/*
 * Copyright 2006, Haiku, Inc. All Rights Reserved.
 * Distributed under the terms of the MIT License.
 */

/*
 * Copyright (c) 1988, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 */

/*
 * Routines to build and maintain radix trees for routing lookups.
 */

#include "radix.h"

#include <KernelExport.h>

#include <stdlib.h>
#include <string.h>


static int      rn_walktree_from(struct radix_node_head *h, void *a, void *m,
                                walktree_f_t *f, void *w);
static int rn_walktree(struct radix_node_head *, walktree_f_t *, void *);
static struct radix_node *rn_insert(void *, struct radix_node_head *, int *,
                        struct radix_node [2]);
static struct radix_node *rn_newpair(void *, int, struct radix_node[2]);
static struct radix_node *rn_search(void *, struct radix_node *);
static struct radix_node *rn_search_m(void *, struct radix_node *, void *);

static int      max_keylen;
static struct radix_mask *rn_mkfreelist;
static struct radix_node_head *mask_rnhead;
/*
 * Work area -- the following point to 3 buffers of size max_keylen,
 * allocated in this order in a block of memory malloc'ed by rn_init.
 */
static uint8 *rn_zeros, *rn_ones, *addmask_key;

#define MKFree(m) { (m)->rm_mklist = rn_mkfreelist; rn_mkfreelist = (m);}

#define rn_masktop (mask_rnhead->rnh_treetop)

static int      rn_lexobetter(void *m_arg, void *n_arg);
static struct radix_mask *rn_new_radix_mask(struct radix_node *tt,
                                        struct radix_mask *next);
static int      rn_satisfies_leaf(char *trial, struct radix_node *leaf,
                                        int skip);

/*
 * The data structure for the keys is a radix tree with one way
 * branching removed.  The index rn_bit at an internal node n represents a bit
 * position to be tested.  The tree is arranged so that all descendants
 * of a node n have keys whose bits all agree up to position rn_bit - 1.
 * (We say the index of n is rn_bit.)
 *
 * There is at least one descendant which has a one bit at position rn_bit,
 * and at least one with a zero there.
 *
 * A route is determined by a pair of key and mask.  We require that the
 * bit-wise logical and of the key and mask to be the key.
 * We define the index of a route to associated with the mask to be
 * the first bit number in the mask where 0 occurs (with bit number 0
 * representing the highest order bit).
 *
 * We say a mask is normal if every bit is 0, past the index of the mask.
 * If a node n has a descendant (k, m) with index(m) == index(n) == rn_bit,
 * and m is a normal mask, then the route applies to every descendant of n.
 * If the index(m) < rn_bit, this implies the trailing last few bits of k
 * before bit b are all 0, (and hence consequently true of every descendant
 * of n), so the route applies to all descendants of the node as well.
 *
 * Similar logic shows that a non-normal mask m such that
 * index(m) <= index(n) could potentially apply to many children of n.
 * Thus, for each non-host route, we attach its mask to a list at an internal
 * node as high in the tree as we can go.
 *
 * The present version of the code makes use of normal routes in short-
 * circuiting an explict mask and compare operation when testing whether
 * a key satisfies a normal route, and also in remembering the unique leaf
 * that governs a subtree.
 */

/*
 * Most of the functions in this code assume that the key/mask arguments
 * are sockaddr-like structures, where the first byte is an u_char
 * indicating the size of the entire structure.
 *
 * To make the assumption more explicit, we use the LEN() macro to access
 * this field. It is safe to pass an expression with side effects
 * to LEN() as the argument is evaluated only once.
 */
#define LEN(x) (*(const u_char *)(x))

/*
 * XXX THIS NEEDS TO BE FIXED
 * In the code, pointers to keys and masks are passed as either
 * 'void *' (because callers use to pass pointers of various kinds), or
 * 'caddr_t' (which is fine for pointer arithmetics, but not very
 * clean when you dereference it to access data). Furthermore, caddr_t
 * is really 'char *', while the natural type to operate on keys and
 * masks would be 'u_char'. This mismatch require a lot of casts and
 * intermediate variables to adapt types that clutter the code.
 */


static int      /* XXX: arbitrary ordering for non-contiguous masks */
rn_lexobetter(void *m_arg, void *n_arg)
{
        register uint8 *mp = m_arg, *np = n_arg, *lim;

        if (LEN(mp) > LEN(np))
                return 1;  /* not really, but need to check longer one first */
        if (LEN(mp) == LEN(np)) {
                for (lim = mp + LEN(mp); mp < lim;) {
                        if (*mp++ > *np++)
                                return 1;
                }
        }
        return 0;
}


