Import of Empire 4.2.12
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177
src/lib/as/as_winnow.c
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177
src/lib/as/as_winnow.c
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/*
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* A* Search - A search library used in Empire to determine paths between
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* objects.
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* Copyright (C) 1990-1998 Phil Lapsley
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "as.h"
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#if !defined(lint) && !defined(SABER)
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static char sccsid[] = "@(#)as_winnow.c 1.8 11/13/90";
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#endif /* not lint */
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static struct as_node *
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as_newnode(struct as_node *backp, struct as_coord c,
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double inclbcost, double lbcost, double knowncost, double seccost);
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/*
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* Take a list of neighbor coordinates and winnow them down into
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* an interesting list of neighbor nodes. This means:
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*
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* For each neighbor,
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* Compute a lower bound on the total cost to target.
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* If this neighbor is already in our queue,
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* See if the new neighbor is cheaper.
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* If so, add it to queue and move the
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* old node to the subsumed list.
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* If not, ignore this neighbor.
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* If this neighbor isn't in the queue, add it.
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*
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*/
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int
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as_winnow(struct as_data *adp, struct as_coord *coords, int ncoords)
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{
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int i = 0;
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int fix_pointer;
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double knowncost;
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double incknowncost;
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double lbcost;
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double inclbcost;
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double seccost;
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struct as_coord *cp;
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struct as_coord *end;
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struct as_queue *qp;
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struct as_node *np;
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for (cp = coords, end = coords + ncoords; cp < end; cp++) {
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fix_pointer = 0;
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incknowncost = (*adp->realcost)(adp->head->np->c, *cp,
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adp->userdata);
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knowncost = adp->head->np->knowncost + incknowncost;
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/*
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* If this neighbor is already in the queue, we can
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* save some time.
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*/
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qp = as_iscinq(adp, *cp);
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inclbcost = qp ? qp->np->inclbcost :
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(*adp->lbcost)(*cp, adp->to, adp->userdata);
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if (inclbcost < 0.0) /* skip bad cases */
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continue;
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lbcost = knowncost + inclbcost;
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#ifdef DEBUG
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fprintf(stderr, "\tneighbor %d, %d, lbcost %f ", cp->x, cp->y, lbcost);
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#endif /* DEBUG */
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/*
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* If this neighbor is already in the queue, check to
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* see which has the lower cost. If the one already in
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* the queue is cheaper, skip this neighbor as bad. If
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* the neighbor does, delete the one in the queue.
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*/
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if (qp) {
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if (qp->np->lbcost <= lbcost) {
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#ifdef DEBUG
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fprintf(stderr, "old, loses to %f\n", qp->np->lbcost);
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#endif /* DEBUG */
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continue;
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} else {
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#ifdef DEBUG
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fprintf(stderr, "old, wins over %f\n", qp->np->lbcost);
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#endif /* DEBUG */
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if (qp->np->flags & AS_TRIED) {
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/* should "never happen" */
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return (0);
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}
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/*
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* The neighbor is better than a previously visited coordinate;
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* remove the old coordinate from the queue and add it to
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* the subsumed nodes queue. To get here at
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* all we can't be the head, thus qp->prev is defined.
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*/
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/* Delete from main queue */
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qp->prev->next = qp->next;
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if (qp->next)
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qp->next->prev = qp->prev;
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/* Add to subsumed queue */
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if (adp->subsumed) {
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adp->subsumed->prev = qp;
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qp->next = adp->subsumed;
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} else {
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qp->next = NULL;
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}
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adp->subsumed = qp;
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adp->subsumed->prev = NULL;
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fix_pointer = 1;
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/*
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* At this point, the as_iscinq code may contain bogus pointer
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* refs. They'll be fixed when as_merge merges the new
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* neighbors into the main queue.
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*/
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}
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}
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#ifdef DEBUG
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else {
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fprintf(stderr, "new\n");
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}
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#endif /* DEBUG */
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if (qp)
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seccost = qp->np->seccost;
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else
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seccost = (adp->seccost) ?
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(*adp->seccost)(*cp, adp->to, adp->userdata) :
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0.0;
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np = as_newnode(adp->head->np, *cp, inclbcost, lbcost,
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knowncost, seccost);
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if (np == NULL)
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return (0);
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if (fix_pointer) {
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#ifdef DEBUG
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fprintf(stderr, "Fixing pointer for %d, %d\n", adp->subsumed->np->c.x,
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adp->subsumed->np->c.y);
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#endif
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adp->subsumed->np->back = np;
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}
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adp->neighbor_nodes[i++] = np;
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}
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adp->neighbor_nodes[i] = NULL;
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return (i);
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}
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static struct as_node *
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as_newnode(struct as_node *backp, struct as_coord c,
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double inclbcost, double lbcost, double knowncost, double seccost)
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{
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struct as_node *np;
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/* Got an interesting coordinate; make a node for it. */
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AS_NEW_MALLOC(np, struct as_node, NULL);
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np->flags = 0;
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np->c = c;
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np->inclbcost = inclbcost;
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np->lbcost = lbcost;
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np->knowncost = knowncost;
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np->seccost = seccost;
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np->step = backp->step;
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np->back = backp;
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return (np);
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}
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