#!/usr/bin/env perl
use strict;
use warnings;

my $data = 0b1111_1111_1111;

my $offset = 8;
my $nibble_mask = 0xF;

while  (not 1<<$offset-1 & $nibble_mask) {
    $data ^= $nibble_mask;
    $nibble_mask <<= 4;
}
$data = $data ^ $nibble_mask;

printf("%b\n",$data);