Extracting a set of values from a single integer

Question

I have a number of things (let's call them nodes... it doesn't matter), conveniently referred to as node1, node2, ... nodeN.

The tricky part is that i need have a perl subroutine that takes an integer that refers to a set of nodes. My approach is this:

1. Each node is given a value based on powers of 2, like this:

   • node1 = 1
   • node2 = 2
   • node3 = 4
   • node4 = 8
   • ...
   • node8 = 128
   • etc

2. The value for each node is added up to produce an integer. For example, nodes 1, 3, 4 and 7 results in as integer of 77.

Now, how would I go about creating a subroutine that takes an integer like that and returns an array of node numbers?

---

PS:

• The maximum amount of nodes is configurable. 16 is a reasonable max.
• If I am approaching this an overly cumbersome way, I'm open to suggestions for a better way of producing a set of nodes from a single value.

Answer 1

Set $max to the number of nodes (e.g. 16).

sub nodes {
    my $num = shift;
    return grep { $num & 2 ** $_ } 1 .. $max - 1;
}