static struct radix_mask *
rn_new_radix_mask(register struct radix_node *tt, register struct radix_mask *next)
{
        register struct radix_mask *m;

        if (rn_mkfreelist) {
                m = rn_mkfreelist;
                rn_mkfreelist = m->rm_mklist;
        } else
                m = (struct radix_mask *)malloc(sizeof(struct radix_mask));
        if (m == 0) {
                dprintf("Mask for route not entered\n");
                return 0;
        }
        memset(m, 0, sizeof *m);
        m->rm_bit = tt->rn_bit;
        m->rm_flags = tt->rn_flags;
        if (tt->rn_flags & RNF_NORMAL)
                m->rm_leaf = tt;
        else
                m->rm_mask = tt->rn_mask;
        m->rm_mklist = next;
        tt->rn_mklist = m;
        return m;
}


/*!
        Search a node in the tree matching the key.
*/
static struct radix_node *
rn_search(void *v_arg, struct radix_node *head)
{
        register struct radix_node *x;
        register caddr_t v;

        for (x = head, v = v_arg; x->rn_bit >= 0;) {
                if (x->rn_bmask & v[x->rn_offset])
                        x = x->rn_right;
                else
                        x = x->rn_left;
        }
        return x;
}


/*!
        Same as above, but with an additional mask.
        XXX note this function is used only once.
*/
static struct radix_node *
rn_search_m(void *v_arg, struct radix_node *head, void *m_arg)
{
        register struct radix_node *x;
        register caddr_t v = v_arg, m = m_arg;

        for (x = head; x->rn_bit >= 0;) {
                if ((x->rn_bmask & m[x->rn_offset])
                        && (x->rn_bmask & v[x->rn_offset]))
                        x = x->rn_right;
                else
                        x = x->rn_left;
        }
        return x;
}


static int
rn_satisfies_leaf(char *trial, register struct radix_node *leaf, int skip)
{
        register char *cp = trial, *cp2 = leaf->rn_key, *cp3 = leaf->rn_mask;
        char *cplim;
        int length = min(LEN(cp), LEN(cp2));

        if (cp3 == 0)
                cp3 = rn_ones;
        else
                length = min(length, *(u_char *)cp3);
        cplim = cp + length; cp3 += skip; cp2 += skip;
        for (cp += skip; cp < cplim; cp++, cp2++, cp3++)
                if ((*cp ^ *cp2) & *cp3)
                        return 0;
        return 1;
}


/*
 * Whenever we add a new leaf to the tree, we also add a parent node,
 * so we allocate them as an array of two elements: the first one must be
 * the leaf (see RNTORT() in route.c), the second one is the parent.
 * This routine initializes the relevant fields of the nodes, so that
 * the leaf is the left child of the parent node, and both nodes have
 * (almost) all all fields filled as appropriate.
 * (XXX some fields are left unset, see the '#if 0' section).
 * The function returns a pointer to the parent node.
 */

static struct radix_node *
rn_newpair(void *v, int b, struct radix_node nodes[2])
{
        register struct radix_node *tt = nodes, *t = tt + 1;
        t->rn_bit = b;
        t->rn_bmask = 0x80 >> (b & 7);
        t->rn_left = tt;
        t->rn_offset = b >> 3;

#if 0  /* XXX perhaps we should fill these fields as well. */
        t->rn_parent = t->rn_right = NULL;

        tt->rn_mask = NULL;
        tt->rn_dupedkey = NULL;
        tt->rn_bmask = 0;
#endif
        tt->rn_bit = -1;
        tt->rn_key = (caddr_t)v;
        tt->rn_parent = t;
        tt->rn_flags = t->rn_flags = RNF_ACTIVE;
        tt->rn_mklist = t->rn_mklist = 0;
        return t;
}


static struct radix_node *
rn_insert(void *v_arg, struct radix_node_head *head, int *dupentry,
        struct radix_node nodes[2])
{
        uint8 *v = v_arg;
        struct radix_node *top = head->rnh_treetop;
        int head_off = top->rn_offset, vlen = (int)LEN(v);
        register struct radix_node *t = rn_search(v_arg, top);
        register uint8 *cp = v + head_off;
        register int b;
        struct radix_node *tt;
        /*
         * Find first bit at which v and t->rn_key differ
         */
    {
                register uint8 *cp2 = t->rn_key + head_off;
                register int cmp_res;
                uint8 *cplim = v + vlen;

