Round numbers, add to_binary function, add comments

Integrate a patch from Jon Kristensen:

"We rounded the number to remove an error, added a function to_binary/1
which converted a UUID string to binary and commented your functions a
little bit."

Author: travis

uuid.erl

@@ -1,21 +1,21 @@
 % Copyright (c) 2008, Travis Vachon
 % All rights reserved.
-%  
+%
 % Redistribution and use in source and binary forms, with or without
 % modification, are permitted provided that the following conditions are
 % met:
-%  
+%
 %     * Redistributions of source code must retain the above copyright
 %       notice, this list of conditions and the following disclaimer.
-%  
+%
 %     * Redistributions in binary form must reproduce the above copyright
 %       notice, this list of conditions and the following disclaimer in the
 %       documentation and/or other materials provided with the distribution.
-%  
+%
 %     * Neither the name of the author nor the names of its contributors
 %       may be used to endorse or promote products derived from this
 %       software without specific prior written permission.
-%  
+%
 % THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 % "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 % LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
@@ -27,17 +27,33 @@
 % LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 % NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 % SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-%  
+%
 -module(uuid).
--export([v4/0, to_string/1, get_parts/1]).
+-export([v4/0, to_string/1, get_parts/1, to_binary/1]).
 -import(random).
 
+% Generates a random binary UUID.
 v4() ->
-    v4(random:uniform(math:pow(2, 48)) - 1, random:uniform(math:pow(2, 12)) - 1, random:uniform(math:pow(2, 32)) - 1, random:uniform(math:pow(2, 30)) - 1).
+  v4(random:uniform(round(math:pow(2, 48))) - 1, random:uniform(round(math:pow(2, 12))) - 1, random:uniform(round(math:pow(2, 32))) - 1, random:uniform(round(math:pow(2, 30))) - 1).
 v4(R1, R2, R3, R4) ->
     <<R1:48, 4:4, R2:12, 2:2, R3:32, R4: 30>>.
+
+% Returns a string representation of a binary UUID.
 to_string(U) ->
     lists:flatten(io_lib:format("~8.16.0b-~4.16.0b-~4.16.0b-~2.16.0b~2.16.0b-~12.16.0b", get_parts(U))).
 
+% Returns the 32, 16, 16, 8, 8, 48 parts of a binary UUID.
 get_parts(<<TL:32, TM:16, THV:16, CSR:8, CSL:8, N:48>>) ->
     [TL, TM, THV, CSR, CSL, N].
+
+% Converts a UUID string in the format of 550e8400-e29b-41d4-a716-446655440000
+% (with or without the dashes) to binary.
+to_binary(U)->
+    convert(lists:filter(fun(Elem) -> Elem /= $- end, U), []).
+
+% Converts a list of pairs of hex characters (00-ff) to bytes.
+convert([], Acc)->
+    list_to_binary(lists:reverse(Acc));
+convert([X, Y | Tail], Acc)->
+    {ok, [Byte], _} = io_lib:fread("~16u", [X, Y]),
+    convert(Tail, [Byte | Acc]).