avl.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
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/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */
 
/*
 * AVL - generic AVL tree implementation for kernel use
 *
 * A complete description of AVL trees can be found in many CS textbooks.
 *
 * Here is a very brief overview. An AVL tree is a binary search tree that is
 * almost perfectly balanced. By "almost" perfectly balanced, we mean that at
 * any given node, the left and right subtrees are allowed to differ in height
 * by at most 1 level.
 *
 * This relaxation from a perfectly balanced binary tree allows doing
 * insertion and deletion relatively efficiently. Searching the tree is
 * still a fast operation, roughly O(log(N)).
 *
 * The key to insertion and deletion is a set of tree maniuplations called
 * rotations, which bring unbalanced subtrees back into the semi-balanced state.
 *
 * This implementation of AVL trees has the following peculiarities:
 *
 *  - The AVL specific data structures are physically embedded as fields
 *    in the "using" data structures.  To maintain generality the code
 *    must constantly translate between "avl_node_t *" and containing
 *    data structure "void *"s by adding/subracting the avl_offset.
 *
 *  - Since the AVL data is always embedded in other structures, there is
 *    no locking or memory allocation in the AVL routines. This must be
 *    provided for by the enclosing data structure's semantics. Typically,
 *    avl_insert()/_add()/_remove()/avl_insert_here() require some kind of
 *    exclusive write lock. Other operations require a read lock.
 *
 *      - The implementation uses iteration instead of explicit recursion,
 *    since it is intended to run on limited size kernel stacks. Since
 *    there is no recursion stack present to move "up" in the tree,
 *    there is an explicit "parent" link in the avl_node_t.
 *
 *      - The left/right children pointers of a node are in an array.
 *    In the code, variables (instead of constants) are used to represent
 *    left and right indices.  The implementation is written as if it only
 *    dealt with left handed manipulations.  By changing the value assigned
 *    to "left", the code also works for right handed trees.  The
 *    following variables/terms are frequently used:
 *
 *      int left;   // 0 when dealing with left children,
 *              // 1 for dealing with right children
 *
 *      int left_heavy; // -1 when left subtree is taller at some node,
 *              // +1 when right subtree is taller
 *
 *      int right;  // will be the opposite of left (0 or 1)
 *      int right_heavy;// will be the opposite of left_heavy (-1 or 1)
 *
 *      int direction;  // 0 for "<" (ie. left child); 1 for ">" (right)
 *
 *    Though it is a little more confusing to read the code, the approach
 *    allows using half as much code (and hence cache footprint) for tree
 *    manipulations and eliminates many conditional branches.
 *
 *  - The avl_index_t is an opaque "cookie" used to find nodes at or
 *    adjacent to where a new value would be inserted in the tree. The value
 *    is a modified "avl_node_t *".  The bottom bit (normally 0 for a
 *    pointer) is set to indicate if that the new node has a value greater
 *    than the value of the indicated "avl_node_t *".
 */
 
#include <string.h>
#include <stdlib.h>
 
#include <acfutils/assert.h>
#include <acfutils/avl.h>
#include <acfutils/helpers.h>
 
/*
 * Small arrays to translate between balance (or diff) values and child indeces.
 *
 * Code that deals with binary tree data structures will randomly use
 * left and right children when examining a tree.  C "if()" statements
 * which evaluate randomly suffer from very poor hardware branch prediction.
 * In this code we avoid some of the branch mispredictions by using the
 * following translation arrays. They replace random branches with an
 * additional memory reference. Since the translation arrays are both very
 * small the data should remain efficiently in cache.
 */
static const int  avl_child2balance[2]  = {-1, 1};
static const int  avl_balance2child[]   = {0, 0, 1};
 
 
/*
 * Walk from one node to the previous valued node (ie. an infix walk
 * towards the left). At any given node we do one of 2 things:
 *
 * - If there is a left child, go to it, then to it's rightmost descendant.
 *
 * - otherwise we return thru parent nodes until we've come from a right child.
 *
 * Return Value:
 * NULL - if at the end of the nodes
 * otherwise next node
 */
void *
avl_walk(const avl_tree_t *tree, const void *oldnode, int left)
{
    size_t off = tree->avl_offset;
    const avl_node_t *node = AVL_DATA2NODE(oldnode, off);
    int right = 1 - left;
    int was_child;
 