                while (cp < cplim) {
                        if (*cp2++ != *cp++)
                                goto on1;
                }
                *dupentry = 1;
                return t;
        on1:
                *dupentry = 0;
                cmp_res = (cp[-1] ^ cp2[-1]) & 0xff;
                for (b = (cp - v) << 3; cmp_res; b--) {
                        cmp_res >>= 1;
                }
    }
    {
                register struct radix_node *p, *x = top;
                cp = v;
                do {
                        p = x;
                        if (cp[x->rn_offset] & x->rn_bmask)
                                x = x->rn_right;
                        else
                                x = x->rn_left;
                } while (b > (unsigned) x->rn_bit);
                                        /* x->rn_bit < b && x->rn_bit >= 0 */
                t = rn_newpair(v_arg, b, nodes); 
                tt = t->rn_left;
                if ((cp[p->rn_offset] & p->rn_bmask) == 0)
                        p->rn_left = t;
                else
                        p->rn_right = t;
                x->rn_parent = t;
                t->rn_parent = p; /* frees x, p as temp vars below */
                if ((cp[t->rn_offset] & t->rn_bmask) == 0) {
                        t->rn_right = x;
                } else {
                        t->rn_right = tt;
                        t->rn_left = x;
                }
    }
        return tt;
}


/*!
        This is the same as rn_walktree() except for the parameters and the
        exit.
*/
static int
rn_walktree_from(struct radix_node_head *h, void *a, void *m, walktree_f_t *f, void *w)
{
        int error;
        struct radix_node *base, *next;
        u_char *xa = (u_char *)a;
        u_char *xm = (u_char *)m;
        register struct radix_node *rn, *last = 0 /* shut up gcc */;
        int stopping = 0;
        int lastb;

        /*
         * rn_search_m is sort-of-open-coded here. We cannot use the
         * function because we need to keep track of the last node seen.
         */
        /* printf("about to search\n"); */
        for (rn = h->rnh_treetop; rn->rn_bit >= 0; ) {
                last = rn;
                /* printf("rn_bit %d, rn_bmask %x, xm[rn_offset] %x\n",
                       rn->rn_bit, rn->rn_bmask, xm[rn->rn_offset]); */
                if (!(rn->rn_bmask & xm[rn->rn_offset])) {
                        break;
                }
                if (rn->rn_bmask & xa[rn->rn_offset]) {
                        rn = rn->rn_right;
                } else {
                        rn = rn->rn_left;
                }
        }
        /* printf("done searching\n"); */

        /*
         * Two cases: either we stepped off the end of our mask,
         * in which case last == rn, or we reached a leaf, in which
         * case we want to start from the last node we looked at.
         * Either way, last is the node we want to start from.
         */
        rn = last;
        lastb = rn->rn_bit;

        /* printf("rn %p, lastb %d\n", rn, lastb);*/

        /*
         * This gets complicated because we may delete the node
         * while applying the function f to it, so we need to calculate
         * the successor node in advance.
         */
        while (rn->rn_bit >= 0) {
                rn = rn->rn_left;
        }

        while (!stopping) {
                /* printf("node %p (%d)\n", rn, rn->rn_bit); */
                base = rn;
                /* If at right child go back up, otherwise, go right */
                while (rn->rn_parent->rn_right == rn
                        && !(rn->rn_flags & RNF_ROOT)) {
                        rn = rn->rn_parent;

                        /* if went up beyond last, stop */
                        if (rn->rn_bit <= lastb) {
                                stopping = 1;
                                /* printf("up too far\n"); */
                                /*
                                 * XXX we should jump to the 'Process leaves'
                                 * part, because the values of 'rn' and 'next'
                                 * we compute will not be used. Not a big deal
                                 * because this loop will terminate, but it is
                                 * inefficient and hard to understand!
                                 */
                        }
                }

                /* 
                 * At the top of the tree, no need to traverse the right
                 * half, prevent the traversal of the entire tree in the
                 * case of default route.
                 */
                if (rn->rn_parent->rn_flags & RNF_ROOT)
                        stopping = 1;

