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+%% @author Bob Ippolito <bob@mochimedia.com>
+%% @copyright 2006 Mochi Media, Inc.
+
+%% @doc Utilities for working with hexadecimal strings.
+
+-module(mochihex).
+-author('bob@mochimedia.com').
+
+-export([to_hex/1, to_bin/1, to_int/1, dehex/1, hexdigit/1]).
+
+%% @type iolist() = [char() | binary() | iolist()]
+%% @type iodata() = iolist() | binary()
+
+%% @spec to_hex(integer | iolist()) -> string()
+%% @doc Convert an iolist to a hexadecimal string.
+to_hex(0) ->
+    "0";
+to_hex(I) when is_integer(I), I > 0 ->
+    to_hex_int(I, []);
+to_hex(B) ->
+    to_hex(iolist_to_binary(B), []).
+
+%% @spec to_bin(string()) -> binary()
+%% @doc Convert a hexadecimal string to a binary.
+to_bin(L) ->
+    to_bin(L, []).
+
+%% @spec to_int(string()) -> integer()
+%% @doc Convert a hexadecimal string to an integer.
+to_int(L) ->
+    erlang:list_to_integer(L, 16).
+
+%% @spec dehex(char()) -> integer()
+%% @doc Convert a hex digit to its integer value.
+dehex(C) when C >= $0, C =< $9 ->
+    C - $0;
+dehex(C) when C >= $a, C =< $f ->
+    C - $a + 10;
+dehex(C) when C >= $A, C =< $F ->
+    C - $A + 10.
+
+%% @spec hexdigit(integer()) -> char()
+%% @doc Convert an integer less than 16 to a hex digit.
+hexdigit(C) when C >= 0, C =< 9 ->
+    C + $0;
+hexdigit(C) when C =< 15 ->
+    C + $a - 10.
+
+%% Internal API
+
+to_hex(<<>>, Acc) ->
+    lists:reverse(Acc);
+to_hex(<<C1:4, C2:4, Rest/binary>>, Acc) ->
+    to_hex(Rest, [hexdigit(C2), hexdigit(C1) | Acc]).
+
+to_hex_int(0, Acc) ->
+    Acc;
+to_hex_int(I, Acc) ->
+    to_hex_int(I bsr 4, [hexdigit(I band 15) | Acc]).
+
+to_bin([], Acc) ->
+    iolist_to_binary(lists:reverse(Acc));
+to_bin([C1, C2 | Rest], Acc) ->
+    to_bin(Rest, [(dehex(C1) bsl 4) bor dehex(C2) | Acc]).
+
+
+
+%%
+%% Tests
+%%
+-include_lib("eunit/include/eunit.hrl").
+-ifdef(TEST).
+
+to_hex_test() ->
+    "ff000ff1" = to_hex([255, 0, 15, 241]),
+    "ff000ff1" = to_hex(16#ff000ff1),
+    "0" = to_hex(16#0),
+    ok.
+
+to_bin_test() ->
+    <<255, 0, 15, 241>> = to_bin("ff000ff1"),
+    <<255, 0, 10, 161>> = to_bin("Ff000aA1"),
+    ok.
+
+to_int_test() ->
+    16#ff000ff1 = to_int("ff000ff1"),
+    16#ff000aa1 = to_int("FF000Aa1"),
+    16#0 = to_int("0"),
+    ok.
+
+-endif.