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poly.c

/*<html><pre>  -<a                             href="qh-poly.htm"
  >-------------------------------</a><a name="TOP">-</a>

   poly.c 
   implements polygons and simplices

   see qh-poly.htm, poly.h and qhull.h

   infrequent code is in poly2.c 
   (all but top 50 and their callers 12/3/95)

   copyright (c) 1993-2002, The Geometry Center
*/

#include "qhull_a.h"

/*======== functions in alphabetical order ==========*/

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="appendfacet">-</a>
  
  qh_appendfacet( facet )
    appends facet to end of qh.facet_list,

  returns:
    updates qh.newfacet_list, facet_next, facet_list
    increments qh.numfacets
  
  notes:
    assumes qh.facet_list/facet_tail is defined (createsimplex)

  see:
    qh_removefacet()

*/
void qh_appendfacet(facetT *facet) {
  facetT *tail= qh facet_tail;

  if (tail == qh newfacet_list)
    qh newfacet_list= facet;
  if (tail == qh facet_next)
    qh facet_next= facet;
  facet->previous= tail->previous;
  facet->next= tail;
  if (tail->previous)
    tail->previous->next= facet;
  else
    qh facet_list= facet;
  tail->previous= facet;
  qh num_facets++;
  trace4((qh ferr, "qh_appendfacet: append f%d to facet_list\n", facet->id));
} /* appendfacet */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="appendvertex">-</a>
  
  qh_appendvertex( vertex )
    appends vertex to end of qh.vertex_list,

  returns:
    sets vertex->newlist
    updates qh.vertex_list, newvertex_list
    increments qh.num_vertices

  notes:
    assumes qh.vertex_list/vertex_tail is defined (createsimplex)

*/
void qh_appendvertex (vertexT *vertex) {
  vertexT *tail= qh vertex_tail;

  if (tail == qh newvertex_list)
    qh newvertex_list= vertex;
  vertex->newlist= True;
  vertex->previous= tail->previous;
  vertex->next= tail;
  if (tail->previous)
    tail->previous->next= vertex;
  else
    qh vertex_list= vertex;
  tail->previous= vertex;
  qh num_vertices++;
  trace4((qh ferr, "qh_appendvertex: append v%d to vertex_list\n", vertex->id));
} /* appendvertex */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="attachnewfacets">-</a>
  
  qh_attachnewfacets( )
    attach horizon facets to new facets in qh.newfacet_list
    newfacets have neighbor and ridge links to horizon but not vice versa
    only needed for qh.ONLYgood

  returns:
    set qh.NEWfacets
    horizon facets linked to new facets 
      ridges changed from visible facets to new facets
      simplicial ridges deleted
    qh.visible_list, no ridges valid
    facet->f.replace is a newfacet (if any)

  design:
    delete interior ridges and neighbor sets by
      for each visible, non-simplicial facet
        for each ridge
          if last visit or if neighbor is simplicial
            if horizon neighbor
              delete ridge for horizon's ridge set
            delete ridge
        erase neighbor set
    attach horizon facets and new facets by
      for all new facets
        if corresponding horizon facet is simplicial
          locate corresponding visible facet {may be more than one}
          link visible facet to new facet
          replace visible facet with new facet in horizon
        else it's non-simplicial
          for all visible neighbors of the horizon facet
            link visible neighbor to new facet
            delete visible neighbor from horizon facet
          append new facet to horizon's neighbors
          the first ridge of the new facet is the horizon ridge
          link the new facet into the horizon ridge
*/
void qh_attachnewfacets (void ) {
  facetT *newfacet= NULL, *neighbor, **neighborp, *horizon, *visible;
  ridgeT *ridge, **ridgep;

  qh NEWfacets= True;
  trace3((qh ferr, "qh_attachnewfacets: delete interior ridges\n"));
  qh visit_id++;
  FORALLvisible_facets {
    visible->visitid= qh visit_id;
    if (visible->ridges) {
      FOREACHridge_(visible->ridges) {
      neighbor= otherfacet_(ridge, visible);
      if (neighbor->visitid == qh visit_id
          || (!neighbor->visible && neighbor->simplicial)) {
        if (!neighbor->visible)  /* delete ridge for simplicial horizon */
          qh_setdel (neighbor->ridges, ridge);
        qh_setfree (&(ridge->vertices)); /* delete on 2nd visit */
        qh_memfree (ridge, sizeof(ridgeT));
      }
      }
      SETfirst_(visible->ridges)= NULL;
    }
    SETfirst_(visible->neighbors)= NULL;
  }
  trace1((qh ferr, "qh_attachnewfacets: attach horizon facets to new facets\n"));
  FORALLnew_facets {
    horizon= SETfirstt_(newfacet->neighbors, facetT);
    if (horizon->simplicial) {
      visible= NULL;
      FOREACHneighbor_(horizon) {   /* may have more than one horizon ridge */
      if (neighbor->visible) {
        if (visible) {
          if (qh_setequal_skip (newfacet->vertices, 0, horizon->vertices,
                          SETindex_(horizon->neighbors, neighbor))) {
            visible= neighbor;
            break;
          }
        }else
          visible= neighbor;
      }
      }
      if (visible) {
      visible->f.replace= newfacet;
      qh_setreplace (horizon->neighbors, visible, newfacet);
      }else {
      fprintf (qh ferr, "qhull internal error (qh_attachnewfacets): couldn't find visible facet for horizon f%d of newfacet f%d\n",
             horizon->id, newfacet->id);
      qh_errexit2 (qh_ERRqhull, horizon, newfacet);
      }
    }else { /* non-simplicial, with a ridge for newfacet */
      FOREACHneighbor_(horizon) {    /* may hold for many new facets */
      if (neighbor->visible) {
        neighbor->f.replace= newfacet;
        qh_setdelnth (horizon->neighbors,
                  SETindex_(horizon->neighbors, neighbor));
        neighborp--; /* repeat */
      }
      }
      qh_setappend (&horizon->neighbors, newfacet);
      ridge= SETfirstt_(newfacet->ridges, ridgeT);
      if (ridge->top == horizon)
      ridge->bottom= newfacet;
      else
      ridge->top= newfacet;
      }
  } /* newfacets */
  if (qh PRINTstatistics) {
    FORALLvisible_facets {
      if (!visible->f.replace) 
      zinc_(Zinsidevisible);
    }
  }
} /* attachnewfacets */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="checkflipped">-</a>
  
