mincross.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 v2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
 *
 * Contributors: Details at https://graphviz.org
 *************************************************************************/
 
/*
 * dot_mincross(g) takes a ranked graphs, and finds an ordering
 * that avoids edge crossings.  clusters are expanded.
 * N.B. the rank structure is global (not allocated per cluster)
 * because mincross may compare nodes in different clusters.
 */
 
#include "config.h"
 
#include <assert.h>
#include <cgraph/cgraph.h>
#include <common/utils.h>
#include <dotgen/dot.h>
#include <inttypes.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <util/alloc.h>
#include <util/bitarray.h>
#include <util/exit.h>
#include <util/gv_math.h>
#include <util/itos.h>
#include <util/list.h>
#include <util/streq.h>
 
struct adjmatrix_t {
  size_t nrows;  
  size_t ncols;  
  uint8_t *data; 
};
 
static bool matrix_get(adjmatrix_t *me, size_t row, size_t col) {
  assert(me != NULL);
 
  // if this index is beyond anything allocated, infer it as unset
  if (row >= me->nrows) {
    return false;
  }
  if (col >= me->ncols) {
    return false;
  }
 
  const size_t index = row * me->ncols + col;
  const size_t byte_index = index / 8;
  const size_t bit_index = index % 8;
  return (me->data[byte_index] >> bit_index) & 1;
}
 
static void matrix_set(adjmatrix_t *me, size_t row, size_t col) {
  assert(me != NULL);
 
  // if we are updating beyond allocated space, expand the backing store
  if (row >= me->nrows || col >= me->ncols) {
    // allocate an enlarged space
    const size_t nrows = zmax(me->nrows, row + 1);
    const size_t ncols = zmax(me->ncols, col + 1);
    const size_t bits = nrows * ncols;
    const size_t bytes = bits / 8 + (bits % 8 == 0 ? 0 : 1);
    uint8_t *const data = gv_alloc(bytes);
 
    // replicate set bits
    for (size_t r = 0; r < me->nrows; ++r) {
      for (size_t c = 0; c < me->ncols; ++c) {
        if (!matrix_get(me, r, c)) {
          continue;
        }
        const size_t index = r * ncols + c;
        const size_t byte_index = index / 8;
        const size_t bit_index = index % 8;
        data[byte_index] |= (uint8_t)(UINT8_C(1) << bit_index);
      }
    }
 
    // replace old matrix with newly expanded one
    free(me->data);
    *me = (adjmatrix_t){.nrows = nrows, .ncols = ncols, .data = data};
  }
 
  assert(row < me->nrows);
  assert(col < me->ncols);
 
  const size_t index = row * me->ncols + col;
  const size_t byte_index = index / 8;
  const size_t bit_index = index % 8;
  me->data[byte_index] |= (uint8_t)(UINT8_C(1) << bit_index);
}
 
/* #define DEBUG */
#define MARK(v) (ND_mark(v))
#define saveorder(v) (ND_coord(v)).x
#define flatindex(v) ((size_t)ND_low(v))
 
/* forward declarations */
static bool medians(graph_t *g, int r0, int r1);
static int nodeposcmpf(const void *, const void *);
static int edgeidcmpf(const void *, const void *);
static void flat_breakcycles(graph_t *g);
static void flat_reorder(graph_t *g);
static void flat_search(graph_t *g, node_t *v);
static void init_mincross(graph_t *g);
static void merge2(graph_t *g);
static void init_mccomp(graph_t *g, size_t c);
 
static void cleanup2(graph_t *g, int64_t nc, bool have_vlists);
 
static int64_t mincross_clust(graph_t *g);
static int64_t mincross(graph_t *g, int startpass);
static void mincross_step(graph_t *g, int pass);
static void mincross_options(graph_t *g);
static void save_best(graph_t *g);
static void restore_best(graph_t *g);
 
static adjmatrix_t *new_matrix(size_t initial_rows, size_t initial_columns);
 
static void free_matrix(adjmatrix_t *p);
static int ordercmpf(const void *, const void *);
static int64_t ncross(void);
#ifdef DEBUG
void check_order(void);
void check_vlists(graph_t *g);
void node_in_root_vlist(node_t *n);
#endif
 
/* mincross parameters */
static int MinQuit;
static const double Convergence = .995;
 
static graph_t *Root;
static int GlobalMinRank, GlobalMaxRank;
static edge_t **TE_list;
static int *TI_list;
static bool ReMincross;
 
typedef struct {
  Agrec_t h;
  int x, lo, hi;
  Agnode_t *np;
} info_t;
 
#define ND_x(n) (((info_t *)AGDATA(n))->x)
#define ND_lo(n) (((info_t *)AGDATA(n))->lo)
#define ND_hi(n) (((info_t *)AGDATA(n))->hi)
#define ND_np(n) (((info_t *)AGDATA(n))->np)
#define ND_idx(n) (ND_order(ND_np(n)))
 
static void emptyComp(graph_t *sg) {
  Agnode_t *n;
  Agnode_t *nxt;
 
  for (n = agfstnode(sg); n; n = nxt) {
    nxt = agnxtnode(sg, n);
    agdelnode(sg, n);
  }
}
 
#define isBackedge(e) (ND_idx(aghead(e)) > ND_idx(agtail(e)))
 
static Agnode_t *findSource(Agraph_t *g, Agraph_t *sg) {
  Agnode_t *n;
 
  for (n = agfstnode(sg); n; n = agnxtnode(sg, n))
    if (agdegree(g, n, 1, 0) == 0)
      return n;
  return NULL;
}
 
typedef LIST(node_t *) nodes_t;
 
static nodes_t topsort(Agraph_t *g, Agraph_t *sg) {
  Agnode_t *n;
  Agedge_t *e;
  Agedge_t *nxte;
  nodes_t arr = {0};
 
  while ((n = findSource(g, sg))) {
    LIST_APPEND(&arr, ND_np(n));
    agdelnode(sg, n);
    for (e = agfstout(g, n); e; e = nxte) {
      nxte = agnxtout(g, e);
      agdeledge(g, e);
    }
  }
  return arr;
}
 
static int getComp(graph_t *g, node_t *n, graph_t *comp, int *indices) {
  int backedge = 0;
  Agedge_t *e;
 
