Issue 4067 - Make filter "keys" generated for element hiding filters numeric

lib/filterListener.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 217 matching lines @@
   if (!len)
     return;
 
   let current = (Math.random() * len) | 0;
   let step;
   do
   {
     step = primes[(Math.random() * primes.length) | 0];
   } while (len % step == 0);
 
   for (let i = 0; i < len; i++, current = (current + step) % len)

[kzar, 2016/05/24 12:36:49]

I didn't intuitively understand that this should work, so I tried it out on a
piece of paper. Unless I'm missing something it's not working right, I keep
getting the filters back in sequential order, just starting from a random index?

Take this example:

selectors: ["a", "b", "c", "d", "e", "f"]
len: 6
prime: 61
current: 3

3                  = 3
(3 + 61) % 6       = 4
(4 + 61) % 6       = 5
(5 + 61) % 6       = 0
(0 + 61) % 6       = 1
(1 + 61) % 6       = 2

[Wladimir Palant, 2016/05/24 12:49:50]

That's because 61%6 happens to be 1. On the other hand, 47%6 is 5 so with this
prime you will get reverse order (3, 2, 1, 0, 5, 4). Either way, this is only an
issue if the array length is smaller than the prime used which shouldn't
normally be the case - our filter lists are considerably larger than the primes
used here.

So e.g. with len 7 and prime 3 you get (3, 6, 2, 5, 1, 4, 0).

[kzar, 2016/05/24 12:57:45]

Acknowledged.

     addFilter(filters[current]);
 }
 
 function onSubscriptionAdded(subscription)
 {
   FilterListener.setDirty(1);
 
   if (!subscription.disabled)
   {
-    subscription.filters.forEach(addFilter);
+    addFilters(subscription.filters);
     flushElemHide();
   }
 }
 
 function onSubscriptionRemoved(subscription)
 {
   FilterListener.setDirty(1);
 
   if (!subscription.disabled)
   {
     subscription.filters.forEach(removeFilter);
     flushElemHide();
   }
 }
 
 function onSubscriptionDisabled(subscription, newValue)
 {
   FilterListener.setDirty(1);
 
   if (subscription.url in FilterStorage.knownSubscriptions)
   {
     if (newValue == false)
-      subscription.filters.forEach(addFilter);
+      addFilters(subscription.filters);
     else
       subscription.filters.forEach(removeFilter);
     flushElemHide();
   }
 }
 
 function onSubscriptionUpdated(subscription)
 {
   FilterListener.setDirty(1);
 
   if (subscription.url in FilterStorage.knownSubscriptions &&
       !subscription.disabled)
   {
     subscription.oldFilters.forEach(removeFilter);
-    subscription.filters.forEach(addFilter);
+    addFilters(subscription.filters);
     flushElemHide();
   }
 }
 
 function onFilterHitCount(filter, newValue)
 {
   if (newValue == 0)
     FilterListener.setDirty(0);
   else
     FilterListener.setDirty(0.002);
@@ skipping 52 matching lines @@
   for (let subscription of FilterStorage.subscriptions)
     if (!subscription.disabled)
       addFilters(subscription.filters);
   flushElemHide();
 }
 
 function onSave()
 {
   isDirty = 0;
 }