                /* Find the next *leaf* since next node might vanish, too */
                for (rn = rn->rn_parent->rn_right; rn->rn_bit >= 0;)
                        rn = rn->rn_left;
                next = rn;
                /* Process leaves */
                while ((rn = base) != 0) {
                        base = rn->rn_dupedkey;
                        /* printf("leaf %p\n", rn); */
                        if (!(rn->rn_flags & RNF_ROOT)
                            && (error = (*f)(rn, w)))
                                return (error);
                }
                rn = next;

                if (rn->rn_flags & RNF_ROOT) {
                        /* printf("root, stopping"); */
                        stopping = 1;
                }
        }
        return 0;
}


static int
rn_walktree(struct radix_node_head *h, walktree_f_t *f, void *w)
{
        int error;
        struct radix_node *base, *next;
        register struct radix_node *rn = h->rnh_treetop;
        /*
         * This gets complicated because we may delete the node
         * while applying the function f to it, so we need to calculate
         * the successor node in advance.
         */
        /* First time through node, go left */
        while (rn->rn_bit >= 0) {
                rn = rn->rn_left;
        }
        for (;;) {
                base = rn;
                /* If at right child go back up, otherwise, go right */
                while (rn->rn_parent->rn_right == rn
                        && (rn->rn_flags & RNF_ROOT) == 0) {
                        rn = rn->rn_parent;
                }
                /* Find the next *leaf* since next node might vanish, too */
                for (rn = rn->rn_parent->rn_right; rn->rn_bit >= 0;) {
                        rn = rn->rn_left;
                }
                next = rn;
                /* Process leaves */
                while ((rn = base)) {
                        base = rn->rn_dupedkey;
                        if (!(rn->rn_flags & RNF_ROOT)
                            && (error = (*f)(rn, w)))
                                return error;
                }
                rn = next;
                if (rn->rn_flags & RNF_ROOT)
                        return 0;
        }
        /* NOTREACHED */
}


//      #pragma mark - public API


struct radix_node *
rn_lookup(void *v_arg, void *m_arg, struct radix_node_head *head)
{
        register struct radix_node *x;
        uint8 *netmask = NULL;

        if (m_arg) {
                x = rn_addmask(m_arg, 1, head->rnh_treetop->rn_offset);
                if (x == 0)
                        return 0;
                netmask = x->rn_key;
        }
        x = rn_match(v_arg, head);
        if (x && netmask) {
                while (x && x->rn_mask != netmask)
                        x = x->rn_dupedkey;
        }
        return x;
}


struct radix_node *
rn_match(void *v_arg, struct radix_node_head *head)
{
        caddr_t v = v_arg;
        register struct radix_node *t = head->rnh_treetop, *x;
        register caddr_t cp = v, cp2;
        caddr_t cplim;
        struct radix_node *saved_t, *top = t;
        int off = t->rn_offset, vlen = LEN(cp), matched_off;
        register int test, b, rn_bit;

        /*
         * Open code rn_search(v, top) to avoid overhead of extra
         * subroutine call.
         */
        for (; t->rn_bit >= 0; ) {
                if (t->rn_bmask & cp[t->rn_offset])
                        t = t->rn_right;
                else
                        t = t->rn_left;
        }
        /*
         * See if we match exactly as a host destination
         * or at least learn how many bits match, for normal mask finesse.
         *
         * It doesn't hurt us to limit how many bytes to check
         * to the length of the mask, since if it matches we had a genuine
         * match and the leaf we have is the most specific one anyway;
         * if it didn't match with a shorter length it would fail
         * with a long one.  This wins big for class B&C netmasks which
         * are probably the most common case...
         */
        if (t->rn_mask)
                vlen = *(u_char *)t->rn_mask;
        cp += off; cp2 = t->rn_key + off; cplim = v + vlen;
        for (; cp < cplim; cp++, cp2++) {
                if (*cp != *cp2)
                        goto on1;
        }
        /*
         * This extra grot is in case we are explicitly asked
         * to look up the default.  Ugh!
         *
         * Never return the root node itself, it seems to cause a
         * lot of confusion.
         */
        if (t->rn_flags & RNF_ROOT)
                t = t->rn_dupedkey;
        return t;
on1:
        test = (*cp ^ *cp2) & 0xff; /* find first bit that differs */
        for (b = 7; (test >>= 1) > 0;)
                b--;
        matched_off = cp - v;
        b += matched_off << 3;
        rn_bit = -1 - b;
        /*
         * If there is a host route in a duped-key chain, it will be first.
         */
        if ((saved_t = t)->rn_mask == 0)
                t = t->rn_dupedkey;
        for (; t; t = t->rn_dupedkey) {
                /*
                 * Even if we don't match exactly as a host,
                 * we may match if the leaf we wound up at is
                 * a route to a net.
                 */
                if (t->rn_flags & RNF_NORMAL) {
                        if (rn_bit <= t->rn_bit)
                                return t;
                } else if (rn_satisfies_leaf(v, t, matched_off))
                                return t;
        }