  ND_x(n) = 1;
  indices[agnnodes(comp)] = ND_idx(n);
  agsubnode(comp, n, 1);
  for (e = agfstout(g, n); e; e = agnxtout(g, e)) {
    if (isBackedge(e))
      backedge++;
    if (!ND_x(aghead(e)))
      backedge += getComp(g, aghead(e), comp, indices);
  }
  for (e = agfstin(g, n); e; e = agnxtin(g, e)) {
    if (isBackedge(e))
      backedge++;
    if (!ND_x(agtail(e)))
      backedge += getComp(g, agtail(e), comp, indices);
  }
  return backedge;
}
 
static void fixLabelOrder(graph_t *g, rank_t *rk) {
  bool haveBackedge = false;
  Agraph_t *sg;
  Agnode_t *n;
  Agnode_t *nxtp;
  Agnode_t *v;
 
  for (n = agfstnode(g); n; n = nxtp) {
    v = nxtp = agnxtnode(g, n);
    for (; v; v = agnxtnode(g, v)) {
      if (ND_hi(v) <= ND_lo(n)) {
        haveBackedge = true;
        agedge(g, v, n, NULL, 1);
      } else if (ND_hi(n) <= ND_lo(v)) {
        agedge(g, n, v, NULL, 1);
      }
    }
  }
  if (!haveBackedge)
    return;
 
  sg = agsubg(g, "comp", 1);
  int *indices = gv_calloc(agnnodes_z(g), sizeof(int));
 
  for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
    if (ND_x(n) || agdegree(g, n, 1, 1) == 0)
      continue;
    if (getComp(g, n, sg, indices)) {
      // `topsort()` drains `sg` via `agdelnode()`, so the node count must be
      // sampled before the call, not after
      const size_t sz_before = agnnodes_z(sg);
      nodes_t arr = topsort(g, sg);
      assert(LIST_SIZE(&arr) == sz_before);
      qsort(indices, LIST_SIZE(&arr), sizeof(int), ordercmpf);
      for (size_t i = 0; i < LIST_SIZE(&arr); i++) {
        ND_order(LIST_GET(&arr, i)) = indices[i];
        rk->v[indices[i]] = LIST_GET(&arr, i);
      }
      LIST_FREE(&arr);
    }
    emptyComp(sg);
  }
  free(indices);
}
 
/* Check that the ordering of labels for flat edges is consistent.
 * This is necessary because dot_position will attempt to force the label
 * to be between the edge's vertices. This can lead to an infeasible problem.
 *
 * We check each rank for any flat edge labels (as dummy nodes) and create a
 * graph with a node for each label. If the graph contains more than 1 node, we
 * call fixLabelOrder to see if there really is a problem and, if so, fix it.
 */
void checkLabelOrder(graph_t *g) {
  graph_t *lg = NULL;
 
  for (int r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    rank_t *const rk = GD_rank(g) + r;
    for (int j = 0; j < rk->n; j++) {
      Agnode_t *const u = rk->v[j];
      if (ND_alg(u)) {
        if (!lg)
          lg = agopen("lg", Agstrictdirected, 0);
        Agnode_t *const n = agnode(lg, ITOS(j), 1);
        agbindrec(n, "info", sizeof(info_t), true);
        int lo = ND_order(aghead(ND_out(u).list[0]));
        int hi = ND_order(aghead(ND_out(u).list[1]));
        if (lo > hi) {
          SWAP(&lo, &hi);
        }
        ND_lo(n) = lo;
        ND_hi(n) = hi;
        ND_np(n) = u;
      }
    }
    if (lg) {
      if (agnnodes(lg) > 1)
        fixLabelOrder(lg, rk);
      agclose(lg);
      lg = NULL;
    }
  }
}
 
/* Minimize edge crossings
 * Note that nodes are not placed into GD_rank(g) until mincross()
 * is called.
 */
int dot_mincross(graph_t *g) {
  int64_t nc;
  char *s;
 
  int rc = 0;
 
  /* check whether malformed input has led to empty cluster that the crossing
   * functions will not anticipate
   */
  {
    size_t i;
    for (i = 1; i <= (size_t)GD_n_cluster(g);) {
      if (agfstnode(GD_clust(g)[i]) == NULL) {
        agwarningf("removing empty cluster\n");
        memmove(&GD_clust(g)[i], &GD_clust(g)[i + 1],
                ((size_t)GD_n_cluster(g) - i) * sizeof(GD_clust(g)[0]));
        --GD_n_cluster(g);
      } else {
        ++i;
      }
    }
  }
 
  init_mincross(g);
  bool has_set_vlists = false;
 
  size_t comp;
  for (nc = 0, comp = 0; comp < GD_comp(g).size; comp++) {
    init_mccomp(g, comp);
    const int64_t mc = mincross(g, 0);
    if (mc < 0) {
      rc = -1;
      goto done;
    }
    nc += mc;
  }
 
  merge2(g);
 
  /* run mincross on contents of each cluster */
  for (int c = 1; c <= GD_n_cluster(g); c++) {
    const int64_t mc = mincross_clust(GD_clust(g)[c]);
    if (mc < 0) {
      rc = -1;
      goto done;
    }
    nc += mc;
#ifdef DEBUG
    check_vlists(GD_clust(g)[c]);
    check_order();
#endif
  }
  has_set_vlists = true;
 
  if (GD_n_cluster(g) > 0 && (!(s = agget(g, "remincross")) || mapbool(s))) {
    mark_lowclusters(g);
    ReMincross = true;
    const int64_t mc = mincross(g, 2);
    if (mc < 0) {
      rc = -1;
      goto done;
    }
    nc = mc;
#ifdef DEBUG
    for (int c = 1; c <= GD_n_cluster(g); c++)
      check_vlists(GD_clust(g)[c]);
#endif
  }
done:
  cleanup2(g, nc, has_set_vlists);
  return rc;
}
 
static adjmatrix_t *new_matrix(size_t initial_rows, size_t initial_columns) {
  adjmatrix_t *rv = gv_alloc(sizeof(adjmatrix_t));
  const size_t bits = initial_rows * initial_columns;
  const size_t bytes = bits / 8 + (bits % 8 == 0 ? 0 : 1);
  uint8_t *const data = gv_alloc(bytes);
  *rv = (adjmatrix_t){
      .nrows = initial_rows, .ncols = initial_columns, .data = data};
  return rv;
}
 
static void free_matrix(adjmatrix_t *p) {
  if (p) {
    free(p->data);
    free(p);
  }
}
 
static void init_mccomp(graph_t *g, size_t c) {
  int r;
 
  GD_nlist(g) = GD_comp(g).list[c];
  if (c > 0) {
    for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
      GD_rank(g)[r].v = GD_rank(g)[r].v + GD_rank(g)[r].n;
      GD_rank(g)[r].n = 0;
    }
  }
}
 
static int betweenclust(edge_t *e) {
  while (ED_to_orig(e))
    e = ED_to_orig(e);
  return ND_clust(agtail(e)) != ND_clust(aghead(e));
}
 
static void do_ordering_node(graph_t *g, node_t *n, bool outflag) {
  int i, ne;
  node_t *u, *v;
  edge_t *e, *f, *fe;
  edge_t **sortlist = TE_list;
 
  if (ND_clust(n))
    return;
  if (outflag) {
    for (i = ne = 0; (e = ND_out(n).list[i]); i++)
      if (!betweenclust(e))
        sortlist[ne++] = e;
  } else {
    for (i = ne = 0; (e = ND_in(n).list[i]); i++)
      if (!betweenclust(e))
        sortlist[ne++] = e;
  }
  if (ne <= 1)
    return;
  // Write null terminator at end of list. Requires +1 in TE_list allocation.
  sortlist[ne] = 0;
  qsort(sortlist, ne, sizeof(sortlist[0]), edgeidcmpf);
  for (ne = 1; (f = sortlist[ne]); ne++) {
    e = sortlist[ne - 1];
    if (outflag) {
      u = aghead(e);
      v = aghead(f);
    } else {
      u = agtail(e);
      v = agtail(f);
    }
    if (find_flat_edge(u, v))
      return;
    fe = new_virtual_edge(u, v, NULL);
    ED_edge_type(fe) = FLATORDER;
    flat_edge(g, fe);
  }
}
 
static void do_ordering(graph_t *g, bool outflag) {
  /* Order all nodes in graph */
  node_t *n;
 
  for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
    do_ordering_node(g, n, outflag);
  }
}
 
static void do_ordering_for_nodes(graph_t *g) {
  /* Order nodes which have the "ordered" attribute */
  node_t *n;
  const char *ordering;
 
  for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
    if ((ordering = late_string(n, N_ordering, NULL))) {
      if (streq(ordering, "out"))
        do_ordering_node(g, n, true);
      else if (streq(ordering, "in"))
        do_ordering_node(g, n, false);
      else if (ordering[0])
        agerrorf("ordering '%s' not recognized for node '%s'.\n", ordering,
                 agnameof(n));
    }
  }
}
 