 
    /*
     * nowhere to walk to if tree is empty
     */
    if (node == NULL)
        return (NULL);
 
    /*
     * Visit the previous valued node. There are two possibilities:
     *
     * If this node has a left child, go down one left, then all
     * the way right.
     */
    if (node->avl_child[left] != NULL) {
        for (node = node->avl_child[left];
            node->avl_child[right] != NULL;
            node = node->avl_child[right])
            ;
    /*
     * Otherwise, return thru left children as far as we can.
     */
    } else {
        for (;;) {
            was_child = AVL_XCHILD(node);
            node = AVL_XPARENT(node);
            if (node == NULL)
                return (NULL);
            if (was_child == right)
                break;
        }
    }
 
    return (AVL_NODE2DATA(node, off));
}
 
/*
 * Return the lowest valued node in a tree or NULL.
 * (leftmost child from root of tree)
 */
void *
avl_first(const avl_tree_t *tree)
{
    const avl_node_t *node;
    const avl_node_t *prev = NULL;
    size_t off = tree->avl_offset;
 
    for (node = tree->avl_root; node != NULL; node = node->avl_child[0])
        prev = node;
 
    if (prev != NULL)
        return (AVL_NODE2DATA(prev, off));
    return (NULL);
}
 
/*
 * Return the highest valued node in a tree or NULL.
 * (rightmost child from root of tree)
 */
void *
avl_last(const avl_tree_t *tree)
{
    const avl_node_t *node;
    const avl_node_t *prev = NULL;
    size_t off = tree->avl_offset;
 
    for (node = tree->avl_root; node != NULL; node = node->avl_child[1])
        prev = node;
 
    if (prev != NULL)
        return (AVL_NODE2DATA(prev, off));
    return (NULL);
}
 
/*
 * Access the node immediately before or after an insertion point.
 *
 * "avl_index_t" is a (avl_node_t *) with the bottom bit indicating a child
 *
 * Return value:
 *  NULL: no node in the given direction
 *  "void *"  of the found tree node
 */
void *
avl_nearest(const avl_tree_t *tree, avl_index_t where, int direction)
{
    int child = AVL_INDEX2CHILD(where);
    avl_node_t *node = AVL_INDEX2NODE(where);
    void *data;
    size_t off = tree->avl_offset;
 
    if (node == NULL) {
        ASSERT(tree->avl_root == NULL);
        return (NULL);
    }
    data = AVL_NODE2DATA(node, off);
    if (child != direction)
        return (data);
 
    return (avl_walk(tree, data, direction));
}
 
 
/*
 * Search for the node which contains "value".  The algorithm is a
 * simple binary tree search.
 *
 * return value:
 *  NULL: the value is not in the AVL tree
 *      *where (if not NULL)  is set to indicate the insertion point
 *  "void *"  of the found tree node
 */
void *
avl_find(const avl_tree_t *tree, const void *value, avl_index_t *where)
{
    avl_node_t *node;
    avl_node_t *prev = NULL;
    int child = 0;
    int diff;
    size_t off = tree->avl_offset;
 
    for (node = tree->avl_root; node != NULL;
        node = node->avl_child[child]) {
 
        prev = node;
 
        diff = tree->avl_compar(value, AVL_NODE2DATA(node, off));
        ASSERT(-1 <= diff && diff <= 1);
        if (diff == 0) {
#ifdef DEBUG
            if (where != NULL)
                *where = 0;
#endif
            return (AVL_NODE2DATA(node, off));
        }
        child = avl_balance2child[1 + diff];
 
    }
 
    if (where != NULL)
        *where = AVL_MKINDEX(prev, child);
 
    return (NULL);
}
 
 
/*
 * Perform a rotation to restore balance at the subtree given by depth.
 *
 * This routine is used by both insertion and deletion. The return value
 * indicates:
 *   0 : subtree did not change height
 *  !0 : subtree was reduced in height
 *
 * The code is written as if handling left rotations, right rotations are
 * symmetric and handled by swapping values of variables right/left[_heavy]
 *
 * On input balance is the "new" balance at "node". This value is either
 * -2 or +2.
 */
static int
avl_rotation(avl_tree_t *tree, avl_node_t *node, int balance)
{
    int left = !(balance < 0);  /* when balance = -2, left will be 0 */
    int right = 1 - left;
    int left_heavy = balance >> 1;
    int right_heavy = -left_heavy;
    avl_node_t *parent = AVL_XPARENT(node);
    avl_node_t *child = node->avl_child[left];
    avl_node_t *cright;
    avl_node_t *gchild;
    avl_node_t *gright;
    avl_node_t *gleft;
    int which_child = AVL_XCHILD(node);
    int child_bal = AVL_XBALANCE(child);
 