        t = saved_t;
        /* start searching up the tree */
        do {
                register struct radix_mask *m;
                t = t->rn_parent;
                m = t->rn_mklist;
                /*
                 * If non-contiguous masks ever become important
                 * we can restore the masking and open coding of
                 * the search and satisfaction test and put the
                 * calculation of "off" back before the "do".
                 */
                while (m) {
                        if (m->rm_flags & RNF_NORMAL) {
                                if (rn_bit <= m->rm_bit)
                                        return (m->rm_leaf);
                        } else {
                                off = min(t->rn_offset, matched_off);
                                x = rn_search_m(v, t, m->rm_mask);
                                while (x && x->rn_mask != m->rm_mask)
                                        x = x->rn_dupedkey;
                                if (x && rn_satisfies_leaf(v, x, off))
                                        return x;
                        }
                        m = m->rm_mklist;
                }
        } while (t != top);

        return 0;
}


struct radix_node *
rn_addmask(void *n_arg, int search, int skip)
{
        uint8 *netmask = (uint8 *)n_arg;
        register struct radix_node *x;
        register uint8 *cp, *cplim;
        register int b = 0, mlen, j;
        int maskduplicated, m0, isnormal;
        struct radix_node *saved_x;
        static int last_zeroed = 0;

        if ((mlen = LEN(netmask)) > max_keylen)
                mlen = max_keylen;
        if (skip == 0)
                skip = 1;
        if (mlen <= skip)
                return mask_rnhead->rnh_nodes;
        if (skip > 1)
                memcpy(addmask_key + 1, rn_ones + 1, skip - 1);
        if ((m0 = mlen) > skip)
                memcpy(addmask_key + skip, netmask + skip, mlen - skip);
        /*
         * Trim trailing zeroes.
         */
        for (cp = addmask_key + mlen; (cp > addmask_key) && cp[-1] == 0;)
                cp--;
        mlen = cp - addmask_key;
        if (mlen <= skip) {
                if (m0 >= last_zeroed)
                        last_zeroed = mlen;
                return (mask_rnhead->rnh_nodes);
        }
        if (m0 < last_zeroed)
                memset(addmask_key + m0, 0, last_zeroed - m0);
        *addmask_key = last_zeroed = mlen;
        x = rn_search(addmask_key, rn_masktop);
        if (memcmp(addmask_key, x->rn_key, mlen) != 0)
                x = 0;
        if (x || search)
                return x;
        x = (struct radix_node *)calloc(1, max_keylen + 2 * sizeof(*x));
        if ((saved_x = x) == 0)
                return 0;
        netmask = cp = (caddr_t)(x + 2);
        memcpy(cp, addmask_key, mlen);
        x = rn_insert(cp, mask_rnhead, &maskduplicated, x);
        if (maskduplicated) {
                dprintf("rn_addmask: mask impossibly already in tree\n");
                free(saved_x);
                return x;
        }
        /*
         * Calculate index of mask, and check for normalcy.
         * First find the first byte with a 0 bit, then if there are
         * more bits left (remember we already trimmed the trailing 0's),
         * the pattern must be one of those in normal_chars[], or we have
         * a non-contiguous mask.
         */
        cplim = netmask + mlen;
        isnormal = 1;
        for (cp = netmask + skip; (cp < cplim) && *(u_char *)cp == 0xff;) {
                cp++;
        }
        if (cp != cplim) {
                static char normal_chars[] = {
                        0, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe, 0xff};

                for (j = 0x80; (j & *cp) != 0; j >>= 1)
                        b++;
                if (*cp != normal_chars[b] || cp != (cplim - 1))
                        isnormal = 0;
        }
        b += (cp - netmask) << 3;
        x->rn_bit = -1 - b;
        if (isnormal)
                x->rn_flags |= RNF_NORMAL;
        return x;
}


struct radix_node *
rn_addroute(void *v_arg, void *n_arg, struct radix_node_head *head,
        struct radix_node treenodes[2])
{
        uint8 *v = (uint8 *)v_arg, *netmask = (uint8 *)n_arg;
        register struct radix_node *t, *x = 0, *tt;
        struct radix_node *saved_tt, *top = head->rnh_treetop;
        short b = 0, b_leaf = 0;
        int keyduplicated;
        uint8 *mmask;
        struct radix_mask *m, **mp;

