/*
  This file is part of p4est.
  p4est is a C library to manage a collection (a forest) of multiple
  connected adaptive quadtrees or octrees in parallel.

  Copyright (C) 2010 The University of Texas System
  Additional copyright (C) 2011 individual authors
  Written by Carsten Burstedde, Lucas C. Wilcox, and Tobin Isaac

  p4est is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  p4est is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with p4est; if not, write to the Free Software Foundation, Inc.,
  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/

#ifndef P4_TO_P8
#include <p4est_bits.h>
#include <p4est_extended.h>
#include <p4est_iterate.h>
#include <p4est_mesh.h>
#include <p4est_search.h>
#else /* P4_TO_P8 */
#include <p8est_bits.h>
#include <p8est_extended.h>
#include <p8est_iterate.h>
#include <p8est_mesh.h>
#include <p8est_search.h>
#endif /* P4_TO_P8 */

/*********************** constructor functions ***********************/

/** Populate mesh information for corners across tree boundaries, i.e. every
 *  neighborhood scenario where we need more information (like orientation) than
 *  a single index. Note that this function only allocates the memory, correct
 *  values have to be set separately
 *
 * \param [in][out] mesh     The mesh structure to which we will add corner
 *                           information
 * \param [in]      clen     Number of quadrants to be added
 * \param [in]      pcquad   List of quadrant indices
 * \param [in]      pccorner List of quadrant encodings
 */
static              p4est_locidx_t
mesh_corner_allocate (p4est_mesh_t * mesh, p4est_locidx_t clen,
                      p4est_locidx_t ** pcquad, int8_t ** pccorner)
{
  p4est_locidx_t      cornerid, cstart, cend;

  P4EST_ASSERT (clen > 0);
  P4EST_ASSERT (mesh->corner_offset->elem_count ==
                (size_t) (mesh->local_num_corners + 1));

  cornerid = mesh->local_num_corners++;
  cstart = *(p4est_locidx_t *) sc_array_index (mesh->corner_offset, cornerid);
  cend = cstart + clen;
  *(p4est_locidx_t *) sc_array_push (mesh->corner_offset) = cend;

  P4EST_ASSERT (mesh->corner_offset->elem_count ==
                (size_t) (mesh->local_num_corners + 1));

  P4EST_ASSERT (mesh->corner_quad->elem_count == (size_t) cstart);
  *pcquad = (p4est_locidx_t *) sc_array_push_count (mesh->corner_quad, clen);
  P4EST_ASSERT (mesh->corner_quad->elem_count == (size_t) cend);

  P4EST_ASSERT (mesh->corner_corner->elem_count == (size_t) cstart);
  *pccorner = (int8_t *) sc_array_push_count (mesh->corner_corner, clen);
  P4EST_ASSERT (mesh->corner_corner->elem_count == (size_t) cend);

  return cornerid;
}

#ifdef P4_TO_P8
/** Populate mesh information for hanging edges and edges across tree
 *  boundaries, i.e. every neighborhood scenario where we need more information
 *  (like orientation) than a single index. Note that this function only pushes
 *  an address whose data has to be set separately.
 *
 * \param [in][out] mesh     The mesh structure to which we will add edge
 *                           information
 * \param [in]      elen     Number of quadrants to be added
 * \param [in]      pequad   List of quadrant indices
 * \param [in]      peedge   List of quadrant encodings
 */
static              p4est_locidx_t
mesh_edge_allocate (p4est_mesh_t * mesh, p4est_locidx_t elen,
                    p4est_locidx_t ** pequad, int8_t ** peedge)
{
  p4est_locidx_t      edgeid, estart, eend;

  P4EST_ASSERT (elen > 0);
  P4EST_ASSERT (mesh->edge_offset->elem_count ==
                (size_t) (mesh->local_num_edges + 1));
  edgeid = mesh->local_num_edges++;
  estart = *(p4est_locidx_t *) sc_array_index (mesh->edge_offset, edgeid);
  eend = estart + elen;
  *(p4est_locidx_t *) sc_array_push (mesh->edge_offset) = eend;

  P4EST_ASSERT (mesh->edge_offset->elem_count ==
                (size_t) (mesh->local_num_edges + 1));

  P4EST_ASSERT (mesh->edge_quad->elem_count == (size_t) estart);
  *pequad = (p4est_locidx_t *) sc_array_push_count (mesh->edge_quad, elen);
  P4EST_ASSERT (mesh->edge_quad->elem_count == (size_t) eend);

  P4EST_ASSERT (mesh->edge_edge->elem_count == (size_t) estart);
  *peedge = (int8_t *) sc_array_push_count (mesh->edge_edge, elen);
  P4EST_ASSERT (mesh->edge_edge->elem_count == (size_t) eend);

  return edgeid;
}

/** Process inter-tree edge neighbors
 * \param[in]      info        General iterator information
 * \param[in]      side1       Currently processed edge
 * \param[in]      subedge_id  Sub edge index in 0..1 for hanging edges, -1
 *                             for full edges
 * \param[in][out] mesh        The mesh structure that will be filled
 *                             with the edge neighbors along current edge
 * \param[in]      cz          Number of adjacent trees
 * \param[in]      zz          internal number of currently processed edge
 */
static int
mesh_edge_process_inter_tree_edges (p8est_iter_edge_info_t * info,
                                    p8est_iter_edge_side_t * side1,
                                    int subedge_id,
                                    p4est_mesh_t * mesh, int cz, int zz)
{
  int                 ignore, j, k, iz;
  int                 nAdjacentQuads, qid1, qid2, edgeid;
  p8est_iter_edge_side_t *side2;
  p4est_tree_t       *tree1, *tree2;
  int8_t             *eedges;
  p4est_locidx_t     *equads;
  int8_t             *peedge;
  p4est_locidx_t     *pequad;
  int                 goodones = 0;
  int                 edgeid_offset =
    mesh->local_num_quadrants + mesh->ghost_num_quadrants;

  /* sanity check for subedge_id */
  P4EST_ASSERT (-1 <= subedge_id && subedge_id < 2);

  /* overestimate number of adjacent quads:
   * Due to hanging edges we cannot avoid iterating over all
   * quadrants, if we want to know the exact number. so assume
   * that each edge is hanging (which cannot be the case; it would
   * be 2 separate edges if they were) and allocate space for
   * twice the number of adjacent quadrants.
   * However, we can consider that the quadrant itself is not
   * stored as its own neighbor. */
  nAdjacentQuads = 2 * cz - 1;

  equads = P4EST_ALLOC (p4est_locidx_t, nAdjacentQuads);
  eedges = P4EST_ALLOC (int8_t, nAdjacentQuads);

  P4EST_ASSERT (0 <= side1->treeid &&
                side1->treeid < info->p4est->connectivity->num_trees);
  tree1 = p4est_tree_array_index (info->p4est->trees, side1->treeid);
  if (0 <= subedge_id) {
    P4EST_ASSERT (side1->is_hanging);
    qid1 = side1->is.hanging.quadid[subedge_id] + tree1->quadrants_offset;
    P4EST_ASSERT (!side1->is.hanging.is_ghost[subedge_id]);
  }
  else {
    P4EST_ASSERT (!side1->is_hanging);
    qid1 = side1->is.full.quadid + tree1->quadrants_offset;
    P4EST_ASSERT (!side1->is.full.is_ghost);
  }
  P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);

  /* Go through edge neighbors and collect the true edges */
  for (iz = 0; iz < cz; ++iz) {
    if (iz == zz) {
      /* We do not count ourselves as a neighbor */
      continue;
    }
    ignore = 0;
    P4EST_ASSERT (0 <= iz && iz < (int) info->sides.elem_count);
    side2 = (p8est_iter_edge_side_t *) sc_array_index (&info->sides, iz);
    P4EST_ASSERT (side2->edge >= 0 && side2->edge < P8EST_EDGES);

    P4EST_ASSERT (info->tree_boundary <= P8EST_CONNECT_EDGE);
    for (ignore = 0, j = 0; !ignore && j < 2; ++j) {
      for (k = 0; k < 2; ++k) {
        if (side1->faces[j] == side2->faces[k]) {
          ignore = 1;
          break;
        }
      }
    }
    if (!ignore) {
      /* Record this edge neighbor if we don't ignore it */
      int8_t              localOri =
        (side1->orientation + side2->orientation) % 2;

      P4EST_ASSERT (0 <= side2->treeid &&
                    side2->treeid < info->p4est->connectivity->num_trees);
      tree2 = p4est_tree_array_index (info->p4est->trees, side2->treeid);

      if (side1->is_hanging && side2->is_hanging) {
        /* both sides are hanging; only store the one that shares
         * the same part of the the half edge */
        int8_t              subEdgeIdx = (subedge_id + localOri) % 2;
        qid2 =
          side2->is.hanging.quadid[subEdgeIdx] +
          (side2->is.hanging.is_ghost[subEdgeIdx] ?
           mesh->local_num_quadrants : tree2->quadrants_offset);
        equads[goodones] = qid2;
        eedges[goodones] = P8EST_EDGES * localOri + (int) side2->edge;
        ++goodones;
      }
      else if (!side1->is_hanging && side2->is_hanging) {
        /* check if we have to swap hanging quads in order to store
         * them wrt. edge corners, i.e. first subquad that is adjacent
         * to corner of edge with lower corner index
         */
        for (j = 0; j < 2; ++j) {
          int                 pos = (localOri + j) % 2;
          qid2 =
            side2->is.hanging.quadid[pos] +
            (side2->is.hanging.is_ghost[pos] ?
             mesh->local_num_quadrants : tree2->quadrants_offset);

          /* populate mesh information */
          equads[goodones] = qid2;
          eedges[goodones] = -24 + P8EST_EDGES * localOri + side2->edge;
          ++goodones;
        }
      }
      else if (side1->is_hanging && !side2->is_hanging) {
        /* there is no need for a loop, because the function is called for both
         * hanging quadrants of side1 separately and only if current subquad of
         * side1 is a local one. */
        qid2 = side2->is.full.quadid +
          (side2->is.full.is_ghost ?
           mesh->local_num_quadrants : tree2->quadrants_offset);
        /* update mesh */
        int                 pos = (localOri + subedge_id) % 2;
        equads[goodones] = qid2;
        eedges[goodones] =
          24 + 24 * pos + P8EST_EDGES * localOri + side2->edge;
        ++goodones;
      }
      else {
        /* neither side1 nor side2 are hanging, i.e. both full quadrants */
        qid2 = side2->is.full.quadid +
          (side2->is.full.is_ghost ?
           mesh->local_num_quadrants : tree2->quadrants_offset);
        equads[goodones] = qid2;
        eedges[goodones] = P8EST_EDGES * localOri + side2->edge;
        ++goodones;
      }
    }
  }

