my @luhnmap_1 = (0,2,4,6,8,1,3,5,7,9);
my @luhnmap_2 = ();
for my $x (0..9) {
  for my $y (0..9) {
    @luhnmap_2[$y*10+$x]=$luhnmap_1[$y]+$x;
  }
}

sub LUHN10 {
  my $num = shift;
  my $sum = 0;
  while ($str = substr $num, -2, 2, "") {
    $sum+=$bigmap[$str];
  }
  return $sum % 10 ? 0 : 1;
}