static int qr_finder_centers_locate(qr_finder_center **_centers,
 qr_finder_edge_pt **_edge_pts, qr_reader *reader,
 int _width,int _height){
  qr_finder_line     *hlines = reader->finder_lines[0].lines;
  int                 nhlines = reader->finder_lines[0].nlines;
  qr_finder_line     *vlines = reader->finder_lines[1].lines;
  int                 nvlines = reader->finder_lines[1].nlines;

  qr_finder_line    **hneighbors;
  qr_finder_cluster  *hclusters;
  int                 nhclusters;
  qr_finder_line    **vneighbors;
  qr_finder_cluster  *vclusters;
  int                 nvclusters;
  int                 ncenters;

  /*Cluster the detected lines.*/
  hneighbors=(qr_finder_line **)mymalloc(SRAMEX, nhlines*sizeof(*hneighbors));
  /*We require more than one line per cluster, so there are at most nhlines/2.*/
  hclusters=(qr_finder_cluster *)mymalloc(SRAMEX, (nhlines>>1)*sizeof(*hclusters));
  nhclusters=qr_finder_cluster_lines(hclusters,hneighbors,hlines,nhlines,0);
  /*We need vertical lines to be sorted by X coordinate, with ties broken by Y
     coordinate, for clustering purposes.
    We scan the image in the opposite order for cache efficiency, so sort the
     lines we found here.*/
  qsort(vlines,nvlines,sizeof(*vlines),qr_finder_vline_cmp);
  vneighbors=(qr_finder_line **)mymalloc(SRAMEX, nvlines*sizeof(*vneighbors));
  /*We require more than one line per cluster, so there are at most nvlines/2.*/
  vclusters=(qr_finder_cluster *)mymalloc(SRAMEX, (nvlines>>1)*sizeof(*vclusters));
  nvclusters=qr_finder_cluster_lines(vclusters,vneighbors,vlines,nvlines,1);
  /*Find line crossings among the clusters.*/
  if(nhclusters>=3&&nvclusters>=3){
    qr_finder_edge_pt  *edge_pts;
    qr_finder_center   *centers;
    int                 nedge_pts;
    int                 i;
    nedge_pts=0;
    for(i=0;i<nhclusters;i++)nedge_pts+=hclusters[i].nlines;
    for(i=0;i<nvclusters;i++)nedge_pts+=vclusters[i].nlines;
    nedge_pts<<=1;
    edge_pts=(qr_finder_edge_pt *)mymalloc(SRAMEX, nedge_pts*sizeof(*edge_pts));
    centers=(qr_finder_center *)mymalloc(SRAMEX,
     QR_MINI(nhclusters,nvclusters)*sizeof(*centers));
    ncenters=qr_finder_find_crossings(centers,edge_pts,
     hclusters,nhclusters,vclusters,nvclusters);
    *_centers=centers;
    *_edge_pts=edge_pts;
  }
  else ncenters=0;
  myfree(SRAMEX, vclusters);
  myfree(SRAMEX, vneighbors);
  myfree(SRAMEX, hclusters);
  myfree(SRAMEX, hneighbors);
  return ncenters;
}