Question

Can anybody explain the following Perl code for me, please?
I think its in Perl and I have no clue about Perl programming. Please explain what the following code does?

$t = test(10);
sub test() {
  my $str = unpack("B32", pack("N",shift));
  $str2 = substr($str,16,length($str));
  return $str2;
}

Answer 1

The pack, unpack and substr functions are documented here, here and here, respectively.

pack("N"...) packs a number into a four-byte network-order representation. unpack("B32"...) unpacks this packed number as a string of bits (zeros and ones). The substr call takes the second half of this bit string (from bit 16 onwards), which represents the lower 16 bits of the original 32-bit number.

Why it does it this way is a mystery to me. A simpler and faster solution is to deal with the lower 16 bits at the outset (note the lower case "n"):

sub test($) {
  return unpack("B16", pack("n",shift));
}