Math.Factorial doesn't work

CHANGES.md

@@ -15,6 +15,7 @@ Change Log
 * Fixed a bug where image requests that returned HTTP code 204 would prevent any future request from succeeding on browsers that supported ImageBitmap. [#7914](https://github.com/AnalyticalGraphicsInc/cesium/pull/7914/)
 * Fixed polyline colors when `scene.highDynamicRange` is enabled. [#7924](https://github.com/AnalyticalGraphicsInc/cesium/pull/7924)
 * Fixed a bug in the inspector where the min/max height values of a picked tile were undefined. [#7904](https://github.com/AnalyticalGraphicsInc/cesium/pull/7904)
+* Fixed `Math.factorial` to return the correct values. (https://github.com/AnalyticalGraphicsInc/cesium/pull/7969)
 
 ### 1.58.1 - 2018-06-03
 _This is an npm-only release to fix a publishing issue_.

Source/Core/Math.js

@@ -732,7 +732,9 @@ define([
         if (n >= length) {
             var sum = factorials[length - 1];
             for (var i = length; i <= n; i++) {
-                factorials.push(sum * i);
+                var next = sum * i;
+                factorials.push(next);
+                sum = next;
             }
         }
         return factorials[n];

Specs/Core/MathSpec.js

@@ -383,8 +383,26 @@ defineSuite([
         var factorials = [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000,
                           121645100408832000, 2432902008176640000, 51090942171709440000, 1124000727777607680000, 25852016738884976640000, 620448401733239439360000];
 
-        for ( var i = 0; i < factorials.length; i++) {
-            expect(CesiumMath.factorial(i)).toEqual(factorials[i]);
+        var length = factorials.length;
+        var i;
+        var indices = [];
+
+        // Populate indices array
+        for (i = 0; i < length; i++) {
+            indices.push(i);
+        }
+
+        // Randomize the indices array
+        for (i = 0; i < length; i++) {
+            var tmp = indices[i];
+            var randomIndex = Math.floor(Math.random() * length);
+            indices[i] = indices[randomIndex];
+            indices[randomIndex] = tmp;
+        }
+
+        for (i = 0; i < length; i++) {
+            var index = indices[i];
+            expect(CesiumMath.factorial(index)).toEqual(factorials[index]);
         }
     });