    /* BEGIN CSTYLED */
    /*
     * case 1 : node is overly left heavy, the left child is balanced or
     * also left heavy. This requires the following rotation.
     *
     *                   (node bal:-2)
     *                    /           \
     *                   /             \
     *              (child bal:0 or -1)
     *              /    \
     *             /      \
     *                     cright
     *
     * becomes:
     *
     *              (child bal:1 or 0)
     *              /        \
     *             /          \
     *                        (node bal:-1 or 0)
     *                         /     \
     *                        /       \
     *                     cright
     *
     * we detect this situation by noting that child's balance is not
     * right_heavy.
     */
    /* END CSTYLED */
    if (child_bal != right_heavy) {
 
        /*
         * compute new balance of nodes
         *
         * If child used to be left heavy (now balanced) we reduced
         * the height of this sub-tree -- used in "return...;" below
         */
        child_bal += right_heavy; /* adjust towards right */
 
        /*
         * move "cright" to be node's left child
         */
        cright = child->avl_child[right];
        node->avl_child[left] = cright;
        if (cright != NULL) {
            AVL_SETPARENT(cright, node);
            AVL_SETCHILD(cright, left);
        }
 
        /*
         * move node to be child's right child
         */
        child->avl_child[right] = node;
        AVL_SETBALANCE(node, -child_bal);
        AVL_SETCHILD(node, right);
        AVL_SETPARENT(node, child);
 
        /*
         * update the pointer into this subtree
         */
        AVL_SETBALANCE(child, child_bal);
        AVL_SETCHILD(child, which_child);
        AVL_SETPARENT(child, parent);
        if (parent != NULL)
            parent->avl_child[which_child] = child;
        else
            tree->avl_root = child;
 
        return (child_bal == 0);
    }
 
    /* BEGIN CSTYLED */
    /*
     * case 2 : When node is left heavy, but child is right heavy we use
     * a different rotation.
     *
     *                   (node b:-2)
     *                    /   \
     *                   /     \
     *                  /       \
     *             (child b:+1)
     *              /     \
     *             /       \
     *                   (gchild b: != 0)
     *                     /  \
     *                    /    \
     *                 gleft   gright
     *
     * becomes:
     *
     *              (gchild b:0)
     *              /       \
     *             /         \
     *            /           \
     *        (child b:?)   (node b:?)
     *         /  \          /   \
     *        /    \        /     \
     *            gleft   gright
     *
     * computing the new balances is more complicated. As an example:
     *   if gchild was right_heavy, then child is now left heavy
     *      else it is balanced
     */
    /* END CSTYLED */
    gchild = child->avl_child[right];
    gleft = gchild->avl_child[left];
    gright = gchild->avl_child[right];
 
    /*
     * move gright to left child of node and
     *
     * move gleft to right child of node
     */
    node->avl_child[left] = gright;
    if (gright != NULL) {
        AVL_SETPARENT(gright, node);
        AVL_SETCHILD(gright, left);
    }
 
    child->avl_child[right] = gleft;
    if (gleft != NULL) {
        AVL_SETPARENT(gleft, child);
        AVL_SETCHILD(gleft, right);
    }
 
    /*
     * move child to left child of gchild and
     *
     * move node to right child of gchild and
     *
     * fixup parent of all this to point to gchild
     */
    balance = AVL_XBALANCE(gchild);
    gchild->avl_child[left] = child;
    AVL_SETBALANCE(child, (balance == right_heavy ? left_heavy : 0));
    AVL_SETPARENT(child, gchild);
    AVL_SETCHILD(child, left);
 
    gchild->avl_child[right] = node;
    AVL_SETBALANCE(node, (balance == left_heavy ? right_heavy : 0));
    AVL_SETPARENT(node, gchild);
    AVL_SETCHILD(node, right);
 