  /* we have excluded between 0 and all quadrants. */
  P4EST_ASSERT (0 <= goodones && goodones < nAdjacentQuads);

  if (goodones > 0) {
    /* Allocate and fill edge information in the mesh structure */
    edgeid = mesh_edge_allocate (mesh, goodones, &pequad, &peedge);
    /* "link" to arrays encoding inter-tree edge-neighborhood */
    P4EST_ASSERT (mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] == -1);
    mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] =
      edgeid_offset + edgeid;
    /* populate allocated memory */
    memcpy (pequad, equads, goodones * sizeof (p4est_locidx_t));
    memcpy (peedge, eedges, goodones * sizeof (int8_t));
  }
  else if (0 == goodones) {
    mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] = -3;
  }
  else {
    SC_ABORT_NOT_REACHED ();
  }
  P4EST_FREE (equads);
  P4EST_FREE (eedges);

  return 0;
}
#endif /* P4_TO_P8 */

/** Process inter-tree corner neighbors
 * \param[in]      info        General iterator information
 * \param[in]      side1       Currently processed corner
 * \param[in][out] mesh        The mesh structure which will be updated.
 * \param[in]      cz          Number of adjacent quadrants
 * \param[in]      zz          Internal number of currently processed corner
 */
static int
mesh_corner_process_inter_tree_corners (p4est_iter_corner_info_t * info,
                                        p4est_iter_corner_side_t * side1,
                                        p4est_mesh_t * mesh, int cz, int zz)
{
  int                 ignore, j, k, iz;
  int                 n_adjacent_quads, qid1, qid2, corner_id;
  p4est_iter_corner_side_t *side2;
  p4est_tree_t       *tree1, *tree2;
  int8_t             *ccorners;
  p4est_locidx_t     *cquads;
  int8_t             *pccorner;
  p4est_locidx_t     *pcquad;
  int                 cornerid_offset =
    mesh->local_num_quadrants + mesh->ghost_num_quadrants;

  /* overestimate number of adjacent quads:
   * We know that the quadrant itself is not stored as its own neighbor but do
   * not make any other assumptions regarding the number of corner neighbors
   * here. */
  n_adjacent_quads = cz - 1;

  cquads = P4EST_ALLOC (p4est_locidx_t, n_adjacent_quads);
  ccorners = P4EST_ALLOC (int8_t, n_adjacent_quads);

  P4EST_ASSERT (0 <= side1->treeid &&
                side1->treeid < info->p4est->connectivity->num_trees);

  /* currently processed quadrant must be local */
  tree1 = p4est_tree_array_index (info->p4est->trees, side1->treeid);
  qid1 = side1->quadid + tree1->quadrants_offset;
  P4EST_ASSERT (!side1->is_ghost);
  P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);

  /* Go through corner neighbors and collect the true corners */
  int                 goodones = 0;
  for (iz = 0; iz < cz; ++iz) {
    if (iz == zz) {
      /* We do not count ourselves as a neighbor */
      continue;
    }
    ignore = 0;
    P4EST_ASSERT (0 <= iz && iz < (int) info->sides.elem_count);
    side2 = (p4est_iter_corner_side_t *) sc_array_index (&info->sides, iz);
    P4EST_ASSERT (side2->corner >= 0 && side2->corner < P4EST_CHILDREN);

    /* check if current side2 is among the face or edge neighbors */
    for (ignore = 0, j = 0; !ignore && j < P4EST_DIM; ++j) {
      for (k = 0; k < P4EST_DIM; ++k) {
        if (side1->faces[j] == side2->faces[k]
#ifdef P4_TO_P8
            || side1->edges[j] == side2->edges[k]
#endif /* P4_TO_P8 */
          ) {
          ignore = 1;
          break;
        }
      }
    }
    if (!ignore) {
      /* Record this corner neighbor if we don't ignore it */
      P4EST_ASSERT (0 <= side2->treeid &&
                    side2->treeid < info->p4est->connectivity->num_trees);
      tree2 = p4est_tree_array_index (info->p4est->trees, side2->treeid);

      qid2 = side2->quadid + (side2->is_ghost ?
                              mesh->local_num_quadrants :
                              tree2->quadrants_offset);
      cquads[goodones] = qid2;
      ccorners[goodones] = (int) side2->corner;
      if (side2->is_ghost) {
        P4EST_ASSERT (mesh->local_num_quadrants <= qid2 &&
                      qid2 < cornerid_offset);
      }
      else {
        P4EST_ASSERT (0 <= qid2 && qid2 < mesh->local_num_quadrants);
      }
      ++goodones;
    }
  }

  /* we have excluded between 0 and all quadrants. */
  P4EST_ASSERT (0 <= goodones && goodones < n_adjacent_quads);

  if (goodones > 0) {
    /* Allocate and fill corner information in the mesh structure */
    corner_id = mesh_corner_allocate (mesh, goodones, &pcquad, &pccorner);
    /* "link" to arrays encoding inter-tree corner-neighborhood */
    P4EST_ASSERT
      (mesh->quad_to_corner[P4EST_CHILDREN * qid1 + side1->corner] == -1);
    mesh->quad_to_corner[P4EST_CHILDREN * qid1 + side1->corner] =
      cornerid_offset + corner_id;
    /* populate allocated memory */
    memcpy (pcquad, cquads, goodones * sizeof (p4est_locidx_t));
    memcpy (pccorner, ccorners, goodones * sizeof (int8_t));
  }
  else if (0 == goodones) {
    mesh->quad_to_corner[P4EST_CHILDREN * qid1 + side1->corner] = -3;
  }
  else {
    SC_ABORT_NOT_REACHED ();
  }
  P4EST_FREE (cquads);
  P4EST_FREE (ccorners);

  return 0;
}

static void
mesh_iter_corner (p4est_iter_corner_info_t * info, void *user_data)
{
  int                 i, j;
  int                 visited[P4EST_CHILDREN];
  size_t              cz, zz;
  p4est_locidx_t      qoffset, qid1, qid2;
  p4est_mesh_t       *mesh = (p4est_mesh_t *) user_data;
  p4est_iter_corner_side_t *side1, *side2;
  p4est_tree_t       *tree1;
  sc_array_t         *trees = info->p4est->trees;

  /* Check the case when the corner does not involve neighbors */
  cz = info->sides.elem_count;
  P4EST_ASSERT (cz > 0);
  P4EST_ASSERT (info->tree_boundary || cz == P4EST_CHILDREN);

  if (cz == 1) {
    side1 = (p4est_iter_corner_side_t *) sc_array_index (&info->sides, 0);
    P4EST_ASSERT (!side1->is_ghost);
    tree1 = p4est_tree_array_index (trees, side1->treeid);
    qid1 = side1->quadid + tree1->quadrants_offset;
    P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);

    P4EST_ASSERT (mesh->quad_to_corner[P4EST_CHILDREN * qid1 +
                                       side1->corner] == -1);
    mesh->quad_to_corner[P4EST_CHILDREN * qid1 + side1->corner] = -3;

    return;
  }

  if (info->tree_boundary) {
    for (zz = 0; zz < cz; ++zz) {
      side1 = (p4est_iter_corner_side_t *) sc_array_index (&info->sides, zz);
      if (!side1->is_ghost) {
        mesh_corner_process_inter_tree_corners (info, side1, mesh, cz, zz);
      }
    }
    return;
  }

  /* Process a corner inside the tree in pairs of diagonal neighbors */
  P4EST_ASSERT (!info->tree_boundary);
  P4EST_ASSERT (cz == P4EST_CHILDREN);

  side1 = (p4est_iter_corner_side_t *) sc_array_index (&info->sides, 0);
  tree1 = p4est_tree_array_index (trees, side1->treeid);
  qoffset = tree1->quadrants_offset;

  memset (visited, 0, P4EST_CHILDREN * sizeof (int));
  for (i = 0; i < P4EST_HALF; ++i) {
    side1 = side2 = NULL;
    qid1 = qid2 = -2;
    for (j = 0; j < P4EST_CHILDREN; ++j) {
      if (visited[j]) {
        continue;
      }

      /* Remember the first side we want to pair up */
      if (side1 == NULL) {
        side1 =
          (p4est_iter_corner_side_t *) sc_array_index_int (&info->sides, j);
        qid1 = side1->quadid +
          (side1->is_ghost ? mesh->local_num_quadrants : qoffset);
        visited[j] = 1;
        continue;
      }

      /* Examine a potential second side */
      /* The diagonally opposite corner is found by adding the corner indices
       * in p4est's naming-convention. Diagonally opposite corner indices add up
       * to 3 in 2D and to 7 in 3D, i.e. P4EST_CHILDREN - 1. */
      P4EST_ASSERT (side2 == NULL);
      side2 =
        (p4est_iter_corner_side_t *) sc_array_index_int (&info->sides, j);
      P4EST_ASSERT (side1->treeid == side2->treeid);
      if (side1->corner + side2->corner != P4EST_CHILDREN - 1) {
        side2 = NULL;
        continue;
      }

      /* We have found a diagonally opposite second side */
      qid2 = side2->quadid +
        (side2->is_ghost ? mesh->local_num_quadrants : qoffset);
      if (!side1->is_ghost) {
        P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
        P4EST_ASSERT (mesh->quad_to_corner[P4EST_CHILDREN * qid1 +
                                           side1->corner] == -1);
        mesh->quad_to_corner[P4EST_CHILDREN * qid1 + side1->corner] = qid2;
      }
      if (!side2->is_ghost) {
        P4EST_ASSERT (0 <= qid2 && qid2 < mesh->local_num_quadrants);
        P4EST_ASSERT (mesh->quad_to_corner[P4EST_CHILDREN * qid2 +
                                           side2->corner] == -1);
        mesh->quad_to_corner[P4EST_CHILDREN * qid2 + side2->corner] = qid1;
      }
      visited[j] = 1;
      break;
    }
    P4EST_ASSERT (side1 != NULL && side2 != NULL);
  }
}

#ifdef P4_TO_P8

static void
mesh_iter_edge (p8est_iter_edge_info_t * info, void *user_data)
{
  int8_t              visited[P4EST_HALF];
  size_t              iz, cz, zz;
  int                 j, k;
  int                 swapsides;
  p4est_locidx_t      qid1, qid2, qls1[2], qoffset;
  p4est_locidx_t      eid1, eid2;
  p4est_locidx_t      edgeid;
  p4est_locidx_t      in_qtoe, edgeid_offset;
  p4est_mesh_t       *mesh = (p4est_mesh_t *) user_data;
  p8est_iter_edge_side_t *side1, *side2, *tempside;
  p4est_tree_t       *tree1;

  edgeid_offset = mesh->local_num_quadrants + mesh->ghost_num_quadrants;

  /* general sanity checks */
  cz = info->sides.elem_count;
  P4EST_ASSERT (cz > 0);
  P4EST_ASSERT (info->tree_boundary || cz == P4EST_HALF);

