Thanks for everyone above replied.
The max value is always 31, and those input are read from a parsed file.
The output should be (\d+:\d+) so which is required by the Verilog syntax I had to use.
Here is what I have tried. 
sub get_reserved {
  my $bits_ref = shift;
  my @bits = @{$bits_ref};
  
  my @digits = map {
    chomp;
    if ( m/(\d+):(\d+)/) {
      ($1 > $2) ? ($2 .. $1) : ($1 .. $2);
    }
    else {
      $_;
    } 
  } @bits;

  my @reg32set = map {0} 0 .. 31;
  my @index;
  
  if (@digits ne '') {
    map {$reg32set[$_] = 1;} @digits;
    @index = grep {if ($reg32set[$_] == 0) {$_;}} 0..31;
  }
  else {
    undef @index;
  }
}

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In reply to Re^2: screen out an untained array from a special array by Hanken
in thread screen out an untained array from a special array by Hanken

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