src/lib/as/as_merge.c

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/*
 *  A* Search - A search library used in Empire to determine paths between
 *              objects.
 *  Copyright (C) 1990-1998 Phil Lapsley
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <config.h>

#include <stdlib.h>
#include "as.h"

/*
 * Merge neighbors into queue, keeping it sorted.  "neighbors" is sorted,
 * both by lower bound cost and then by secondary cost.
 */
struct as_queue *
as_merge(struct as_data *adp, struct as_queue *head,
         struct as_node **neighbors)
{
    struct as_queue *qp;
    struct as_queue *pp;        /* previous pointer */
    struct as_queue *ip;        /* insert pointer */
    struct as_node *np;
    int i;

    qp = head;
    pp = NULL;
    for (i = 0; neighbors[i]; i++) {
        np = neighbors[i];
        /* scan until qp points to a node we should go in front of */
        while (qp && (qp->np->lbcost < np->lbcost)) {
            pp = qp;
            qp = qp->next;
        }
        /* check for equal lower bounds, and use secondary cost if = */
        if (qp && qp->np->lbcost == np->lbcost) {
            while (qp && (qp->np->lbcost == np->lbcost) &&
                   (qp->np->seccost < np->seccost)) {
                pp = qp;
                qp = qp->next;
            }
        }
        AS_NEW_MALLOC(ip, struct as_queue, NULL);
        /* if there was such a node, insert us in front of it */
        if (qp) {
            ip->prev = qp->prev;
            if (ip->prev)
                ip->prev->next = ip;
            ip->next = qp;
            qp->prev = ip;
            if (qp == head)
                head = ip;
        } else {                /* otherwise add us to end of queue */
            ip->next = NULL;
            ip->prev = pp;
            if (ip->prev)
                ip->prev->next = ip;
            else {
                head = ip;
            }
            pp = ip;
        }
        ip->np = np;
        as_setcinq(adp, np->c, ip);
        np->step++;
    }

    return head;
}

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