title: redis HLL too many false positives
body: <p>Hyperlog log is a probablistic algorithm 
  According to the redis HLL document , we could get 0.81% of error but I get errors like 17-20% </p>
  
  <p>I think there is something wrong .. This is my simple perl test script. Is there some error  </p>
  
  <pre><code>#!/usr/bin/perl -w                                                                                                                                                       
  use Redis;
  my $redis = Redis-&gt;new(server=&gt;'192.168.50.166:6379') or die;
  my $fp=0;
  my $HLL="HLL";
  
  $redis-&gt;del($HLL);
  foreach my $i (1..10000) {
    my $s1 = $redis-&gt;pfadd($HLL,$i);
    if($s1 == 0){ 
      print "False positive on $i\n";
      $fp++;
    }
  }
  print "count of false positives $fp\n";
  </code></pre>