in reply to 30 Spaces- 1 question

Benchmarks, first the code: (GAK! See post from dchetlin) 
use strict;
use Benchmark qw(cmpthese);

my @x;

$x[0]= "mark " x 35;
$x[1]= "asdfasdfasdfasdfasdf " x 35;
$x[2]= "as " x 31;
$x[3]= "asdfasdfasdfasdfasdfasdf " x 100;
$x[4]= "asdfasdfasdfasdfasdfasdf " x 10;

# http://www.cpan.org/doc/manual/html/pod/perlfunc/index.html
#
# Well, that was no help... fricking http conventions
#

cmpthese (1000000, {

'regexp' => ' foreach (@x) {
        /^((?:\S+\s*){1,30})/;
        print $1;
} ',

'split_join' => ' foreach (@x) {
        print join ( " ", (split " ", $_,31)[0..29] );
} ',

'for_index_substr' => ' foreach (@x) {
        my $ind = index ($_, " ");
        for (0..29) {
                last if $ind == -1;
                $ind = index $_, " ", $ind;
        }
        print substr($_,0,$ind);
} ',
} );

[download]

and now the results (basically, a huge fricking waste of time, we are talking a MILLION reps on p166 here.) 

                    Rate       split_join for_index_substr           regexp
split_join       69061/s               --              -7%              -7%
for_index_substr 73910/s               7%               --              -1%
regexp           74627/s               8%               1%               --
### second run, no changes... hmmm....
                    Rate for_index_substr       split_join           regexp
for_index_substr 68027/s               --              -9%              -9%
split_join       74349/s               9%               --              -0%
regexp           74516/s              10%               0%               --

At those rates, any of those would likely be waiting on the harddrive to feed them data. My dataset is about 3.5kB so that means 232MB/s feedrate on the WORST run there and 255MB/s on the best. =) Do it anyway you want. Not going to matter, not one iota, in the long run.

--
$you = new YOU;
honk() if $you->love(perl)

Replies are listed 'Best First'.
(dchetlin: Benchmark fixes) 30 Spaces- 1 question
by dchetlin (Friar) on Oct 10, 2000 at 06:40 UTC
    Hmm. Sorry to be the parade-rainer, but the benchmark isn't actually measuring what it should be. @x is a lexical here, and when Benchmark takes those strings and evaluates them, @x is out of scope. That's why they're all going so fast; there's nothing to loop over.

    Also, and more minorly, your for_index_substr routine isn't working -- $_ is being re-aliased on the second for loop and the actual target string is being lost.

    I took the liberty of making a couple of changes and re-running: 

    use strict;
use Benchmark qw(cmpthese);

my @x;
my @result;

$x[0]= "mark " x 35;
$x[1]= "asdfasdfasdfasdfasdf " x 35;
$x[2]= "as " x 31;
$x[3]= "asdfasdfasdfasdfasdfasdf " x 100;
$x[4]= "asdfasdfasdfasdfasdfasdf " x 10;

cmpthese (-5, {
    'regexp' =>
        sub {
            my $i;
            foreach (@x) {
                /^((?:\S+\s*){1,30})/;
                $result[$i++]{REx} = $1;
            }
        },
    'split_join' =>
        sub {
            my $i;
            foreach (@x) {
                $result[$i++]{split} =
                    join " ", (split " ", $_,31)[0..29];
            }
        },
    'for_index_substr' =>
        sub {
            my $i;
            foreach (@x) {
                my $ind = index ($_, " ");
                for my $foo (0..28) {
                    last if $ind == -1;
                    $ind = index $_, " ", $ind + 1;
                }
                $result[$i++]{index} = substr($_,0,$ind);
            }
        },
} );

for (@result) {
    print "bad!" unless ($_{REx} eq $_{split} and
                         $_{split} eq $_{index});
}

    [download]

    This produces: 

                       Rate       split_join for_index_substr           regexp
split_join       4294/s               --              -7%             -27%
for_index_substr 4618/s               8%               --             -21%
regexp           5849/s              36%              27%               --

    -dlc

[reply]
[d/l]
[select]

      *sigh* That will teach me, eh? I should have run it with it not printing to STDERR and that piped to /dev/null =)

      Also, in my defense, it was after my bedtime =) Don't apologize for being sharp...

      What is worse it that I tested a working version of the for_index_substr but "cleaned it up" for the final run.

      I normally use vars ... to avoid the scope issue. =( *woe is me*

      OTOH, I don't get your numbers when running your code. Number one, your results check should be: 

      foreach (@result) {
        print "bad!" unless ($_->{REx} eq $_->{split} and
                $_->{split} eq $_->{index});
}

      [download]

      Those arrows are important. Second, the comparison will always fail because your regex includes the terminal space and the split version doesn't. Also, if there were multiple spaces or other types of whitespace they would fail but we both agreed to ignore that. =)

      Third, I still get equivalent results, (split_join_2 has the non-magical /\s+/ regex, just for fun. I get this with cmpthese 20,000. (using cmpthese -10 gives the equivalent results.) 

                         Rate split_join_2   split_join        regexp for_index_substr
split_join_2     3205/s           --          -0%           -4%              -6%
split_join       3205/s           0%           --           -4%              -6%
regexp           3344/s           4%           4%            --              -2%
for_index_substr 3413/s           6%           6%            2%               --

      Worse, the array slice hack on the end of (split...)[0..29] throws warnings on -w if there are too few items in the slice to join. Join doesn't like undef it appears =)

      All in all, I'm now less enlightened now. Did I cut-n-paste wrong? I print debugged to verify that bits were working all thru it. *sigh*

      --
      $you = new YOU;
      honk() if $you->love(perl)

[reply]
[d/l]
[select]

        Hmm, that was dumb of me. But as you point out, as long as we know it's working, the comparison is unnecessary anyways.

        I'm much more intrigued that you're getting different results than I am. What version of Perl are you running? 

        [~] $ perl -v

This is perl, v5.6.0 built for i686-linux
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2000, Larry Wall

Binary build 618 provided by ActiveState Tool Corp. http://www.ActiveS
+tate.com
Built 04:53:25 Sep 14 2000

        [download]

        Update: Hmm. I can't get any consistency out of this benchmark. Out of the various machines I tried it on, the REx solution is about half of the time way ahead of the pack, and the other half they're all about the same. Weird. Eerie.

        -dlc

[reply]
[d/l]
RE: Re: 30 Spaces- 1 question
by AgentM (Curate) on Oct 09, 2000 at 18:59 UTC
[reply]

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