SYSENTER/SYSCALL support

[minix.git] / common / lib / libprop / prop_rb.c

/*      $NetBSD: prop_rb.c,v 1.9 2008/06/17 21:29:47 thorpej Exp $      */

/*-
 * Copyright (c) 2001 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Matt Thomas <matt@3am-software.com>.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <prop/proplib.h>

#include "prop_object_impl.h"
#include "prop_rb_impl.h"

#undef KASSERT
#ifdef RBDEBUG
#define KASSERT(x)      _PROP_ASSERT(x)
#else
#define KASSERT(x)      /* nothing */
#endif

#ifndef __predict_false
#define __predict_false(x)      (x)
#endif

static void rb_tree_reparent_nodes(struct rb_tree *, struct rb_node *,
                                   unsigned int);
static void rb_tree_insert_rebalance(struct rb_tree *, struct rb_node *);
static void rb_tree_removal_rebalance(struct rb_tree *, struct rb_node *,
        unsigned int);
#ifdef RBDEBUG
static const struct rb_node *rb_tree_iterate_const(const struct rb_tree *,
        const struct rb_node *, unsigned int);
static bool rb_tree_check_node(const struct rb_tree *, const struct rb_node *,
        const struct rb_node *, bool);
#endif

#ifdef RBDEBUG
#define RBT_COUNT_INCR(rbt)     (rbt)->rbt_count++
#define RBT_COUNT_DECR(rbt)     (rbt)->rbt_count--
#else
#define RBT_COUNT_INCR(rbt)     /* nothing */
#define RBT_COUNT_DECR(rbt)     /* nothing */
#endif

#define RBUNCONST(a)    ((void *)(unsigned long)(const void *)(a))

/*
 * Rather than testing for the NULL everywhere, all terminal leaves are
 * pointed to this node (and that includes itself).  Note that by setting
 * it to be const, that on some architectures trying to write to it will
 * cause a fault.
 */
static const struct rb_node sentinel_node = {
        .rb_nodes = { RBUNCONST(&sentinel_node),
                      RBUNCONST(&sentinel_node),
                      NULL },
        .rb_u = { .u_s = { .s_sentinel = 1 } },
};

void
_prop_rb_tree_init(struct rb_tree *rbt, const struct rb_tree_ops *ops)
{
        RB_TAILQ_INIT(&rbt->rbt_nodes);
#ifdef RBDEBUG
        rbt->rbt_count = 0;
#endif
        rbt->rbt_ops = ops;
        *((const struct rb_node **)&rbt->rbt_root) = &sentinel_node;
}

/*
 * Swap the location and colors of 'self' and its child @ which.  The child
 * can not be a sentinel node.
 */
/*ARGSUSED*/
static void
rb_tree_reparent_nodes(struct rb_tree *rbt _PROP_ARG_UNUSED,
    struct rb_node *old_father, unsigned int which)
{
        const unsigned int other = which ^ RB_NODE_OTHER;
        struct rb_node * const grandpa = old_father->rb_parent;
        struct rb_node * const old_child = old_father->rb_nodes[which];
        struct rb_node * const new_father = old_child;
        struct rb_node * const new_child = old_father;
        unsigned int properties;

        KASSERT(which == RB_NODE_LEFT || which == RB_NODE_RIGHT);

        KASSERT(!RB_SENTINEL_P(old_child));
        KASSERT(old_child->rb_parent == old_father);

        KASSERT(rb_tree_check_node(rbt, old_father, NULL, false));
        KASSERT(rb_tree_check_node(rbt, old_child, NULL, false));
        KASSERT(RB_ROOT_P(old_father) || rb_tree_check_node(rbt, grandpa, NULL, false));

        /*
         * Exchange descendant linkages.
         */
        grandpa->rb_nodes[old_father->rb_position] = new_father;
        new_child->rb_nodes[which] = old_child->rb_nodes[other];
        new_father->rb_nodes[other] = new_child;

        /*
         * Update ancestor linkages
         */
        new_father->rb_parent = grandpa;
        new_child->rb_parent = new_father;

        /*
         * Exchange properties between new_father and new_child.  The only
         * change is that new_child's position is now on the other side.
         */
        properties = old_child->rb_properties;
        new_father->rb_properties = old_father->rb_properties;
        new_child->rb_properties = properties;
        new_child->rb_position = other;

        /*
         * Make sure to reparent the new child to ourself.
         */
        if (!RB_SENTINEL_P(new_child->rb_nodes[which])) {
                new_child->rb_nodes[which]->rb_parent = new_child;
                new_child->rb_nodes[which]->rb_position = which;
        }