/* handle case where graph specifies edge ordering
 * If the graph does not have an ordering attribute, we then
 * check for nodes having the attribute.
 * Note that, in this implementation, the value of G_ordering
 * dominates the value of N_ordering.
 */
static void ordered_edges(graph_t *g) {
  char *ordering;
 
  if (!G_ordering && !N_ordering)
    return;
  if ((ordering = late_string(g, G_ordering, NULL))) {
    if (streq(ordering, "out"))
      do_ordering(g, true);
    else if (streq(ordering, "in"))
      do_ordering(g, false);
    else if (ordering[0])
      agerrorf("ordering '%s' not recognized.\n", ordering);
  } else {
    graph_t *subg;
 
    for (subg = agfstsubg(g); subg; subg = agnxtsubg(subg)) {
      /* clusters are processed by separate calls to ordered_edges */
      if (!is_a_cluster(subg))
        ordered_edges(subg);
    }
    if (N_ordering)
      do_ordering_for_nodes(g);
  }
}
 
static int64_t mincross_clust(graph_t *g) {
  int c;
 
  if (expand_cluster(g) != 0) {
    return -1;
  }
  ordered_edges(g);
  flat_breakcycles(g);
  flat_reorder(g);
  int64_t nc = mincross(g, 2);
  if (nc < 0) {
    return nc;
  }
 
  for (c = 1; c <= GD_n_cluster(g); c++) {
    const int64_t mc = mincross_clust(GD_clust(g)[c]);
    if (mc < 0) {
      return mc;
    }
    nc += mc;
  }
 
  save_vlist(g);
  return nc;
}
 
static bool left2right(graph_t *g, node_t *v, node_t *w) {
  /* CLUSTER indicates orig nodes of clusters, and vnodes of skeletons */
  if (!ReMincross) {
    if (ND_clust(v) != ND_clust(w) && ND_clust(v) && ND_clust(w)) {
      /* the following allows cluster skeletons to be swapped */
      if (ND_ranktype(v) == CLUSTER && ND_node_type(v) == VIRTUAL)
        return false;
      if (ND_ranktype(w) == CLUSTER && ND_node_type(w) == VIRTUAL)
        return false;
      return true;
    }
  } else {
    if (ND_clust(v) != ND_clust(w))
      return true;
  }
  adjmatrix_t *const M = GD_rank(g)[ND_rank(v)].flat;
  if (M == NULL)
    return false;
  if (GD_flip(g)) {
    SWAP(&v, &w);
  }
  return matrix_get(M, (size_t)flatindex(v), (size_t)flatindex(w));
}
 
static int64_t in_cross(node_t *v, node_t *w) {
  edge_t **e1, **e2;
  int inv, t;
  int64_t cross = 0;
 
  for (e2 = ND_in(w).list; *e2; e2++) {
    int cnt = ED_xpenalty(*e2);
 
    inv = ND_order(agtail(*e2));
 
    for (e1 = ND_in(v).list; *e1; e1++) {
      t = ND_order(agtail(*e1)) - inv;
      if (t > 0 || (t == 0 && ED_tail_port(*e1).p.x > ED_tail_port(*e2).p.x))
        cross += ED_xpenalty(*e1) * cnt;
    }
  }
  return cross;
}
 
static int out_cross(node_t *v, node_t *w) {
  edge_t **e1, **e2;
  int inv, cross = 0, t;
 
  for (e2 = ND_out(w).list; *e2; e2++) {
    int cnt = ED_xpenalty(*e2);
    inv = ND_order(aghead(*e2));
 
    for (e1 = ND_out(v).list; *e1; e1++) {
      t = ND_order(aghead(*e1)) - inv;
      if (t > 0 || (t == 0 && ED_head_port(*e1).p.x > ED_head_port(*e2).p.x))
        cross += ED_xpenalty(*e1) * cnt;
    }
  }
  return cross;
}
 
static void exchange(node_t *v, node_t *w) {
  int vi, wi, r;
 
  r = ND_rank(v);
  vi = ND_order(v);
  wi = ND_order(w);
  ND_order(v) = wi;
  GD_rank(Root)[r].v[wi] = v;
  ND_order(w) = vi;
  GD_rank(Root)[r].v[vi] = w;
}
 
static int64_t transpose_step(graph_t *g, int r, bool reverse) {
  int i;
  node_t *v, *w;
 
  int64_t rv = 0;
  GD_rank(g)[r].candidate = false;
  for (i = 0; i < GD_rank(g)[r].n - 1; i++) {
    v = GD_rank(g)[r].v[i];
    w = GD_rank(g)[r].v[i + 1];
    assert(ND_order(v) < ND_order(w));
    if (left2right(g, v, w))
      continue;
    int64_t c0 = 0;
    int64_t c1 = 0;
    if (r > 0) {
      c0 += in_cross(v, w);
      c1 += in_cross(w, v);
    }
    if (GD_rank(g)[r + 1].n > 0) {
      c0 += out_cross(v, w);
      c1 += out_cross(w, v);
    }
    if (c1 < c0 || (c0 > 0 && reverse && c1 == c0)) {
      exchange(v, w);
      rv += c0 - c1;
      GD_rank(Root)[r].valid = false;
      GD_rank(g)[r].candidate = true;
 
      if (r > GD_minrank(g)) {
        GD_rank(Root)[r - 1].valid = false;
        GD_rank(g)[r - 1].candidate = true;
      }
      if (r < GD_maxrank(g)) {
        GD_rank(Root)[r + 1].valid = false;
        GD_rank(g)[r + 1].candidate = true;
      }
    }
  }
  return rv;
}
 
static void transpose(graph_t *g, bool reverse) {
  int r;
 
