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%% taken from: http://user.it.uu.se/~pergu/utf8.erl
%% written by Per Gustafsson http://user.it.uu.se/~pergu
-module(utf8).
-export([from_binary/1, to_binary/1]).
%% Given a binary of UTF-8 encoded text, return a UTF-32 String
%% (i.e. each element is a unicode code point).
from_binary(Bin) ->
decode_binary(Bin, []).
decode_binary(<<>>, Str) ->
{ok, lists:reverse(Str)};
%% 0-7F 0zzzzzzz
decode_binary(<<2#0:1,CodePoint:7,Rest/binary>>, Str) ->
decode_binary(Rest, [CodePoint|Str]);
%% 110yyyyy 10zzzzzz
decode_binary(<<2#110:3,Y:5,2#10:2,Z:6,Rest/binary>>, Str) ->
<<CodePoint:16>> = <<0:5,Y:5,Z:6>>,
decode_binary(Rest, [CodePoint|Str]);
%% 1110xxxx 10yyyyyy 10zzzzzz
decode_binary(<<2#1110:4,X:4,2#10:2,Y:6,2#10:2,Z:6,Rest/binary>>, Str) ->
<<CodePoint:16>> = <<X:4,Y:6,Z:6>>,
decode_binary(Rest, [CodePoint|Str]);
%% 11110www 10xxxxxx 10yyyyyy 10zzzzzz
decode_binary(<<2#11110:5,W:3,2#10:2,X:6,
2#10:2,Y:6,2#10:2,Z:6,Rest/binary>>, Str) ->
<<CodePoint:24>> = <<0:3,W:3,X:6,Y:6,Z:6>>,
decode_binary(Rest, [CodePoint|Str]).
%% Given a list of unicode code points, return a binary of UTF-8
%% encoded text.
to_binary(Str) ->
encode_utf32(Str, []).
encode_utf32([], Utf8) ->
{ok, list_to_binary(lists:reverse(Utf8))};
%% 0-7F 0zzzzzzz -> 0zzzzzzz
encode_utf32([U32|Str], Utf8) when U32 < 16#80 ->
encode_utf32(Str, [U32|Utf8]);
%% 80-7FF yyy yyzzzzzz -> 110yyyyy 10zzzzzz
encode_utf32([U32|Str], Utf8) when U32 < 16#800 ->
<<_:5,Y:5,Z:6>> = <<U32:16>>,
encode_utf32(Str, [<<2#110:3,Y:5,2#10:2,Z:6>>|Utf8]);
%% 800-FFFF xxxxyyyy yyzzzzzz -> 1110xxxx 10yyyyyy 10zzzzzz
encode_utf32([U32|Str], Utf8) when U32 < 16#10000 ->
<<X:4,Y:6,Z:6>> = <<U32:16>>,
encode_utf32(Str, [<<2#1110:4,X:4,2#10:2,Y:6,2#10:2,Z:6>>|Utf8]);
%% 10000-10FFFF wwwxx xxxxyyyy yyzzzzzz -> 11110www 10xxxxxx 10yyyyyy 10zzzzzz
encode_utf32([U32|Str], Utf8) when U32 < 16#110000 ->
<<0:3,W:3,X:6,Y:6,Z:6>> = <<U32:24>>,
encode_utf32(Str, [<<2#11110:5,W:3,2#10:2,X:6,
2#10:2,Y:6,2#10:2,Z:6>>|Utf8]).
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