent = x;
	    if (y->pavl_link[1] != NULL)
		y->pavl_link[1]->pavl_parent = y;
	}
    }
    else
	return &n->pavl_data;

    if (w->pavl_parent != NULL)
	w->pavl_parent->pavl_link[y != w->pavl_parent->pavl_link[0]] = w;
    else
	tree->pavl_root = w;

    return &n->pavl_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 *pavl_insert(struct pavl_table *table, void *item)
{
    void **p = pavl_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 *pavl_replace(struct pavl_table *table, void *item)
{
    void **p = pavl_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 *pavl_delete(struct pavl_table *tree, const void *item)
{
    struct pavl_node *p;	/* Traverses tree to find node to delete. */
    struct pavl_node *q;	/* Parent of |p|. */
    int dir;			/* Side of |q| on which |p| is linked. */
    int cmp;			/* Result of comparison between |item| and |p|. */

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

    p = tree->pavl_root;
    dir = 0;
    while (p != NULL) {
	cmp = tree->pavl_compare(item, p->pavl_data);

	if (cmp == 0)
	    break;

	dir = cmp > 0;
	p = p->pavl_link[dir];
    }
    if (p == NULL)
	return NULL;

    item = p->pavl_data;

    q = p->pavl_parent;
    if (q == NULL) {
	q = (struct pavl_node *)&tree->pavl_root;
	dir = 0;
    }

    if (p->pavl_link[1] == NULL) {
	q->pavl_link[dir] = p->pavl_link[0];
	if (q->pavl_link[dir] != NULL)
	    q->pavl_link[dir]->pavl_parent = p->pavl_parent;
    }
    else {
	struct pavl_node *r = p->pavl_link[1];

	if (r->pavl_link[0] == NULL) {
	    r->pavl_link[0] = p->pavl_link[0];
	    q->pavl_link[dir] = r;
	    r->pavl_parent = p->pavl_parent;
	    if (r->pavl_link[0] != NULL)
		r->pavl_link[0]->pavl_parent = r;
	    r->pavl_balance = p->pavl_balance;
	    q = r;
	    dir = 1;
	}
	else {
	    struct pavl_node *s = r->pavl_link[0];

	    while (s->pavl_link[0] != NULL)
		s = s->pavl_link[0];
	    r = s->pavl_parent;
	    r->pavl_link[0] = s->pavl_link[1];
	    s->pavl_link[0] = p->pavl_link[0];
	    s->pavl_link[1] = p->pavl_link[1];
	    q->pavl_link[dir] = s;
	    if (s->pavl_link[0] != NULL)
		s->pavl_link[0]->pavl_parent = s;
	    s->pavl_link[1]->pavl_parent = s;
	    s->pavl_parent = p->pavl_parent;
	    if (r->pavl_link[0] != NULL)
		r->pavl_link[0]->pavl_parent = r;
	    s->pavl_balance = p->pavl_balance;
	    q = r;
	    dir = 0;
	}
    }
    tree->pavl_alloc->libavl_free(p);

    while (q != (struct pavl_node *)&tree->pavl_root) {
	struct pavl_node *y = q;

	if (y->pavl_parent != NULL)
	    q = y->pavl_parent;
	else
	    q = (struct pavl_node *)&tree->pavl_root;

	if (dir == 0) {
	    dir = q->pavl_link[0] != y;
	    y->pavl_balance++;
	    if (y->pavl_balance == +1)
		break;
	    else if (y->pavl_balance == +2) {
		struct pavl_node *x = y->pavl_link[1];

		if (x->pavl_balance == -1) {
		    struct pavl_node *w;