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++)
    GD_rank(g)[r].candidate = true;
  int64_t delta;
  do {
    delta = 0;
    for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
      if (GD_rank(g)[r].candidate) {
        delta += transpose_step(g, r, reverse);
      }
    }
  } while (delta >= 1);
}
 
static int64_t mincross(graph_t *g, int startpass) {
  const int endpass = 2;
  int maxthispass = 0, iter, trying, pass;
  int64_t cur_cross, best_cross;
 
  if (startpass > 1) {
    cur_cross = best_cross = ncross();
    save_best(g);
  } else
    cur_cross = best_cross = INT64_MAX;
  for (pass = startpass; pass <= endpass; pass++) {
    if (pass <= 1) {
      maxthispass = MIN(4, MaxIter);
      if (g == dot_root(g))
        if (build_ranks(g, pass) != 0) {
          return -1;
        }
      if (pass == 0)
        flat_breakcycles(g);
      flat_reorder(g);
 
      if ((cur_cross = ncross()) <= best_cross) {
        save_best(g);
        best_cross = cur_cross;
      }
    } else {
      maxthispass = MaxIter;
      if (cur_cross > best_cross)
        restore_best(g);
      cur_cross = best_cross;
    }
    trying = 0;
    for (iter = 0; iter < maxthispass; iter++) {
      if (Verbose)
        fprintf(stderr,
                "mincross: pass %d iter %d trying %d cur_cross %" PRId64
                " best_cross %" PRId64 "\n",
                pass, iter, trying, cur_cross, best_cross);
      if (trying++ >= MinQuit)
        break;
      if (cur_cross == 0)
        break;
      mincross_step(g, iter);
      if ((cur_cross = ncross()) <= best_cross) {
        save_best(g);
        if (cur_cross < Convergence * (double)best_cross)
          trying = 0;
        best_cross = cur_cross;
      }
    }
    if (cur_cross == 0)
      break;
  }
  if (cur_cross > best_cross)
    restore_best(g);
  if (best_cross > 0) {
    transpose(g, false);
    best_cross = ncross();
  }
 
  return best_cross;
}
 
static void restore_best(graph_t *g) {
  node_t *n;
  int i, r;
 
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      n = GD_rank(g)[r].v[i];
      ND_order(n) = saveorder(n);
    }
  }
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    GD_rank(Root)[r].valid = false;
    qsort(GD_rank(g)[r].v, GD_rank(g)[r].n, sizeof(GD_rank(g)[0].v[0]),
          nodeposcmpf);
  }
}
 
static void save_best(graph_t *g) {
  node_t *n;
  int i, r;
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      n = GD_rank(g)[r].v[i];
      saveorder(n) = ND_order(n);
    }
  }
}
 
/* merges the connected components of g */
static void merge_components(graph_t *g) {
  node_t *u, *v;
 
  if (GD_comp(g).size <= 1)
    return;
  u = NULL;
  for (size_t c = 0; c < GD_comp(g).size; c++) {
    v = GD_comp(g).list[c];
    if (u)
      ND_next(u) = v;
    ND_prev(v) = u;
    while (ND_next(v)) {
      v = ND_next(v);
    }
    u = v;
  }
  GD_comp(g).size = 1;
  GD_nlist(g) = GD_comp(g).list[0];
  GD_minrank(g) = GlobalMinRank;
  GD_maxrank(g) = GlobalMaxRank;
}
 
/* merge connected components, create globally consistent rank lists */
static void merge2(graph_t *g) {
  int i, r;
  node_t *v;
 
  /* merge the components and rank limits */
  merge_components(g);
 
  /* install complete ranks */
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    GD_rank(g)[r].n = GD_rank(g)[r].an;
    GD_rank(g)[r].v = GD_rank(g)[r].av;
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      v = GD_rank(g)[r].v[i];
      if (v == NULL) {
        if (Verbose)
          fprintf(stderr, "merge2: graph %s, rank %d has only %d < %d nodes\n",
                  agnameof(g), r, i, GD_rank(g)[r].n);
        GD_rank(g)[r].n = i;
        break;
      }
      ND_order(v) = i;
    }
  }
}
 
static void cleanup2(graph_t *g, int64_t nc, bool has_vlists) {
  int i, j, r, c;
  node_t *v;
  edge_t *e;
 
  if (TI_list) {
    free(TI_list);
    TI_list = NULL;
  }
  if (TE_list) {
    free(TE_list);
    TE_list = NULL;
  }
  /* fix vlists of clusters */
  for (c = 1; has_vlists && c <= GD_n_cluster(g); c++)
    rec_reset_vlists(GD_clust(g)[c]);
 
  /* remove node temporary edges for ordering nodes */
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      v = GD_rank(g)[r].v[i];
      ND_order(v) = i;
      if (ND_flat_out(v).list) {
        for (j = 0; (e = ND_flat_out(v).list[j]); j++)
          if (ED_edge_type(e) == FLATORDER) {
            delete_flat_edge(e);
            free(e->base.data);
            free(e);
            j--;
          }
      }
    }
    free_matrix(GD_rank(g)[r].flat);
  }
  if (Verbose)
    fprintf(stderr, "mincross %s: %" PRId64 " crossings, %.2f secs.\n",
            agnameof(g), nc, elapsed_sec());
}
 
static node_t *neighbor(node_t *v, int dir) {
  node_t *rv = NULL;
  assert(v);
  if (dir < 0) {
    if (ND_order(v) > 0)
      rv = GD_rank(Root)[ND_rank(v)].v[ND_order(v) - 1];
  } else
    rv = GD_rank(Root)[ND_rank(v)].v[ND_order(v) + 1];
  assert(rv == 0 || (ND_order(rv) - ND_order(v)) * dir > 0);
  return rv;
}
 
static bool is_a_normal_node_of(graph_t *g, node_t *v) {
  return ND_node_type(v) == NORMAL && agcontains(g, v);
}
 
static bool is_a_vnode_of_an_edge_of(graph_t *g, node_t *v) {
  if (ND_node_type(v) == VIRTUAL && ND_in(v).size == 1 && ND_out(v).size == 1) {
    edge_t *e = ND_out(v).list[0];
    while (ED_edge_type(e) != NORMAL)
      e = ED_to_orig(e);
    if (agcontains(g, e))
      return true;
  }
  return false;
}
 
static bool inside_cluster(graph_t *g, node_t *v) {
  return is_a_normal_node_of(g, v) || is_a_vnode_of_an_edge_of(g, v);
}
 
static node_t *furthestnode(graph_t *g, node_t *v, int dir) {
  node_t *rv = v;
  for (node_t *u = v; (u = neighbor(u, dir));) {
    if (is_a_normal_node_of(g, u))
      rv = u;
    else if (is_a_vnode_of_an_edge_of(g, u))
      rv = u;
  }
  return rv;
}
 
void save_vlist(graph_t *g) {
  int r;
 
  if (GD_rankleader(g))
    for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
      GD_rankleader(g)[r] = GD_rank(g)[r].v[0];
    }
}
 
void rec_save_vlists(graph_t *g) {
  int c;
 
  save_vlist(g);
  for (c = 1; c <= GD_n_cluster(g); c++)
    rec_save_vlists(GD_clust(g)[c]);
}
 
void rec_reset_vlists(graph_t *g) {
  // fix vlists of sub-clusters
  for (int c = 1; c <= GD_n_cluster(g); c++)
    rec_reset_vlists(GD_clust(g)[c]);
 
  if (GD_rankleader(g))
    for (int r = GD_minrank(g); r <= GD_maxrank(g); r++) {
      node_t *const v = GD_rankleader(g)[r];
      if (v == NULL) {
        continue;
      }
#ifdef DEBUG
      node_in_root_vlist(v);
#endif
      node_t *const u = furthestnode(g, v, -1);
      node_t *const w = furthestnode(g, v, 1);
      GD_rankleader(g)[r] = u;
#ifdef DEBUG
      assert(GD_rank(dot_root(g))[r].v[ND_order(u)] == u);
#endif
      GD_rank(g)[r].v = GD_rank(dot_root(g))[r].v + ND_order(u);
      GD_rank(g)[r].n = ND_order(w) - ND_order(u) + 1;
    }
}
 
