codepoint.erl

-module(codepoint).
-export([codepoint_to_utf8/1, test/0]).

%% See: http://en.wikipedia.org/wiki/Utf-8#Description
%% TODO: endianess

codepoint_to_utf8(CP) when CP =< 16#7F ->
    [CP];

codepoint_to_utf8(CP) when CP =< 16#7FF ->
    [2#11000000 bor (CP bsr 6),
     2#10000000 bor (CP band 2#111111)];

codepoint_to_utf8(CP) when CP =< 16#FFFF ->
    [2#11100000 bor (CP bsr 12),
     2#10000000 bor ((CP bsr 6) band 2#111111),
     2#10000000 bor (CP band 2#111111)];

codepoint_to_utf8(CP) when CP =< 16#10FFFF ->
    [2#11110000 bor (CP bsr 18),
     2#10000000 bor ((CP bsr 12) band 2#111111),
     2#10000000 bor ((CP bsr 6) band 2#111111),
     2#10000000 bor (CP band 2#111111)].


test() ->
    " " = codepoint_to_utf8(32),
    "Ï" = codepoint_to_utf8(207),
    "€" = codepoint_to_utf8(16#20AC),
    "�" = codepoint_to_utf8(16#FFFD),
    "𐑇" = codepoint_to_utf8(66631),
    ok.