		    assert(x->pavl_balance == -1);
		    w = x->pavl_link[0];
		    x->pavl_link[0] = w->pavl_link[1];
		    w->pavl_link[1] = x;
		    y->pavl_link[1] = w->pavl_link[0];
		    w->pavl_link[0] = y;
		    if (w->pavl_balance == +1)
			x->pavl_balance = 0, y->pavl_balance = -1;
		    else if (w->pavl_balance == 0)
			x->pavl_balance = y->pavl_balance = 0;
		    else	/* |w->pavl_balance == -1| */
			x->pavl_balance = +1, y->pavl_balance = 0;
		    w->pavl_balance = 0;
		    w->pavl_parent = y->pavl_parent;
		    x->pavl_parent = y->pavl_parent = w;
		    if (x->pavl_link[0] != NULL)
			x->pavl_link[0]->pavl_parent = x;
		    if (y->pavl_link[1] != NULL)
			y->pavl_link[1]->pavl_parent = y;
		    q->pavl_link[dir] = w;
		}
		else {
		    y->pavl_link[1] = x->pavl_link[0];
		    x->pavl_link[0] = y;
		    x->pavl_parent = y->pavl_parent;
		    y->pavl_parent = x;
		    if (y->pavl_link[1] != NULL)
			y->pavl_link[1]->pavl_parent = y;
		    q->pavl_link[dir] = x;
		    if (x->pavl_balance == 0) {
			x->pavl_balance = -1;
			y->pavl_balance = +1;
			break;
		    }
		    else {
			x->pavl_balance = y->pavl_balance = 0;
			y = x;
		    }
		}
	    }
	}
	else {
	    dir = q->pavl_link[0] != y;
	    y->pavl_balance--;
	    if (y->pavl_balance == -1)
		break;
	    else if (y->pavl_balance == -2) {
		struct pavl_node *x = y->pavl_link[0];

		if (x->pavl_balance == +1) {
		    struct pavl_node *w;

		    assert(x->pavl_balance == +1);
		    w = x->pavl_link[1];
		    x->pavl_link[1] = w->pavl_link[0];
		    w->pavl_link[0] = x;
		    y->pavl_link[0] = w->pavl_link[1];
		    w->pavl_link[1] = y;
		    if (w->pavl_balance == -1)
			x->pavl_balance = 0, y->pavl_balance = +1;
		    else if (w->pavl_balance == 0)
			x->pavl_balance = y->pavl_balance = 0;
		    else	/* |w->pavl_balance == +1| */
			x->pavl_balance = -1, y->pavl_balance = 0;
		    w->pavl_balance = 0;
		    w->pavl_parent = y->pavl_parent;
		    x->pavl_parent = y->pavl_parent = w;
		    if (x->pavl_link[1] != NULL)
			x->pavl_link[1]->pavl_parent = x;
		    if (y->pavl_link[0] != NULL)
			y->pavl_link[0]->pavl_parent = y;
		    q->pavl_link[dir] = w;
		}
		else {
		    y->pavl_link[0] = x->pavl_link[1];
		    x->pavl_link[1] = y;
		    x->pavl_parent = y->pavl_parent;
		    y->pavl_parent = x;
		    if (y->pavl_link[0] != NULL)
			y->pavl_link[0]->pavl_parent = y;
		    q->pavl_link[dir] = x;
		    if (x->pavl_balance == 0) {
			x->pavl_balance = +1;
			y->pavl_balance = -1;
			break;
		    }
		    else {
			x->pavl_balance = y->pavl_balance = 0;
			y = x;
		    }
		}
	    }
	}
    }

    tree->pavl_count--;
    return (void *)item;
}

/* Initializes |trav| for use with |tree|
   and selects the null node. */
void pavl_t_init(struct pavl_traverser *trav, struct pavl_table *tree)
{
    trav->pavl_table = tree;
    trav->pavl_node = NULL;
}

/* Initializes |trav| for |tree|.
   Returns data item in |tree| with the least value,
   or |NULL| if |tree| is empty. */
void *pavl_t_first(struct pavl_traverser *trav, struct pavl_table *tree)
{
    assert(tree != NULL && trav != NULL);

    trav->pavl_table = tree;
    trav->pavl_node = tree->pavl_root;
    if (trav->pavl_node != NULL) {
	while (trav->pavl_node->pavl_link[0] != NULL)
	    trav->pavl_node = trav->pavl_node->pavl_link[0];

	return trav->pavl_node->pavl_data;
    }
    else
	return NULL;
}

/* Initializes |trav| for |tree|.
   Returns data item in |tree| with the greatest value,
   or |NULL| if |tree| is empty. */
void *pavl_t_last(struct pavl_traverser *trav, struct pavl_table *tree)
{
    assert(tree != NULL && trav != NULL);

    trav->pavl_table = tree;
    trav->pavl_node = tree->pavl_root;
    if (trav->pavl_node != NULL) {
	while (trav->pavl_node->pavl_link[1] != NULL)
	    trav->pavl_node = trav->pavl_node->pavl_link[1];

	return trav->pavl_node->pavl_data;
    }
    else
	return 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 *pavl_t_find(struct pavl_traverser *trav, struct pavl_table *tree,
		  void *item)
{
    struct pavl_node *p;