  qh_checkflipped( facet, dist, allerror )
    checks facet orientation to interior point

    if allerror set,
      tests against qh.DISTround
    else
      tests against 0 since tested against DISTround before

  returns:
    False if it flipped orientation (sets facet->flipped)
    distance if non-NULL
*/
boolT qh_checkflipped (facetT *facet, realT *distp, boolT allerror) {
  realT dist;

  if (facet->flipped && !distp)
    return False;
  zzinc_(Zdistcheck);
  qh_distplane(qh interior_point, facet, &dist);
  if (distp)
    *distp= dist;
  if ((allerror && dist > -qh DISTround)|| (!allerror && dist >= 0.0)) {
    facet->flipped= True;
    zzinc_(Zflippedfacets);
    trace0((qh ferr, "qh_checkflipped: facet f%d is flipped, distance= %6.12g during p%d\n",
              facet->id, dist, qh furthest_id));
    qh_precision ("flipped facet");
    return False;
  }
  return True;
} /* checkflipped */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="delfacet">-</a>
  
  qh_delfacet( facet )
    removes facet from facet_list and frees up its memory

  notes:
    assumes vertices and ridges already freed
*/
void qh_delfacet(facetT *facet) {
  void **freelistp; /* used !qh_NOmem */

  trace4((qh ferr, "qh_delfacet: delete f%d\n", facet->id));
  if (facet == qh tracefacet)
    qh tracefacet= NULL;
  if (facet == qh GOODclosest)
    qh GOODclosest= NULL;
  qh_removefacet(facet);
  if (!facet->tricoplanar || facet->keepcentrum) {
    qh_memfree_(facet->normal, qh normal_size, freelistp);
    if (qh CENTERtype == qh_ASvoronoi) {   /* uses macro calls */
      qh_memfree_(facet->center, qh center_size, freelistp);
    }else /* AScentrum */ {
      qh_memfree_(facet->center, qh normal_size, freelistp);
    }
  }
  qh_setfree(&(facet->neighbors));
  if (facet->ridges)
    qh_setfree(&(facet->ridges));
  qh_setfree(&(facet->vertices));
  if (facet->outsideset)
    qh_setfree(&(facet->outsideset));
  if (facet->coplanarset)
    qh_setfree(&(facet->coplanarset));
  qh_memfree_(facet, sizeof(facetT), freelistp);
} /* delfacet */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="deletevisible">-</a>
  
  qh_deletevisible()
    delete visible facets and vertices

  returns:
    deletes each facet and removes from facetlist
    at exit, qh.visible_list empty (== qh.newfacet_list)

  notes:
    ridges already deleted
    horizon facets do not reference facets on qh.visible_list
    new facets in qh.newfacet_list
    uses   qh.visit_id;
*/
void qh_deletevisible (void /*qh visible_list*/) {
  facetT *visible, *nextfacet;
  vertexT *vertex, **vertexp;
  int numvisible= 0, numdel= qh_setsize(qh del_vertices);

  trace1((qh ferr, "qh_deletevisible: delete %d visible facets and %d vertices\n",
         qh num_visible, numdel));
  for (visible= qh visible_list; visible && visible->visible; 
                visible= nextfacet) { /* deleting current */
    nextfacet= visible->next;        
    numvisible++;
    qh_delfacet(visible);
  }
  if (numvisible != qh num_visible) {
    fprintf (qh ferr, "qhull internal error (qh_deletevisible): qh num_visible %d is not number of visible facets %d\n",
             qh num_visible, numvisible);
    qh_errexit (qh_ERRqhull, NULL, NULL);
  }
  qh num_visible= 0;
  zadd_(Zvisfacettot, numvisible);
  zmax_(Zvisfacetmax, numvisible);
  zzadd_(Zdelvertextot, numdel);
  zmax_(Zdelvertexmax, numdel);
  FOREACHvertex_(qh del_vertices) 
    qh_delvertex (vertex);
  qh_settruncate (qh del_vertices, 0);
} /* deletevisible */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="facetintersect">-</a>
  
