anchor.diff:  test1() ->
       N = 16#AA,
       InfoHash = list_to_binary(lists:duplicate(20, N)),
  -    PieceSet = allowed_fast(1313, {80,4,4,200}, 7, InfoHash),
  +    {value, PieceSet} = allowed_fast(1313, {80,4,4,200}, 7, InfoHash),
       Pieces = lists:sort(sets:to_list(PieceSet)),
       [287, 376, 431, 808, 1059, 1188, 1217] = Pieces.
   
   test2() ->
       N = 16#AA,
       InfoHash = list_to_binary(lists:duplicate(20, N)),
  -    PieceSet = allowed_fast(1313, {80,4,4,200}, 9, InfoHash),
  +    {value, PieceSet} = allowed_fast(1313, {80,4,4,200}, 9, InfoHash),
       Pieces = lists:sort(sets:to_list(PieceSet)),
       [287, 353, 376, 431, 508, 808, 1059, 1188, 1217] = Pieces.
   
  
positive.code: %%         InfoHash ::= binary() - infohash of torrent.
  %% Description: Compute the allowed fast set for a peer
  %%--------------------------------------------------------------------
  allowed_fast(Sz, {B1, B2, B3, B4}, K, InfoHash) ->
      B = <<B1:8/integer, B2:8/integer, B3:8/integer, B4:8/integer>>,
      allowed_fast(Sz, B, K, InfoHash);
  
negative.code: %%====================================================================
  %% Internal functions
  %%====================================================================
  rnd(0, _X, _Sz, Set) -> {value, Set};
  rnd(K, X, Sz, Set) ->
      %% Start a new round. Each round hashes the previous round to gen.
      %%  a pseudo-random sequence
  