        KASSERT(rb_tree_check_node(rbt, new_father, NULL, false));
        KASSERT(rb_tree_check_node(rbt, new_child, NULL, false));
        KASSERT(RB_ROOT_P(new_father) || rb_tree_check_node(rbt, grandpa, NULL, false));
}

bool
_prop_rb_tree_insert_node(struct rb_tree *rbt, struct rb_node *self)
{
        struct rb_node *parent, *tmp;
        rb_compare_nodes_fn compare_nodes = rbt->rbt_ops->rbto_compare_nodes;
        unsigned int position;

        self->rb_properties = 0;
        tmp = rbt->rbt_root;
        /*
         * This is a hack.  Because rbt->rbt_root is just a struct rb_node *,
         * just like rb_node->rb_nodes[RB_NODE_LEFT], we can use this fact to
         * avoid a lot of tests for root and know that even at root,
         * updating rb_node->rb_parent->rb_nodes[rb_node->rb_position] will
         * rbt->rbt_root.
         */
        /* LINTED: see above */
        parent = (struct rb_node *)&rbt->rbt_root;
        position = RB_NODE_LEFT;

        /*
         * Find out where to place this new leaf.
         */
        while (!RB_SENTINEL_P(tmp)) {
                const int diff = (*compare_nodes)(tmp, self);
                if (__predict_false(diff == 0)) {
                        /*
                         * Node already exists; don't insert.
                         */
                        return false;
                }
                parent = tmp;
                KASSERT(diff != 0);
                if (diff < 0) {
                        position = RB_NODE_LEFT;
                } else {
                        position = RB_NODE_RIGHT;
                }
                tmp = parent->rb_nodes[position];
        }

#ifdef RBDEBUG
        {
                struct rb_node *prev = NULL, *next = NULL;

                if (position == RB_NODE_RIGHT)
                        prev = parent;
                else if (tmp != rbt->rbt_root)
                        next = parent;

                /*
                 * Verify our sequential position
                 */
                KASSERT(prev == NULL || !RB_SENTINEL_P(prev));
                KASSERT(next == NULL || !RB_SENTINEL_P(next));
                if (prev != NULL && next == NULL)
                        next = TAILQ_NEXT(prev, rb_link);
                if (prev == NULL && next != NULL)
                        prev = TAILQ_PREV(next, rb_node_qh, rb_link);
                KASSERT(prev == NULL || !RB_SENTINEL_P(prev));
                KASSERT(next == NULL || !RB_SENTINEL_P(next));
                KASSERT(prev == NULL
                        || (*compare_nodes)(prev, self) > 0);
                KASSERT(next == NULL
                        || (*compare_nodes)(self, next) > 0);
        }
#endif

        /*
         * Initialize the node and insert as a leaf into the tree.
         */
        self->rb_parent = parent;
        self->rb_position = position;
        /* LINTED: rbt_root hack */
        if (__predict_false(parent == (struct rb_node *) &rbt->rbt_root)) {
                RB_MARK_ROOT(self);
        } else {
                KASSERT(position == RB_NODE_LEFT || position == RB_NODE_RIGHT);
                KASSERT(!RB_ROOT_P(self));      /* Already done */
        }
        KASSERT(RB_SENTINEL_P(parent->rb_nodes[position]));
        self->rb_left = parent->rb_nodes[position];
        self->rb_right = parent->rb_nodes[position];
        parent->rb_nodes[position] = self;
        KASSERT(self->rb_left == &sentinel_node &&
            self->rb_right == &sentinel_node);

        /*
         * Insert the new node into a sorted list for easy sequential access
         */
        RBT_COUNT_INCR(rbt);
#ifdef RBDEBUG
        if (RB_ROOT_P(self)) {
                RB_TAILQ_INSERT_HEAD(&rbt->rbt_nodes, self, rb_link);
        } else if (position == RB_NODE_LEFT) {
                KASSERT((*compare_nodes)(self, self->rb_parent) > 0);
                RB_TAILQ_INSERT_BEFORE(self->rb_parent, self, rb_link);
        } else {
                KASSERT((*compare_nodes)(self->rb_parent, self) > 0);
                RB_TAILQ_INSERT_AFTER(&rbt->rbt_nodes, self->rb_parent,
                    self, rb_link);
        }
#endif

#if 0
        /*
         * Validate the tree before we rebalance
         */
        _prop_rb_tree_check(rbt, false);
#endif

        /*
         * Rebalance tree after insertion
         */
        rb_tree_insert_rebalance(rbt, self);

#if 0
        /*
         * Validate the tree after we rebalanced
         */
        _prop_rb_tree_check(rbt, true);
#endif

        return true;
}
\f
static void
rb_tree_insert_rebalance(struct rb_tree *rbt, struct rb_node *self)
{
        RB_MARK_RED(self);

        while (!RB_ROOT_P(self) && RB_RED_P(self->rb_parent)) {
                const unsigned int which =
                     (self->rb_parent == self->rb_parent->rb_parent->rb_left
                        ? RB_NODE_LEFT
                        : RB_NODE_RIGHT);
                const unsigned int other = which ^ RB_NODE_OTHER;
                struct rb_node * father = self->rb_parent;
                struct rb_node * grandpa = father->rb_parent;
                struct rb_node * const uncle = grandpa->rb_nodes[other];

