@b = qw[ 1 0 0 0 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
8


@b = qw[ 0 1 1 1 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
7