  /* edge limits domain or is located on a face limitting the domain */
  /* sanity checks */
  if (cz == 1) {
    P4EST_ASSERT (info->tree_boundary);
    side1 = (p8est_iter_edge_side_t *) sc_array_index (&info->sides, 0);
    P4EST_ASSERT (0 <= side1->treeid
                  && side1->treeid < info->p4est->connectivity->num_trees);
    P4EST_ASSERT (0 <= side1->edge && side1->edge < P8EST_EDGES);
    if (!side1->is_hanging) {
      if (!side1->is.full.is_ghost) {
        tree1 = p4est_tree_array_index (info->p4est->trees, side1->treeid);
        qid1 = side1->is.full.quadid + tree1->quadrants_offset;

        P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
        P4EST_ASSERT
          (mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] == -1);

        mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] = -3;
      }
    }
    return;
  }
  if (cz == 2) {
    for (iz = 0; iz < cz; ++iz) {
      side1 = (p8est_iter_edge_side_t *) sc_array_index (&info->sides, iz);
      P4EST_ASSERT (0 <= side1->treeid &&
                    side1->treeid < info->p4est->connectivity->num_trees);
      P4EST_ASSERT (0 <= side1->edge && side1->edge < P8EST_EDGES);

      if (info->tree_boundary) {
        if (side1->is_hanging) {
          for (j = 0; j < 2; ++j) {
            if (!side1->is.hanging.is_ghost[j]) {
              mesh_edge_process_inter_tree_edges (info, side1, j, mesh, cz,
                                                  iz);
            }
          }
        }
        else {
          if (!side1->is.full.is_ghost) {
            mesh_edge_process_inter_tree_edges (info, side1, -1, mesh, cz,
                                                iz);
          }
        }
      }
      else {
        if (!side1->is_hanging) {
          if (!side1->is.full.is_ghost) {
            tree1 =
              p4est_tree_array_index (info->p4est->trees, side1->treeid);
            qid1 = side1->is.full.quadid + tree1->quadrants_offset;

            P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
            P4EST_ASSERT
              (mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] == -1);

            mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] = -3;
          }
        }
        else {
          for (j = 0; j < 2; ++j) {
            if (!side1->is.hanging.is_ghost[j]) {
              tree1 =
                p4est_tree_array_index (info->p4est->trees, side1->treeid);
              qid1 = side1->is.hanging.quadid[j] + tree1->quadrants_offset;

              P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);

              P4EST_ASSERT
                (mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] == -1);
              mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] = -3;
            }
          }
        }
      }
    }
    return;
  }
  else {
    /* edges on tree boundaries */
    if (info->tree_boundary) {
      /* Loop through all edge sides, that is the quadrants touching it.  For
       * each of these quadrants, determine the edge sides that can potentially
       * occur by being a face neighbor as well.  Exclude these face neighbors
       * and the quadrant itself, record all others as edge neighbors.
       */
      for (zz = 0; zz < cz; ++zz) {
        side1 = (p8est_iter_edge_side_t *) sc_array_index (&info->sides, zz);
        P4EST_ASSERT (0 <= side1->treeid &&
                      side1->treeid < info->p4est->connectivity->num_trees);
        P4EST_ASSERT (0 <= side1->edge && side1->edge < P8EST_EDGES);

        /* We only create edge information for processor-local quadrants */
        if (side1->is_hanging) {
          for (j = 0; j < 2; ++j) {
            if (!side1->is.hanging.is_ghost[j]) {
              mesh_edge_process_inter_tree_edges (info, side1, j, mesh, cz,
                                                  zz);
            }
          }
        }
        else {
          if (!side1->is.full.is_ghost) {
            mesh_edge_process_inter_tree_edges (info, side1, -1, mesh, cz,
                                                zz);
          }
        }
      }
      return;
    }

    /* intra-tree */
    else {
      int8_t             *peedge;
      p4est_locidx_t     *pequad;

      P4EST_ASSERT (!info->tree_boundary);

      side1 = (p8est_iter_edge_side_t *) sc_array_index (&info->sides, 0);
      P4EST_ASSERT (0 <= side1->treeid &&
                    side1->treeid < info->p4est->connectivity->num_trees);
      tree1 = p4est_tree_array_index (info->p4est->trees, side1->treeid);
      qoffset = tree1->quadrants_offset;

      memset (visited, 0, P4EST_HALF * sizeof (int8_t));

      /* TODO: someone has time double-checking this loop bound? */
      for (iz = 0; iz < ((cz + 1) >> 1); ++iz) {
        side1 = side2 = NULL;
        qid1 = -1;
        eid1 = -1;

        for (j = 0; j < P4EST_HALF; ++j) {
          if (visited[j]) {
            continue;
          }

          /* remember first side */
          if (side1 == NULL) {
            side1 =
              (p8est_iter_edge_side_t *) sc_array_index_int (&info->sides, j);
            P4EST_ASSERT (0 <= side1->edge && side1->edge < P8EST_EDGES);
            eid1 = side1->edge;
            visited[j] = 1;
            continue;
          }

          /* By now first edge number has stabilized */
          P4EST_ASSERT (eid1 >= 0);

          /* Examine second side */
          P4EST_ASSERT (side2 == NULL);
          side2 =
            (p8est_iter_edge_side_t *) sc_array_index_int (&info->sides, j);
          P4EST_ASSERT (0 <= side2->edge && side2->edge < P8EST_EDGES);
          eid2 = side2->edge;
          P4EST_ASSERT (side2->treeid == side1->treeid);

          /* edge is diagonal opposite if e1 XOR 3 = e2 */
          if ((eid1 ^ 3) != eid2) {
            side2 = NULL;
            continue;
          }

          /* we found a pair of diagonal edges */
          if (!side1->is_hanging && !side2->is_hanging) {
            /* case 1: equally sized cells */
            /* this is the standard case. we do not store any encoding for
             * this case */
            if (side1->is.full.is_ghost && side2->is.full.is_ghost) {
              continue;
            }
            P4EST_ASSERT (!side1->is.full.is_ghost ||
                          !side2->is.full.is_ghost);

            /* get correct id depending on whether cell is a ghost or not */
            if (!side1->is.full.is_ghost) {
              qid1 = side1->is.full.quadid + qoffset;
              P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
            }
            else {
              P4EST_ASSERT (side1->is.full.quad != NULL);
              P4EST_ASSERT (0 <= side1->is.full.quadid &&
                            side1->is.full.quadid <
                            mesh->ghost_num_quadrants);
              qid1 = mesh->local_num_quadrants + side1->is.full.quadid;
            }
            if (!side2->is.full.is_ghost) {
              qid2 = side2->is.full.quadid + qoffset;
              P4EST_ASSERT (0 <= qid2 && qid2 < mesh->local_num_quadrants);
            }
            else {
              P4EST_ASSERT (side2->is.full.quad != NULL);
              P4EST_ASSERT (0 <= side2->is.full.quadid &&
                            side2->is.full.quadid <
                            mesh->ghost_num_quadrants);
              qid2 = mesh->local_num_quadrants + side2->is.full.quadid;
            }

            /* write info to correct position in quad_to_edge array if cell
             * is not part of the ghost layer */
            if (!side1->is.full.is_ghost) {
              P4EST_ASSERT (mesh->quad_to_edge[P8EST_EDGES * qid1 +
                                               side1->edge] == -1);
              mesh->quad_to_edge[P8EST_EDGES * qid1 + side1->edge] = qid2;
            }
            if (!side2->is.full.is_ghost) {
              P4EST_ASSERT (mesh->quad_to_edge[P8EST_EDGES * qid2 +
                                               side2->edge] == -1);
              mesh->quad_to_edge[P8EST_EDGES * qid2 + side2->edge] = qid1;
            }
          }
          else if ((!side1->is_hanging && side2->is_hanging) ||
                   (side1->is_hanging && !side2->is_hanging)) {
            /* one side is hanging. assert it is always side2. */
            swapsides = side1->is_hanging;
            if (swapsides) {
              tempside = side1;
              side1 = side2;
              side2 = tempside;
            }
            P4EST_ASSERT (!side1->is_hanging && side2->is_hanging);

            if (side1->is.full.is_ghost && side2->is.hanging.is_ghost[0] &&
                side2->is.hanging.is_ghost[1]) {
              continue;
            }

            /* determine quadrant number for non-hanging large quadrant */
            if (!side1->is.full.is_ghost) {
              qid1 = side1->is.full.quadid + qoffset;
              P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
            }
            else {
              P4EST_ASSERT (side1->is.full.quad != NULL);
              P4EST_ASSERT (0 <= side1->is.full.quadid &&
                            side1->is.full.quadid <
                            mesh->ghost_num_quadrants);
              qid1 = mesh->local_num_quadrants + side1->is.full.quadid;
            }

            /* determine quadrant numbers for both hanging quadrants */
            for (k = 0; k < 2; ++k) {
              if (!side2->is.hanging.is_ghost[k]) {
                qls1[k] = side2->is.hanging.quadid[k] + qoffset;
                P4EST_ASSERT (0 <= qls1[k]
                              && qls1[k] < mesh->local_num_quadrants);
              }
              else {
                P4EST_ASSERT (side2->is.hanging.quad[k] != NULL);
                P4EST_ASSERT (0 <= side2->is.hanging.quadid[k]
                              && side2->is.hanging.quadid[k] <
                              mesh->ghost_num_quadrants);
                qls1[k] =
                  mesh->local_num_quadrants + side2->is.hanging.quadid[k];
              }
            }

            /* encode quadrant neighborhood:
             * inside an octree the orientation is always 0. All we need to
             * encode is the information, if it is the first or second quadrant
             * along the edge */
            /* again: check before writing that values are untouched */
            if (!side1->is.full.is_ghost) {
              /* determine position for quad_to_edge */
              in_qtoe = P8EST_EDGES * qid1 + side1->edge;

              /* allocate space for encodings */
              int8_t             *eedges;
              eedges = P4EST_ALLOC (int8_t, 2);

              /* assert there is no entry for this cell yet */
              P4EST_ASSERT (mesh->quad_to_edge[in_qtoe] == -1);

              /* calculate encodings */
              for (k = 0; k < 2; ++k) {
                eedges[k] = -24 + side2->edge;
              }

              edgeid = mesh_edge_allocate (mesh, 2, &pequad, &peedge);
              memcpy (pequad, qls1, 2 * sizeof (p4est_locidx_t));
              memcpy (peedge, eedges, 2 * sizeof (int8_t));

              P4EST_FREE (eedges);

              /* refer to "special" arrays */
              mesh->quad_to_edge[in_qtoe] = edgeid_offset + edgeid;
            }

            for (k = 0; k < 2; ++k) {
              if (!side2->is.hanging.is_ghost[k]) {
                in_qtoe = P8EST_EDGES * qls1[k] + side2->edge;

                P4EST_ASSERT (mesh->quad_to_edge[in_qtoe] == -1);

                edgeid = mesh_edge_allocate (mesh, 1, &pequad, &peedge);
                *pequad = qid1;