    AVL_SETBALANCE(gchild, 0);
    AVL_SETPARENT(gchild, parent);
    AVL_SETCHILD(gchild, which_child);
    if (parent != NULL)
        parent->avl_child[which_child] = gchild;
    else
        tree->avl_root = gchild;
 
    return (1); /* the new tree is always shorter */
}
 
 
/*
 * Insert a new node into an AVL tree at the specified (from avl_find()) place.
 *
 * Newly inserted nodes are always leaf nodes in the tree, since avl_find()
 * searches out to the leaf positions.  The avl_index_t indicates the node
 * which will be the parent of the new node.
 *
 * After the node is inserted, a single rotation further up the tree may
 * be necessary to maintain an acceptable AVL balance.
 */
void
avl_insert(avl_tree_t *tree, void *new_data, avl_index_t where)
{
    avl_node_t *node;
    avl_node_t *parent = AVL_INDEX2NODE(where);
    int old_balance;
    int new_balance;
    int which_child = AVL_INDEX2CHILD(where);
    size_t off = tree->avl_offset;
 
    ASSERT(tree);
#ifdef _LP64
    ASSERT(((uintptr_t)new_data & 0x7) == 0);
#endif
 
    node = AVL_DATA2NODE(new_data, off);
 
    /*
     * First, add the node to the tree at the indicated position.
     */
    ++tree->avl_numnodes;
 
    node->avl_child[0] = NULL;
    node->avl_child[1] = NULL;
 
    AVL_SETCHILD(node, which_child);
    AVL_SETBALANCE(node, 0);
    AVL_SETPARENT(node, parent);
    if (parent != NULL) {
        ASSERT(parent->avl_child[which_child] == NULL);
        parent->avl_child[which_child] = node;
    } else {
        ASSERT(tree->avl_root == NULL);
        tree->avl_root = node;
    }
    /*
     * Now, back up the tree modifying the balance of all nodes above the
     * insertion point. If we get to a highly unbalanced ancestor, we
     * need to do a rotation.  If we back out of the tree we are done.
     * If we brought any subtree into perfect balance (0), we are also done.
     */
    for (;;) {
        node = parent;
        if (node == NULL)
            return;
 
        /*
         * Compute the new balance
         */
        old_balance = AVL_XBALANCE(node);
        new_balance = old_balance + avl_child2balance[which_child];
 
        /*
         * If we introduced equal balance, then we are done immediately
         */
        if (new_balance == 0) {
            AVL_SETBALANCE(node, 0);
            return;
        }
 
        /*
         * If both old and new are not zero we went
         * from -1 to -2 balance, do a rotation.
         */
        if (old_balance != 0)
            break;
 
        AVL_SETBALANCE(node, new_balance);
        parent = AVL_XPARENT(node);
        which_child = AVL_XCHILD(node);
    }
 
    /*
     * perform a rotation to fix the tree and return
     */
    (void) avl_rotation(tree, node, new_balance);
}
 
/*
 * Insert "new_data" in "tree" in the given "direction" either after or
 * before (AVL_AFTER, AVL_BEFORE) the data "here".
 *
 * Insertions can only be done at empty leaf points in the tree, therefore
 * if the given child of the node is already present we move to either
 * the AVL_PREV or AVL_NEXT and reverse the insertion direction. Since
 * every other node in the tree is a leaf, this always works.
 *
 * To help developers using this interface, we assert that the new node
 * is correctly ordered at every step of the way in DEBUG kernels.
 */
void
avl_insert_here(
    avl_tree_t *tree,
    void *new_data,
    void *here,
    int direction)
{
    avl_node_t *node;
    int child = direction;  /* rely on AVL_BEFORE == 0, AVL_AFTER == 1 */
#ifdef DEBUG
    int diff;
#endif
 
    ASSERT(tree != NULL);
    ASSERT(new_data != NULL);
    ASSERT(here != NULL);
    ASSERT(direction == AVL_BEFORE || direction == AVL_AFTER);
 
    /*
     * If corresponding child of node is not NULL, go to the neighboring
     * node and reverse the insertion direction.
     */
    node = AVL_DATA2NODE(here, tree->avl_offset);
 