                KASSERT(!RB_SENTINEL_P(self));
                /*
                 * We are red and our parent is red, therefore we must have a
                 * grandfather and he must be black.
                 */
                KASSERT(RB_RED_P(self)
                        && RB_RED_P(father)
                        && RB_BLACK_P(grandpa));

                if (RB_RED_P(uncle)) {
                        /*
                         * Case 1: our uncle is red
                         *   Simply invert the colors of our parent and
                         *   uncle and make our grandparent red.  And
                         *   then solve the problem up at his level.
                         */
                        RB_MARK_BLACK(uncle);
                        RB_MARK_BLACK(father);
                        RB_MARK_RED(grandpa);
                        self = grandpa;
                        continue;
                }
                /*
                 * Case 2&3: our uncle is black.
                 */
                if (self == father->rb_nodes[other]) {
                        /*
                         * Case 2: we are on the same side as our uncle
                         *   Swap ourselves with our parent so this case
                         *   becomes case 3.  Basically our parent becomes our
                         *   child.
                         */
                        rb_tree_reparent_nodes(rbt, father, other);
                        KASSERT(father->rb_parent == self);
                        KASSERT(self->rb_nodes[which] == father);
                        KASSERT(self->rb_parent == grandpa);
                        self = father;
                        father = self->rb_parent;
                }
                KASSERT(RB_RED_P(self) && RB_RED_P(father));
                KASSERT(grandpa->rb_nodes[which] == father);
                /*
                 * Case 3: we are opposite a child of a black uncle.
                 *   Swap our parent and grandparent.  Since our grandfather
                 *   is black, our father will become black and our new sibling
                 *   (former grandparent) will become red.
                 */
                rb_tree_reparent_nodes(rbt, grandpa, which);
                KASSERT(self->rb_parent == father);
                KASSERT(self->rb_parent->rb_nodes[self->rb_position ^ RB_NODE_OTHER] == grandpa);
                KASSERT(RB_RED_P(self));
                KASSERT(RB_BLACK_P(father));
                KASSERT(RB_RED_P(grandpa));
                break;
        }

        /*
         * Final step: Set the root to black.
         */
        RB_MARK_BLACK(rbt->rbt_root);
}
\f
struct rb_node *
_prop_rb_tree_find(struct rb_tree *rbt, const void *key)
{
        struct rb_node *parent = rbt->rbt_root;
        rb_compare_key_fn compare_key = rbt->rbt_ops->rbto_compare_key;

        while (!RB_SENTINEL_P(parent)) {
                const int diff = (*compare_key)(parent, key);
                if (diff == 0)
                        return parent;
                parent = parent->rb_nodes[diff > 0];
        }

        return NULL;
}
\f
static void
rb_tree_prune_node(struct rb_tree *rbt, struct rb_node *self, int rebalance)
{
        const unsigned int which = self->rb_position;
        struct rb_node *father = self->rb_parent;

        KASSERT(rebalance || (RB_ROOT_P(self) || RB_RED_P(self)));
        KASSERT(!rebalance || RB_BLACK_P(self));
        KASSERT(RB_CHILDLESS_P(self));
        KASSERT(rb_tree_check_node(rbt, self, NULL, false));

        father->rb_nodes[which] = self->rb_left;

        /*
         * Remove ourselves from the node list and decrement the count.
         */
        RB_TAILQ_REMOVE(&rbt->rbt_nodes, self, rb_link);
        RBT_COUNT_DECR(rbt);

        if (rebalance)
                rb_tree_removal_rebalance(rbt, father, which);
        KASSERT(RB_ROOT_P(self) || rb_tree_check_node(rbt, father, NULL, true));
}

static void
rb_tree_swap_prune_and_rebalance(struct rb_tree *rbt, struct rb_node *self,
        struct rb_node *standin)
{
        unsigned int standin_which = standin->rb_position;
        unsigned int standin_other = standin_which ^ RB_NODE_OTHER;
        struct rb_node *standin_child;
        struct rb_node *standin_father;
        bool rebalance = RB_BLACK_P(standin);

        if (standin->rb_parent == self) {
                /*
                 * As a child of self, any childen would be opposite of
                 * our parent (self).
                 */
                KASSERT(RB_SENTINEL_P(standin->rb_nodes[standin_other]));
                standin_child = standin->rb_nodes[standin_which];
        } else {
                /*
                 * Since we aren't a child of self, any childen would be
                 * on the same side as our parent (self).
                 */
                KASSERT(RB_SENTINEL_P(standin->rb_nodes[standin_which]));
                standin_child = standin->rb_nodes[standin_other];
        }

        /*
         * the node we are removing must have two children.
         */
        KASSERT(RB_TWOCHILDREN_P(self));
        /*
         * If standin has a child, it must be red.
         */
        KASSERT(RB_SENTINEL_P(standin_child) || RB_RED_P(standin_child));

