anchor.diff:      set_bitmap(R, I + 1, B1).
   
   get_bitmap(Pos, M = #mfile{bitmaps = BMPs}) ->
  -    case maps:find(Pos, BMPs) of
  +    case btrie:find(<<Pos:32>>, BMPs) of
           {ok, B} ->
               {B, M};
           error ->
  
positive.code:     update_btime(F).
  
  write_bitmap(F = #mfile{otime = OTime, name = File, bitmaps = BMPs}) ->
      case {maps:size(BMPs), filelib:last_modified(File ++ ".bitmap")} of
          {0, _} ->
              F;
          {_, OTimeA} when OTimeA =< OTime ->
  
negative.code:           index = btrie:new(),
            next = 0,
            otime = undefined,
            bitmaps = btrie:new()
           }).
  -opaque mfile() :: #mfile{}.
  
  