  qh_facetintersect( facetA, facetB, skipa, skipB, prepend )
    return vertices for intersection of two simplicial facets
    may include 1 prepended entry (if more, need to settemppush)
    
  returns:
    returns set of qh.hull_dim-1 + prepend vertices
    returns skipped index for each test and checks for exactly one

  notes:
    does not need settemp since set in quick memory
  
  see also:
    qh_vertexintersect and qh_vertexintersect_new
    use qh_setnew_delnthsorted to get nth ridge (no skip information)

  design:
    locate skipped vertex by scanning facet A's neighbors
    locate skipped vertex by scanning facet B's neighbors
    intersect the vertex sets
*/
setT *qh_facetintersect (facetT *facetA, facetT *facetB,
                   int *skipA,int *skipB, int prepend) {
  setT *intersect;
  int dim= qh hull_dim, i, j;
  facetT **neighborsA, **neighborsB;

  neighborsA= SETaddr_(facetA->neighbors, facetT);
  neighborsB= SETaddr_(facetB->neighbors, facetT);
  i= j= 0;
  if (facetB == *neighborsA++)
    *skipA= 0;
  else if (facetB == *neighborsA++)
    *skipA= 1;
  else if (facetB == *neighborsA++)
    *skipA= 2;
  else {
    for (i= 3; i < dim; i++) {
      if (facetB == *neighborsA++) {
        *skipA= i;
        break;
      }
    }
  }
  if (facetA == *neighborsB++)
    *skipB= 0;
  else if (facetA == *neighborsB++)
    *skipB= 1;
  else if (facetA == *neighborsB++)
    *skipB= 2;
  else {
    for (j= 3; j < dim; j++) {
      if (facetA == *neighborsB++) {
        *skipB= j;
        break;
      }
    }
  }
  if (i >= dim || j >= dim) {
    fprintf (qh ferr, "qhull internal error (qh_facetintersect): f%d or f%d not in others neighbors\n",
            facetA->id, facetB->id);
    qh_errexit2 (qh_ERRqhull, facetA, facetB);
  }
  intersect= qh_setnew_delnthsorted (facetA->vertices, qh hull_dim, *skipA, prepend);
  trace4((qh ferr, "qh_facetintersect: f%d skip %d matches f%d skip %d\n",
        facetA->id, *skipA, facetB->id, *skipB));
  return(intersect);
} /* facetintersect */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="gethash">-</a>
  
  qh_gethash( hashsize, set, size, firstindex, skipelem )
    return hashvalue for a set with firstindex and skipelem

  notes:
    assumes at least firstindex+1 elements
    assumes skipelem is NULL, in set, or part of hash
    
    hashes memory addresses which may change over different runs of the same data
    using sum for hash does badly in high d
*/
unsigned qh_gethash (int hashsize, setT *set, int size, int firstindex, void *skipelem) {
  void **elemp= SETelemaddr_(set, firstindex, void);
  ptr_intT hash = 0, elem;
  int i;

  switch (size-firstindex) {
  case 1:
    hash= (ptr_intT)(*elemp) - (ptr_intT) skipelem;
    break;
  case 2:
    hash= (ptr_intT)(*elemp) + (ptr_intT)elemp[1] - (ptr_intT) skipelem;
    break;
  case 3:
    hash= (ptr_intT)(*elemp) + (ptr_intT)elemp[1] + (ptr_intT)elemp[2]
      - (ptr_intT) skipelem;
    break;
  case 4:
    hash= (ptr_intT)(*elemp) + (ptr_intT)elemp[1] + (ptr_intT)elemp[2]
      + (ptr_intT)elemp[3] - (ptr_intT) skipelem;
    break;
  case 5:
    hash= (ptr_intT)(*elemp) + (ptr_intT)elemp[1] + (ptr_intT)elemp[2]
      + (ptr_intT)elemp[3] + (ptr_intT)elemp[4] - (ptr_intT) skipelem;
    break;
  case 6:
    hash= (ptr_intT)(*elemp) + (ptr_intT)elemp[1] + (ptr_intT)elemp[2]
      + (ptr_intT)elemp[3] + (ptr_intT)elemp[4]+ (ptr_intT)elemp[5]
      - (ptr_intT) skipelem;
    break;
  default:
    hash= 0;
    i= 3;
    do {     /* this is about 10% in 10-d */
      if ((elem= (ptr_intT)*elemp++) != (ptr_intT)skipelem) {
        hash ^= (elem << i) + (elem >> (32-i));
      i += 3;
      if (i >= 32)
        i -= 32;
      }
    }while(*elemp);
    break;
  }
  hash %= (ptr_intT) hashsize;
  /* hash= 0; for debugging purposes */
  return hash;
} /* gethash */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="makenewfacet">-</a>
  
  qh_makenewfacet( vertices, toporient, horizon )
    creates a toporient? facet from vertices

  returns:
    returns newfacet
      adds newfacet to qh.facet_list
      newfacet->vertices= vertices
      if horizon
        newfacet->neighbor= horizon, but not vice versa
    newvertex_list updated with vertices
*/
facetT *qh_makenewfacet(setT *vertices, boolT toporient,facetT *horizon) {
  facetT *newfacet;
  vertexT *vertex, **vertexp;