        /*
         * Verify things are sane.
         */
        KASSERT(rb_tree_check_node(rbt, self, NULL, false));
        KASSERT(rb_tree_check_node(rbt, standin, NULL, false));

        if (!RB_SENTINEL_P(standin_child)) {
                /*
                 * We know we have a red child so if we swap them we can
                 * void flipping standin's child to black afterwards.
                 */
                KASSERT(rb_tree_check_node(rbt, standin_child, NULL, true));
                rb_tree_reparent_nodes(rbt, standin,
                    standin_child->rb_position);
                KASSERT(rb_tree_check_node(rbt, standin, NULL, true));
                KASSERT(rb_tree_check_node(rbt, standin_child, NULL, true));
                /*
                 * Since we are removing a red leaf, no need to rebalance.
                 */
                rebalance = false;
                /*
                 * We know that standin can not be a child of self, so
                 * update before of that.
                 */
                KASSERT(standin->rb_parent != self);
                standin_which = standin->rb_position;
                standin_other = standin_which ^ RB_NODE_OTHER;
        }
        KASSERT(RB_CHILDLESS_P(standin));

        /*
         * If we are about to delete the standin's father, then when we call
         * rebalance, we need to use ourselves as our father.  Otherwise
         * remember our original father.  Also, if we are our standin's father
         * we only need to reparent the standin's brother.
         */
        if (standin->rb_parent == self) {
                /*
                 * |   R   -->   S   |
                 * | Q   S --> Q   * |
                 * |       -->       |
                 */
                standin_father = standin;
                KASSERT(RB_SENTINEL_P(standin->rb_nodes[standin_other]));
                KASSERT(!RB_SENTINEL_P(self->rb_nodes[standin_other]));
                KASSERT(self->rb_nodes[standin_which] == standin);
                /*
                 * Make our brother our son.
                 */
                standin->rb_nodes[standin_other] = self->rb_nodes[standin_other];
                standin->rb_nodes[standin_other]->rb_parent = standin;
                KASSERT(standin->rb_nodes[standin_other]->rb_position == standin_other);
        } else {
                /*
                 * |  P      -->  P    |
                 * |      S  -->    Q  |
                 * |    Q    -->       |
                 */
                standin_father = standin->rb_parent;
                standin_father->rb_nodes[standin_which] =
                    standin->rb_nodes[standin_which];
                standin->rb_left = self->rb_left;
                standin->rb_right = self->rb_right;
                standin->rb_left->rb_parent = standin;
                standin->rb_right->rb_parent = standin;
        }

        /*
         * Now copy the result of self to standin and then replace
         * self with standin in the tree.
         */
        standin->rb_parent = self->rb_parent;
        standin->rb_properties = self->rb_properties;
        standin->rb_parent->rb_nodes[standin->rb_position] = standin;

        /*
         * Remove ourselves from the node list and decrement the count.
         */
        RB_TAILQ_REMOVE(&rbt->rbt_nodes, self, rb_link);
        RBT_COUNT_DECR(rbt);

        KASSERT(rb_tree_check_node(rbt, standin, NULL, false));
        KASSERT(rb_tree_check_node(rbt, standin_father, NULL, false));

        if (!rebalance)
                return;

        rb_tree_removal_rebalance(rbt, standin_father, standin_which);
        KASSERT(rb_tree_check_node(rbt, standin, NULL, true));
}

/*
 * We could do this by doing
 *      rb_tree_node_swap(rbt, self, which);
 *      rb_tree_prune_node(rbt, self, false);
 *
 * But it's more efficient to just evalate and recolor the child.
 */
/*ARGSUSED*/
static void
rb_tree_prune_blackred_branch(struct rb_tree *rbt _PROP_ARG_UNUSED,
    struct rb_node *self, unsigned int which)
{
        struct rb_node *parent = self->rb_parent;
        struct rb_node *child = self->rb_nodes[which];

        KASSERT(which == RB_NODE_LEFT || which == RB_NODE_RIGHT);
        KASSERT(RB_BLACK_P(self) && RB_RED_P(child));
        KASSERT(!RB_TWOCHILDREN_P(child));
        KASSERT(RB_CHILDLESS_P(child));
        KASSERT(rb_tree_check_node(rbt, self, NULL, false));
        KASSERT(rb_tree_check_node(rbt, child, NULL, false));

        /*
         * Remove ourselves from the tree and give our former child our
         * properties (position, color, root).
         */
        parent->rb_nodes[self->rb_position] = child;
        child->rb_parent = parent;
        child->rb_properties = self->rb_properties;

        /*
         * Remove ourselves from the node list and decrement the count.
         */
        RB_TAILQ_REMOVE(&rbt->rbt_nodes, self, rb_link);
        RBT_COUNT_DECR(rbt);