        /*
         * In dealing with non-contiguous masks, there may be
         * many different routes which have the same mask.
         * We will find it useful to have a unique pointer to
         * the mask to speed avoiding duplicate references at
         * nodes and possibly save time in calculating indices.
         */
        if (netmask)  {
                if ((x = rn_addmask(netmask, 0, top->rn_offset)) == 0)
                        return (0);
                b_leaf = x->rn_bit;
                b = -1 - x->rn_bit;
                netmask = x->rn_key;
        }
        /*
         * Deal with duplicated keys: attach node to previous instance
         */
        saved_tt = tt = rn_insert(v, head, &keyduplicated, treenodes);
        if (keyduplicated) {
                for (t = tt; tt; t = tt, tt = tt->rn_dupedkey) {
                        if (tt->rn_mask == netmask)
                                return (0);
                        if (netmask == 0 ||
                            (tt->rn_mask &&
                             ((b_leaf < tt->rn_bit) /* index(netmask) > node */
                              || rn_refines(netmask, tt->rn_mask)
                              || rn_lexobetter(netmask, tt->rn_mask))))
                                break;
                }
                /*
                 * If the mask is not duplicated, we wouldn't
                 * find it among possible duplicate key entries
                 * anyway, so the above test doesn't hurt.
                 *
                 * We sort the masks for a duplicated key the same way as
                 * in a masklist -- most specific to least specific.
                 * This may require the unfortunate nuisance of relocating
                 * the head of the list.
                 *
                 * We also reverse, or doubly link the list through the
                 * parent pointer.
                 */
                if (tt == saved_tt) {
                        struct  radix_node *xx = x;
                        /* link in at head of list */
                        (tt = treenodes)->rn_dupedkey = t;
                        tt->rn_flags = t->rn_flags;
                        tt->rn_parent = x = t->rn_parent;
                        t->rn_parent = tt;                      /* parent */
                        if (x->rn_left == t)
                                x->rn_left = tt;
                        else
                                x->rn_right = tt;
                        saved_tt = tt; x = xx;
                } else {
                        (tt = treenodes)->rn_dupedkey = t->rn_dupedkey;
                        t->rn_dupedkey = tt;
                        tt->rn_parent = t;                      /* parent */
                        if (tt->rn_dupedkey)                    /* parent */
                                tt->rn_dupedkey->rn_parent = tt; /* parent */
                }
                tt->rn_key = (caddr_t) v;
                tt->rn_bit = -1;
                tt->rn_flags = RNF_ACTIVE;
        }
        /*
         * Put mask in tree.
         */
        if (netmask) {
                tt->rn_mask = netmask;
                tt->rn_bit = x->rn_bit;
                tt->rn_flags |= x->rn_flags & RNF_NORMAL;
        }
        t = saved_tt->rn_parent;
        if (keyduplicated)
                goto on2;
        b_leaf = -1 - t->rn_bit;
        if (t->rn_right == saved_tt)
                x = t->rn_left;
        else
                x = t->rn_right;
        /* Promote general routes from below */
        if (x->rn_bit < 0) {
            for (mp = &t->rn_mklist; x; x = x->rn_dupedkey)
                if (x->rn_mask && (x->rn_bit >= b_leaf) && x->rn_mklist == 0) {
                        *mp = m = rn_new_radix_mask(x, 0);
                        if (m)
                                mp = &m->rm_mklist;
                }
        } else if (x->rn_mklist) {
                /*
                 * Skip over masks whose index is > that of new node
                 */
                for (mp = &x->rn_mklist; (m = *mp); mp = &m->rm_mklist)
                        if (m->rm_bit >= b_leaf)
                                break;
                t->rn_mklist = m; *mp = 0;
        }
on2:
        /* Add new route to highest possible ancestor's list */
        if ((netmask == 0) || (b > t->rn_bit ))
                return tt; /* can't lift at all */
        b_leaf = tt->rn_bit;
        do {
                x = t;
                t = t->rn_parent;
        } while (b <= t->rn_bit && x != top);
        /*
         * Search through routes associated with node to
         * insert new route according to index.
         * Need same criteria as when sorting dupedkeys to avoid
         * double loop on deletion.
         */
        for (mp = &x->rn_mklist; (m = *mp); mp = &m->rm_mklist) {
                if (m->rm_bit < b_leaf)
                        continue;
                if (m->rm_bit > b_leaf)
                        break;
                if (m->rm_flags & RNF_NORMAL) {
                        mmask = m->rm_leaf->rn_mask;
                        if (tt->rn_flags & RNF_NORMAL) {
                            dprintf("Non-unique normal route, mask not entered\n");
                                return tt;
                        }
                } else
                        mmask = m->rm_mask;
                if (mmask == netmask) {
                        m->rm_refs++;
                        tt->rn_mklist = m;
                        return tt;
                }
                if (rn_refines(netmask, mmask)
                    || rn_lexobetter(netmask, mmask))
                        break;
        }
        *mp = rn_new_radix_mask(tt, *mp);
        return tt;
}