  FOREACHvertex_(vertices) {
    if (!vertex->newlist) {
      qh_removevertex (vertex);
      qh_appendvertex (vertex);
    }
  }
  newfacet= qh_newfacet();
  newfacet->vertices= vertices;
  newfacet->toporient= toporient;
  if (horizon)
    qh_setappend(&(newfacet->neighbors), horizon);
  qh_appendfacet(newfacet);
  return(newfacet);
} /* makenewfacet */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="makenewplanes">-</a>
  
  qh_makenewplanes()
    make new hyperplanes for facets on qh.newfacet_list

  returns:
    all facets have hyperplanes or are marked for   merging
    doesn't create hyperplane if horizon is coplanar (will merge)
    updates qh.min_vertex if qh.JOGGLEmax

  notes:
    facet->f.samecycle is defined for facet->mergehorizon facets
*/
void qh_makenewplanes (void /* newfacet_list */) {
  facetT *newfacet;

  FORALLnew_facets {
    if (!newfacet->mergehorizon)
      qh_setfacetplane (newfacet);  
  }
  if (qh JOGGLEmax < REALmax/2)  
    minimize_(qh min_vertex, -wwval_(Wnewvertexmax));
} /* makenewplanes */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="makenew_nonsimplicial">-</a>
  
  qh_makenew_nonsimplicial( visible, apex, numnew )
    make new facets for ridges of a visible facet
    
  returns:
    first newfacet, bumps numnew as needed
    attaches new facets if !qh.ONLYgood
    marks ridge neighbors for simplicial visible
    if (qh.ONLYgood)
      ridges on newfacet, horizon, and visible
    else
      ridge and neighbors between newfacet and   horizon
      visible facet's ridges are deleted    

  notes:
    qh.visit_id if visible has already been processed
    sets neighbor->seen for building f.samecycle
      assumes all 'seen' flags initially false
    
  design:
    for each ridge of visible facet
      get neighbor of visible facet
      if neighbor was already processed
        delete the ridge (will delete all visible facets later)
      if neighbor is a horizon facet
        create a new facet
        if neighbor coplanar
          adds newfacet to f.samecycle for later merging
        else 
          updates neighbor's neighbor set
          (checks for non-simplicial facet with multiple ridges to visible facet)
        updates neighbor's ridge set
        (checks for simplicial neighbor to non-simplicial visible facet)
      (deletes ridge if neighbor is simplicial)
          
*/
#ifndef qh_NOmerge
facetT *qh_makenew_nonsimplicial (facetT *visible, vertexT *apex, int *numnew) {
  void **freelistp; /* used !qh_NOmem */
  ridgeT *ridge, **ridgep;
  facetT *neighbor, *newfacet= NULL, *samecycle;
  setT *vertices;
  boolT toporient;
  int ridgeid;

  FOREACHridge_(visible->ridges) {
    ridgeid= ridge->id;
    neighbor= otherfacet_(ridge, visible);
    if (neighbor->visible) {
      if (!qh ONLYgood) {
        if (neighbor->visitid == qh visit_id) {
          qh_setfree (&(ridge->vertices));  /* delete on 2nd visit */
        qh_memfree_(ridge, sizeof(ridgeT), freelistp);
      }
      }
    }else {  /* neighbor is an horizon facet */
      toporient= (ridge->top == visible);
      vertices= qh_setnew (qh hull_dim); /* makes sure this is quick */
      qh_setappend (&vertices, apex);
      qh_setappend_set (&vertices, ridge->vertices);
      newfacet= qh_makenewfacet(vertices, toporient, neighbor);
      (*numnew)++;
      if (neighbor->coplanar) {
      newfacet->mergehorizon= True;
        if (!neighbor->seen) {
          newfacet->f.samecycle= newfacet;
          neighbor->f.newcycle= newfacet;
        }else {
          samecycle= neighbor->f.newcycle;
          newfacet->f.samecycle= samecycle->f.samecycle;
          samecycle->f.samecycle= newfacet;
      }
      }
      if (qh ONLYgood) {
        if (!neighbor->simplicial)
        qh_setappend(&(newfacet->ridges), ridge);
      }else {  /* qh_attachnewfacets */
        if (neighbor->seen) {
        if (neighbor->simplicial) {
          fprintf (qh ferr, "qhull internal error (qh_makenew_nonsimplicial): simplicial f%d sharing two ridges with f%d\n", 
                 neighbor->id, visible->id);
          qh_errexit2 (qh_ERRqhull, neighbor, visible);
        }
        qh_setappend (&(neighbor->neighbors), newfacet);
      }else
          qh_setreplace (neighbor->neighbors, visible, newfacet);
        if (neighbor->simplicial) {
          qh_setdel (neighbor->ridges, ridge);
          qh_setfree (&(ridge->vertices)); 
        qh_memfree (ridge, sizeof(ridgeT));
      }else {
        qh_setappend(&(newfacet->ridges), ridge);
        if (toporient)
          ridge->top= newfacet;
        else
          ridge->bottom= newfacet;
      }
      trace4((qh ferr, "qh_makenew_nonsimplicial: created facet f%d from v%d and r%d of horizon f%d\n",
          newfacet->id, apex->id, ridgeid, neighbor->id));
      }
    }
    neighbor->seen= True;        
  } /* for each ridge */
  if (!qh ONLYgood)
    SETfirst_(visible->ridges)= NULL;
  return newfacet;
} /* makenew_nonsimplicial */
#else /* qh_NOmerge */
facetT *qh_makenew_nonsimplicial (facetT *visible, vertexT *apex, int *numnew) {
  return NULL;
}
#endif /* qh_NOmerge */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="makenew_simplicial">-</a>
  
