** Local variables for this module
*/
static struct {
  PathNode *pCurrent;   /* Current generation of nodes */
  PathNode *pAll;       /* All nodes */
  Bag seen;             /* Nodes seen before */
  int nStep;            /* Number of steps from first to last */
  int nNotHidden;       /* Number of steps not counting hidden nodes */
  PathNode *pStart;     /* Earliest node */
  PathNode *pEnd;       /* Most recent */
} path;

/*
** Return the first (last) element of the computed path.
*/
PathNode *path_first(void){ return path.pStart; }
PathNode *path_last(void){ return path.pEnd; }

/*
** Return the number of steps in the computed path.
*/
int path_length(void){ return path.nStep; }

/*
** Return the number of non-hidden steps in the computed path.
*/
int path_length_not_hidden(void){ return path.nNotHidden; }

/*
** Create a new node
*/
static PathNode *path_new_node(int rid, PathNode *pFrom, int isParent){
  PathNode *p;

  p = fossil_malloc( sizeof(*p) );

**
** Return NULL if no path is found.
*/
PathNode *path_shortest(
  int iFrom,          /* Path starts here */
  int iTo,            /* Path ends here */
  int directOnly,     /* No merge links if true */
  int oneWayOnly,     /* Parent->child only if true */
  Bag *pHidden        /* Hidden nodes */
){
  Stmt s;
  PathNode *pPrev;
  PathNode *p;

  path_reset();
  path.pStart = path_new_node(iFrom, 0, 0);

    while( pPrev ){
      db_bind_int(&s, ":pid", pPrev->rid);
      while( db_step(&s)==SQLITE_ROW ){
        int cid = db_column_int(&s, 0);
        int isParent = db_column_int(&s, 1);
        if( bag_find(&path.seen, cid) ) continue;
        p = path_new_node(cid, pPrev, isParent);
        if( pHidden && bag_find(pHidden,cid) ) p->isHidden = 1;
        if( cid==iTo ){
          db_finalize(&s);
          path.pEnd = p;
          path_reverse_path();
          for(p=path.pStart->u.pTo; p; p=p->u.pTo ){
            if( !p->isHidden ) path.nNotHidden++;
          }
          return path.pStart;
        }
      }
      db_reset(&s);
      pPrev = pPrev->u.pPeer;
    }
  }
  db_finalize(&s);
  path_reset();
  return 0;
}

/*
** Find the mid-point of the path.  If the path contains fewer than
** 2 steps, return 0.
*/
PathNode *path_midpoint(void){
  PathNode *p;
  int i;
  if( path.nNotHidden<2 ) return 0;
  for(p=path.pEnd, i=0; p && (p->isHidden || i<path.nNotHidden/2); p=p->pFrom){
    if( !p->isHidden ) i++;
  }
  return p;
}

/*
** Return an estimate of the number of comparisons remaining in order
** to bisect path.  This is based on the log2() of path.nStep.
*/
int path_search_depth(void){
  int i, j;
  for(i=0, j=1; j<path.nNotHidden; i++, j+=j){}
  return i;
}

/*
** Compute the shortest path between two check-ins and then transfer
** that path into the "ancestor" table.  This is a utility used by
** both /annotate and /finfo.  See also: compute_direct_ancestors().
*/
void path_shortest_stored_in_ancestor_table(
  int origid,     /* RID for check-in at start of the path */
  int cid         /* RID for check-in at the end of the path */
){
  PathNode *pPath;
  int gen = 0;
  Stmt ins;
  pPath = path_shortest(cid, origid, 1, 0, 0);
  db_multi_exec(
    "CREATE TEMP TABLE IF NOT EXISTS ancestor("
    "  rid INT UNIQUE,"
    "  generation INTEGER PRIMARY KEY"
    ");"
    "DELETE FROM ancestor;"
  );

  db_find_and_open_repository(0,0);
  directOnly = find_option("no-merge",0,0)!=0;
  oneWay = find_option("one-way",0,0)!=0;
  if( g.argc!=4 ) usage("VERSION1 VERSION2");
  iFrom = name_to_rid(g.argv[2]);
  iTo = name_to_rid(g.argv[3]);
  p = path_shortest(iFrom, iTo, directOnly, oneWay, 0);
  if( p==0 ){
    fossil_fatal("no path from %s to %s", g.argv[1], g.argv[2]);
  }
  for(n=1, p=path.pStart; p; p=p->u.pTo, n++){
    char *z;
    z = db_text(0,
      "SELECT substr(uuid,1,12) || ' ' || datetime(mtime)"

  if(0==iFrom){
    fossil_fatal("Invalid 'from' RID: 0");
  }else if(0==iTo){
    fossil_fatal("Invalid 'to' RID: 0");
  }
  if( iFrom==iTo ) return;
  path_reset();
  p = path_shortest(iFrom, iTo, 1, revOk==0, 0);
  if( p==0 ) return;
  path_reverse_path();
  db_prepare(&q1,
     "SELECT pfnid, fnid FROM mlink"
     " WHERE mid=:mid AND (pfnid>0 OR fid==0)"
     " ORDER BY pfnid"
  );