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

    trav->pavl_table = tree;
    
    p = tree->pavl_root;
    while (p != NULL) {
	int cmp = tree->pavl_compare(item, p->pavl_data);

	if (cmp == 0) {
	    trav->pavl_node = p;

	    return p->pavl_data;
	}

	p = p->pavl_link[cmp > 0];
    }

    trav->pavl_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 *pavl_t_insert(struct pavl_traverser *trav,
		    struct pavl_table *tree, void *item)
{
    void **p;

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

    p = pavl_probe(tree, item);
    if (p != NULL) {
	trav->pavl_table = tree;
	trav->pavl_node = ((struct pavl_node *)((char *)p -
						offsetof(struct pavl_node,
							 pavl_data)));

	return *p;
    }
    else {
	pavl_t_init(trav, tree);

	return NULL;
    }
}

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

    trav->pavl_table = src->pavl_table;
    trav->pavl_node = src->pavl_node;

    return trav->pavl_node != NULL ? trav->pavl_node->pavl_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 *pavl_t_next(struct pavl_traverser *trav)
{
    assert(trav != NULL);

    if (trav->pavl_node == NULL)
	return pavl_t_first(trav, trav->pavl_table);
    else if (trav->pavl_node->pavl_link[1] == NULL) {
	struct pavl_node *q, *p;	/* Current node and its child. */

	for (p = trav->pavl_node, q = p->pavl_parent;;
	     p = q, q = q->pavl_parent)
	    if (q == NULL || p == q->pavl_link[0]) {
		trav->pavl_node = q;

		return trav->pavl_node != NULL ?
		    trav->pavl_node->pavl_data : NULL;
	    }
    }
    else {
	trav->pavl_node = trav->pavl_node->pavl_link[1];
	while (trav->pavl_node->pavl_link[0] != NULL)
	    trav->pavl_node = trav->pavl_node->pavl_link[0];

	return trav->pavl_node->pavl_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 *pavl_t_prev(struct pavl_traverser *trav)
{
    assert(trav != NULL);

    if (trav->pavl_node == NULL)
	return pavl_t_last(trav, trav->pavl_table);
    else if (trav->pavl_node->pavl_link[0] == NULL) {
	struct pavl_node *q, *p;	/* Current node and its child. */

	for (p = trav->pavl_node, q = p->pavl_parent;;
	     p = q, q = q->pavl_parent)
	    if (q == NULL || p == q->pavl_link[1]) {
		trav->pavl_node = q;

		return trav->pavl_node != NULL ?
		    trav->pavl_node->pavl_data : NULL;
	    }
    }
    else {
	trav->pavl_node = trav->pavl_node->pavl_link[0];
	while (trav->pavl_node->pavl_link[1] != NULL)
	    trav->pavl_node = trav->pavl_node->pavl_link[1];

	return trav->pavl_node->pavl_data;
    }
}

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

    return trav->pavl_node != NULL ? trav->pavl_node->pavl_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 *pavl_t_replace(struct pavl_traverser *trav, void *new)
{
    void *old;

    assert(trav != NULL && trav->pavl_node != NULL && new != NULL);
    old = trav->pavl_node->pavl_data;
    trav->pavl_node->pavl_data = new;

    return old;
}

/* Destroys |new| with |pavl_destroy (new, destroy)|,
   first initializing right links in |new| that have
   not yet been initialized at time of call. */
static void
copy_error_recovery(struct pavl_node *q,
		    struct pavl_table *new, pavl_item_func * destroy)
{
    assert(q != NULL && new != NULL);

    for (;;) {
	struct pavl_node *p = q;

	q = q->pavl_parent;
	if (q == NULL)
	    break;