  qh_makenew_simplicial( visible, apex, numnew )
    make new facets for simplicial visible facet and apex

  returns:
    attaches new facets if (!qh.ONLYgood)
      neighbors between newfacet and horizon

  notes:
    nop if neighbor->seen or neighbor->visible (see qh_makenew_nonsimplicial)

  design:
    locate neighboring horizon facet for visible facet
    determine vertices and orientation
    create new facet
    if coplanar,
      add new facet to f.samecycle
    update horizon facet's neighbor list        
*/
facetT *qh_makenew_simplicial (facetT *visible, vertexT *apex, int *numnew) {
  facetT *neighbor, **neighborp, *newfacet= NULL;
  setT *vertices;
  boolT flip, toporient;
  int horizonskip, visibleskip;

  FOREACHneighbor_(visible) {
    if (!neighbor->seen && !neighbor->visible) {
      vertices= qh_facetintersect(neighbor,visible, &horizonskip, &visibleskip, 1);
      SETfirst_(vertices)= apex;
      flip= ((horizonskip & 0x1) ^ (visibleskip & 0x1));
      if (neighbor->toporient)         
      toporient= horizonskip & 0x1;
      else
      toporient= (horizonskip & 0x1) ^ 0x1;
      newfacet= qh_makenewfacet(vertices, toporient, neighbor);
      (*numnew)++;
      if (neighbor->coplanar && (qh PREmerge || qh MERGEexact)) {
#ifndef qh_NOmerge
      newfacet->f.samecycle= newfacet;
      newfacet->mergehorizon= True;
#endif
      }
      if (!qh ONLYgood)
        SETelem_(neighbor->neighbors, horizonskip)= newfacet;
      trace4((qh ferr, "qh_makenew_simplicial: create facet f%d top %d from v%d and horizon f%d skip %d top %d and visible f%d skip %d, flip? %d\n",
          newfacet->id, toporient, apex->id, neighbor->id, horizonskip,
            neighbor->toporient, visible->id, visibleskip, flip));
    }
  }
  return newfacet;
} /* makenew_simplicial */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="matchneighbor">-</a>
  
  qh_matchneighbor( newfacet, newskip, hashsize, hashcount )
    either match subridge of newfacet with neighbor or add to hash_table

  returns:
    duplicate ridges are unmatched and marked by qh_DUPLICATEridge

  notes:
    ridge is newfacet->vertices w/o newskip vertex
    do not allocate memory (need to free hash_table cleanly)
    uses linear hash chains
  
  see also:
    qh_matchduplicates

  design:
    for each possible matching facet in qh.hash_table
      if vertices match
        set ismatch, if facets have opposite orientation
        if ismatch and matching facet doesn't have a match
          match the facets by updating their neighbor sets
        else
          indicate a duplicate ridge
          set facet hyperplane for later testing
          add facet to hashtable
          unless the other facet was already a duplicate ridge
            mark both facets with a duplicate ridge
            add other facet (if defined) to hash table
*/
void qh_matchneighbor (facetT *newfacet, int newskip, int hashsize, int *hashcount) {
  boolT newfound= False;   /* True, if new facet is already in hash chain */
  boolT same, ismatch;
  int hash, scan;
  facetT *facet, *matchfacet;
  int skip, matchskip;

