Merge pull request ckknight#10 from pariser/mt-with-index

Add getUseCount() method to mt19937 engine

Author: ckknight

lib/random.js

@@ -111,6 +111,7 @@
       function mt19937() {
         var data = new Int32Array(624);
         var index = 0;
+        var uses = 0;
 
         function next() {
           if ((index | 0) >= 624) {
@@ -120,9 +121,14 @@
 
           var value = data[index];
           index = (index + 1) | 0;
+          uses += 1;
           return temper(value) | 0;
         }
+        next.getUseCount = function() {
+          return uses;
+        };
         next.discard = function (count) {
+          uses += count;
           if ((index | 0) >= 624) {
             refreshData(data);
             index = 0;
@@ -143,6 +149,7 @@
             data[i] = previous = (imul((previous ^ (previous >>> 30)), 0x6c078965) + i) | 0;
           }
           index = 624;
+          uses = 0;
           return next;
         };
         next.seedWithArray = function (source) {