-module(iolist).
%% A small part of beam_asm.
-export([encode/2]).
-spec encode(non_neg_integer(), integer()) -> iolist().
encode(Tag, N) when Tag >= 0, N < 0 ->
encode1(Tag, negative_to_bytes(N));
encode(Tag, N) when Tag >= 0, N < 16 ->
(N bsl 4) bor Tag; % not in the specification
encode(Tag, N) when Tag >= 0, N < 16#800 ->
[((N bsr 3) band 2#11100000) bor Tag bor 2#00001000, N band 16#ff];
encode(Tag, N) when Tag >= 0 ->
encode1(Tag, to_bytes(N)).
encode1(Tag, Bytes) ->
case iolist_size(Bytes) of
Num when 2 =< Num, Num =< 8 ->
[((Num-2) bsl 5) bor 2#00011000 bor Tag| Bytes];
Num when 8 < Num ->
[2#11111000 bor Tag, encode(0, Num-9)| Bytes]
end.
to_bytes(N) ->
Bin = binary:encode_unsigned(N),
case Bin of
<<0:1,_/bits>> -> Bin;
<<1:1,_/bits>> -> [0,Bin]
end.
negative_to_bytes(N) when N >= -16#8000 ->
<<N:16>>;
negative_to_bytes(N) ->
Bytes = byte_size(binary:encode_unsigned(-N)),
Bin = <<N:Bytes/unit:8>>,
case Bin of
<<0:1,_/bits>> -> [16#ff,Bin];
<<1:1,_/bits>> -> Bin
end.