  hash= (int)qh_gethash (hashsize, newfacet->vertices, qh hull_dim, 1, 
                     SETelem_(newfacet->vertices, newskip));
  trace4((qh ferr, "qh_matchneighbor: newfacet f%d skip %d hash %d hashcount %d\n",
        newfacet->id, newskip, hash, *hashcount));
  zinc_(Zhashlookup);
  for (scan= hash; (facet= SETelemt_(qh hash_table, scan, facetT)); 
       scan= (++scan >= hashsize ? 0 : scan)) {
    if (facet == newfacet) {
      newfound= True;
      continue;
    }
    zinc_(Zhashtests);
    if (qh_matchvertices (1, newfacet->vertices, newskip, facet->vertices, &skip, &same)) {
      if (SETelem_(newfacet->vertices, newskip) == 
          SETelem_(facet->vertices, skip)) {
        qh_precision ("two facets with the same vertices");
        fprintf (qh ferr, "qhull precision error: Vertex sets are the same for f%d and f%d.  Can not force output.\n",
          facet->id, newfacet->id);
        qh_errexit2 (qh_ERRprec, facet, newfacet);
      }
      ismatch= (same == (newfacet->toporient ^ facet->toporient));
      matchfacet= SETelemt_(facet->neighbors, skip, facetT);
      if (ismatch && !matchfacet) {
        SETelem_(facet->neighbors, skip)= newfacet;
        SETelem_(newfacet->neighbors, newskip)= facet;
        (*hashcount)--;
        trace4((qh ferr, "qh_matchneighbor: f%d skip %d matched with new f%d skip %d\n",
           facet->id, skip, newfacet->id, newskip));
        return;
      }
      if (!qh PREmerge && !qh MERGEexact) {
        qh_precision ("a ridge with more than two neighbors");
      fprintf (qh ferr, "qhull precision error: facets f%d, f%d and f%d meet at a ridge with more than 2 neighbors.  Can not continue.\n",
             facet->id, newfacet->id, getid_(matchfacet));
      qh_errexit2 (qh_ERRprec, facet, newfacet);
      }
      SETelem_(newfacet->neighbors, newskip)= qh_DUPLICATEridge;
      newfacet->dupridge= True;
      if (!newfacet->normal)
      qh_setfacetplane (newfacet);
      qh_addhash (newfacet, qh hash_table, hashsize, hash);
      (*hashcount)++;
      if (!facet->normal)
      qh_setfacetplane (facet);
      if (matchfacet != qh_DUPLICATEridge) {
      SETelem_(facet->neighbors, skip)= qh_DUPLICATEridge;
      facet->dupridge= True;
      if (!facet->normal)
        qh_setfacetplane (facet);
      if (matchfacet) {
        matchskip= qh_setindex (matchfacet->neighbors, facet);
        SETelem_(matchfacet->neighbors, matchskip)= qh_DUPLICATEridge;
        matchfacet->dupridge= True;
        if (!matchfacet->normal)
          qh_setfacetplane (matchfacet);
        qh_addhash (matchfacet, qh hash_table, hashsize, hash);
        *hashcount += 2;
      }
      }
      trace4((qh ferr, "qh_matchneighbor: new f%d skip %d duplicates ridge for f%d skip %d matching f%d ismatch %d at hash %d\n",
         newfacet->id, newskip, facet->id, skip, 
         (matchfacet == qh_DUPLICATEridge ? -2 : getid_(matchfacet)), 
         ismatch, hash));
      return; /* end of duplicate ridge */
    }
  }
  if (!newfound) 
    SETelem_(qh hash_table, scan)= newfacet;  /* same as qh_addhash */
  (*hashcount)++;
  trace4((qh ferr, "qh_matchneighbor: no match for f%d skip %d at hash %d\n",
           newfacet->id, newskip, hash));
} /* matchneighbor */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="matchnewfacets">-</a>
  
  qh_matchnewfacets()
    match newfacets in qh.newfacet_list to their newfacet neighbors

  returns:
    qh.newfacet_list with full neighbor sets
      get vertices with nth neighbor by deleting nth vertex
    if qh.PREmerge/MERGEexact or qh.FORCEoutput 
      sets facet->flippped if flipped normal (also prevents point partitioning)
    if duplicate ridges and qh.PREmerge/MERGEexact
      sets facet->dupridge
      missing neighbor links identifies extra ridges to be merging (qh_MERGEridge)

  notes:
    newfacets already have neighbor[0] (horizon facet)
    assumes qh.hash_table is NULL
    vertex->neighbors has not been updated yet
    do not allocate memory after qh.hash_table (need to free it cleanly)

  design:
    delete neighbor sets for all new facets
    initialize a hash table
    for all new facets
      match facet with neighbors
    if unmatched facets (due to duplicate ridges)
      for each new facet with a duplicate ridge
        match it with a facet
    check for flipped facets
*/
void qh_matchnewfacets (void /* qh newfacet_list */) {
  int numnew=0, hashcount=0, newskip;
  facetT *newfacet, *neighbor;
  int dim= qh hull_dim, hashsize, neighbor_i, neighbor_n;
  setT *neighbors;
#ifndef qh_NOtrace
  int facet_i, facet_n, numfree= 0;
  facetT *facet;
#endif
  
  trace1((qh ferr, "qh_matchnewfacets: match neighbors for new facets.\n"));
  FORALLnew_facets {
    numnew++;
    {  /* inline qh_setzero (newfacet->neighbors, 1, qh hull_dim); */
      neighbors= newfacet->neighbors;
      neighbors->e[neighbors->maxsize].i= dim+1; /*may be overwritten*/
      memset ((char *)SETelemaddr_(neighbors, 1, void), 0, dim * SETelemsize);
    }    
  }
  qh_newhashtable (numnew*(qh hull_dim-1)); /* twice what is normally needed,
                                     but every ridge could be DUPLICATEridge */
  hashsize= qh_setsize (qh hash_table);
  FORALLnew_facets {
    for (newskip=1; newskip<qh hull_dim; newskip++) /* furthest/horizon already matched */
      qh_matchneighbor (newfacet, newskip, hashsize, &hashcount);
#if 0   /* use the following to trap hashcount errors */
    {
      int count= 0, k;
      facetT *facet, *neighbor;

