sgraph.c

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/*************************************************************************
 * Copyright (c) 2011 AT&T Intellectual Property 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors: Details at https://graphviz.org
 *************************************************************************/
 
 
#include "config.h"
#include <cgraph/alloc.h>
#include <limits.h>
#include <ortho/sgraph.h>
#include <ortho/fPQ.h>
 
void
gsave (sgraph* G)
{
    int i;
    G->save_nnodes = G->nnodes;
    G->save_nedges = G->nedges;
    for (i = 0; i < G->nnodes; i++)
        G->nodes[i].save_n_adj =  G->nodes[i].n_adj;
}
 
void 
reset(sgraph* G)
{
    int i;
    G->nnodes = G->save_nnodes;
    G->nedges = G->save_nedges;
    for (i = 0; i < G->nnodes; i++)
        G->nodes[i].n_adj = G->nodes[i].save_n_adj;
    for (; i < G->nnodes+2; i++)
        G->nodes[i].n_adj = 0;
}
 
void
initSEdges (sgraph* g, int maxdeg)
{
    int i;
    int* adj = gv_calloc(6 * g->nnodes + 2 * maxdeg, sizeof(int));
    g->edges = gv_calloc(3 * g->nnodes + maxdeg, sizeof(sedge));
    for (i = 0; i < g->nnodes; i++) {
        g->nodes[i].adj_edge_list = adj;
        adj += 6;
    }
    for (; i < g->nnodes+2; i++) {
        g->nodes[i].adj_edge_list = adj;
        adj += maxdeg;
    }
}
 
sgraph*
createSGraph (int nnodes)
{
    sgraph* g = gv_alloc(sizeof(sgraph));
 
        /* create the nodes vector in the search graph */
    g->nnodes = 0;
    g->nodes = gv_calloc(nnodes, sizeof(snode));
    return g;
}
 
snode*
createSNode (sgraph* g)
{
    snode* np = g->nodes+g->nnodes;
    np->index = g->nnodes;
    g->nnodes++;
    return np;
}
 
static void
addEdgeToNode (snode* np, int idx)
{
    np->adj_edge_list[np->n_adj] = idx;
    np->n_adj++;
}
 
sedge*
createSEdge (sgraph* g, snode* v1, snode* v2, double wt)
{
    sedge* e;
    int idx = g->nedges++;
 
    e = g->edges + idx;
    e->v1 = v1->index;
    e->v2 = v2->index;
    e->weight = wt;
    e->cnt = 0;
 
    addEdgeToNode (v1, idx);
    addEdgeToNode (v2, idx);
 
    return e;
}
 
void
freeSGraph (sgraph* g)
{
    free (g->nodes[0].adj_edge_list);
    free (g->nodes);
    free (g->edges);
    free (g);
}
 
#include <ortho/fPQ.h>
 
/* shortest path:
 * Constructs the path of least weight between from and to.
 * 
 * Assumes graph, node and edge type, and that nodes
 * have associated values N_VAL, N_IDX, and N_DAD, the first two
 * being ints, the last being a node*. Edges have a E_WT function 
 * to specify the edge length or weight.
 * 
 * Assumes there are functions:
 *  agnnodes: graph -> int           number of nodes in the graph
 *  agfstnode, agnxtnode : iterators over the nodes in the graph
 *  agfstedge, agnxtedge : iterators over the edges attached to a node
 *  adjacentNode : given an edge e and an endpoint n of e, returns the
 *                 other endpoint.
 * 
 * The path is given by
 *  to, N_DAD(to), N_DAD(N_DAD(to)), ..., from
 */
 
#define UNSEEN INT_MIN
 
static snode*
adjacentNode(sgraph* g, sedge* e, snode* n)
{
    if (e->v1==n->index)
        return &g->nodes[e->v2];
    else
        return &g->nodes[e->v1];
}
 
int
shortPath (sgraph* g, snode* from, snode* to)
{
    snode* n;
    sedge* e;
    snode* adjn;
    int d;
    int   x, y;
 
    for (x = 0; x<g->nnodes; x++) {
        snode* temp = &g->nodes[x];
        N_VAL(temp) = UNSEEN;
    }
    
    PQinit();
    if (PQ_insert (from)) return 1;
    N_DAD(from) = NULL;
    N_VAL(from) = 0;
    
    while ((n = PQremove())) {
#ifdef DEBUG
        fprintf (stderr, "process %d\n", n->index);
#endif
        N_VAL(n) *= -1;
        if (n == to) break;
        for (y=0; y<n->n_adj; y++) {
            e = &g->edges[n->adj_edge_list[y]];
            adjn = adjacentNode(g, e, n);
            if (N_VAL(adjn) < 0) {
                d = -(N_VAL(n) + E_WT(e));
                if (N_VAL(adjn) == UNSEEN) {
#ifdef DEBUG
                    fprintf (stderr, "new %d (%d)\n", adjn->index, -d);
#endif
                    N_VAL(adjn) = d;
                    if (PQ_insert(adjn)) return 1;
                    N_DAD(adjn) = n;
                    N_EDGE(adjn) = e;
                }
                else {
                    if (N_VAL(adjn) < d) {
#ifdef DEBUG
                        fprintf (stderr, "adjust %d (%d)\n", adjn->index, -d);
#endif
                        PQupdate(adjn, d);
                        N_DAD(adjn) = n;
                        N_EDGE(adjn) = e;
                    }
                }
            }
        }
    }
 
    return 0;
}