        KASSERT(RB_ROOT_P(self) || rb_tree_check_node(rbt, parent, NULL, true));
        KASSERT(rb_tree_check_node(rbt, child, NULL, true));
}
/*
 *
 */
void
_prop_rb_tree_remove_node(struct rb_tree *rbt, struct rb_node *self)
{
        struct rb_node *standin;
        unsigned int which;
        /*
         * In the following diagrams, we (the node to be removed) are S.  Red
         * nodes are lowercase.  T could be either red or black.
         *
         * Remember the major axiom of the red-black tree: the number of
         * black nodes from the root to each leaf is constant across all
         * leaves, only the number of red nodes varies.
         *
         * Thus removing a red leaf doesn't require any other changes to a
         * red-black tree.  So if we must remove a node, attempt to rearrange
         * the tree so we can remove a red node.
         *
         * The simpliest case is a childless red node or a childless root node:
         *
         * |    T  -->    T  |    or    |  R  -->  *  |
         * |  s    -->  *    |
         */
        if (RB_CHILDLESS_P(self)) {
                if (RB_RED_P(self) || RB_ROOT_P(self)) {
                        rb_tree_prune_node(rbt, self, false);
                        return;
                }
                rb_tree_prune_node(rbt, self, true);
                return;
        }
        KASSERT(!RB_CHILDLESS_P(self));
        if (!RB_TWOCHILDREN_P(self)) {
                /*
                 * The next simpliest case is the node we are deleting is
                 * black and has one red child.
                 *
                 * |      T  -->      T  -->      T  |
                 * |    S    -->  R      -->  R      |
                 * |  r      -->    s    -->    *    |
                 */
                which = RB_LEFT_SENTINEL_P(self) ? RB_NODE_RIGHT : RB_NODE_LEFT;
                KASSERT(RB_BLACK_P(self));
                KASSERT(RB_RED_P(self->rb_nodes[which]));
                KASSERT(RB_CHILDLESS_P(self->rb_nodes[which]));
                rb_tree_prune_blackred_branch(rbt, self, which);
                return;
        }
        KASSERT(RB_TWOCHILDREN_P(self));

        /*
         * We invert these because we prefer to remove from the inside of
         * the tree.
         */
        which = self->rb_position ^ RB_NODE_OTHER;

        /*
         * Let's find the node closes to us opposite of our parent
         * Now swap it with ourself, "prune" it, and rebalance, if needed.
         */
        standin = _prop_rb_tree_iterate(rbt, self, which);
        rb_tree_swap_prune_and_rebalance(rbt, self, standin);
}

static void
rb_tree_removal_rebalance(struct rb_tree *rbt, struct rb_node *parent,
        unsigned int which)
{
        KASSERT(!RB_SENTINEL_P(parent));
        KASSERT(RB_SENTINEL_P(parent->rb_nodes[which]));
        KASSERT(which == RB_NODE_LEFT || which == RB_NODE_RIGHT);

        while (RB_BLACK_P(parent->rb_nodes[which])) {
                unsigned int other = which ^ RB_NODE_OTHER;
                struct rb_node *brother = parent->rb_nodes[other];