      count= 0;
      FORALLfacet_(qh newfacet_list) {  /* newfacet already in use */
      for (k=1; k < qh hull_dim; k++) {
        neighbor= SETelemt_(facet->neighbors, k, facetT);
        if (!neighbor || neighbor == qh_DUPLICATEridge)
          count++;
      }
      if (facet == newfacet)
        break;
      }
      if (count != hashcount) {
      fprintf (qh ferr, "qh_matchnewfacets: after adding facet %d, hashcount %d != count %d\n",
             newfacet->id, hashcount, count);
      qh_errexit (qh_ERRqhull, newfacet, NULL);
      }
    }
#endif  /* end of trap code */
  }
  if (hashcount) {
    FORALLnew_facets {
      if (newfacet->dupridge) {
        FOREACHneighbor_i_(newfacet) {
          if (neighbor == qh_DUPLICATEridge) {
            qh_matchduplicates (newfacet, neighbor_i, hashsize, &hashcount);
                /* this may report MERGEfacet */
        }
        }
      }
    }
  }
  if (hashcount) {
    fprintf (qh ferr, "qhull internal error (qh_matchnewfacets): %d neighbors did not match up\n",
        hashcount);
    qh_printhashtable (qh ferr);
    qh_errexit (qh_ERRqhull, NULL, NULL);
  }
#ifndef qh_NOtrace
  if (qh IStracing >= 2) {
    FOREACHfacet_i_(qh hash_table) {
      if (!facet)
        numfree++;
    }
    fprintf (qh ferr, "qh_matchnewfacets: %d new facets, %d unused hash entries .  hashsize %d\n",
           numnew, numfree, qh_setsize (qh hash_table));
  }
#endif /* !qh_NOtrace */
  qh_setfree (&qh hash_table);
  if (qh PREmerge || qh MERGEexact) {
    if (qh IStracing >= 4)
      qh_printfacetlist (qh newfacet_list, NULL, qh_ALL);
    FORALLnew_facets {
      if (newfacet->normal)
      qh_checkflipped (newfacet, NULL, qh_ALL);
    }
  }else if (qh FORCEoutput)
    qh_checkflipped_all (qh newfacet_list);  /* prints warnings for flipped */
} /* matchnewfacets */

    
/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="matchvertices">-</a>
  
  qh_matchvertices( firstindex, verticesA, skipA, verticesB, skipB, same )
    tests whether vertices match with a single skip
    starts match at firstindex since all new facets have a common vertex

  returns:
    true if matched vertices
    skip index for each set
    sets same iff vertices have the same orientation

  notes:
    assumes skipA is in A and both sets are the same size

  design:
    set up pointers
    scan both sets checking for a match
    test orientation
*/
boolT qh_matchvertices (int firstindex, setT *verticesA, int skipA, 
       setT *verticesB, int *skipB, boolT *same) {
  vertexT **elemAp, **elemBp, **skipBp=NULL, **skipAp;

  elemAp= SETelemaddr_(verticesA, firstindex, vertexT);
  elemBp= SETelemaddr_(verticesB, firstindex, vertexT);
  skipAp= SETelemaddr_(verticesA, skipA, vertexT);
  do if (elemAp != skipAp) {
    while (*elemAp != *elemBp++) {
      if (skipBp)
        return False;
      skipBp= elemBp;  /* one extra like FOREACH */
    }
  }while(*(++elemAp));
  if (!skipBp)
    skipBp= ++elemBp;
  *skipB= SETindex_(verticesB, skipB);
  *same= !(((ptr_intT)skipA & 0x1) ^ ((ptr_intT)*skipB & 0x1));
  trace4((qh ferr, "qh_matchvertices: matched by skip %d (v%d) and skip %d (v%d) same? %d\n",
        skipA, (*skipAp)->id, *skipB, (*(skipBp-1))->id, *same));
  return (True);
} /* matchvertices */

/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="newfacet">-</a>
  
  qh_newfacet()
    return a new facet 

  returns:
    all fields initialized or cleared   (NULL)
    preallocates neighbors set
*/
facetT *qh_newfacet(void) {
  facetT *facet;
  void **freelistp; /* used !qh_NOmem */
  
  qh_memalloc_(sizeof(facetT), freelistp, facet, facetT);
  memset ((char *)facet, 0, sizeof(facetT));
  if (qh facet_id == qh tracefacet_id)
    qh tracefacet= facet;
  facet->id= qh facet_id++;
  facet->neighbors= qh_setnew(qh hull_dim);
#if !qh_COMPUTEfurthest
  facet->furthestdist= 0.0;
#endif
#if qh_MAXoutside
  if (qh FORCEoutput && qh APPROXhull)
    facet->maxoutside= qh MINoutside;
  else
    facet->maxoutside= qh DISTround;
#endif
  facet->simplicial= True;
  facet->good= True;
  facet->newfacet= True;
  trace4((qh ferr, "qh_newfacet: created facet f%d\n", facet->id));
  return (facet);
} /* newfacet */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="newridge">-</a>
  
  qh_newridge()
    return a new ridge
*/
ridgeT *qh_newridge(void) {
  ridgeT *ridge;
  void **freelistp;   /* used !qh_NOmem */

  qh_memalloc_(sizeof(ridgeT), freelistp, ridge, ridgeT);
  memset ((char *)ridge, 0, sizeof(ridgeT));
  zinc_(Ztotridges);
  if (qh ridge_id == 0xFFFFFF) {
    fprintf(qh ferr, "\
qhull warning: more than %d ridges.  ID field overflows and two ridges\n\
may have the same identifier.  Otherwise output ok.\n", 0xFFFFFF);
  }
  ridge->id= qh ridge_id++;     
  trace4((qh ferr, "qh_newridge: created ridge r%d\n", ridge->id));
  return (ridge);
} /* newridge */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="pointid">-</a>
  