#ifdef DEBUG
    diff = tree->avl_compar(new_data, here);
    ASSERT(-1 <= diff && diff <= 1);
    ASSERT(diff != 0);
    ASSERT(diff > 0 ? child == 1 : child == 0);
#endif
 
    if (node->avl_child[child] != NULL) {
        node = node->avl_child[child];
        child = 1 - child;
        while (node->avl_child[child] != NULL) {
#ifdef DEBUG
            diff = tree->avl_compar(new_data,
                AVL_NODE2DATA(node, tree->avl_offset));
            ASSERT(-1 <= diff && diff <= 1);
            ASSERT(diff != 0);
            ASSERT(diff > 0 ? child == 1 : child == 0);
#endif
            node = node->avl_child[child];
        }
#ifdef DEBUG
        diff = tree->avl_compar(new_data,
            AVL_NODE2DATA(node, tree->avl_offset));
        ASSERT(-1 <= diff && diff <= 1);
        ASSERT(diff != 0);
        ASSERT(diff > 0 ? child == 1 : child == 0);
#endif
    }
    ASSERT(node->avl_child[child] == NULL);
 
    avl_insert(tree, new_data, AVL_MKINDEX(node, child));
}
 
/*
 * Add a new node to an AVL tree.
 */
void
avl_add(avl_tree_t *tree, void *new_node)
{
    avl_index_t where;
 
    /*
     * This is unfortunate.  We want to call panic() here, even for
     * non-DEBUG kernels.  In userland, however, we can't depend on anything
     * in libc or else the rtld build process gets confused.  So, all we can
     * do in userland is resort to a normal ASSERT().
     */
    memset(&where, 0, sizeof (where));
    VERIFY3P(avl_find(tree, new_node, &where), ==, NULL);
    avl_insert(tree, new_node, where);
}
 
/*
 * Delete a node from the AVL tree.  Deletion is similar to insertion, but
 * with 2 complications.
 *
 * First, we may be deleting an interior node. Consider the following subtree:
 *
 *     d           c            c
 *    / \         / \          / \
 *   b   e       b   e        b   e
 *  / \         / \          /
 * a   c       a            a
 *
 * When we are deleting node (d), we find and bring up an adjacent valued leaf
 * node, say (c), to take the interior node's place. In the code this is
 * handled by temporarily swapping (d) and (c) in the tree and then using
 * common code to delete (d) from the leaf position.
 *
 * Secondly, an interior deletion from a deep tree may require more than one
 * rotation to fix the balance. This is handled by moving up the tree through
 * parents and applying rotations as needed. The return value from
 * avl_rotation() is used to detect when a subtree did not change overall
 * height due to a rotation.
 */
void
avl_remove(avl_tree_t *tree, void *data)
{
    avl_node_t *delete;
    avl_node_t *parent;
    avl_node_t *node;
    avl_node_t tmp;
    int old_balance;
    int new_balance;
    int left;
    int right;
    int which_child;
    size_t off = tree->avl_offset;
 
    ASSERT(tree);
 
    delete = AVL_DATA2NODE(data, off);
 
    /*
     * Deletion is easiest with a node that has at most 1 child.
     * We swap a node with 2 children with a sequentially valued
     * neighbor node. That node will have at most 1 child. Note this
     * has no effect on the ordering of the remaining nodes.
     *
     * As an optimization, we choose the greater neighbor if the tree
     * is right heavy, otherwise the left neighbor. This reduces the
     * number of rotations needed.
     */
    if (delete->avl_child[0] != NULL && delete->avl_child[1] != NULL) {
 
        /*
         * choose node to swap from whichever side is taller
         */
        old_balance = AVL_XBALANCE(delete);
        left = avl_balance2child[old_balance + 1];
        right = 1 - left;
 
        /*
         * get to the previous value'd node
         * (down 1 left, as far as possible right)
         */
        for (node = delete->avl_child[left];
            node->avl_child[right] != NULL;
            node = node->avl_child[right])
            ;
 
        /*
         * create a temp placeholder for 'node'
         * move 'node' to delete's spot in the tree
         */
        tmp = *node;
 
        *node = *delete;
        if (node->avl_child[left] == node)
            node->avl_child[left] = &tmp;
 
        parent = AVL_XPARENT(node);
        if (parent != NULL)
            parent->avl_child[AVL_XCHILD(node)] = node;
        else
            tree->avl_root = node;
        AVL_SETPARENT(node->avl_child[left], node);
        AVL_SETPARENT(node->avl_child[right], node);
 
