[erlang-questions] Parsing binaries performance

[Sebastian Dehne]

Thanks for all the comments and explanations. Results: without changing 
my suggested code (posted in the first message in the thread), I 
upgraded to the latest version which did the test within 250ms. After 
enabling +native, I got even 90ms. This doesn't match Java's 21ms, but 
that's fine with me. (I like Erlang for all the other goodies!) 90ms is 
much batter than 1500ms which I got first. Thanks!

Sebastian


On 06/26/2008 10:48 AM, Per Gustafsson wrote:
> I would suggest that you update your system to R12B-3. On my computer 
> your program is roughly 6 times faster on R12B-3 than on R11B-5 this is 
> due to a specific optimization for this kind of code. It will still be 
> slower than the Java code, but if you use native compilation it should 
> approach the same speed.
> 
> Per
> 
> 
> Sebastian Dehne wrote:
>> Hello list,
>>
>> I'm trying to write a parser in Erlang for a byte-stream (which I 
>> receive from the TCP socket), but I realise that my code is slow 
>> compared to the java version which I have. I've attached both version.
>>
>> The java prints version:
>> Done: 93
>>
>> The erlang version prints:
>> $ erl
>> Erlang (BEAM) emulator version 5.5.5 [source] [async-threads:0] 
>> [kernel-poll:false]
>>
>> Eshell V5.5.5  (abort with ^G)
>> 1> c(test).
>> {ok,test}
>> 2> Data1 = <<"Somestringcontainingcrlf\r\nandsomemoretextbehind\r\n">>.
>> <<"Somestringcontainingcrlf\r\nandsomemoretextbehind\r\n">>
>> 3>
>> 3> test:testwrapper(Data1, 500000).
>> Erlang Elapsed 1570 (runtime) 1586 (wall clock) milliseconds
>> ok
>>
>> Both tests are run on the same machine. I also run the test several 
>> times. Quite a difference between 93ms and 1586ms.
>>
>> What am I doing wrong? How should I write the code in Erlang such that 
>> it matches the performance of Java?
>>
>>
>> Thanks
>>
>> Sebastian
>> ------------------------------------------------------------------------
>>
>> import java.io.File;
>> import java.io.FileInputStream;
>> import java.io.IOException;
>> import java.util.ArrayList;
>> import java.util.LinkedList;
>> import java.util.List;
>>
>> public class Test {
>>     public static void main(String[] args) throws Exception {
>>         test2();
>>     }
>>
>>     public static void test2() throws Exception {
>>         final byte[] data = 
>> "Somestringcontainingcrlf\r\nandsomemoretextbehind\r\n".getBytes();
>>
>>         long start = System.currentTimeMillis();
>>         for (int i = 0; i < 500000; i++) {
>>             if (findPos(data) == -1) {
>>                 throw new Exception("Error");
>>             }
>>         }
>>         System.out.println("Done: " + (System.currentTimeMillis() - 
>> start));
>>     }
>>
>>     public static int findPos(byte[] data) {
>>         boolean cr_found = false;
>>         int pos = 0;
>>         for (byte b : data) {
>>             ++pos;
>>             if (b == '\r') {
>>                 cr_found = true;
>>             } else if (cr_found && b == '\n') {
>>                 return pos;
>>             } else {
>>                 cr_found = false;
>>             }
>>         }
>>         return -1;
>>     }
>>
>> }
>>
>>   
>> ------------------------------------------------------------------------
>>
>> -module(test).
>> -compile(export_all).
>>
>> testwrapper(Data, I) ->
>>   statistics(runtime),
>>   statistics(wall_clock),
>>   test(Data, I),
>>   {_, Time1} = statistics(runtime),
>>   {_, Time2} = statistics(wall_clock),
>>   io:format("Erlang Elapsed ~p (runtime) ~p (wall clock) 
>> milliseconds~n", [Time1, Time2]).
>>
>> test(_Data, 0) ->
>>   done;
>> test(Data, I) ->
>>   {true, _Pos} = find_crlf_or_end(Data, 0),
>>   test(Data, I - 1).
>>
>> % Find the position of the first '\r\n'
>> find_crlf_or_end(<<$\r, $\n, _/binary>>, Pos) ->
>>   {true, Pos};
>> find_crlf_or_end(<<_, Rest/binary>>, Pos) ->
>>   find_crlf_or_end(Rest, Pos + 1);
>> find_crlf_or_end(<<>>, Pos) ->
>>   {true, Pos}.
>>
>>
>>   
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> erlang-questions mailing list
>> erlang-questions@REDACTED
>> http://www.erlang.org/mailman/listinfo/erlang-questions
>