                /* orientation is 0 as we are in the same tree */
                *peedge = 24 + 24 * k + side1->edge;

                mesh->quad_to_edge[in_qtoe] = edgeid_offset + edgeid;
              }
            }
          }
          /* end of hanging intra-tree edge */
          else {
            /* both sides are hanging with respect to a bigger edge that is not
             * diagonally opposite */
            /* determine quadrant numbers for both "hanging" edges and write
             * them directly to the corresponding positions */
            for (k = 0; k < 2; ++k) {
              /* do not record anything if both sides are ghost */
              if (side1->is.hanging.is_ghost[k] &&
                  side2->is.hanging.is_ghost[k]) {
                continue;
              }

              /* get qid1 and qid2 */
              if (!side1->is.hanging.is_ghost[k]) {
                qid1 = side1->is.hanging.quadid[k] + qoffset;
                P4EST_ASSERT (0 <= qid1 && qid1 < mesh->local_num_quadrants);
              }
              else {
                P4EST_ASSERT (side1->is.hanging.quad[k] != NULL);
                P4EST_ASSERT (0 <= side1->is.hanging.quadid[k] &&
                              side1->is.hanging.quadid[k] <
                              mesh->ghost_num_quadrants);
                qid1 =
                  mesh->local_num_quadrants + side1->is.hanging.quadid[k];
              }
              if (!side2->is.hanging.is_ghost[k]) {
                qid2 = side2->is.hanging.quadid[k] + qoffset;
                P4EST_ASSERT (0 <= qid2 && qid2 < mesh->local_num_quadrants);
              }
              else {
                P4EST_ASSERT (side2->is.hanging.quad[k] != NULL);
                P4EST_ASSERT (0 <= side2->is.hanging.quadid[k] &&
                              side2->is.hanging.quadid[k] <
                              mesh->ghost_num_quadrants);
                qid2 =
                  mesh->local_num_quadrants + side2->is.hanging.quadid[k];
              }

              /* write values */
              if (!side1->is.hanging.is_ghost[k]) {
                in_qtoe = P8EST_EDGES * qid1 + side1->edge;
                P4EST_ASSERT (mesh->quad_to_edge[in_qtoe] == -1);
                mesh->quad_to_edge[in_qtoe] = qid2;
              }
              if (!side2->is.hanging.is_ghost[k]) {
                in_qtoe = P8EST_EDGES * qid2 + side2->edge;
                P4EST_ASSERT (mesh->quad_to_edge[in_qtoe] == -1);
                mesh->quad_to_edge[in_qtoe] = qid1;
              }
            }
          }
          visited[j] = 1;
          side1 = side2 = NULL;
        }
      }
    }
  }
}

#endif /* P4_TO_P8 */

static void
mesh_iter_face (p4est_iter_face_info_t * info, void *user_data)
{
  int                 h;
  int                 swapsides;
  p4est_mesh_t       *mesh = (p4est_mesh_t *) user_data;
  p4est_locidx_t      jl, jl2, jls[P4EST_HALF];
  p4est_locidx_t      in_qtoq, halfindex;
  p4est_locidx_t     *halfentries;
  p4est_tree_t       *tree;
  p4est_iter_face_side_t *side, *side2, *tempside;

  if (info->sides.elem_count == 1) {
    /* this face is on an outside boundary of the forest */
    P4EST_ASSERT (info->orientation == 0);
    P4EST_ASSERT (info->tree_boundary);

    side = (p4est_iter_face_side_t *) sc_array_index (&info->sides, 0);
    P4EST_ASSERT (0 <= side->treeid &&
                  side->treeid < info->p4est->connectivity->num_trees);
    P4EST_ASSERT (0 <= side->face && side->face < P4EST_FACES);
    P4EST_ASSERT (!side->is_hanging && !side->is.full.is_ghost);

    tree = p4est_tree_array_index (info->p4est->trees, side->treeid);
    jl = side->is.full.quadid + tree->quadrants_offset;
    P4EST_ASSERT (0 <= jl && jl < mesh->local_num_quadrants);
    in_qtoq = P4EST_FACES * jl + side->face;
    mesh->quad_to_quad[in_qtoq] = jl;   /* put in myself and my own face */
    mesh->quad_to_face[in_qtoq] = side->face;
  }
  else {
    /* this face is between two quadrants */
    P4EST_ASSERT (info->orientation == 0 || info->tree_boundary);
    P4EST_ASSERT (info->sides.elem_count == 2);
    side = (p4est_iter_face_side_t *) sc_array_index (&info->sides, 0);
    side2 = (p4est_iter_face_side_t *) sc_array_index (&info->sides, 1);
    P4EST_ASSERT (info->tree_boundary || side->treeid == side2->treeid);
    P4EST_ASSERT (!side->is_hanging || !side2->is_hanging);
    if (!side->is_hanging && !side2->is_hanging) {
      /* same-size face neighbors */
      P4EST_ASSERT (!side->is.full.is_ghost || !side2->is.full.is_ghost);

      /* determine both quadrant numbers */
      if (!side->is.full.is_ghost) {
        tree = p4est_tree_array_index (info->p4est->trees, side->treeid);
        jl = side->is.full.quadid + tree->quadrants_offset;
        P4EST_ASSERT (0 <= jl && jl < mesh->local_num_quadrants);
      }
      else {
        P4EST_ASSERT (side->is.full.quad != NULL);
        P4EST_ASSERT (side->is.full.quadid >= 0);
        jl = mesh->local_num_quadrants + side->is.full.quadid;
      }
      if (!side2->is.full.is_ghost) {
        tree = p4est_tree_array_index (info->p4est->trees, side2->treeid);
        jl2 = side2->is.full.quadid + tree->quadrants_offset;
        P4EST_ASSERT (0 <= jl2 && jl2 < mesh->local_num_quadrants);
      }
      else {
        P4EST_ASSERT (side2->is.full.quad != NULL);
        P4EST_ASSERT (side2->is.full.quadid >= 0);
        jl2 = mesh->local_num_quadrants + side2->is.full.quadid;
      }

      /* encode quadrant neighborhood */
      /* check that nothing has been written to that spot, i.e. nothing is
       * overwritten and at the position we want to write to we still find the
       * initially set values. */
      if (!side->is.full.is_ghost) {
        in_qtoq = P4EST_FACES * jl + side->face;
        P4EST_ASSERT (mesh->quad_to_quad[in_qtoq] == -1);
        P4EST_ASSERT (mesh->quad_to_face[in_qtoq] == -25);
        mesh->quad_to_quad[in_qtoq] = jl2;
        mesh->quad_to_face[in_qtoq] =
          P4EST_FACES * info->orientation + side2->face;
      }
      if (!side2->is.full.is_ghost) {
        in_qtoq = P4EST_FACES * jl2 + side2->face;
        P4EST_ASSERT (mesh->quad_to_quad[in_qtoq] == -1);
        P4EST_ASSERT (mesh->quad_to_face[in_qtoq] == -25);
        mesh->quad_to_quad[in_qtoq] = jl;
        mesh->quad_to_face[in_qtoq] =
          P4EST_FACES * info->orientation + side->face;
      }
    }
    else {
      /* one of the faces is hanging, rename so it's always side2 */
      swapsides = side->is_hanging;
      if (swapsides) {
        tempside = side;
        side = side2;
        side2 = tempside;
      }
      P4EST_ASSERT (!side->is_hanging && side2->is_hanging);

      /* determine quadrant number for non-hanging large face */
      if (!side->is.full.is_ghost) {
        tree = p4est_tree_array_index (info->p4est->trees, side->treeid);
        jl = side->is.full.quadid + tree->quadrants_offset;
        P4EST_ASSERT (0 <= jl && jl < mesh->local_num_quadrants);
      }
      else {
        P4EST_ASSERT (side->is.full.quad != NULL);
        P4EST_ASSERT (side->is.full.quadid >= 0);
        jl = mesh->local_num_quadrants + side->is.full.quadid;
      }

      /* determine quadrant numbers for all hanging faces */
      for (h = 0; h < P4EST_HALF; ++h) {
        int                 pos =
          p4est_connectivity_face_neighbor_face_corner
          (h, side->face, side2->face, info->orientation);
        if (side->is.full.is_ghost && side2->is.hanging.is_ghost[pos]) {
          continue;
        }

        if (!side2->is.hanging.is_ghost[pos]) {
          tree = p4est_tree_array_index (info->p4est->trees, side2->treeid);
          jls[h] = side2->is.hanging.quadid[pos] + tree->quadrants_offset;
          P4EST_ASSERT (0 <= jls[h] && jls[h] < mesh->local_num_quadrants);
        }
        else {
          P4EST_ASSERT (side2->is.hanging.quad[pos] != NULL);
          P4EST_ASSERT (side2->is.hanging.quadid[pos] >= 0);
          jls[h] = mesh->local_num_quadrants + side2->is.hanging.quadid[pos];
        }
      }

      /* encode quadrant neighborhood */
      /* again: check before writing that corresponding values are untouched */
      if (!side->is.full.is_ghost) {
        in_qtoq = P4EST_FACES * jl + side->face;
        P4EST_ASSERT (mesh->quad_to_quad[in_qtoq] == -1);
        P4EST_ASSERT (mesh->quad_to_face[in_qtoq] == -25);
        halfindex = (p4est_locidx_t) mesh->quad_to_half->elem_count;
        mesh->quad_to_quad[in_qtoq] = halfindex;
        mesh->quad_to_face[in_qtoq] =
          P4EST_FACES * (info->orientation - P4EST_HALF) + side2->face;
        halfentries = (p4est_locidx_t *) sc_array_push (mesh->quad_to_half);
        for (h = 0; h < P4EST_HALF; ++h) {
          halfentries[h] = jls[h];
        }
      }
      for (h = 0; h < P4EST_HALF; ++h) {
        int                 pos =
          p4est_connectivity_face_neighbor_face_corner
          (h, side->face, side2->face, info->orientation);

        if (!side2->is.hanging.is_ghost[pos]) {
          in_qtoq = P4EST_FACES * jls[h] + side2->face;
          P4EST_ASSERT (mesh->quad_to_quad[in_qtoq] == -1);
          P4EST_ASSERT (mesh->quad_to_face[in_qtoq] == -25);
          mesh->quad_to_quad[in_qtoq] = jl;
          mesh->quad_to_face[in_qtoq] =
            P4EST_FACES * (info->orientation + (h + 1) * P4EST_HALF) +
            side->face;
        }
      }
    }
  }
}

static void
mesh_iter_volume (p4est_iter_volume_info_t * info, void *user_data)
{
  p4est_mesh_t       *mesh = (p4est_mesh_t *) user_data;
  p4est_tree_t       *tree;
  p4est_locidx_t     *quadid, qid;
  int                 level = info->quad->level;