struct radix_node *
rn_delete(void *v_arg, void *netmask_arg, struct radix_node_head *head)
{
        register struct radix_node *t, *p, *x, *tt;
        struct radix_mask *m, *saved_m, **mp;
        struct radix_node *dupedkey, *saved_tt, *top;
        uint8 *v, *netmask;
        int b, head_off, vlen;

        v = v_arg;
        netmask = netmask_arg;
        x = head->rnh_treetop;
        tt = rn_search(v, x);
        head_off = x->rn_offset;
        vlen =  LEN(v);
        saved_tt = tt;
        top = x;
        if (tt == 0
                || memcmp(v + head_off, tt->rn_key + head_off, vlen - head_off))
                return 0;
        /*
         * Delete our route from mask lists.
         */
        if (netmask) {
                if ((x = rn_addmask(netmask, 1, head_off)) == 0)
                        return 0;
                netmask = x->rn_key;
                while (tt->rn_mask != netmask)
                        if ((tt = tt->rn_dupedkey) == 0)
                                return 0;
        }
        if (tt->rn_mask == 0 || (saved_m = m = tt->rn_mklist) == 0)
                goto on1;
        if (tt->rn_flags & RNF_NORMAL) {
                if (m->rm_leaf != tt || m->rm_refs > 0) {
                        dprintf("rn_delete: inconsistent annotation\n");
                        return 0;  /* dangling ref could cause disaster */
                }
        } else {
                if (m->rm_mask != tt->rn_mask) {
                        dprintf("rn_delete: inconsistent annotation\n");
                        goto on1;
                }
                if (--m->rm_refs >= 0)
                        goto on1;
        }
        b = -1 - tt->rn_bit;
        t = saved_tt->rn_parent;
        if (b > t->rn_bit)
                goto on1; /* Wasn't lifted at all */
        do {
                x = t;
                t = t->rn_parent;
        } while (b <= t->rn_bit && x != top);
        for (mp = &x->rn_mklist; (m = *mp); mp = &m->rm_mklist)
                if (m == saved_m) {
                        *mp = m->rm_mklist;
                        MKFree(m);
                        break;
                }
        if (m == 0) {
                dprintf("rn_delete: couldn't find our annotation\n");
                if (tt->rn_flags & RNF_NORMAL)
                        return 0; /* Dangling ref to us */
        }
on1:
        /*
         * Eliminate us from tree
         */
        if (tt->rn_flags & RNF_ROOT)
                return 0;
        t = tt->rn_parent;
        dupedkey = saved_tt->rn_dupedkey;
        if (dupedkey) {
                /*
                 * Here, tt is the deletion target and
                 * saved_tt is the head of the dupekey chain.
                 */
                if (tt == saved_tt) {
                        /* remove from head of chain */
                        x = dupedkey; x->rn_parent = t;
                        if (t->rn_left == tt)
                                t->rn_left = x;
                        else
                                t->rn_right = x;
                } else {
                        /* find node in front of tt on the chain */
                        for (x = p = saved_tt; p && p->rn_dupedkey != tt;)
                                p = p->rn_dupedkey;
                        if (p) {
                                p->rn_dupedkey = tt->rn_dupedkey;
                                if (tt->rn_dupedkey)            /* parent */
                                        tt->rn_dupedkey->rn_parent = p;
                                                                /* parent */
                        } else
                                dprintf("rn_delete: couldn't find us\n");
                }
                t = tt + 1;
                if  (t->rn_flags & RNF_ACTIVE) {
                        *++x = *t;
                        p = t->rn_parent;
                        if (p->rn_left == t)
                                p->rn_left = x;
                        else
                                p->rn_right = x;
                        x->rn_left->rn_parent = x;
                        x->rn_right->rn_parent = x;
                }
                goto out;
        }
        if (t->rn_left == tt)
                x = t->rn_right;
        else
                x = t->rn_left;
        p = t->rn_parent;
        if (p->rn_right == t)
                p->rn_right = x;
        else
                p->rn_left = x;
        x->rn_parent = p;
        /*
         * Demote routes attached to us.
         */
        if (t->rn_mklist) {
                if (x->rn_bit >= 0) {
                        for (mp = &x->rn_mklist; (m = *mp);)
                                mp = &m->rm_mklist;
                        *mp = t->rn_mklist;
                } else {
                        /* If there are any key,mask pairs in a sibling
                           duped-key chain, some subset will appear sorted
                           in the same order attached to our mklist */
                        for (m = t->rn_mklist; m && x; x = x->rn_dupedkey) {
                                if (m == x->rn_mklist) {
                                        struct radix_mask *mm = m->rm_mklist;
                                        x->rn_mklist = 0;
                                        if (--(m->rm_refs) < 0)
                                                MKFree(m);
                                        m = mm;
                                }
                        }
                        if (m) {
                                dprintf("rn_delete: Orphaned Mask %p at %p\n",
                                    (void *)m, (void *)x);
                        }
                }
        }
        /*
         * We may be holding an active internal node in the tree.
         */
        x = tt + 1;
        if (t != x) {
                *t = *x;
                t->rn_left->rn_parent = t;
                t->rn_right->rn_parent = t;
                p = x->rn_parent;
                if (p->rn_left == x)
                        p->rn_left = t;
                else
                        p->rn_right = t;
        }
out:
        tt->rn_flags &= ~RNF_ACTIVE;
        tt[1].rn_flags &= ~RNF_ACTIVE;
        return tt;
}