	if (p == q->pavl_link[0])
	    q->pavl_link[1] = NULL;
    }

    pavl_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;
   |NULL| return values are 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 pavl_table *pavl_copy(const struct pavl_table *org,
			     pavl_copy_func * copy, pavl_item_func * destroy,
			     struct libavl_allocator *allocator)
{
    struct pavl_table *new;
    const struct pavl_node *x;
    struct pavl_node *y;

    assert(org != NULL);
    new = pavl_create(org->pavl_compare,
		      allocator != NULL ? allocator : org->pavl_alloc);
    if (new == NULL)
	return NULL;

    new->pavl_count = org->pavl_count;
    if (new->pavl_count == 0)
	return new;

    x = (const struct pavl_node *)&org->pavl_root;
    y = (struct pavl_node *)&new->pavl_root;
    while (x != NULL) {
	while (x->pavl_link[0] != NULL) {
	    y->pavl_link[0] =
		new->pavl_alloc->libavl_malloc(sizeof *y->pavl_link[0]);
	    if (y->pavl_link[0] == NULL) {
		if (y != (struct pavl_node *)&new->pavl_root) {
		    y->pavl_data = NULL;
		    y->pavl_link[1] = NULL;
		}

		copy_error_recovery(y, new, destroy);

		return NULL;
	    }
	    y->pavl_link[0]->pavl_parent = y;

	    x = x->pavl_link[0];
	    y = y->pavl_link[0];
	}
	y->pavl_link[0] = NULL;

	for (;;) {
	    y->pavl_balance = x->pavl_balance;
	    if (copy == NULL)
		y->pavl_data = x->pavl_data;
	    else {
		y->pavl_data = copy(x->pavl_data);
		if (y->pavl_data == NULL) {
		    y->pavl_link[1] = NULL;
		    copy_error_recovery(y, new, destroy);

		    return NULL;
		}
	    }

	    if (x->pavl_link[1] != NULL) {
		y->pavl_link[1] =
		    new->pavl_alloc->libavl_malloc(sizeof *y->pavl_link[1]);
		if (y->pavl_link[1] == NULL) {
		    copy_error_recovery(y, new, destroy);

		    return NULL;
		}
		y->pavl_link[1]->pavl_parent = y;

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

	    for (;;) {
		const struct pavl_node *w = x;

		x = x->pavl_parent;
		if (x == NULL) {
		    new->pavl_root->pavl_parent = NULL;
		    return new;
		}
		y = y->pavl_parent;

		if (w == x->pavl_link[0])
		    break;
	    }
	}
    }

    return new;
}

/* Frees storage allocated for |tree|.
   If |destroy != NULL|, applies it to each data item in inorder. */
void pavl_destroy(struct pavl_table *tree, pavl_item_func * destroy)
{
    struct pavl_node *p, *q;

    assert(tree != NULL);

    p = tree->pavl_root;
    while (p != NULL) {
	if (p->pavl_link[0] == NULL) {
	    q = p->pavl_link[1];
	    if (destroy != NULL && p->pavl_data != NULL)
		destroy(p->pavl_data);
	    tree->pavl_alloc->libavl_free(p);
	}
	else {
	    q = p->pavl_link[0];
	    p->pavl_link[0] = q->pavl_link[1];
	    q->pavl_link[1] = p;
	}
	p = q;
    }

    tree->pavl_alloc->libavl_free(tree);
}

/* Allocates |size| bytes of space using |malloc()|.
   Returns a null pointer if allocation fails. */
void *pavl_malloc(size_t size)
{
    if (size > 0)
	return malloc(size);

    return NULL;
}

/* Frees |block|. */
void pavl_free(void *block)
{
    if (block)
	free(block);
}

/* Default memory allocator that uses |malloc()| and |free()|. */
struct libavl_allocator pavl_allocator_default = {
    pavl_malloc,
    pavl_free
};

#undef NDEBUG
#include <assert.h>

/* Asserts that |pavl_insert()| succeeds at inserting |item| into |table|. */
void (pavl_assert_insert) (struct pavl_table * table, void *item)
{
    void **p = pavl_probe(table, item);

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

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

    assert(p != NULL);

    return p;
}