anchor.diff:  %% --------------------------------------------------------------------
   is_pos_code(<<Depth:8,
                 _PathCode:(3*?DEFAULT_MAX_DEPTH)/bits,
  -              _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>) 
  -  when Depth >= ?DEFAULT_MAX_DEPTH -> false; 
  +              _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>)
  +  when Depth >= ?DEFAULT_MAX_DEPTH -> false;
   
  -is_pos_code(<<_Depth:8, 
  +is_pos_code(<<_Depth:8,
                 _PathCode:(3*?DEFAULT_MAX_DEPTH)/bits,
                 _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>)  -> true;
   
  
positive.code: %% @end
  -spec to_pos_code(#ot_node_id{}) -> pos_code().
  %% --------------------------------------------------------------------
  to_pos_code(NId) ->
      Spec = quperl_octree:to_node_list(NId),
      
      {Depth, PosCode} = lists:foldl(fun add_pos_code/2, {0,<<>>}, Spec),
      
      <<Depth,
        PosCode/bits, 0:((?DEFAULT_MAX_DEPTH-Depth)*3),
        0:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)>>.
  
  
  
  
negative.code: %% @author sage
  %% @doc compute and manage a binary position code for a node in an octree.
  %%
  %% <p>Functions to compute and modify an position code, which identifies a specific
  %% node in an octree and is encoded as a binary string, to be used as a key for
  %% object lookups.
  %%
  %% <p>The binary is structured as follows:
  