use strict ; use warnings ;

              #1234567890123456789012345678901234567890123456789012345678901234
my $vlans = '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
             .'ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
             .'ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
             .'fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffe' ;

my $vlan_vec = to_vec($vlans) ; # Convert long hex integer to bit-vector

# VLAN numbers are mapped to/from $vlan_vec by vec($vlan_vec, 1, $vn)

# This scans the bit-vector looking for ranges of VLAN numbers.
#
# Note that we can read one bit beyond the given range, and get 0

my $r = undef ;
my @s = () ;
for my $vn (0..length($vlan_vec) * 8) {
  if (vec($vlan_vec, $vn, 1)) {
    if (!defined($r)) { push @s, "$vn.." ; } ;
    $r = $vn ;
  }
  else {
    if (defined($r))  { $s[-1] .= "$r" ;  $r = undef ; } ;
  } ;
} ;

print "Ranges: ", join(', ', @s), "\n" ;

# Convert long hex integer to bit-vector.
#
# Combination of 'h*' and reverse gives bits in right order in the bit-vector. 

sub to_vec {
  my ($hex) = @_ ;
  $hex =~ s/^0x// ;
  return pack('h*', scalar reverse $hex) ;
} ;

# Convert bit-vector to long integer.  Again 'h*' and reverse sorts out bit order.

sub from_vec {
  my ($vec) = @_ ;
  return '0x'. scalar reverse(unpack('h*', $vec)) ;
} ;