use strict;
use warnings;

use feature qw{ say };
my $sep = sub { say q{-} x 24; };

my $baseStr = q{{0,f}};
my $width   = 4;
my $globStr = $baseStr x $width;

$sep->();
foreach my $offset ( 3, 5, 8, 9 )
{
    say qq{Offset - $offset};
    my @bitStrs = map { pack q{H*}, $_ } glob $globStr;

    my $div           = int( $offset / 4 );
    my $rem           = $offset % 4;
    my $nybblesToMask = $div + ( $rem ? 1 : 0 );
    my $mask          = pack q{H*},
       q{f} x ( $width - $nybblesToMask ) . q{0} x $nybblesToMask;

    say q{Mask         - }, unpack qq{B@{ [ $width * 4 ]}}, $mask;
    say q{Element 5    - }, unpack qq{B@{ [ $width * 4 ]}}, $bitStrs[ 5 ];
    say q{E. 5 & mask  - }, unpack qq{B@{ [ $width * 4 ]}},
       $bitStrs[ 5 ] & $mask;

    say q{Element 15   - }, unpack qq{B@{ [ $width * 4 ]}}, $bitStrs[ 15 ];
    say q{E. 15 & mask - }, unpack qq{B@{ [ $width * 4 ]}},
       $bitStrs[ 15 ] & $mask;

    $sep->();
}

##</code><code>##

------------------------
Offset - 3
Mask         - 1111111111110000
Element 5    - 0000111100001111
E. 5 & mask  - 0000111100000000
Element 15   - 1111111111111111
E. 15 & mask - 1111111111110000
------------------------
Offset - 5
Mask         - 1111111100000000
Element 5    - 0000111100001111
E. 5 & mask  - 0000111100000000
Element 15   - 1111111111111111
E. 15 & mask - 1111111100000000
------------------------
Offset - 8
Mask         - 1111111100000000
Element 5    - 0000111100001111
E. 5 & mask  - 0000111100000000
Element 15   - 1111111111111111
E. 15 & mask - 1111111100000000
------------------------
Offset - 9
Mask         - 1111000000000000
Element 5    - 0000111100001111
E. 5 & mask  - 0000000000000000
Element 15   - 1111111111111111
E. 15 & mask - 1111000000000000
------------------------