/* The structures in crossing minimization and positioning require
 * that clusters have some node on each rank. This function recursively
 * guarantees this property. It takes into account nodes and edges in
 * a cluster, the latter causing dummy nodes for intervening ranks.
 * For any rank without node, we create a real node of small size. This
 * is stored in the subgraph sg, for easy removal later.
 *
 * I believe it is not necessary to do this for the root graph, as these
 * are laid out one component at a time and these will necessarily have a
 * node on each rank from source to sink levels.
 */
static Agraph_t *realFillRanks(Agraph_t *g, bitarray_t *ranks, Agraph_t *sg) {
  int i, c;
  Agedge_t *e;
  Agnode_t *n;
 
  for (c = 1; c <= GD_n_cluster(g); c++)
    sg = realFillRanks(GD_clust(g)[c], ranks, sg);
 
  if (dot_root(g) == g)
    return sg;
  bitarray_clear(ranks);
  for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
    bitarray_set(ranks, ND_rank(n), true);
    for (e = agfstout(g, n); e; e = agnxtout(g, e)) {
      for (i = ND_rank(n) + 1; i <= ND_rank(aghead(e)); i++)
        bitarray_set(ranks, i, true);
    }
  }
  for (i = GD_minrank(g); i <= GD_maxrank(g); i++) {
    if (!bitarray_get(*ranks, i)) {
      if (!sg) {
        sg = agsubg(dot_root(g), "_new_rank", 1);
      }
      n = agnode(sg, NULL, 1);
      agbindrec(n, "Agnodeinfo_t", sizeof(Agnodeinfo_t), true);
      ND_rank(n) = i;
      ND_lw(n) = ND_rw(n) = 0.5;
      ND_ht(n) = 1;
      ND_UF_size(n) = 1;
      alloc_elist(4, ND_in(n));
      alloc_elist(4, ND_out(n));
      agsubnode(g, n, 1);
    }
  }
  return sg;
}
 
static void fillRanks(Agraph_t *g) {
  int rnks_sz = GD_maxrank(g) + 2;
  bitarray_t rnks = bitarray_new(rnks_sz);
  realFillRanks(g, &rnks, NULL);
  bitarray_reset(&rnks);
}
 
static void init_mincross(graph_t *g) {
  int size;
 
  if (Verbose)
    start_timer();
 
  ReMincross = false;
  Root = g;
  /* alloc +1 for the null terminator usage in do_ordering() */
  size = agnedges(dot_root(g)) + 1;
  TE_list = gv_calloc(size, sizeof(edge_t *));
  TI_list = gv_calloc(size, sizeof(int));
  mincross_options(g);
  if (GD_flags(g) & NEW_RANK)
    fillRanks(g);
  class2(g);
  decompose(g, 1);
  allocate_ranks(g);
  ordered_edges(g);
  GlobalMinRank = GD_minrank(g);
  GlobalMaxRank = GD_maxrank(g);
}
 
static void flat_rev(Agraph_t *g, Agedge_t *e) {
  int j;
  Agedge_t *rev;
 
  if (!ND_flat_out(aghead(e)).list)
    rev = NULL;
  else
    for (j = 0; (rev = ND_flat_out(aghead(e)).list[j]); j++)
      if (aghead(rev) == agtail(e))
        break;
  if (rev) {
    merge_oneway(e, rev);
    if (ED_edge_type(rev) == FLATORDER && ED_to_orig(rev) == 0)
      ED_to_orig(rev) = e;
    elist_append(e, ND_other(agtail(e)));
  } else {
    rev = new_virtual_edge(aghead(e), agtail(e), e);
    if (ED_edge_type(e) == FLATORDER)
      ED_edge_type(rev) = FLATORDER;
    else
      ED_edge_type(rev) = REVERSED;
    ED_label(rev) = ED_label(e);
    flat_edge(g, rev);
  }
}
 
static void flat_search(graph_t *g, node_t *v) {
  int i;
  bool hascl;
  edge_t *e;
  adjmatrix_t *M = GD_rank(g)[ND_rank(v)].flat;
 
  ND_mark(v) = true;
  ND_onstack(v) = true;
  hascl = GD_n_cluster(dot_root(g)) > 0;
  if (ND_flat_out(v).list)
    for (i = 0; (e = ND_flat_out(v).list[i]); i++) {
      if (hascl && !(agcontains(g, agtail(e)) && agcontains(g, aghead(e))))
        continue;
      if (ED_weight(e) == 0)
        continue;
      if (ND_onstack(aghead(e))) {
        matrix_set(M, (size_t)flatindex(aghead(e)),
                   (size_t)flatindex(agtail(e)));
        delete_flat_edge(e);
        i--;
        if (ED_edge_type(e) == FLATORDER)
          continue;
        flat_rev(g, e);
      } else {
        matrix_set(M, (size_t)flatindex(agtail(e)),
                   (size_t)flatindex(aghead(e)));
        if (!ND_mark(aghead(e)))
          flat_search(g, aghead(e));
      }
    }
  ND_onstack(v) = false;
}
 
static void flat_breakcycles(graph_t *g) {
  int i, r;
  node_t *v;
 
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    bool flat = false;
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      v = GD_rank(g)[r].v[i];
      ND_mark(v) = false;
      ND_onstack(v) = false;
      ND_low(v) = i;
      if (ND_flat_out(v).size > 0 && !flat) {
        GD_rank(g)[r].flat =
            new_matrix((size_t)GD_rank(g)[r].n, (size_t)GD_rank(g)[r].n);
        flat = true;
      }
    }
    if (flat) {
      for (i = 0; i < GD_rank(g)[r].n; i++) {
        v = GD_rank(g)[r].v[i];
        if (!ND_mark(v))
          flat_search(g, v);
      }
    }
  }
}
 
/* Allocate rank structure, determining number of nodes per rank.
 * Note that no nodes are put into the structure yet.
 */
void allocate_ranks(graph_t *g) {
  int r, low, high;
  node_t *n;
  edge_t *e;
 
  int *cn = gv_calloc(GD_maxrank(g) + 2,
                      sizeof(int)); // must be 0 based, not GD_minrank
  for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
    cn[ND_rank(n)]++;
    for (e = agfstout(g, n); e; e = agnxtout(g, e)) {
      low = ND_rank(agtail(e));
      high = ND_rank(aghead(e));
      if (low > high) {
        SWAP(&low, &high);
      }
      for (r = low + 1; r < high; r++)
        cn[r]++;
    }
  }
  GD_rank(g) = gv_calloc(GD_maxrank(g) + 2, sizeof(rank_t));
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    GD_rank(g)[r].an = GD_rank(g)[r].n = cn[r] + 1;
    GD_rank(g)[r].av = GD_rank(g)[r].v = gv_calloc(cn[r] + 1, sizeof(node_t *));
  }
  free(cn);
}
 