        /*
         * Put tmp where node used to be (just temporary).
         * It always has a parent and at most 1 child.
         */
        delete = &tmp;
        parent = AVL_XPARENT(delete);
        parent->avl_child[AVL_XCHILD(delete)] = delete;
        which_child = (delete->avl_child[1] != 0);
        if (delete->avl_child[which_child] != NULL)
            AVL_SETPARENT(delete->avl_child[which_child], delete);
    }
 
 
    /*
     * Here we know "delete" is at least partially a leaf node. It can
     * be easily removed from the tree.
     */
    ASSERT(tree->avl_numnodes > 0);
    --tree->avl_numnodes;
    parent = AVL_XPARENT(delete);
    which_child = AVL_XCHILD(delete);
    if (delete->avl_child[0] != NULL)
        node = delete->avl_child[0];
    else
        node = delete->avl_child[1];
 
    /*
     * Connect parent directly to node (leaving out delete).
     */
    if (node != NULL) {
        AVL_SETPARENT(node, parent);
        AVL_SETCHILD(node, which_child);
    }
    if (parent == NULL) {
        tree->avl_root = node;
        return;
    }
    parent->avl_child[which_child] = node;
 
 
    /*
     * Since the subtree is now shorter, begin adjusting parent balances
     * and performing any needed rotations.
     */
    do {
 
        /*
         * Move up the tree and adjust the balance
         *
         * Capture the parent and which_child values for the next
         * iteration before any rotations occur.
         */
        node = parent;
        old_balance = AVL_XBALANCE(node);
        new_balance = old_balance - avl_child2balance[which_child];
        parent = AVL_XPARENT(node);
        which_child = AVL_XCHILD(node);
 
        /*
         * If a node was in perfect balance but isn't anymore then
         * we can stop, since the height didn't change above this point
         * due to a deletion.
         */
        if (old_balance == 0) {
            AVL_SETBALANCE(node, new_balance);
            break;
        }
 
        /*
         * If the new balance is zero, we don't need to rotate
         * else
         * need a rotation to fix the balance.
         * If the rotation doesn't change the height
         * of the sub-tree we have finished adjusting.
         */
        if (new_balance == 0)
            AVL_SETBALANCE(node, new_balance);
        else if (!avl_rotation(tree, node, new_balance))
            break;
    } while (parent != NULL);
}
 
#define AVL_REINSERT(tree, obj)     \
    avl_remove((tree), (obj));  \
    avl_add((tree), (obj))
 
bool_t
avl_update_lt(avl_tree_t *t, void *obj)
{
    void *neighbor;
 
    ASSERT(((neighbor = AVL_NEXT(t, obj)) == NULL) ||
        (t->avl_compar(obj, neighbor) <= 0));
 
    neighbor = AVL_PREV(t, obj);
    if ((neighbor != NULL) && (t->avl_compar(obj, neighbor) < 0)) {
        AVL_REINSERT(t, obj);
        return (B_TRUE);
    }
 
    return (B_FALSE);
}
 
bool_t
avl_update_gt(avl_tree_t *t, void *obj)
{
    void *neighbor;
 
    ASSERT(((neighbor = AVL_PREV(t, obj)) == NULL) ||
        (t->avl_compar(obj, neighbor) >= 0));
 
    neighbor = AVL_NEXT(t, obj);
    if ((neighbor != NULL) && (t->avl_compar(obj, neighbor) > 0)) {
        AVL_REINSERT(t, obj);
        return (B_TRUE);
    }
 
    return (B_FALSE);
}
 
bool_t
avl_update(avl_tree_t *t, void *obj)
{
    void *neighbor;
 
    neighbor = AVL_PREV(t, obj);
    if ((neighbor != NULL) && (t->avl_compar(obj, neighbor) < 0)) {
        AVL_REINSERT(t, obj);
        return (B_TRUE);
    }
 
    neighbor = AVL_NEXT(t, obj);
    if ((neighbor != NULL) && (t->avl_compar(obj, neighbor) > 0)) {
        AVL_REINSERT(t, obj);
        return (B_TRUE);
    }
 
    return (B_FALSE);
}
 
/*
 * initialize a new AVL tree
 */
void
avl_create(avl_tree_t *tree, int (*compar) (const void *, const void *),
    size_t size, size_t offset)
{
    ASSERT(tree);
    ASSERT(compar);
    ASSERT(size > 0);
    ASSERT(size >= offset + sizeof (avl_node_t));
#ifdef _LP64
    ASSERT((offset & 0x7) == 0);
#endif
 
    tree->avl_compar = compar;
    tree->avl_root = NULL;
    tree->avl_numnodes = 0;
    tree->avl_size = size;
    tree->avl_offset = offset;
}
 
