acyclic.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
 *************************************************************************/
 
 
/*
 * Break cycles in a directed graph by depth-first search.
 */
 
#include <dotgen/dot.h>
#include <stdbool.h>
#include <stddef.h>
 
void reverse_edge(edge_t * e)
{
    edge_t *f;
 
    delete_fast_edge(e);
    if ((f = find_fast_edge(aghead(e), agtail(e))))
        merge_oneway(e, f);
    else
        virtual_edge(aghead(e), agtail(e), e);
}
 
static void 
dfs(node_t * n)
{
    int i;
    edge_t *e;
    node_t *w;
 
    if (ND_mark(n))
        return;
    ND_mark(n) = true;
    ND_onstack(n) = true;
    for (i = 0; (e = ND_out(n).list[i]); i++) {
        w = aghead(e);
        if (ND_onstack(w)) {
            reverse_edge(e);
            i--;
        } else {
            if (!ND_mark(w))
                dfs(w);
        }
    }
    ND_onstack(n) = false;
}
 
 
void acyclic(graph_t * g)
{
    node_t *n;
 
    for (size_t c = 0; c < GD_comp(g).size; c++) {
        GD_nlist(g) = GD_comp(g).list[c];
        for (n = GD_nlist(g); n; n = ND_next(n))
            ND_mark(n) = false;
        for (n = GD_nlist(g); n; n = ND_next(n))
            dfs(n);
    }
}