# for each character, count the on bits in that character
my %bits_in;
foreach my $char ( map { chr } 0 .. 255 ) {
    foreach my $bit ( 0 .. 7 ) {
        $bits_in{ $char } += vec( $char, $bit, 1 );
    }
}

my $count;
$count += $bits_in{ $1 } while ( $bools =~ m{([^\000])}g );