                KASSERT(!RB_SENTINEL_P(brother));
                /*
                 * For cases 1, 2a, and 2b, our brother's children must
                 * be black and our father must be black
                 */
                if (RB_BLACK_P(parent)
                    && RB_BLACK_P(brother->rb_left)
                    && RB_BLACK_P(brother->rb_right)) {
                        /*
                         * Case 1: Our brother is red, swap its position
                         * (and colors) with our parent.  This is now case 2b.
                         *
                         *    B         ->        D
                         *  x     d     ->    b     E
                         *      C   E   ->  x   C
                         */
                        if (RB_RED_P(brother)) {
                                KASSERT(RB_BLACK_P(parent));
                                rb_tree_reparent_nodes(rbt, parent, other);
                                brother = parent->rb_nodes[other];
                                KASSERT(!RB_SENTINEL_P(brother));
                                KASSERT(RB_BLACK_P(brother));
                                KASSERT(RB_RED_P(parent));
                                KASSERT(rb_tree_check_node(rbt, brother, NULL, false));
                                KASSERT(rb_tree_check_node(rbt, parent, NULL, false));
                        } else {
                                /*
                                 * Both our parent and brother are black.
                                 * Change our brother to red, advance up rank
                                 * and go through the loop again.
                                 *
                                 *    B         ->    B
                                 *  A     D     ->  A     d
                                 *      C   E   ->      C   E
                                 */
                                RB_MARK_RED(brother);
                                KASSERT(RB_BLACK_P(brother->rb_left));
                                KASSERT(RB_BLACK_P(brother->rb_right));
                                if (RB_ROOT_P(parent))
                                        return;
                                KASSERT(rb_tree_check_node(rbt, brother, NULL, false));
                                KASSERT(rb_tree_check_node(rbt, parent, NULL, false));
                                which = parent->rb_position;
                                parent = parent->rb_parent;
                        }
                } else if (RB_RED_P(parent)
                    && RB_BLACK_P(brother)
                    && RB_BLACK_P(brother->rb_left)
                    && RB_BLACK_P(brother->rb_right)) {
                        KASSERT(RB_BLACK_P(brother));
                        KASSERT(RB_BLACK_P(brother->rb_left));
                        KASSERT(RB_BLACK_P(brother->rb_right));
                        RB_MARK_BLACK(parent);
                        RB_MARK_RED(brother);
                        KASSERT(rb_tree_check_node(rbt, brother, NULL, true));
                        break;          /* We're done! */
                } else {
                        KASSERT(RB_BLACK_P(brother));
                        KASSERT(!RB_CHILDLESS_P(brother));
                        /*
                         * Case 3: our brother is black, our left nephew is
                         * red, and our right nephew is black.  Swap our
                         * brother with our left nephew.   This result in a
                         * tree that matches case 4.
                         *
                         *     B         ->       D
                         * A       D     ->   B     E
                         *       c   e   -> A   C
                         */
                        if (RB_BLACK_P(brother->rb_nodes[other])) {
                                KASSERT(RB_RED_P(brother->rb_nodes[which]));
                                rb_tree_reparent_nodes(rbt, brother, which);
                                KASSERT(brother->rb_parent == parent->rb_nodes[other]);
                                brother = parent->rb_nodes[other];
                                KASSERT(RB_RED_P(brother->rb_nodes[other]));
                        }
                        /*
                         * Case 4: our brother is black and our right nephew
                         * is red.  Swap our parent and brother locations and
                         * change our right nephew to black.  (these can be
                         * done in either order so we change the color first).
                         * The result is a valid red-black tree and is a
                         * terminal case.
                         *
                         *     B         ->       D
                         * A       D     ->   B     E
                         *       c   e   -> A   C
                         */
                        RB_MARK_BLACK(brother->rb_nodes[other]);
                        rb_tree_reparent_nodes(rbt, parent, other);
                        break;          /* We're done! */
                }
        }
        KASSERT(rb_tree_check_node(rbt, parent, NULL, true));
}

struct rb_node *
_prop_rb_tree_iterate(struct rb_tree *rbt, struct rb_node *self,
        unsigned int direction)
{
        const unsigned int other = direction ^ RB_NODE_OTHER;
        KASSERT(direction == RB_NODE_LEFT || direction == RB_NODE_RIGHT);

        if (self == NULL) {
                self = rbt->rbt_root;
                if (RB_SENTINEL_P(self))
                        return NULL;
                while (!RB_SENTINEL_P(self->rb_nodes[other]))
                        self = self->rb_nodes[other];
                return self;
        }
        KASSERT(!RB_SENTINEL_P(self));
        /*
         * We can't go any further in this direction.  We proceed up in the
         * opposite direction until our parent is in direction we want to go.
         */
        if (RB_SENTINEL_P(self->rb_nodes[direction])) {
                while (!RB_ROOT_P(self)) {
                        if (other == self->rb_position)
                                return self->rb_parent;
                        self = self->rb_parent;
                }
                return NULL;
        }

        /*
         * Advance down one in current direction and go down as far as possible
         * in the opposite direction.
         */
        self = self->rb_nodes[direction];
        KASSERT(!RB_SENTINEL_P(self));
        while (!RB_SENTINEL_P(self->rb_nodes[other]))
                self = self->rb_nodes[other];
        return self;
}

#ifdef RBDEBUG
static const struct rb_node *
rb_tree_iterate_const(const struct rb_tree *rbt, const struct rb_node *self,
        unsigned int direction)
{
        const unsigned int other = direction ^ RB_NODE_OTHER;
        KASSERT(direction == RB_NODE_LEFT || direction == RB_NODE_RIGHT);

        if (self == NULL) {
                self = rbt->rbt_root;
                if (RB_SENTINEL_P(self))
                        return NULL;
                while (!RB_SENTINEL_P(self->rb_nodes[other]))
                        self = self->rb_nodes[other];
                return self;
        }
        KASSERT(!RB_SENTINEL_P(self));
        /*
         * We can't go any further in this direction.  We proceed up in the
         * opposite direction until our parent is in direction we want to go.
         */
        if (RB_SENTINEL_P(self->rb_nodes[direction])) {
                while (!RB_ROOT_P(self)) {
                        if (other == self->rb_position)
                                return self->rb_parent;
                        self = self->rb_parent;
                }
                return NULL;
        }

        /*
         * Advance down one in current direction and go down as far as possible
         * in the opposite direction.
         */
        self = self->rb_nodes[direction];
        KASSERT(!RB_SENTINEL_P(self));
        while (!RB_SENTINEL_P(self->rb_nodes[other]))
                self = self->rb_nodes[other];
        return self;
}

static bool
rb_tree_check_node(const struct rb_tree *rbt, const struct rb_node *self,
        const struct rb_node *prev, bool red_check)
{
        KASSERT(!self->rb_sentinel);
        KASSERT(self->rb_left);
        KASSERT(self->rb_right);
        KASSERT(prev == NULL ||
                (*rbt->rbt_ops->rbto_compare_nodes)(prev, self) > 0);

