Merge pull request phpredis#1656 from rlunar/HyperLogLogs

Hyper log logs

Author: yatsukhnenko

README.markdown

@@ -33,6 +33,7 @@ If you've found phpredis useful and would like to buy the maintainers a coffee (
    * [Lists](#lists)
    * [Sets](#sets)
    * [Sorted sets](#sorted-sets)
+   * [HyperLogLogs](#hyperloglogs)
    * [Geocoding](#geocoding)
    * [Streams](#streams)
    * [Pub/sub](#pubsub)
@@ -3114,6 +3115,86 @@ while($arr_matches = $redis->zScan('zset', $it, '*pattern*')) {
 }
 ~~~
 
+## HyperLogLogs
+
+### pfAdd
+-----
+
+_**Description**_:  Adds the specified elements to the specified HyperLogLog.
+
+##### *Prototype*  
+~~~php
+$redis->pfAdd($key, Array $elements);
+~~~
+
+##### *Parameters*
+_Key_  
+_Array of values_  
+
+##### *Return value*
+*Integer*:  1 if at least 1 HyperLogLog internal register was altered. 0 otherwise.
+
+##### *Example*
+~~~php
+$redis->pfAdd('hll', ['a', 'b', 'c']); // (int) 1
+$redis->pfAdd('hll', ['a', 'b']); // (int) 0
+~~~
+
+### pfCount
+-----
+
+_**Description**_:  Return the approximated cardinality of the set(s) observed by the HyperLogLog at key(s).
+
+##### *Prototype*  
+~~~php
+$redis->pfCount($key);
+$redis->pfCount(Array $keys);
+~~~
+
+##### *Parameters*
+_Key_ or _Array of keys_  
+
+##### *Return value*
+*Integer*:  The approximated number of unique elements observed via [pfAdd](#pfAdd).
+
+##### *Example*
+~~~php
+$redis->pfAdd('hll1', ['a', 'b', 'c']); // (int) 1
+$redis->pfCount('hll1'); // (int) 3
+
+$redis->pfAdd('hll2', ['d', 'e', 'a']); // (int) 1
+$redis->pfCount('hll2'); // (int) 3
+
+$redis->pfCount(['hll1', 'hll2']); // (int) 5
+~~~
+
+### pfMerge
+-----
+
+_**Description**_:  Merge N different HyperLogLogs into a single one.
+
+##### *Prototype*  
+~~~php
+$redis->pfMerge($destkey, Array $sourceKeys);
+~~~
+
+##### *Parameters*
+_Destination Key_  
+_Array of Source Keys_  
+
+##### *Return value*
+*BOOL*: `TRUE` on success, `FALSE` on error.
+
+##### *Example*
+~~~php
+$redis->pfAdd('hll1', ['a', 'b', 'c']); // (int) 1
+$redis->pfAdd('hll2', ['d', 'e', 'a']); // (int) 1
+
+$redis->pfMerge('hll3', ['hll1', 'hll2']); // true
+
+$redis->pfCount('hll3'); // (int) 5
+~~~
+
 ## Geocoding
 
 ### geoAdd