$state = $prev | $curr | $next;

if ( FULL == count_bits( $state ) ) {

   # unset these bits in other blocks
   for my $block ( @grid ){
       $block &= ~$state;

       # cache block if appropriate
       if ( TERMINAL == count_bits( $block) ) {
           push @feed_thru, $block;
       }elsif ( FULL == count_bits( $block ) ) {
           push  @propagate, $block;
       }
   }
}