        /*
         * Verify our relationship to our parent.
         */
        if (RB_ROOT_P(self)) {
                KASSERT(self == rbt->rbt_root);
                KASSERT(self->rb_position == RB_NODE_LEFT);
                KASSERT(self->rb_parent->rb_nodes[RB_NODE_LEFT] == self);
                KASSERT(self->rb_parent == (const struct rb_node *) &rbt->rbt_root);
        } else {
                KASSERT(self != rbt->rbt_root);
                KASSERT(!RB_PARENT_SENTINEL_P(self));
                if (self->rb_position == RB_NODE_LEFT) {
                        KASSERT((*rbt->rbt_ops->rbto_compare_nodes)(self, self->rb_parent) > 0);
                        KASSERT(self->rb_parent->rb_nodes[RB_NODE_LEFT] == self);
                } else {
                        KASSERT((*rbt->rbt_ops->rbto_compare_nodes)(self, self->rb_parent) < 0);
                        KASSERT(self->rb_parent->rb_nodes[RB_NODE_RIGHT] == self);
                }
        }

        /*
         * Verify our position in the linked list against the tree itself.
         */
        {
                const struct rb_node *prev0 = rb_tree_iterate_const(rbt, self, RB_NODE_LEFT);
                const struct rb_node *next0 = rb_tree_iterate_const(rbt, self, RB_NODE_RIGHT);
                KASSERT(prev0 == TAILQ_PREV(self, rb_node_qh, rb_link));
                if (next0 != TAILQ_NEXT(self, rb_link))
                        next0 = rb_tree_iterate_const(rbt, self, RB_NODE_RIGHT);
                KASSERT(next0 == TAILQ_NEXT(self, rb_link));
        }

        /*
         * The root must be black.
         * There can never be two adjacent red nodes. 
         */
        if (red_check) {
                KASSERT(!RB_ROOT_P(self) || RB_BLACK_P(self));
                if (RB_RED_P(self)) {
                        const struct rb_node *brother;
                        KASSERT(!RB_ROOT_P(self));
                        brother = self->rb_parent->rb_nodes[self->rb_position ^ RB_NODE_OTHER];
                        KASSERT(RB_BLACK_P(self->rb_parent));
                        /* 
                         * I'm red and have no children, then I must either
                         * have no brother or my brother also be red and
                         * also have no children.  (black count == 0)
                         */
                        KASSERT(!RB_CHILDLESS_P(self)
                                || RB_SENTINEL_P(brother)
                                || RB_RED_P(brother)
                                || RB_CHILDLESS_P(brother));
                        /*
                         * If I'm not childless, I must have two children
                         * and they must be both be black.
                         */
                        KASSERT(RB_CHILDLESS_P(self)
                                || (RB_TWOCHILDREN_P(self)
                                    && RB_BLACK_P(self->rb_left)
                                    && RB_BLACK_P(self->rb_right)));
                        /*
                         * If I'm not childless, thus I have black children,
                         * then my brother must either be black or have two
                         * black children.
                         */
                        KASSERT(RB_CHILDLESS_P(self)
                                || RB_BLACK_P(brother)
                                || (RB_TWOCHILDREN_P(brother)
                                    && RB_BLACK_P(brother->rb_left)
                                    && RB_BLACK_P(brother->rb_right)));
                } else {
                        /*
                         * If I'm black and have one child, that child must
                         * be red and childless.
                         */
                        KASSERT(RB_CHILDLESS_P(self)
                                || RB_TWOCHILDREN_P(self)
                                || (!RB_LEFT_SENTINEL_P(self)
                                    && RB_RIGHT_SENTINEL_P(self)
                                    && RB_RED_P(self->rb_left)
                                    && RB_CHILDLESS_P(self->rb_left))
                                || (!RB_RIGHT_SENTINEL_P(self)
                                    && RB_LEFT_SENTINEL_P(self)
                                    && RB_RED_P(self->rb_right)
                                    && RB_CHILDLESS_P(self->rb_right)));

                        /*
                         * If I'm a childless black node and my parent is
                         * black, my 2nd closet relative away from my parent
                         * is either red or has a red parent or red children.
                         */
                        if (!RB_ROOT_P(self)
                            && RB_CHILDLESS_P(self)
                            && RB_BLACK_P(self->rb_parent)) {
                                const unsigned int which = self->rb_position;
                                const unsigned int other = which ^ RB_NODE_OTHER;
                                const struct rb_node *relative0, *relative;

