I read the A Fresh Look at Efficient Perl Sorting paper last week and have been itching to play with packed default sorting so here we go, packed default verses the example code BrowserUK gave above. Sorting two million random records 10 times.

=>cat /tmp/sorttest
#!/usr/opt/perl5/bin/perl
use strict;
use warnings;
use Benchmark;
 
srand(42); # the answer
my $elements = 2000000;
my %hash;
 
for (1..$elements) {
    my ($key, $one, $two) = rand =~/(\d\.\d{2})(\d{2})(\d{4})/;
    $hash{$key} = [$one, $two];
}
 
sub packed_default {
    my @sorted_keys =
        map substr($_,1), 
        sort map {pack('C', $hash{$_}[0])."$_"} 
        keys %hash;
    return @sorted_keys;
}
 
sub BroweserUK {
    my @sorted_keys = sort{ $hash{$a}[0] <=> $hash{$b}[0] } keys %hash
+;
}
 
timethese(10, {
    'packed_default' => \&packed_default,
    'BroweserUK'     => \&BroweserUK,
});

__end__

Benchmark: timing 10 iterations of BroweserUK, packed_default...
BroweserUK: 0 wallclock secs 
(0.07 usr + 0.00 sys = 0.07 CPU) @ 142.86/s (n=10)
            (warning: too few iterations for a reliable count)

packed_default: 0 wallclock secs 
(0.04 usr + 0.00 sys = 0.04 CPU) @ 250.00/s (n=10)
            (warning: too few iterations for a reliable count)
[download]

As they suggest in the paper coercing perl to use the default sort instead of custom sub is almost twice as fast.

Cheers,
R.