  /* We could use a static quadrant counter, but that gets uglier */
  tree = p4est_tree_array_index (info->p4est->trees, info->treeid);
  P4EST_ASSERT (0 <= info->quadid &&
                info->quadid < (p4est_locidx_t) tree->quadrants.elem_count);

  if (mesh->quad_to_tree != NULL) {
    mesh->quad_to_tree[tree->quadrants_offset + info->quadid] = info->treeid;
  }

  if (mesh->quad_level != NULL) {
    quadid = (p4est_locidx_t *) sc_array_push (mesh->quad_level + level);
    qid = tree->quadrants_offset + info->quadid;
    *quadid = qid;
  }
}

size_t
p4est_mesh_memory_used (p4est_mesh_t * mesh)
{
  size_t              lqz, ngz;
  int                 level;
  size_t              qtt_memory = 0;
  size_t              ql_memory = 0;
  size_t              all_memory;

  lqz = (size_t) mesh->local_num_quadrants;
  ngz = (size_t) mesh->ghost_num_quadrants;

  if (mesh->quad_to_tree != NULL) {
    qtt_memory = sizeof (p4est_topidx_t) * lqz;
  }

  if (mesh->quad_level != NULL) {
    ql_memory = sizeof (sc_array_t) * (P4EST_QMAXLEVEL + 1);
    for (level = 0; level <= P4EST_QMAXLEVEL; ++level) {
      ql_memory += sc_array_memory_used (mesh->quad_level + level, 0);
    }
  }

  /* basic memory plus face information */
  all_memory =
    sizeof (p4est_mesh_t) + qtt_memory + ql_memory +
    P4EST_FACES * lqz * (sizeof (p4est_locidx_t) + sizeof (int8_t)) +
    ngz * sizeof (int) + sc_array_memory_used (mesh->quad_to_half, 1);

#ifdef P4_TO_P8
  /* add edge information */
  if (mesh->quad_to_edge != NULL) {
    all_memory +=
      P8EST_EDGES * lqz * sizeof (p4est_locidx_t) +
      sc_array_memory_used (mesh->edge_offset, 1) +
      sc_array_memory_used (mesh->edge_quad, 1) +
      sc_array_memory_used (mesh->edge_edge, 1);
  }
#endif /* P4_TO_P8 */

  /* add corner information */
  if (mesh->quad_to_corner != NULL) {
    all_memory +=
      P4EST_CHILDREN * lqz * sizeof (p4est_locidx_t) +
      sc_array_memory_used (mesh->corner_offset, 1) +
      sc_array_memory_used (mesh->corner_quad, 1) +
      sc_array_memory_used (mesh->corner_corner, 1);
  }

  return all_memory;
}

p4est_mesh_t       *
p4est_mesh_new (p4est_t * p4est, p4est_ghost_t * ghost,
                p4est_connect_type_t btype)
{
  return p4est_mesh_new_ext (p4est, ghost, 0, 0, btype);
}

p4est_mesh_t       *
p4est_mesh_new_ext (p4est_t * p4est, p4est_ghost_t * ghost,
                    int compute_tree_index, int compute_level_lists,
                    p4est_connect_type_t btype)
{
  int                 do_corner = 0;
#ifdef P4_TO_P8
  int                 do_edge = 0;
#endif /* P4_TO_P8 */
  int                 do_volume = 0;
  int                 rank;
  p4est_locidx_t      lq, ng;
  p4est_locidx_t      jl;
  p4est_mesh_t       *mesh;

  /* check whether input condition for p4est is met */
  P4EST_ASSERT (p4est_is_balanced (p4est, btype));

  mesh = P4EST_ALLOC_ZERO (p4est_mesh_t, 1);

  /* number of local quadrants and number of local ghost cells */
  lq = mesh->local_num_quadrants = p4est->local_num_quadrants;
  ng = mesh->ghost_num_quadrants = (p4est_locidx_t) ghost->ghosts.elem_count;

  /* decide which callback function have to be activated */
#ifdef P4_TO_P8
  if (btype >= P8EST_CONNECT_EDGE) {
    do_edge = 1;
  }
#endif
  if (btype >= P4EST_CONNECT_FULL) {
    do_corner = 1;
  }
  do_volume = compute_tree_index || compute_level_lists;

  /* Optional map of tree index for each quadrant */
  if (compute_tree_index) {
    mesh->quad_to_tree = P4EST_ALLOC (p4est_topidx_t, lq);
  }

  /* allocate data structures */
  mesh->ghost_to_proc = P4EST_ALLOC (int, ng);
  mesh->quad_to_quad = P4EST_ALLOC (p4est_locidx_t, P4EST_FACES * lq);
  mesh->quad_to_face = P4EST_ALLOC (int8_t, P4EST_FACES * lq);
  mesh->quad_to_half = sc_array_new (P4EST_HALF * sizeof (p4est_locidx_t));

  /* Allocate optional per-level lists of quadrants */
  if (compute_level_lists) {
    mesh->quad_level = P4EST_ALLOC (sc_array_t, P4EST_QMAXLEVEL + 1);

    for (jl = 0; jl <= P4EST_QMAXLEVEL; ++jl) {
      sc_array_init (mesh->quad_level + jl, sizeof (p4est_locidx_t));
    }
  }

  /* Populate ghost information */
  rank = 0;
  for (jl = 0; jl < ng; ++jl) {
    while (ghost->proc_offsets[rank + 1] <= jl) {
      ++rank;
      P4EST_ASSERT (rank < p4est->mpisize);
    }
    mesh->ghost_to_proc[jl] = rank;
  }

  /* Fill face arrays with default values */
  memset (mesh->quad_to_quad, (char) -1,
          P4EST_FACES * lq * sizeof (p4est_locidx_t));
  memset (mesh->quad_to_face, (char) -25, P4EST_FACES * lq * sizeof (int8_t));

#ifdef P4_TO_P8
  if (do_edge) {
    /* Allocate optional lists for edge information */
    mesh->quad_to_edge = P4EST_ALLOC (p4est_locidx_t, P8EST_EDGES * lq);
    mesh->edge_offset = sc_array_new (sizeof (p4est_locidx_t));
    mesh->edge_quad = sc_array_new (sizeof (p4est_locidx_t));
    mesh->edge_edge = sc_array_new (sizeof (int8_t));

    /* Initialize lists with default values */
    memset (mesh->quad_to_edge, (char) -1,
            P8EST_EDGES * lq * sizeof (p4est_locidx_t));
    *(p4est_locidx_t *) sc_array_push (mesh->edge_offset) = 0;
  }
#endif /* P4_TO_P8 */

  /* Allocate optional lists of corner information */
  if (do_corner) {
    /* Initialize corner information to a consistent state */
    mesh->quad_to_corner = P4EST_ALLOC (p4est_locidx_t, P4EST_CHILDREN * lq);
    memset (mesh->quad_to_corner, (char) -1,
            P4EST_CHILDREN * lq * sizeof (p4est_locidx_t));

    mesh->corner_offset = sc_array_new (sizeof (p4est_locidx_t));
    *(p4est_locidx_t *) sc_array_push (mesh->corner_offset) = 0;

    mesh->corner_quad = sc_array_new (sizeof (p4est_locidx_t));
    mesh->corner_corner = sc_array_new (sizeof (int8_t));
  }

  /* Call the forest iterator to collect face connectivity */
  p4est_iterate (p4est,         /* p4est */
                 ghost,         /* ghost layer */
                 mesh,          /* user_data */
                 (do_volume ? mesh_iter_volume : NULL), mesh_iter_face,
#ifdef P4_TO_P8
                 (do_edge ? mesh_iter_edge : NULL),
#endif /* P4_TO_P8 */
                 (do_corner ? mesh_iter_corner : NULL));

  return mesh;
}

void
p4est_mesh_destroy (p4est_mesh_t * mesh)
{
  int                 level = 0;

  if (mesh->quad_to_tree != NULL) {
    P4EST_FREE (mesh->quad_to_tree);
  }

  if (mesh->quad_level != NULL) {
    for (level = 0; level <= P4EST_QMAXLEVEL; ++level) {
      sc_array_reset (mesh->quad_level + level);
    }
    P4EST_FREE (mesh->quad_level);
  }

  P4EST_FREE (mesh->ghost_to_proc);
  P4EST_FREE (mesh->quad_to_quad);
  P4EST_FREE (mesh->quad_to_face);
  sc_array_destroy (mesh->quad_to_half);

#ifdef P4_TO_P8
  if (mesh->quad_to_edge != NULL) {
    P4EST_FREE (mesh->quad_to_edge);
    sc_array_destroy (mesh->edge_offset);
    sc_array_destroy (mesh->edge_quad);
    sc_array_destroy (mesh->edge_edge);
  }
#endif /* P4_TO_P8 */

  if (mesh->quad_to_corner != NULL) {
    P4EST_FREE (mesh->quad_to_corner);
    sc_array_destroy (mesh->corner_offset);
    sc_array_destroy (mesh->corner_quad);
    sc_array_destroy (mesh->corner_corner);
  }

  P4EST_FREE (mesh);
}

/************************* accessor functions ************************/

p4est_quadrant_t   *
p4est_mesh_get_quadrant (p4est_t * p4est, p4est_mesh_t * mesh,
                         p4est_locidx_t qid)
{
  p4est_tree_t       *tree;
  p4est_topidx_t      treeid;
  p4est_locidx_t      tree_local_qid;

  P4EST_ASSERT (p4est != NULL);
  P4EST_ASSERT (mesh != NULL);

  P4EST_ASSERT (0 <= qid && qid < p4est->local_num_quadrants);
  P4EST_ASSERT (mesh->quad_to_tree != NULL);
  treeid = mesh->quad_to_tree[qid];

  tree = p4est_tree_array_index (p4est->trees, treeid);
  tree_local_qid = qid - tree->quadrants_offset;
  P4EST_ASSERT (0 <= tree_local_qid &&
                tree_local_qid < (p4est_locidx_t) tree->quadrants.elem_count);

  P4EST_ASSERT (&tree->quadrants != NULL);
  return p4est_quadrant_array_index (&tree->quadrants, tree_local_qid);
}

/** Find neighboring quadrants across faces
 * All parameters are defined exactly the same as in
 * \ref p4est_mesh_get_neighbors
 */
static int
get_face_neighbors (p4est_t * p4est, p4est_ghost_t * ghost,
                    p4est_mesh_t * mesh, p4est_locidx_t curr_quad_id,
                    p4est_locidx_t direction, sc_array_t * neighboring_quads,
                    sc_array_t * neighboring_encs,
                    sc_array_t * neighboring_qids)
{
  int                 i;
  p4est_locidx_t      lq = mesh->local_num_quadrants;
  int                 l_same_size, u_same_size, l_double_size, u_double_size;
  int                 l_half_size, u_half_size;
#ifdef P4EST_ENABLE_DEBUG
  p4est_locidx_t      gq = mesh->ghost_num_quadrants;
  p4est_quadrant_t   *curr_quad =
    p4est_mesh_get_quadrant (p4est, mesh, curr_quad_id);
#endif /* P4EST_ENABLE_DEBUG */
  int                 convFace;
  p4est_locidx_t      neighbor_idx, neighbor_encoding;
  p4est_quadrant_t  **quad_ins;
  p4est_quadrant_t   *quad;
  int                *int_ins;