                                relative0 = rb_tree_iterate_const(rbt,
                                    self, other);
                                KASSERT(relative0 != NULL);
                                relative = rb_tree_iterate_const(rbt,
                                    relative0, other);
                                KASSERT(relative != NULL);
                                KASSERT(RB_SENTINEL_P(relative->rb_nodes[which]));
#if 0
                                KASSERT(RB_RED_P(relative)
                                        || RB_RED_P(relative->rb_left)
                                        || RB_RED_P(relative->rb_right)
                                        || RB_RED_P(relative->rb_parent));
#endif
                        }
                }
                /*
                 * A grandparent's children must be real nodes and not
                 * sentinels.  First check out grandparent.
                 */
                KASSERT(RB_ROOT_P(self)
                        || RB_ROOT_P(self->rb_parent)
                        || RB_TWOCHILDREN_P(self->rb_parent->rb_parent));
                /*
                 * If we are have grandchildren on our left, then
                 * we must have a child on our right.
                 */
                KASSERT(RB_LEFT_SENTINEL_P(self)
                        || RB_CHILDLESS_P(self->rb_left)
                        || !RB_RIGHT_SENTINEL_P(self));
                /*
                 * If we are have grandchildren on our right, then
                 * we must have a child on our left.
                 */
                KASSERT(RB_RIGHT_SENTINEL_P(self)
                        || RB_CHILDLESS_P(self->rb_right)
                        || !RB_LEFT_SENTINEL_P(self));

                /*
                 * If we have a child on the left and it doesn't have two
                 * children make sure we don't have great-great-grandchildren on
                 * the right.
                 */
                KASSERT(RB_TWOCHILDREN_P(self->rb_left)
                        || RB_CHILDLESS_P(self->rb_right)
                        || RB_CHILDLESS_P(self->rb_right->rb_left)
                        || RB_CHILDLESS_P(self->rb_right->rb_left->rb_left)
                        || RB_CHILDLESS_P(self->rb_right->rb_left->rb_right)
                        || RB_CHILDLESS_P(self->rb_right->rb_right)
                        || RB_CHILDLESS_P(self->rb_right->rb_right->rb_left)
                        || RB_CHILDLESS_P(self->rb_right->rb_right->rb_right));

                /*
                 * If we have a child on the right and it doesn't have two
                 * children make sure we don't have great-great-grandchildren on
                 * the left.
                 */
                KASSERT(RB_TWOCHILDREN_P(self->rb_right)
                        || RB_CHILDLESS_P(self->rb_left)
                        || RB_CHILDLESS_P(self->rb_left->rb_left)
                        || RB_CHILDLESS_P(self->rb_left->rb_left->rb_left)
                        || RB_CHILDLESS_P(self->rb_left->rb_left->rb_right)
                        || RB_CHILDLESS_P(self->rb_left->rb_right)
                        || RB_CHILDLESS_P(self->rb_left->rb_right->rb_left)
                        || RB_CHILDLESS_P(self->rb_left->rb_right->rb_right));

                /*
                 * If we are fully interior node, then our predecessors and
                 * successors must have no children in our direction.
                 */
                if (RB_TWOCHILDREN_P(self)) {
                        const struct rb_node *prev0;
                        const struct rb_node *next0;

                        prev0 = rb_tree_iterate_const(rbt, self, RB_NODE_LEFT);
                        KASSERT(prev0 != NULL);
                        KASSERT(RB_RIGHT_SENTINEL_P(prev0));

                        next0 = rb_tree_iterate_const(rbt, self, RB_NODE_RIGHT);
                        KASSERT(next0 != NULL);
                        KASSERT(RB_LEFT_SENTINEL_P(next0));
                }
        }

        return true;
}

static unsigned int
rb_tree_count_black(const struct rb_node *self)
{
        unsigned int left, right;

        if (RB_SENTINEL_P(self))
                return 0;

        left = rb_tree_count_black(self->rb_left);
        right = rb_tree_count_black(self->rb_right);

        KASSERT(left == right);

        return left + RB_BLACK_P(self);
}

void
_prop_rb_tree_check(const struct rb_tree *rbt, bool red_check)
{
        const struct rb_node *self;
        const struct rb_node *prev;
        unsigned int count;

        KASSERT(rbt->rbt_root == NULL || rbt->rbt_root->rb_position == RB_NODE_LEFT);

        prev = NULL;
        count = 0;
        TAILQ_FOREACH(self, &rbt->rbt_nodes, rb_link) {
                rb_tree_check_node(rbt, self, prev, false);
                count++;
        }
        KASSERT(rbt->rbt_count == count);
        KASSERT(RB_SENTINEL_P(rbt->rbt_root)
                || rb_tree_count_black(rbt->rbt_root));

        /*
         * The root must be black.
         * There can never be two adjacent red nodes. 
         */
        if (red_check) {
                KASSERT(rbt->rbt_root == NULL || RB_BLACK_P(rbt->rbt_root));
                TAILQ_FOREACH(self, &rbt->rbt_nodes, rb_link) {
                        rb_tree_check_node(rbt, self, NULL, true);
                }
        }
}
#endif /* RBDEBUG */