use strict;
use warnings;

use 5.014;

my $str = q{};
$str   .= chr for 0 .. 31;
say qq{\n}, q{| . . . ^ . . . } x 4; 
say unpack q{H*}, $str;

for my $len ( 8, 4, 2 )
{
    say qq{\nChecking groups of $len};
    my $quant  = $len - 1;
    my @groups =
       map { \ substr $str, $_ * $len, $len }
       0 .. ( length( $str ) / $len ) - 1;

    for my $idx ( 0 .. $#groups )
    {
        say
           qq{Found @{ [ unpack q{H*}, $1 ] } },
           qq{at offset @{ [ $len * $idx ] }}
           if ${ $groups[ $idx ] } =~ m{((.)\2{$quant})};
    }
}

substr $str,  0, 2, qq{\x3e\x3e};
substr $str, 16, 8, qq{\xac} x 8;
substr $str,  4, 4, qq{\x7f} x 4;
substr $str, 26, 4, qq{\x45} x 4;
say qq{\n}, q{| . . . ^ . . . } x 4; 
say unpack q{H*}, $str;

for my $len ( 8, 4, 2 )
{
    say qq{\nChecking groups of $len};
    my $quant  = $len - 1;
    my @groups =
       map { \ substr $str, $_ * $len, $len }
       0 .. ( length( $str ) / $len ) - 1;

    for my $idx ( 0 .. $#groups )
    {
        say
           qq{Found @{ [ unpack q{H*}, $1 ] } },
           qq{at offset @{ [ $len * $idx ] }}
           if ${ $groups[ $idx ] } =~ m{((.)\2{$quant})};
    }
}