Re: Candle Time

[johngg]

I can't find the node at the moment but I remember BrowserUk posting a solution where taking references to substrs of a buffer gave better performance than using unpack. IIRC, this was because unpack had the overhead of re-parseing the template string every time it was invoked. This benchmark seems to bear that out.

use strict;
use warnings;

use Benchmark qw{ cmpthese };
use Test::More qw{ no_plan };

my $buffer    = q{1130508154533};
my $revBuffer = q{3345150805113};

my $template = q{ a3 a2 a2 a2 a2 a2 };

my $rsYr  = \ substr $buffer,  0, 3;
my $rsMon = \ substr $buffer,  3, 2;
my $rsDay = \ substr $buffer,  5, 2;
my $rsHr  = \ substr $buffer,  7, 2;
my $rsMin = \ substr $buffer,  9, 2;
my $rsSec = \ substr $buffer, 11, 2;

open my $dataFH, q{<}, \ <<EOD or die $!;
1130508154533613
EOD
my $start = tell $dataFH;


my %methods = (
   substr => sub {
      seek $dataFH, $start, 0;
      my $rev;
      while ( $buffer = <$dataFH> )
      {
          $rev = join q{},
             $$rsSec, $$rsMin, $$rsHr, $$rsDay, $$rsMon, $$rsYr;
      }
      return $rev;
      },
   unpack => sub {
      seek $dataFH, $start, 0;
      my $rev;
      while ( $buffer = <$dataFH> )
      {
          my @elems = unpack $template, $buffer;
          $rev = join q{}, reverse @elems
      }
      return $rev;
      },
   );
foreach my $method ( sort keys %methods )
{
    ok( $methods{ $method }->() eq $revBuffer, $method );
}

close $dataFH or die $!;

open $dataFH, q{<}, \ <<EOD or die $!;
1130508154533613
1130508160033800
1130508161534113
1130508163034519
1130508164535019
1130508164535019
1130508170035191
1130508171533160
1130508173033660
1130508174534097
1130508180034535
1130424070116695
1130425070118790
1130426070118834
1130427070122888
1130428070123115
1130429070126161
1130430070127538
1130501070128195
1130502070131210
1130503070131969
1130504070135198
EOD

$start = tell $dataFH;

cmpthese(
   -10,
   {
       map
       {
               my $codeStr
                  = q[sub { my $rev = $methods{ ]
                  . $_
                  . q[ }->(); }];
               $_ => eval $codeStr;
       }
       keys %methods
   }
   );

close $dataFH or die $!;

The output.

ok 1 - substr
ok 2 - unpack
          Rate unpack substr
unpack 17980/s     --   -56%
substr 40619/s   126%     --
1..2

I've cocked benchmarks up before so this might be wide of the mark but, hopefully, I have remembered BrowserUk's post correctly and this will be of use.

Update: This is BrowserUk's node that I was remembering.

[Random_Walk]

johngg++ and of course BrowserUK

This is just the kind of cunning solution that I was hoping for

Cheers,
R.