  qh_pointid(  )
    return id for a point, 
    returns -3 if null, -2 if interior, or -1 if not known

  alternative code:
    unsigned long id;
    id= ((unsigned long)point - (unsigned long)qh.first_point)/qh.normal_size;

  notes:
    if point not in point array
      the code does a comparison of unrelated pointers.
*/
int qh_pointid (pointT *point) {
  long offset, id;

  if (!point)
    id= -3;
  else if (point == qh interior_point)
    id= -2;
  else if (point >= qh first_point
  && point < qh first_point + qh num_points * qh hull_dim) {
    offset= point - qh first_point;
    id= offset / qh hull_dim;
  }else if ((id= qh_setindex (qh other_points, point)) != -1)
    id += qh num_points;
  else
    id= -1;
  return (int) id;
} /* pointid */
  
/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="removefacet">-</a>
  
  qh_removefacet( facet )
    unlinks facet from qh.facet_list,

  returns:
    updates qh.facet_list .newfacet_list .facet_next visible_list
    decrements qh.num_facets

  see:
    qh_appendfacet
*/
void qh_removefacet(facetT *facet) {
  facetT *next= facet->next, *previous= facet->previous;
  
  if (facet == qh newfacet_list)
    qh newfacet_list= next;
  if (facet == qh facet_next)
    qh facet_next= next;
  if (facet == qh visible_list)
    qh visible_list= next; 
  if (previous) {
    previous->next= next;
    next->previous= previous;
  }else {  /* 1st facet in qh facet_list */
    qh facet_list= next;
    qh facet_list->previous= NULL;
  }
  qh num_facets--;
  trace4((qh ferr, "qh_removefacet: remove f%d from facet_list\n", facet->id));
} /* removefacet */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="removevertex">-</a>
  
  qh_removevertex( vertex )
    unlinks vertex from qh.vertex_list,

  returns:
    updates qh.vertex_list .newvertex_list 
    decrements qh.num_vertices
*/
void qh_removevertex(vertexT *vertex) {
  vertexT *next= vertex->next, *previous= vertex->previous;
  
  if (vertex == qh newvertex_list)
    qh newvertex_list= next;
  if (previous) {
    previous->next= next;
    next->previous= previous;
  }else {  /* 1st vertex in qh vertex_list */
    qh vertex_list= vertex->next;
    qh vertex_list->previous= NULL;
  }
  qh num_vertices--;
  trace4((qh ferr, "qh_removevertex: remove v%d from vertex_list\n", vertex->id));
} /* removevertex */


/*-<a                             href="qh-poly.htm#TOC"
  >-------------------------------</a><a name="updatevertices">-</a>
  
  qh_updatevertices()
    update vertex neighbors and delete interior vertices

  returns:
    if qh.VERTEXneighbors, updates neighbors for each vertex
      if qh.newvertex_list, 
         removes visible neighbors  from vertex neighbors
      if qh.newfacet_list
         adds new facets to vertex neighbors
    if qh.visible_list
       interior vertices added to qh.del_vertices for later partitioning

  design:
    if qh.VERTEXneighbors
      deletes references to visible facets from vertex neighbors
      appends new facets to the neighbor list for each vertex
      checks all vertices of visible facets
        removes visible facets from neighbor lists
        marks unused vertices for deletion
*/
void qh_updatevertices (void /*qh newvertex_list, newfacet_list, visible_list*/) {
  facetT *newfacet= NULL, *neighbor, **neighborp, *visible;
  vertexT *vertex, **vertexp;

  trace3((qh ferr, "qh_updatevertices: delete interior vertices and update vertex->neighbors\n"));
  if (qh VERTEXneighbors) {
    FORALLvertex_(qh newvertex_list) {
      FOREACHneighbor_(vertex) {
      if (neighbor->visible) 
        SETref_(neighbor)= NULL;
      }
      qh_setcompact (vertex->neighbors);
    }
    FORALLnew_facets {
      FOREACHvertex_(newfacet->vertices)
        qh_setappend (&vertex->neighbors, newfacet);
    }
    FORALLvisible_facets {
      FOREACHvertex_(visible->vertices) {
        if (!vertex->newlist && !vertex->deleted) {
        FOREACHneighbor_(vertex) { /* this can happen under merging */
          if (!neighbor->visible)
            break;
        }
        if (neighbor)
          qh_setdel (vertex->neighbors, visible);
        else {
          vertex->deleted= True;
          qh_setappend (&qh del_vertices, vertex);
          trace2((qh ferr, "qh_updatevertices: delete vertex p%d (v%d) in f%d\n",
              qh_pointid(vertex->point), vertex->id, visible->id));
        }
        }
      }
    }
  }else {  /* !VERTEXneighbors */
    FORALLvisible_facets {
      FOREACHvertex_(visible->vertices) {
        if (!vertex->newlist && !vertex->deleted) {
          vertex->deleted= True;
        qh_setappend (&qh del_vertices, vertex);
        trace2((qh ferr, "qh_updatevertices: delete vertex p%d (v%d) in f%d\n",
              qh_pointid(vertex->point), vertex->id, visible->id));
      }
      }
    }
  }
} /* updatevertices */




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