/* install a node at the current right end of its rank */
int install_in_rank(graph_t *g, node_t *n) {
  int i, r;
 
  r = ND_rank(n);
  i = GD_rank(g)[r].n;
  if (GD_rank(g)[r].an <= 0) {
    agerrorf("install_in_rank, line %d: %s %s rank %d i = %d an = 0\n",
             __LINE__, agnameof(g), agnameof(n), r, i);
    return -1;
  }
 
  GD_rank(g)[r].v[i] = n;
  ND_order(n) = i;
  GD_rank(g)[r].n++;
  assert(GD_rank(g)[r].n <= GD_rank(g)[r].an);
#ifdef DEBUG
  {
    node_t *v;
 
    for (v = GD_nlist(g); v; v = ND_next(v))
      if (v == n)
        break;
    assert(v != NULL);
  }
#endif
  if (ND_order(n) > GD_rank(Root)[r].an) {
    agerrorf("install_in_rank, line %d: ND_order(%s) [%d] > "
             "GD_rank(Root)[%d].an [%d]\n",
             __LINE__, agnameof(n), ND_order(n), r, GD_rank(Root)[r].an);
    return -1;
  }
  if (r < GD_minrank(g) || r > GD_maxrank(g)) {
    agerrorf("install_in_rank, line %d: rank %d not in rank range [%d,%d]\n",
             __LINE__, r, GD_minrank(g), GD_maxrank(g));
    return -1;
  }
  if (GD_rank(g)[r].v + ND_order(n) > GD_rank(g)[r].av + GD_rank(Root)[r].an) {
    agerrorf("install_in_rank, line %d: GD_rank(g)[%d].v + ND_order(%s) [%d] > "
             "GD_rank(g)[%d].av + GD_rank(Root)[%d].an [%d]\n",
             __LINE__, r, agnameof(n), ND_order(n), r, r, GD_rank(Root)[r].an);
    return -1;
  }
  return 0;
}
 
/*      install nodes in ranks. the initial ordering ensure that series-parallel
 *      graphs such as trees are drawn with no crossings.  it tries searching
 *      in- and out-edges and takes the better of the two initial orderings.
 */
int build_ranks(graph_t *g, int pass) {
  int i, j;
  node_t *n, *ns;
  edge_t **otheredges;
  node_queue_t q = {0};
  for (n = GD_nlist(g); n; n = ND_next(n))
    MARK(n) = false;
 
#ifdef DEBUG
  {
    edge_t *e;
    for (n = GD_nlist(g); n; n = ND_next(n)) {
      for (i = 0; (e = ND_out(n).list[i]); i++)
        assert(!MARK(aghead(e)));
      for (i = 0; (e = ND_in(n).list[i]); i++)
        assert(!MARK(agtail(e)));
    }
  }
#endif
 
  for (i = GD_minrank(g); i <= GD_maxrank(g); i++)
    GD_rank(g)[i].n = 0;
 
  const bool walkbackwards = g != agroot(g); // if this is a cluster, need to
                                             // walk GD_nlist backward to
                                             // preserve input node order
  if (walkbackwards) {
    for (ns = GD_nlist(g); ND_next(ns); ns = ND_next(ns)) {
      ;
    }
  } else {
    ns = GD_nlist(g);
  }
  for (n = ns; n; n = walkbackwards ? ND_prev(n) : ND_next(n)) {
    otheredges = pass == 0 ? ND_in(n).list : ND_out(n).list;
    if (otheredges[0] != NULL)
      continue;
    if (!MARK(n)) {
      MARK(n) = true;
      LIST_PUSH_BACK(&q, n);
      while (!LIST_IS_EMPTY(&q)) {
        node_t *n0 = LIST_POP_FRONT(&q);
        if (ND_ranktype(n0) != CLUSTER) {
          if (install_in_rank(g, n0) != 0) {
            LIST_FREE(&q);
            return -1;
          }
          enqueue_neighbors(&q, n0, pass);
        } else {
          const int rc = install_cluster(g, n0, pass, &q);
          if (rc != 0) {
            LIST_FREE(&q);
            return rc;
          }
        }
      }
    }
  }
  assert(LIST_IS_EMPTY(&q));
  for (i = GD_minrank(g); i <= GD_maxrank(g); i++) {
    GD_rank(Root)[i].valid = false;
    if (GD_flip(g) && GD_rank(g)[i].n > 0) {
      node_t **vlist = GD_rank(g)[i].v;
      int num_nodes_1 = GD_rank(g)[i].n - 1;
      int half_num_nodes_1 = num_nodes_1 / 2;
      for (j = 0; j <= half_num_nodes_1; j++)
        exchange(vlist[j], vlist[num_nodes_1 - j]);
    }
  }
 
  if (g == dot_root(g) && ncross() > 0)
    transpose(g, false);
  LIST_FREE(&q);
  return 0;
}
 
void enqueue_neighbors(node_queue_t *q, node_t *n0, int pass) {
  edge_t *e;
 
  if (pass == 0) {
    for (size_t i = 0; i < ND_out(n0).size; i++) {
      e = ND_out(n0).list[i];
      if (!MARK(aghead(e))) {
        MARK(aghead(e)) = true;
        LIST_PUSH_BACK(q, aghead(e));
      }
    }
  } else {
    for (size_t i = 0; i < ND_in(n0).size; i++) {
      e = ND_in(n0).list[i];
      if (!MARK(agtail(e))) {
        MARK(agtail(e)) = true;
        LIST_PUSH_BACK(q, agtail(e));
      }
    }
  }
}
 
static bool constraining_flat_edge(Agraph_t *g, Agedge_t *e) {
  if (ED_weight(e) == 0)
    return false;
  if (!inside_cluster(g, agtail(e)))
    return false;
  if (!inside_cluster(g, aghead(e)))
    return false;
  return true;
}
 
/* construct nodes reachable from 'here' in post-order.
 * This is the same as doing a topological sort in reverse order.
 */
static void postorder(graph_t *g, node_t *v, nodes_t *list, int r) {
  edge_t *e;
  int i;
 
  MARK(v) = true;
  if (ND_flat_out(v).size > 0) {
    for (i = 0; (e = ND_flat_out(v).list[i]); i++) {
      if (!constraining_flat_edge(g, e))
        continue;
      if (!MARK(aghead(e)))
        postorder(g, aghead(e), list, r);
    }
  }
  assert(ND_rank(v) == r);
  LIST_APPEND(list, v);
}
 
static void flat_reorder(graph_t *g) {
  int i, r, local_in_cnt, local_out_cnt, base_order;
  node_t *v;
  nodes_t temprank = {0};
  edge_t *flat_e, *e;
 
  if (!GD_has_flat_edges(g))
    return;
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    if (GD_rank(g)[r].n == 0)
      continue;
    base_order = ND_order(GD_rank(g)[r].v[0]);
    for (i = 0; i < GD_rank(g)[r].n; i++)
      MARK(GD_rank(g)[r].v[i]) = false;
    LIST_CLEAR(&temprank);
 
