use strict;

srand(2);

# create a random string of 1's and 0's (string length = $l) 
sub make_rand_str{
  my ($l) = @_;

  if ($l%8!=0){
    print STDERR "not a divider of a byte 8-bits)\n";
    die;
  }

  my $res = '';
  for (1..$l){
    $res .= int(rand(2));
  }
  return $res;
}

# take a string and randomly flip 1's/0's for  <= $n number of positions
sub flip {

  my ($n,$str) = @_;

  my $res = '';
  my @str = split("",$str);
  for (0..($n-1)){
    my $i = int(rand(length($str)-1));
    $str[$i] = ($str[$i] eq '1' ? '0': '1' );
  }

  return join("", @str);
}


# pack the string

sub pack_str {
  my ($s) = @_;

  my $res = '';
  my @str = split("",$s);
  for(my $i=0; $i<@str; $i+=8){
    my $st = join("",@str[$i..($i+7)]);
    $res .= pack('B8',$st);
  }
  return $res;
}




#------------------------Main---------------------#


# though the string length here is set to 80 in reality it is anywhere between 300-1000

my $str_len = 80;

my $num_of_flips = int($str_len * 0.25);

my $randstr = &make_rand_str($str_len);
print $randstr . "\n";

open(UNPACKED,">", "unpacked.str") || die $!;
open(PACKED,">:raw", "packed.str") || die $!;


for (1..1000){
  my $mut_str = &flip($num_of_flips,$randstr);
  print UNPACKED "$mut_str\n";
  my $packed_str = &pack_str($mut_str);
  print PACKED "$packed_str";
}


close UNPACKED;
close PACKED;


system("cat unpacked.str | gzip -9 -c - > unpacked.str.gz");
system("cat packed.str | gzip -9 -c - > packed.str.gz");



##</code><code>##

 
bytes  file
-----------------
11000  packed.str
9979   packed.str.gz
81000  unpacked.str
12777  unpacked.str.gz