#!perl
use 5.006;

# file: pack.t

use strict;
use warnings;

use Benchmark qw(:all) ;
use Data::Dumper;

use List::Util qw(pairs);

my @diffs = map { $_,$_; } (0..49);
#print '@diffs: ',Dumper(\@diffs),"\n";

my $packed0 = pack('V*',@diffs);
my $a = [];

#print 'len: ',length( $packed0),"\n";

my $packed = $packed0;
while (length( $packed)) {
    push @$a,[unpack ('VV', substr( $packed, 0, 8, ''))];
}

#print Dumper($a);

    timethese( 50_000, {
       'unpack while' => sub {
            my $packed = $packed0;
			while (length( $packed)) {
    			my ($x,$y)= unpack ('VV', substr( $packed, 0, 8, ''));
			}
        },
       'unpack while single' => sub {
            my $packed = $packed0;
			while (length( $packed)) {
    			my $x = unpack ('V', substr( $packed, 0, 4, ''));
			}
        },
       'unpack while push' => sub {
            my $packed = $packed0;
            $a = [];
			while (length( $packed)) {
    			push @$a,[unpack ('VV', substr( $packed, 0, 8, ''))];
			}
        },
       'unpack for' => sub {
        	for ( my $i = 0;$i < length( $packed0)-1; $i += 8 ) {
		    	my ($x,$y)= unpack ('VV', substr( $packed0, $i, 8));
			} 
        }, 
       'unpack for push' => sub {
            $a = [];
        	for ( my $i = 0;$i < length( $packed0)-1; $i += 8 ) {
		    	push @$a,[unpack ('VV', substr( $packed0, $i, 8))];
			} 
        },        
    });
 ########
$ perl pack.t 
Benchmark: timing 50000 iterations of unpack for, unpack for push, unpack while, unpack while push, unpack while single...
unpack for:  1 wallclock secs ( 1.01 usr +  0.00 sys =  1.01 CPU) @ 49504.95/s (n=50000)
unpack for push:  2 wallclock secs ( 1.84 usr +  0.00 sys =  1.84 CPU) @ 27173.91/s (n=50000)
unpack while:  1 wallclock secs ( 0.84 usr +  0.00 sys =  0.84 CPU) @ 59523.81/s (n=50000)
unpack while push:  2 wallclock secs ( 1.75 usr +  0.00 sys =  1.75 CPU) @ 28571.43/s (n=50000)
unpack while single:  1 wallclock secs ( 1.28 usr +  0.00 sys =  1.28 CPU) @ 39062.50/s (n=50000)