    /* construct reverse topological sort order in temprank */
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      if (GD_flip(g))
        v = GD_rank(g)[r].v[i];
      else
        v = GD_rank(g)[r].v[GD_rank(g)[r].n - i - 1];
 
      local_in_cnt = local_out_cnt = 0;
      for (size_t j = 0; j < ND_flat_in(v).size; j++) {
        flat_e = ND_flat_in(v).list[j];
        if (constraining_flat_edge(g, flat_e))
          local_in_cnt++;
      }
      for (size_t j = 0; j < ND_flat_out(v).size; j++) {
        flat_e = ND_flat_out(v).list[j];
        if (constraining_flat_edge(g, flat_e))
          local_out_cnt++;
      }
      if (local_in_cnt == 0 && local_out_cnt == 0)
        LIST_APPEND(&temprank, v);
      else {
        if (!MARK(v) && local_in_cnt == 0) {
          postorder(g, v, &temprank, r);
        }
      }
    }
 
    if (!LIST_IS_EMPTY(&temprank)) {
      if (!GD_flip(g)) {
        LIST_REVERSE(&temprank);
      }
      for (i = 0; i < GD_rank(g)[r].n; i++) {
        v = GD_rank(g)[r].v[i] = LIST_GET(&temprank, (size_t)i);
        ND_order(v) = i + base_order;
      }
 
      /* nonconstraint flat edges must be made LR */
      for (i = 0; i < GD_rank(g)[r].n; i++) {
        v = GD_rank(g)[r].v[i];
        if (ND_flat_out(v).list) {
          for (size_t j = 0; (e = ND_flat_out(v).list[j]); j++) {
            if ((!GD_flip(g) && ND_order(aghead(e)) < ND_order(agtail(e))) ||
                (GD_flip(g) && ND_order(aghead(e)) > ND_order(agtail(e)))) {
              assert(!constraining_flat_edge(g, e));
              delete_flat_edge(e);
              j--;
              flat_rev(g, e);
            }
          }
        }
      }
      /* postprocess to restore intended order */
    }
    /* else do no harm! */
    GD_rank(Root)[r].valid = false;
  }
  LIST_FREE(&temprank);
}
 
static void reorder(graph_t *g, int r, bool reverse, bool hasfixed) {
  int changed = 0, nelt;
  node_t **vlist = GD_rank(g)[r].v;
  node_t **lp, **rp, **ep = vlist + GD_rank(g)[r].n;
 
  for (nelt = GD_rank(g)[r].n - 1; nelt >= 0; nelt--) {
    lp = vlist;
    while (lp < ep) {
      /* find leftmost node that can be compared */
      while (lp < ep && ND_mval(*lp) < 0)
        lp++;
      if (lp >= ep)
        break;
      /* find the node that can be compared */
      bool sawclust = false;
      bool muststay = false;
      for (rp = lp + 1; rp < ep; rp++) {
        if (sawclust && ND_clust(*rp))
          continue; /* ### */
        if (left2right(g, *lp, *rp)) {
          muststay = true;
          break;
        }
        if (ND_mval(*rp) >= 0)
          break;
        if (ND_clust(*rp))
          sawclust = true; /* ### */
      }
      if (rp >= ep)
        break;
      if (!muststay) {
        const double p1 = ND_mval(*lp);
        const double p2 = ND_mval(*rp);
        if (p1 > p2 || (p1 >= p2 && reverse)) {
          exchange(*lp, *rp);
          changed++;
        }
      }
      lp = rp;
    }
    if (!hasfixed && !reverse)
      ep--;
  }
 
  if (changed) {
    GD_rank(Root)[r].valid = false;
    if (r > 0)
      GD_rank(Root)[r - 1].valid = false;
  }
}
 
static void mincross_step(graph_t *g, int pass) {
  int r, other, first, last, dir;
 
  bool reverse = pass % 4 < 2;
 
  if (pass % 2 == 0) { /* down pass */
    first = GD_minrank(g) + 1;
    if (GD_minrank(g) > GD_minrank(Root))
      first--;
    last = GD_maxrank(g);
    dir = 1;
  } else { /* up pass */
    first = GD_maxrank(g) - 1;
    last = GD_minrank(g);
    if (GD_maxrank(g) < GD_maxrank(Root))
      first++;
    dir = -1;
  }
 
  for (r = first; r != last + dir; r += dir) {
    other = r - dir;
    bool hasfixed = medians(g, r, other);
    reorder(g, r, reverse, hasfixed);
  }
  transpose(g, !reverse);
}
 
static int local_cross(elist l, int dir) {
  int i, j;
  int cross = 0;
  edge_t *e, *f;
  bool is_out = dir > 0;
  for (i = 0; (e = l.list[i]); i++) {
    if (is_out)
      for (j = i + 1; (f = l.list[j]); j++) {
        if ((ND_order(aghead(f)) - ND_order(aghead(e))) *
                (ED_tail_port(f).p.x - ED_tail_port(e).p.x) <
            0)
          cross += ED_xpenalty(e) * ED_xpenalty(f);
      }
    else
      for (j = i + 1; (f = l.list[j]); j++) {
        if ((ND_order(agtail(f)) - ND_order(agtail(e))) *
                (ED_head_port(f).p.x - ED_head_port(e).p.x) <
            0)
          cross += ED_xpenalty(e) * ED_xpenalty(f);
      }
  }
  return cross;
}
 
static int64_t rcross(graph_t *g, int r) {
  int top, bot, max, i, k;
  node_t **rtop, *v;
 
  int64_t cross = 0;
  max = 0;
  rtop = GD_rank(g)[r].v;
 
  int *Count = gv_calloc(GD_rank(Root)[r + 1].n + 1, sizeof(int));
 
  for (top = 0; top < GD_rank(g)[r].n; top++) {
    edge_t *e;
    if (max > 0) {
      for (i = 0; (e = ND_out(rtop[top]).list[i]); i++) {
        for (k = ND_order(aghead(e)) + 1; k <= max; k++)
          cross += Count[k] * ED_xpenalty(e);
      }
    }
    for (i = 0; (e = ND_out(rtop[top]).list[i]); i++) {
      int inv = ND_order(aghead(e));
      if (inv > max)
        max = inv;
      Count[inv] += ED_xpenalty(e);
    }
  }
  for (top = 0; top < GD_rank(g)[r].n; top++) {
    v = GD_rank(g)[r].v[top];
    if (ND_has_port(v))
      cross += local_cross(ND_out(v), 1);
  }
  for (bot = 0; bot < GD_rank(g)[r + 1].n; bot++) {
    v = GD_rank(g)[r + 1].v[bot];
    if (ND_has_port(v))
      cross += local_cross(ND_in(v), -1);
  }
  free(Count);
  return cross;
}
 
static int64_t ncross(void) {
  int r;
 
  graph_t *g = Root;
  int64_t count = 0;
  for (r = GD_minrank(g); r < GD_maxrank(g); r++) {
    if (GD_rank(g)[r].valid)
      count += GD_rank(g)[r].cache_nc;
    else {
      const int64_t nc = GD_rank(g)[r].cache_nc = rcross(g, r);
      count += nc;
      GD_rank(g)[r].valid = true;
    }
  }
  return count;
}
 
static int ordercmpf(const void *x, const void *y) {
  const int *i0 = x;
  const int *i1 = y;
  if (*i0 < *i1) {
    return -1;
  }
  if (*i0 > *i1) {
    return 1;
  }
  return 0;
}
 