int
rn_refines(void *m_arg, void *n_arg)
{
        register caddr_t m = m_arg, n = n_arg;
        register caddr_t lim, lim2 = lim = n + LEN(n);
        int longer = LEN(n++) - (int)LEN(m++);
        int masks_are_equal = 1;

        if (longer > 0)
                lim -= longer;
        while (n < lim) {
                if (*n & ~(*m))
                        return 0;
                if (*n++ != *m++)
                        masks_are_equal = 0;
        }

        while (n < lim2) {
                if (*n++)
                        return 0;
        }

        if (masks_are_equal && (longer < 0)) {
                for (lim2 = m - longer; m < lim2; ) {
                        if (*m++)
                                return 1;
                }
        }

        return !masks_are_equal;
}


/*!
        Allocate and initialize an empty tree. This has 3 nodes, which are
        part of the radix_node_head (in the order <left,root,right>) and are
        marked RNF_ROOT so they cannot be freed.
        The leaves have all-zero and all-one keys, with significant
        bits starting at 'off'.
        Return 1 on success, 0 on error.
*/
int
rn_inithead(void **head, int off)
{
        register struct radix_node_head *rnh;
        register struct radix_node *t, *tt, *ttt;
        if (*head)
                return 1;
        rnh = (struct radix_node_head *)calloc(1, sizeof(*rnh));
        if (rnh == NULL)
                return 0;

        *head = rnh;
        t = rn_newpair(rn_zeros, off, rnh->rnh_nodes);
        ttt = rnh->rnh_nodes + 2;
        t->rn_right = ttt;
        t->rn_parent = t;
        tt = t->rn_left;        /* ... which in turn is rnh->rnh_nodes */
        tt->rn_flags = t->rn_flags = RNF_ROOT | RNF_ACTIVE;
        tt->rn_bit = -1 - off;
        *ttt = *tt;
        ttt->rn_key = rn_ones;
        rnh->rnh_addaddr = rn_addroute;
        rnh->rnh_deladdr = rn_delete;
        rnh->rnh_matchaddr = rn_match;
        rnh->rnh_lookup = rn_lookup;
        rnh->rnh_walktree = rn_walktree;
        rnh->rnh_walktree_from = rn_walktree_from;
        rnh->rnh_treetop = t;
        return 1;
}


void
rn_init()
{
        char *cp, *cplim;
#ifdef _KERNEL
        struct domain *dom;

        for (dom = domains; dom; dom = dom->dom_next)
                if (dom->dom_maxrtkey > max_keylen)
                        max_keylen = dom->dom_maxrtkey;
#endif
        if (max_keylen == 0) {
                dprintf("rn_init: radix functions require max_keylen be set\n");
                return;
        }
        rn_zeros = (char *)malloc(3 * max_keylen);
        if (rn_zeros == NULL)
                panic("rn_init");
        memset(rn_zeros, 0, 3 * max_keylen);
        rn_ones = cp = rn_zeros + max_keylen;
        addmask_key = cplim = rn_ones + max_keylen;
        while (cp < cplim)
                *cp++ = -1;
        if (rn_inithead((void **)(void *)&mask_rnhead, 0) == 0)
                panic("rn_init 2");
}