#ifdef P4_TO_P8
  l_same_size = 0;
  u_same_size = 4 * P4EST_FACES;
  l_double_size = u_same_size;
  u_double_size = 120;
  l_half_size = -24;
  u_half_size = l_same_size;
#else /* P4_TO_P8 */
  l_same_size = 0;
  u_same_size = 2 * P4EST_FACES;
  l_double_size = u_same_size;
  u_double_size = 24;
  l_half_size = -8;
  u_half_size = l_same_size;
#endif /* P4_TO_P8 */
  convFace = -l_half_size + u_double_size;

  neighbor_idx = mesh->quad_to_quad[P4EST_FACES * curr_quad_id + direction];
  neighbor_encoding =
    mesh->quad_to_face[P4EST_FACES * curr_quad_id + direction];

  /** no neighbor present */
  if ((neighbor_idx == curr_quad_id) && neighbor_encoding == direction) {
    return 0;
  }

  if (l_same_size <= neighbor_encoding && neighbor_encoding < u_same_size) {
    /** same size neighbor: */
    if (neighbor_idx < lq) {
        /** neighbor is part of quadrants owned by processor */
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad = p4est_mesh_get_quadrant (p4est, mesh, neighbor_idx);
      }
        /** convert encoding */
      ++neighbor_encoding;
    }
    else {
      neighbor_idx -= lq;
      P4EST_ASSERT (0 <= neighbor_idx && neighbor_idx < gq);
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad =
          (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                   neighbor_idx);
      }
      neighbor_encoding = -(neighbor_encoding + 1);
    }
#ifdef P4EST_ENABLE_DEBUG
    /** sanity check level */
    P4EST_ASSERT (quad->level == curr_quad->level);
#endif /* P4EST_ENABLE_DEBUG */

    if (neighboring_quads != NULL) {
      quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
      *quad_ins = quad;
    }

    int_ins = (int *) sc_array_push (neighboring_encs);
    *int_ins = neighbor_encoding;

    if (neighboring_qids != NULL) {
      int_ins = (int *) sc_array_push (neighboring_qids);
      *int_ins = neighbor_idx;
    }
  }
  else if (l_double_size <= neighbor_encoding
           && neighbor_encoding < u_double_size) {
    /** double size neighbor: */
    if (neighbor_idx < lq) {
        /** neighbor is part of quadrants owned by processor */
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad = p4est_mesh_get_quadrant (p4est, mesh, neighbor_idx);
      }

        /** convert encoding */
      ++neighbor_encoding;
    }
    else {
        /** neighbor is part of ghost layer */
      neighbor_idx -= lq;
      P4EST_ASSERT (0 <= neighbor_idx && neighbor_idx < gq);
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad =
          (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                   neighbor_idx);
      }

        /** convert encoding */
      neighbor_encoding = -neighbor_encoding - 1;
    }
#ifdef P4EST_ENABLE_DEBUG
    /* sanity check level */
    P4EST_ASSERT (quad->level == curr_quad->level - 1);
#endif /* P4EST_ENABLE_DEBUG */

    if (neighboring_quads != NULL) {
      quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
      *quad_ins = quad;
    }

    int_ins = (int *) sc_array_push (neighboring_encs);
    *int_ins = neighbor_encoding;

    if (neighboring_qids != NULL) {
      int_ins = (int *) sc_array_push (neighboring_qids);
      *int_ins = neighbor_idx;
    }
  }
  else if (l_half_size <= neighbor_encoding
           && neighbor_encoding < u_half_size) {
    /** half size neighbor: */
    p4est_locidx_t      quad_idx;
    p4est_locidx_t     *quad_ptr;
    quad_ptr =
      (p4est_locidx_t *) sc_array_index (mesh->quad_to_half, neighbor_idx);
    int                 nenc;

    for (i = 0; i < P4EST_HALF; ++i) {
      nenc = neighbor_encoding + convFace;
      quad_idx = quad_ptr[i];
      if (quad_idx < lq) {
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
        {
          quad = p4est_mesh_get_quadrant (p4est, mesh, quad_idx);
        }
        ++nenc;
      }
      else {
        quad_idx -= lq;
        P4EST_ASSERT (0 <= quad_idx && quad_idx < gq);
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
        {
          quad =
            (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                     quad_idx);
        }
        nenc = -nenc - 1;
      }
#ifdef P4EST_ENABLE_DEBUG
      /* sanity check level */
      P4EST_ASSERT (quad->level == curr_quad->level + 1);
#endif /* P4EST_ENABLE_DEBUG */

      if (neighboring_quads != NULL) {
        quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
        *quad_ins = quad;
      }

      int_ins = (int *) sc_array_push (neighboring_encs);
      *int_ins = nenc;

      if (neighboring_qids != NULL) {
        int_ins = (int *) sc_array_push (neighboring_qids);
        *int_ins = quad_idx;
      }
    }
  }
  else {
    SC_ABORT_NOT_REACHED ();
  }

  return 0;
}

#ifdef P4_TO_P8
static int
get_edge_neighbors (p4est_t * p4est, p4est_ghost_t * ghost,
                    p4est_mesh_t * mesh, p4est_locidx_t curr_quad_id,
                    p4est_locidx_t direction, sc_array_t * neighboring_quads,
                    sc_array_t * neighboring_encs,
                    sc_array_t * neighboring_qids)
{
  int                 i;
  p4est_locidx_t      lq = mesh->local_num_quadrants;
  p4est_locidx_t      gq = mesh->ghost_num_quadrants;
  int                 l_half_size, u_double_size;
#ifdef P4EST_ENABLE_DEBUG
  int                 u_half_size, l_double_size;
  int                 l_same_size, u_same_size;
  p4est_quadrant_t   *curr_quad =
    p4est_mesh_get_quadrant (p4est, mesh, curr_quad_id);
#endif /* P4EST_ENABLE_DEBUG */
  p4est_locidx_t      neighbor_idx, neighbor_encoding;
  int                 is_ghost = 0;
  p4est_quadrant_t  **quad_ins;
  p4est_quadrant_t   *quad;
  int                 convEdge;
  int                *int_ins;

  u_double_size = 72;
  l_half_size = -24;
#ifdef P4EST_ENABLE_DEBUG
  l_same_size = 0;
  u_same_size = 2 * P8EST_EDGES;
  l_double_size = u_same_size;
  u_half_size = l_same_size;
#endif /* P4EST_ENABLE_DEBUG */

  convEdge = -l_half_size + u_double_size;
  neighbor_idx = mesh->quad_to_edge[P8EST_EDGES * curr_quad_id + (direction)];

  /** Domain boundary or hanging edge: No neighbor present */
  if (neighbor_idx == -3 || neighbor_idx == -1) {
    return 0;
  }

  /** Same size, intra tree neighbor */
  if (0 <= neighbor_idx && neighbor_idx < (lq + gq)) {
    neighbor_encoding = (direction) ^ 3;

    if (0 <= neighbor_idx && neighbor_idx < lq) {
      /* same size neighbor, same proc */
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad = p4est_mesh_get_quadrant (p4est, mesh, neighbor_idx);
      }
      ++neighbor_encoding;
    }
    else {
      P4EST_ASSERT (lq <= neighbor_idx && neighbor_idx < (lq + gq));
      neighbor_idx -= lq;
#ifndef P4EST_ENABLE_DEBUG
      if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
      {
        quad =
          (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                   neighbor_idx);
      }
      neighbor_encoding = -neighbor_encoding - 1;
    }

#ifdef P4EST_ENABLE_DEBUG
    /* sanity check level */
    P4EST_ASSERT (quad->level == curr_quad->level);
#endif /* P4EST_ENABLE_DEBUG */

    if (neighboring_quads != NULL) {
      quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
      *quad_ins = quad;
    }

    int_ins = (int *) sc_array_push (neighboring_encs);
    *int_ins = neighbor_encoding;

    if (neighboring_qids != NULL) {
      int_ins = (int *) sc_array_push (neighboring_qids);
      *int_ins = neighbor_idx;
    }
    return 0;
  }

  else if ((lq + gq) <= neighbor_idx) {
    /* anything else */
    /* normalize neighbor index */
    neighbor_idx -= (lq + gq);
    P4EST_ASSERT (0 <= neighbor_idx && neighbor_idx < mesh->local_num_edges);
    p4est_locidx_t      n_adj_quads, offset;

    /* get offset and number of adjacent quads */
    offset = *((p4est_locidx_t *)
               sc_array_index_int (mesh->edge_offset, neighbor_idx));
    n_adj_quads = *((p4est_locidx_t *)
                    sc_array_index_int (mesh->edge_offset,
                                        neighbor_idx + 1)) - offset;

    p4est_locidx_t      quad_idx;
    for (i = 0; i < n_adj_quads; ++i) {
      is_ghost = 0;
      quad_idx = *((p4est_locidx_t *)
                   sc_array_index_int (mesh->edge_quad, offset + i));
      neighbor_encoding = *((int8_t *)
                            sc_array_index_int (mesh->edge_edge, offset + i));

      if (0 <= quad_idx && quad_idx < lq) {
        /* neighbor is part of quadrants owned by processor */
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
        {
          quad = p4est_mesh_get_quadrant (p4est, mesh, quad_idx);
        }
        is_ghost = 0;
      }
      else if (lq <= quad_idx && quad_idx < lq + gq) {
        is_ghost = 1;
        quad_idx -= lq;
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
        {
          quad =
            (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                     quad_idx);
        }
      }
      else {
        SC_ABORT_NOT_REACHED ();
      }

#ifdef P4EST_ENABLE_DEBUG
      /* sanity check level */
      if (l_same_size <= neighbor_encoding && neighbor_encoding < u_same_size) {
        P4EST_ASSERT (quad->level == curr_quad->level);
      }
      else if (l_double_size <= neighbor_encoding
               && neighbor_encoding < u_double_size) {
        P4EST_ASSERT (quad->level == curr_quad->level - 1);
      }
      else if (l_half_size <= neighbor_encoding
               && neighbor_encoding < u_half_size) {
        P4EST_ASSERT (quad->level == curr_quad->level + 1);
      }
      else {
        SC_ABORT_NOT_REACHED ();
      }
#endif /* P4EST_ENABLE_DEBUG */