/* Calculate a mval for nodes with no in or out non-flat edges.
 * Assume (ND_out(n).size == 0) && (ND_in(n).size == 0)
 * Find flat edge a->n where a has the largest order and set
 * n.mval = a.mval+1, assuming a.mval is defined (>=0).
 * If there are no flat in edges, find flat edge n->a where a
 * has the smallest order and set * n.mval = a.mval-1, assuming
 * a.mval is > 0.
 * Return true if n.mval is left -1, indicating a fixed node for sorting.
 */
static bool flat_mval(node_t *n) {
  int i;
  edge_t *e, **fl;
  node_t *nn;
 
  if (ND_flat_in(n).size > 0) {
    fl = ND_flat_in(n).list;
    nn = agtail(fl[0]);
    for (i = 1; (e = fl[i]); i++)
      if (ND_order(agtail(e)) > ND_order(nn))
        nn = agtail(e);
    if (ND_mval(nn) >= 0) {
      ND_mval(n) = ND_mval(nn) + 1;
      return false;
    }
  } else if (ND_flat_out(n).size > 0) {
    fl = ND_flat_out(n).list;
    nn = aghead(fl[0]);
    for (i = 1; (e = fl[i]); i++)
      if (ND_order(aghead(e)) < ND_order(nn))
        nn = aghead(e);
    if (ND_mval(nn) > 0) {
      ND_mval(n) = ND_mval(nn) - 1;
      return false;
    }
  }
  return true;
}
 
#define VAL(node, port) (MC_SCALE * ND_order(node) + (port).order)
 
static bool medians(graph_t *g, int r0, int r1) {
  int i, j0, lspan, rspan, *list;
  node_t *n, **v;
  edge_t *e;
  bool hasfixed = false;
 
  list = TI_list;
  v = GD_rank(g)[r0].v;
  for (i = 0; i < GD_rank(g)[r0].n; i++) {
    n = v[i];
    size_t j = 0;
    if (r1 > r0)
      for (j0 = 0; (e = ND_out(n).list[j0]); j0++) {
        if (ED_xpenalty(e) > 0)
          list[j++] = VAL(aghead(e), ED_head_port(e));
      }
    else
      for (j0 = 0; (e = ND_in(n).list[j0]); j0++) {
        if (ED_xpenalty(e) > 0)
          list[j++] = VAL(agtail(e), ED_tail_port(e));
      }
    switch (j) {
    case 0:
      ND_mval(n) = -1;
      break;
    case 1:
      ND_mval(n) = list[0];
      break;
    case 2:
      ND_mval(n) = (list[0] + list[1]) / 2;
      break;
    default:
      qsort(list, j, sizeof(int), ordercmpf);
      if (j % 2)
        ND_mval(n) = list[j / 2];
      else {
        /* weighted median */
        size_t rm = j / 2;
        size_t lm = rm - 1;
        rspan = list[j - 1] - list[rm];
        lspan = list[lm] - list[0];
        if (lspan == rspan)
          ND_mval(n) = (list[lm] + list[rm]) / 2;
        else {
          double w = list[lm] * (double)rspan + list[rm] * (double)lspan;
          ND_mval(n) = w / (lspan + rspan);
        }
      }
    }
  }
  for (i = 0; i < GD_rank(g)[r0].n; i++) {
    n = v[i];
    if (ND_out(n).size == 0 && ND_in(n).size == 0)
      hasfixed |= flat_mval(n);
  }
  return hasfixed;
}
 
static int nodeposcmpf(const void *x, const void *y) {
  node_t *const *const n0 = x;
  node_t *const *const n1 = y;
  if (ND_order(*n0) < ND_order(*n1)) {
    return -1;
  }
  if (ND_order(*n0) > ND_order(*n1)) {
    return 1;
  }
  return 0;
}
 
static int edgeidcmpf(const void *x, const void *y) {
  edge_t *const *const e0 = x;
  edge_t *const *const e1 = y;
  if (AGSEQ(*e0) < AGSEQ(*e1)) {
    return -1;
  }
  if (AGSEQ(*e0) > AGSEQ(*e1)) {
    return 1;
  }
  return 0;
}
 
/* following code deals with weights of edges of "virtual" nodes */
#define ORDINARY 0
#define SINGLETON 1
#define VIRTUALNODE 2
#define NTYPES 3
 
#define C_EE 1
#define C_VS 2
#define C_SS 2
#define C_VV 4
 
static const int table[NTYPES][NTYPES] = {
    /* ordinary */ {C_EE, C_EE, C_EE},
    /* singleton */ {C_EE, C_SS, C_VS},
    /* virtual */ {C_EE, C_VS, C_VV}};
 
static int endpoint_class(node_t *n) {
  if (ND_node_type(n) == VIRTUAL)
    return VIRTUALNODE;
  if (ND_weight_class(n) <= 1)
    return SINGLETON;
  return ORDINARY;
}
 
void virtual_weight(edge_t *e) {
  int t;
  t = table[endpoint_class(agtail(e))][endpoint_class(aghead(e))];
 
  /* check whether the upcoming computation will overflow */
  assert(t >= 0);
  if (INT_MAX / t < ED_weight(e)) {
    agerrorf("overflow when calculating virtual weight of edge\n");
    graphviz_exit(EXIT_FAILURE);
  }
 
  ED_weight(e) *= t;
}
 
#ifdef DEBUG
void check_order(void) {
  int i, r;
  node_t *v;
  graph_t *g = Root;
 
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    assert(GD_rank(g)[r].v[GD_rank(g)[r].n] == NULL);
    for (i = 0; (v = GD_rank(g)[r].v[i]); i++) {
      assert(ND_rank(v) == r);
      assert(ND_order(v) == i);
    }
  }
}
#endif
 
static void mincross_options(graph_t *g) {
  char *p;
  double f;
 
  /* set default values */
  MinQuit = 8;
  MaxIter = 24;
 
  p = agget(g, "mclimit");
  if (p && (f = atof(p)) > 0.0) {
    MinQuit = MAX(1, scale_clamp(MinQuit, f));
    MaxIter = MAX(1, scale_clamp(MaxIter, f));
  }
}
 
#ifdef DEBUG
void check_vlists(graph_t *g) {
  int c, i, j, r;
  node_t *u;
 
  for (r = GD_minrank(g); r <= GD_maxrank(g); r++) {
    for (i = 0; i < GD_rank(g)[r].n; i++) {
      u = GD_rank(g)[r].v[i];
      j = ND_order(u);
      assert(GD_rank(Root)[r].v[j] == u);
    }
    if (GD_rankleader(g)) {
      u = GD_rankleader(g)[r];
      j = ND_order(u);
      assert(GD_rank(Root)[r].v[j] == u);
    }
  }
  for (c = 1; c <= GD_n_cluster(g); c++)
    check_vlists(GD_clust(g)[c]);
}
 
void node_in_root_vlist(node_t *n) {
  node_t **vptr;
 
  for (vptr = GD_rank(Root)[ND_rank(n)].v; *vptr; vptr++)
    if (*vptr == n)
      break;
  if (*vptr == 0)
    abort();
}
#endif /* DEBUG code */