/*
 * Delete a tree.
 */
/* ARGSUSED */
void
avl_destroy(avl_tree_t *tree)
{
    LACF_UNUSED(tree);
    ASSERT(tree);
    ASSERT(tree->avl_numnodes == 0);
    ASSERT(tree->avl_root == NULL);
}
 
 
/*
 * Return the number of nodes in an AVL tree.
 */
unsigned long
avl_numnodes(const avl_tree_t *tree)
{
    ASSERT(tree);
    return (tree->avl_numnodes);
}
 
bool_t
avl_is_empty(avl_tree_t *tree)
{
    ASSERT(tree);
    return (tree->avl_numnodes == 0);
}
 
#define CHILDBIT    (1L)
 
/*
 * Post-order tree walk used to visit all tree nodes and destroy the tree
 * in post order. This is used for destroying a tree w/o paying any cost
 * for rebalancing it.
 *
 * example:
 *
 *  void *cookie = NULL;
 *  my_data_t *node;
 *
 *  while ((node = avl_destroy_nodes(tree, &cookie)) != NULL)
 *      free(node);
 *  avl_destroy(tree);
 *
 * The cookie is really an avl_node_t to the current node's parent and
 * an indication of which child you looked at last.
 *
 * On input, a cookie value of CHILDBIT indicates the tree is done.
 */
void *
avl_destroy_nodes(avl_tree_t *tree, void **cookie)
{
    avl_node_t  *node;
    avl_node_t  *parent;
    int     child;
    void        *first;
    size_t      off = tree->avl_offset;
 
    /*
     * Initial calls go to the first node or it's right descendant.
     */
    if (*cookie == NULL) {
        first = avl_first(tree);
 
        /*
         * deal with an empty tree
         */
        if (first == NULL) {
            *cookie = (void *)CHILDBIT;
            return (NULL);
        }
 
        node = AVL_DATA2NODE(first, off);
        parent = AVL_XPARENT(node);
        goto check_right_side;
    }
 
    /*
     * If there is no parent to return to we are done.
     */
    parent = (avl_node_t *)((uintptr_t)(*cookie) & ~CHILDBIT);
    if (parent == NULL) {
        if (tree->avl_root != NULL) {
            ASSERT(tree->avl_numnodes == 1);
            tree->avl_root = NULL;
            tree->avl_numnodes = 0;
        }
        return (NULL);
    }
 
    /*
     * Remove the child pointer we just visited from the parent and tree.
     */
    child = (uintptr_t)(*cookie) & CHILDBIT;
    parent->avl_child[child] = NULL;
    ASSERT(tree->avl_numnodes > 1);
    --tree->avl_numnodes;
 
    /*
     * If we just did a right child or there isn't one, go up to parent.
     */
    if (child == 1 || parent->avl_child[1] == NULL) {
        node = parent;
        parent = AVL_XPARENT(parent);
        goto done;
    }
 
    /*
     * Do parent's right child, then leftmost descendent.
     */
    node = parent->avl_child[1];
    while (node->avl_child[0] != NULL) {
        parent = node;
        node = node->avl_child[0];
    }
 
    /*
     * If here, we moved to a left child. It may have one
     * child on the right (when balance == +1).
     */
check_right_side:
    if (node->avl_child[1] != NULL) {
        ASSERT(AVL_XBALANCE(node) == 1);
        parent = node;
        node = node->avl_child[1];
        ASSERT(node->avl_child[0] == NULL &&
            node->avl_child[1] == NULL);
    } else {
        ASSERT(AVL_XBALANCE(node) <= 0);
    }
 
done:
    if (parent == NULL) {
        *cookie = (void *)CHILDBIT;
        ASSERT(node == tree->avl_root);
    } else {
        *cookie = (void *)((uintptr_t)parent | AVL_XCHILD(node));
    }
 
    return (AVL_NODE2DATA(node, off));
}