      /** convert encoding */
      if (!is_ghost) {
        neighbor_encoding = neighbor_encoding < 0 ?
          neighbor_encoding + convEdge + 1 : neighbor_encoding + 1;
      }
      else {
        neighbor_encoding = neighbor_encoding < 0 ?
          -neighbor_encoding - convEdge - 1 : -neighbor_encoding - 1;
      }

      if (neighboring_quads != NULL) {
        quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
        *quad_ins = quad;
      }

      int_ins = (int *) sc_array_push (neighboring_encs);
      *int_ins = neighbor_encoding;

      if (neighboring_qids != NULL) {
        int_ins = (int *) sc_array_push (neighboring_qids);
        *int_ins = quad_idx;
      }
    }
  }
  else {
    SC_ABORT_NOT_REACHED ();
  }

  return 0;
}
#endif /* P4_TO_P8 */

/** Internal function for looking up corner neighbors
 *
 * \param[in]      p4est               The forest.
 * \param[in]      ghost               Ghost layer.
 * \param[in]      mesh                Mesh encoding quadrant neighborhood.
 * \param[in]      curr_quad_id        Quadrant ID of current quadrant.
 * \param[in]      direction           Direction 0 .. P4EST_CHILDREN encoding
 *                                     corner across which to search.
 * \param    [out] neighboring_quads   Container for storing pointer to
 *                                     neighboring p4est_quadrant_t. May be
 *                                     NULL.
 * \param    [out] neighboring_encs    Store encoding of neighboring quadrants,
 *                                     i.e. the corner index that is touching
 *                                     corner of current quadrant.
 * \param    [out] neighboring_qids    Store neighboring quadrant id. May be
 *                                     NULL.
 */
static int
get_corner_neighbors (p4est_t * p4est, p4est_ghost_t * ghost,
                      p4est_mesh_t * mesh, p4est_locidx_t curr_quad_id,
                      p4est_locidx_t direction,
                      sc_array_t * neighboring_quads,
                      sc_array_t * neighboring_encs,
                      sc_array_t * neighboring_qids)
{
  int                 i;
  p4est_locidx_t      lq = mesh->local_num_quadrants;
  p4est_locidx_t      gq = mesh->ghost_num_quadrants;
#ifdef P4EST_ENABLE_DEBUG
  p4est_quadrant_t   *curr_quad =
    p4est_mesh_get_quadrant (p4est, mesh, curr_quad_id);
#endif /* P4EST_ENABLE_DEBUG */
  p4est_locidx_t      neighbor_idx, neighbor_encoding;
  p4est_quadrant_t  **quad_ins;
  p4est_quadrant_t   *quad;
  int                *int_ins;
  int                 encHelper;

#ifdef P4_TO_P8
  encHelper = 7;
#else /* P4_TO_P8 */
  encHelper = 3;
#endif /* P4_TO_P8 */

  neighbor_idx =
    mesh->quad_to_corner[P4EST_CHILDREN * curr_quad_id + direction];

  /* no neighbor present */
  if (neighbor_idx < 0 || neighbor_idx == curr_quad_id) {
    return 0;
  }

  if (neighbor_idx < lq) {
    /* same size neighbor, same proc */
#ifndef P4EST_ENABLE_DEBUG
    if (neighboring_quads != NULL)
#endif /* !P4EST_ENABLE_DEBUG */
    {
      quad = p4est_mesh_get_quadrant (p4est, mesh, neighbor_idx);
    }
#ifdef P4EST_ENABLE_DEBUG
    /* sanity check level */
    P4EST_ASSERT ((quad->level == curr_quad->level) ||
                  (quad->level == curr_quad->level - 1) ||
                  (quad->level == curr_quad->level + 1));
#endif /* P4EST_ENABLE_DEBUG */

    if (neighboring_quads != NULL) {
      quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
      *quad_ins = quad;
    }

    /* create implicitly saved encoding */
    int_ins = (int *) sc_array_push (neighboring_encs);
    neighbor_encoding = (direction) ^ encHelper;
    /* convert encoding */
    ++neighbor_encoding;
    *int_ins = neighbor_encoding;

    if (neighboring_qids != NULL) {
      int_ins = (int *) sc_array_push (neighboring_qids);
      *int_ins = neighbor_idx;
    }
  }

  else if (lq <= neighbor_idx && neighbor_idx < lq + gq) {
    /* same size neighbor, ghost layer */
    neighbor_idx -= lq;
#ifndef P4EST_ENABLE_DEBUG
    if (neighboring_quads != NULL)
#endif /* P4EST_ENABLE_DEBUG */
    {
      quad = (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                      neighbor_idx);
    }
    if (neighboring_quads != NULL) {
      quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
      *quad_ins = quad;
    }

#ifdef P4EST_ENABLE_DEBUG
    /* sanity check level */
    P4EST_ASSERT ((quad->level == curr_quad->level) ||
                  (quad->level == curr_quad->level - 1) ||
                  (quad->level == curr_quad->level + 1));
#endif /* P4EST_ENABLE_DEBUG */

    /* create implicitly saved encoding */
    int_ins = (int *) sc_array_push (neighboring_encs);
    neighbor_encoding = (direction) ^ encHelper;
    /* convert encoding */
    ++neighbor_encoding;
    *int_ins = -neighbor_encoding;

    if (neighboring_qids != NULL) {
      int_ins = (int *) sc_array_push (neighboring_qids);
      *int_ins = neighbor_idx;
    }
  }

  else if ((lq + gq) <= neighbor_idx) {
    /* anything else */
    /* normalize neighbor index */
    neighbor_idx -= (lq + gq);
    P4EST_ASSERT (0 <= neighbor_idx
                  && neighbor_idx < mesh->local_num_corners);
    p4est_locidx_t      n_adj_quads, offset;

    /* get offset and number of adjacent quads */
    offset = *((p4est_locidx_t *)
               sc_array_index_int (mesh->corner_offset, neighbor_idx));
    n_adj_quads = *((p4est_locidx_t *)
                    sc_array_index_int (mesh->corner_offset,
                                        neighbor_idx + 1)) - offset;

    p4est_locidx_t      quad_idx;
    for (i = 0; i < n_adj_quads; ++i) {
      quad_idx = *((p4est_locidx_t *)
                   sc_array_index_int (mesh->corner_quad, offset + i));
      neighbor_encoding = *((int8_t *)
                            sc_array_index_int (mesh->corner_corner,
                                                offset + i));

      if (quad_idx < lq) {
        /* neighbor is part of quadrants owned by processor */
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* P4EST_ENABLE_DEBUG */
        {
          quad = p4est_mesh_get_quadrant (p4est, mesh, quad_idx);
        }
        if (neighboring_quads != NULL) {
          quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
          *quad_ins = quad;
        }

#ifdef P4EST_ENABLE_DEBUG
        /* sanity check level */
        P4EST_ASSERT ((quad->level == curr_quad->level) ||
                      (quad->level == curr_quad->level - 1) ||
                      (quad->level == curr_quad->level + 1));
#endif /* P4EST_ENABLE_DEBUG */

        /* convert encoding */
        int_ins = (int *) sc_array_push (neighboring_encs);
        ++neighbor_encoding;
        *int_ins = neighbor_encoding;
      }
      else {
        /* neighbor is part of ghost layer */
        quad_idx -= lq;
#ifndef P4EST_ENABLE_DEBUG
        if (neighboring_quads != NULL)
#endif /* P4EST_ENABLE_DEBUG */
        {
          quad =
            (p4est_quadrant_t *) sc_array_index_int (&ghost->ghosts,
                                                     quad_idx);
        }

        if (neighboring_quads != NULL) {
          quad_ins = (p4est_quadrant_t **) sc_array_push (neighboring_quads);
          *quad_ins = quad;
        }

#ifdef P4EST_ENABLE_DEBUG
        /* sanity check level */
        P4EST_ASSERT ((quad->level == curr_quad->level) ||
                      (quad->level == curr_quad->level - 1) ||
                      (quad->level == curr_quad->level + 1));
#endif /* P4EST_ENABLE_DEBUG */

        /* convert encoding */
        int_ins = (int *) sc_array_push (neighboring_encs);
        ++neighbor_encoding;
        *int_ins = -neighbor_encoding;
      }
      if (neighboring_qids != NULL) {
        int_ins = (int *) sc_array_push (neighboring_qids);
        *int_ins = quad_idx;
      }
    }
  }
  else {
    SC_ABORT_NOT_REACHED ();
  }
  return 0;
}

p4est_locidx_t
p4est_mesh_get_neighbors (p4est_t * p4est, p4est_ghost_t * ghost,
                          p4est_mesh_t * mesh, p4est_locidx_t curr_quad_id,
                          p4est_locidx_t direction,
                          sc_array_t * neighboring_quads,
                          sc_array_t * neighboring_encs,
                          sc_array_t * neighboring_qids)
{
#ifdef P4EST_ENABLE_DEBUG
  p4est_locidx_t      lq = mesh->local_num_quadrants;

  /* direction must be within the allowed range */
  p4est_locidx_t      limit;

  /* Integrity checks: */
  /* result arrays should be empty, */
  P4EST_ASSERT (neighboring_quads == NULL ||
                neighboring_quads->elem_count == 0);
  P4EST_ASSERT (neighboring_encs->elem_count == 0);
  P4EST_ASSERT (neighboring_qids == NULL ||
                neighboring_qids->elem_count == 0);

  /* result arrays need to have matching element sizes */
  P4EST_ASSERT (neighboring_quads == NULL ||
                neighboring_quads->elem_size == sizeof (p4est_quadrant_t *));
  P4EST_ASSERT (neighboring_encs->elem_size == sizeof (int));
  P4EST_ASSERT (neighboring_qids == NULL ||
                neighboring_qids->elem_size == sizeof (int));

  /** only either one of the vectors may be NULL */
  P4EST_ASSERT (neighboring_quads != NULL || neighboring_qids != NULL);

  /*  mesh has to be created, i.e. not NULL, */
  P4EST_ASSERT (mesh != NULL);
  /*  curr_quad_id must be part of the processors quadrants, */
  P4EST_ASSERT (curr_quad_id < lq);

  switch (ghost->btype) {
  case P4EST_CONNECT_FACE:
    P4EST_ASSERT (direction >= 0 && direction < P4EST_FACES);
    break;

