%% -*- erlang-indent-level: 2 -*-
%%--------------------------------------------------------------------
-module(bs_split).
-export([test/0]).
test() ->
Funs = [fun byte_split_binary/0, fun bit_split_binary/0, fun z_split/0],
lists:foreach(fun (F) -> ok = F() end, Funs).
%%--------------------------------------------------------------------
byte_split_binary() ->
L = lists:seq(0, 57),
B = mkbin(L),
byte_split(L, B, byte_size(B)).
byte_split(L, B, Pos) when Pos >= 0 ->
Sz1 = Pos,
Sz2 = byte_size(B) - Pos,
bs1(L, B, Pos, Sz1, Sz2);
byte_split(_, _, _) -> ok.
bs1(L, B, Pos, Sz1, Sz2) ->
<<B1:Sz1/binary, B2:Sz2/binary>> = B,
bs2(L, B, Pos, B1, B2).
bs2(L, B, Pos, B1, B2) ->
B1 = list_to_binary(lists:sublist(L, 1, Pos)),
bs3(L, B, Pos, B2).
bs3(L, B, Pos, B2) ->
B2 = list_to_binary(lists:nthtail(Pos, L)),
byte_split(L, B, Pos - 1).
%%--------------------------------------------------------------------
bit_split_binary() ->
Fun = fun(Bin, List, SkipBef, N) ->
SkipAft = bit_size(Bin) - N - SkipBef,
%% io:format("~p, ~p, ~p", [SkipBef,N,SkipAft]),
<<_I1:SkipBef,OutBin:N/binary-unit:1,_I2:SkipAft>> = Bin,
OutBin = make_bin_from_list(List, N)
end,
bit_split_binary1(Fun, erlang:md5(<<1,2,3>>)).
bit_split_binary1(Action, Bin) ->
BitList = bits_to_list(binary_to_list(Bin), 16#80),
bit_split_binary2(Action, Bin, BitList, 0).
bit_split_binary2(Action, Bin, [_|T]=List, Bef) ->
bit_split_binary3(Action, Bin, List, Bef, bit_size(Bin)),
bit_split_binary2(Action, Bin, T, Bef+1);
bit_split_binary2(_Action, _Bin, [], _Bef) -> ok.
bit_split_binary3(Action, Bin, List, Bef, Aft) when Bef =< Aft ->
Action(Bin, List, Bef, (Aft-Bef) div 8 * 8),
bit_split_binary3(Action, Bin, List, Bef, Aft - 8);
bit_split_binary3(_, _, _, _, _) -> ok.
make_bin_from_list(_List, 0) ->
mkbin([]);
make_bin_from_list(List, N) ->
list_to_binary([make_int(List, 8, 0),
make_bin_from_list(lists:nthtail(8, List), N - 8)]).
make_int(_List, 0, Acc) -> Acc;
make_int([H|T], N, Acc) -> make_int(T, N-1, Acc bsl 1 bor H).
bits_to_list([_|T], 0) -> bits_to_list(T, 16#80);
bits_to_list([H|_]=List, Mask) ->
[case H band Mask of
0 -> 0;
_ -> 1
end|bits_to_list(List, Mask bsr 1)];
bits_to_list([], _) -> [].
mkbin(L) when is_list(L) -> list_to_binary(L).
%%--------------------------------------------------------------------
%% Splits a series of null terminated segments of a binary without
%% creating any new sub-binaries until the zero is found.
z_split() ->
[<<61,62,63>>] = z_split(<<61,62,63>>),
[<<61,62,63>>, <<>>] = z_split(<<61,62,63,0>>),
[<<61,62,63>>, <<64>>] = z_split(<<61,62,63,0,64>>),
[<<61,62,63>>, <<64,65,66>>] = z_split(<<61,62,63,0,64,65,66>>),
[<<61,62>>, <<64>>, <<>>, <<65,66>>] = z_split(<<61,62,0,64,0,0,65,66>>),
ok.
z_split(B) when is_binary(B) ->
z_split(B, 0).
z_split(B, N) ->
case B of
<<_B1:N/binary,0,_B2/binary>> -> % use skip_bits for B1, B2
<<B1:N/binary,_,B2/binary>> = B, % and postpone the matching
[B1 | z_split(B2)];
<<_:N/binary>> ->
[B];
_ ->
z_split(B, N + 1)
end.
