How do I manipulate arrays of bits?

For example, this sets $vec to have bit N set if $ints[N] was set:

    $vec = '';
    foreach(@ints) { vec($vec,$_,1) = 1 }

And here's how, given a vector in $vec, you can get those bits into your @ints array:

    sub bitvec_to_list {
	my $vec = shift;
	my @ints;
	# Find null-byte density then select best algorithm
	if ($vec =~ tr/\0// / length $vec > 0.95) {
	    use integer;
	    my $i;
	    # This method is faster with mostly null-bytes
	    while($vec =~ /[^\0]/g ) {
		$i = -9 + 8 * pos $vec;
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
		push @ints, $i if vec($vec, ++$i, 1);
	    }
	} else {
	    # This method is a fast general algorithm
	    use integer;
	    my $bits = unpack "b*", $vec;
	    push @ints, 0 if $bits =~ s/^(\d)// && $1;
	    push @ints, pos $bits while($bits =~ /1/g);
	}
	return \@ints;
    }

This method gets faster the more sparse the bit vector is. (Courtesy of Tim Bunce and Winfriend Koenig.)

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