#ifdef P4_TO_P8
  case P8EST_CONNECT_EDGE:
#ifdef P4EST_ENABLE_DEBUG
    limit = P4EST_FACES + P8EST_EDGES;
    P4EST_ASSERT (direction >= 0 && direction < limit);
#endif
    break;
#endif /* P4_TO_P8 */

  case P4EST_CONNECT_CORNER:
#ifdef P4EST_ENABLE_DEBUG
#ifdef P4_TO_P8
    limit = P4EST_FACES + P8EST_EDGES + P4EST_CHILDREN;
#else /* P4_TO_P8 */
    limit = P4EST_FACES + P4EST_CHILDREN;
#endif /* P4_TO_P8 */
    P4EST_ASSERT (direction >= 0 && direction < limit);
#endif /* P4EST_ENABLE_DEBUG */
    break;

  default:
    SC_ABORT_NOT_REACHED ();
  }
#endif /* P4EST_ENABLE_DEBUG */

  /* tools for decoding direction */
#ifndef P4_TO_P8
  p4est_locidx_t      lFace, uFace, lCorner, uCorner;

  lFace = 0;
  uFace = lCorner = P4EST_FACES;
  uCorner = P4EST_FACES + P4EST_CHILDREN;
#else /* !P4_TO_P8 */
  p4est_locidx_t      lFace, uFace, lEdge, uEdge, lCorner, uCorner;

  lFace = 0;
  uFace = lEdge = P4EST_FACES;
  uEdge = lCorner = lEdge + P8EST_EDGES;
  uCorner = lCorner + P4EST_CHILDREN;
#endif /* P4_TO_P8 */

  /* faces */
  if (lFace <= direction && direction < uFace) {
    get_face_neighbors (p4est, ghost, mesh, curr_quad_id, direction,
                        neighboring_quads, neighboring_encs,
                        neighboring_qids);
  }

#ifdef P4_TO_P8
  /* edges (3D only) */
  else if (lEdge <= direction && direction < uEdge) {
    get_edge_neighbors (p4est, ghost, mesh, curr_quad_id, direction - lEdge,
                        neighboring_quads, neighboring_encs,
                        neighboring_qids);
  }
#endif /* P4_TO_P8 */
  /* corners */
  else if (lCorner <= direction && direction < uCorner) {
    get_corner_neighbors (p4est, ghost, mesh, curr_quad_id,
                          direction - lCorner,
                          neighboring_quads, neighboring_encs,
                          neighboring_qids);
  }
  /* must not occur */
  else {
    SC_ABORT_NOT_REACHED ();
  }

  return 0;
}

p4est_quadrant_t   *
p4est_mesh_quadrant_cumulative (p4est_t * p4est, p4est_mesh_t * mesh,
                                p4est_locidx_t cumulative_id,
                                p4est_topidx_t * pwhich_tree,
                                p4est_locidx_t * pquadrant_id)
{
  p4est_topidx_t      which_tree;
  p4est_locidx_t      quadrant_id;
  p4est_quadrant_t   *quadrant;
#ifdef P4EST_ENABLE_DEBUG
  p4est_topidx_t      dwhich_tree;
  p4est_locidx_t      dquadrant_id;
  p4est_quadrant_t   *dquadrant;
#endif
  p4est_tree_t       *tree;

  P4EST_ASSERT (p4est != NULL);
  P4EST_ASSERT (mesh != NULL);
  P4EST_ASSERT (p4est->local_num_quadrants == mesh->local_num_quadrants);

  P4EST_ASSERT (0 <= cumulative_id &&
                cumulative_id < mesh->local_num_quadrants);
  P4EST_ASSERT (NULL == pwhich_tree || *pwhich_tree == -1 ||
                (0 <= *pwhich_tree &&
                 *pwhich_tree < p4est->connectivity->num_trees));

  if (mesh->quad_to_tree != NULL) {
    /* in this case we can do an O(1) lookup */
    which_tree = mesh->quad_to_tree[cumulative_id];
    if (pwhich_tree != NULL) {
#ifdef P4EST_ENABLE_DEBUG
      dwhich_tree = *pwhich_tree;
#endif
      *pwhich_tree = which_tree;
    }
    tree = p4est_tree_array_index (p4est->trees, which_tree);
    P4EST_ASSERT (tree->quadrants_offset <= cumulative_id);
    quadrant_id = cumulative_id - tree->quadrants_offset;
    P4EST_ASSERT (quadrant_id < (p4est_locidx_t) tree->quadrants.elem_count);
    if (pquadrant_id != NULL) {
      *pquadrant_id = quadrant_id;
    }
    quadrant = p4est_quadrant_array_index (&tree->quadrants, quadrant_id);

#ifdef P4EST_ENABLE_DEBUG
    /* we use the more expensive binary search for debugging */
    dquadrant = p4est_find_quadrant_cumulative (p4est, cumulative_id,
                                                &dwhich_tree, &dquadrant_id);
    P4EST_ASSERT (dwhich_tree == which_tree);
    P4EST_ASSERT (dquadrant_id == quadrant_id);
    P4EST_ASSERT (dquadrant == quadrant);
#endif
  }
  else {
    /* we do not have the O(1) lookup table and need to binary search */
    quadrant = p4est_find_quadrant_cumulative (p4est, cumulative_id,
                                               pwhich_tree, pquadrant_id);
  }

  return quadrant;
}

void
p4est_mesh_face_neighbor_init2 (p4est_mesh_face_neighbor_t * mfn,
                                p4est_t * p4est, p4est_ghost_t * ghost,
                                p4est_mesh_t * mesh,
                                p4est_topidx_t which_tree,
                                p4est_locidx_t quadrant_id)
{
  p4est_tree_t       *tree;

  mfn->p4est = p4est;
  mfn->ghost = ghost;
  mfn->mesh = mesh;

  P4EST_ASSERT (0 <= which_tree &&
                which_tree < p4est->connectivity->num_trees);
  mfn->which_tree = which_tree;
  tree = p4est_tree_array_index (p4est->trees, which_tree);

  P4EST_ASSERT (0 <= quadrant_id &&
                (size_t) quadrant_id < tree->quadrants.elem_count);
  mfn->quadrant_id = quadrant_id;
  mfn->quadrant_code = P4EST_FACES * (tree->quadrants_offset + quadrant_id);

  mfn->face = 0;
  mfn->subface = 0;
  mfn->current_qtq = -1;
}

void
p4est_mesh_face_neighbor_init (p4est_mesh_face_neighbor_t * mfn,
                               p4est_t * p4est, p4est_ghost_t * ghost,
                               p4est_mesh_t * mesh, p4est_topidx_t which_tree,
                               p4est_quadrant_t * quadrant)
{
  p4est_locidx_t      quadrant_id;
  p4est_tree_t       *tree;

  mfn->p4est = p4est;
  mfn->ghost = ghost;
  mfn->mesh = mesh;

  P4EST_ASSERT (0 <= which_tree &&
                which_tree < p4est->connectivity->num_trees);
  mfn->which_tree = which_tree;
  tree = p4est_tree_array_index (p4est->trees, which_tree);

  quadrant_id =
    (p4est_locidx_t) sc_array_position (&tree->quadrants, quadrant);
  mfn->quadrant_id = quadrant_id;
  mfn->quadrant_code = P4EST_FACES * (tree->quadrants_offset + quadrant_id);

  mfn->face = 0;
  mfn->subface = 0;
  mfn->current_qtq = -1;
}

p4est_quadrant_t   *
p4est_mesh_face_neighbor_next (p4est_mesh_face_neighbor_t * mfn,
                               p4est_topidx_t * ntree, p4est_locidx_t * nquad,
                               int *nface, int *nrank)
{
  int                 qtf;
  p4est_topidx_t      which_tree;
  p4est_locidx_t      qtq, quadfacecode;
  p4est_locidx_t      lnq, *halfs;
#ifdef P4EST_ENABLE_DEBUG
  p4est_locidx_t      ngh;
#endif
  p4est_quadrant_t   *q;

  /* We have already processed the last quadrant */
  if (mfn->face == P4EST_FACES) {
    mfn->current_qtq = -1;
    P4EST_ASSERT (mfn->subface == 0);
    return NULL;
  }

  /* Make sure we have a valid quadrant face and iterator */
  lnq = mfn->mesh->local_num_quadrants;
#ifdef P4EST_ENABLE_DEBUG
  ngh = mfn->mesh->ghost_num_quadrants;
#endif
  P4EST_ASSERT (mfn->face >= 0 && mfn->face < P4EST_FACES);
  P4EST_ASSERT (mfn->subface >= 0 && mfn->subface < P4EST_HALF);
  P4EST_ASSERT (mfn->p4est->local_num_quadrants == lnq);
  P4EST_ASSERT (mfn->ghost->ghosts.elem_count == (size_t) ngh);

  /* Retrieve face and quadrant codes */
  quadfacecode = mfn->quadrant_code + (p4est_locidx_t) mfn->face;
  qtq = mfn->mesh->quad_to_quad[quadfacecode];
  qtf = (int) mfn->mesh->quad_to_face[quadfacecode];
  if (qtf >= 0) {
    /* Neighbor is same or double size */
    ;

    /* Advance to next quadrant */
    ++mfn->face;
  }
  else {
    /* Neighbors across this face are half size */
    P4EST_ASSERT (qtq >= 0);
    halfs = (p4est_locidx_t *) sc_array_index (mfn->mesh->quad_to_half,
                                               (size_t) qtq);
    qtq = halfs[mfn->subface];

    /* Advance to next quadrant */
    if (++mfn->subface == P4EST_HALF) {
      mfn->subface = 0;
      ++mfn->face;
    }
  }

  mfn->current_qtq = qtq;
  /* From here on face and subface have advanced and can no longer be used */
  P4EST_ASSERT (qtq >= 0);
  if (qtq < lnq) {
    /* Local quadrant */
    which_tree = mfn->which_tree;
    q = p4est_mesh_quadrant_cumulative (mfn->p4est, mfn->mesh,
                                        qtq, &which_tree, nquad);
    if (ntree != NULL) {
      *ntree = which_tree;
    }
    if (nrank != NULL) {
      *nrank = mfn->p4est->mpirank;
    }
  }
  else {
    /* Ghost quadrant */
    qtq -= lnq;
    P4EST_ASSERT (qtq < ngh);
    q = p4est_quadrant_array_index (&mfn->ghost->ghosts, (size_t) qtq);
    if (ntree != NULL) {
      *ntree = q->p.piggy3.which_tree;
    }
    if (nquad != NULL) {
      *nquad = qtq;             /* number of ghost in the ghost layer */
    }
    if (nrank != NULL) {
      *nrank = mfn->mesh->ghost_to_proc[qtq];
    }
  }
  if (nface != NULL) {
    *nface = qtf;
  }

  return q;
}

void               *
p4est_mesh_face_neighbor_data (p4est_mesh_face_neighbor_t * mfn,
                               void *ghost_data)
{
  p4est_locidx_t      qtq = mfn->current_qtq;
  p4est_locidx_t      lnq = mfn->mesh->local_num_quadrants;
  size_t              data_size = mfn->p4est->data_size;

  P4EST_ASSERT (qtq >= 0);

  if (qtq < lnq) {
    p4est_topidx_t      which_tree;
    p4est_quadrant_t   *q;
    /* Local quadrant */
    which_tree = mfn->which_tree;
    q = p4est_mesh_quadrant_cumulative (mfn->p4est, mfn->mesh,
                                        qtq, &which_tree, NULL);
    return q->p.user_data;
  }
  else {
    qtq -= lnq;
    return (void *) ((char *) ghost_data + data_size * qtq);
  }
}
