Merge pull request CesiumGS#1287 from AnalyticalGraphicsInc/nextPowerOfTwo

Added Math.nextPowerOfTwo

Author: bagnell

CHANGES.md

@@ -34,6 +34,7 @@ Beta Releases
 * Added `Quaternion.log`, `Quaternion.exp`, `Quaternion.innerQuadrangle`, and `Quaternion.squad`.
 * Added `LinearSpline` and `QuaternionSpline`.
 * Added `perPositionHeight` option to `PolygonGeometry` and `PolygonOutlineGeometry`.
+* Added `Math.nextPowerOfTwo`.
 
 ### b22 - 2013-11-01
 

Source/Core/Math.js

@@ -540,19 +540,50 @@ define([
      *
      * @returns {Boolean} <code>true</code> if the number if a power of two; otherwise, <code>false</code>.
      *
+     * @exception {DeveloperError} A number greater than or equal to 0 is required.
+     *
      * @example
      * var t = CesiumMath.isPowerOfTwo(16); // true
      * var f = CesiumMath.isPowerOfTwo(20); // false
+     */
+    CesiumMath.isPowerOfTwo = function(n) {
+        if (typeof n !== 'number' || n < 0) {
+            throw new DeveloperError('A number greater than or equal to 0 is required.');
+        }
+
+        return (n !== 0) && ((n & (n - 1)) === 0);
+    };
+
+    /**
+     * Computes the next power-of-two integer greater than or equal to the provided positive integer.
+     *
+     * @memberof CesiumMath
+     *
+     * @param {Number} n The positive integer to test.
+     *
+     * @returns {Number} The next power-of-two integer.
      *
      * @exception {DeveloperError} A number greater than or equal to 0 is required.
+     *
+     * @example
+     * var n = CesiumMath.nextPowerOfTwo(29); // 32
+     * var m = CesiumMath.nextPowerOfTwo(32); // 32
      */
-    CesiumMath.isPowerOfTwo = function(n) {
+    CesiumMath.nextPowerOfTwo = function(n) {
         if (typeof n !== 'number' || n < 0) {
             throw new DeveloperError('A number greater than or equal to 0 is required.');
         }
 
-        var m = defaultValue(n, 0);
-        return (m !== 0) && ((m & (m - 1)) === 0);
+        // From http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+        --n;
+        n |= n >> 1;
+        n |= n >> 2;
+        n |= n >> 4;
+        n |= n >> 8;
+        n |= n >> 16;
+        ++n;
+
+        return n;
     };
 
     /**

Specs/Core/MathSpec.js

@@ -140,6 +140,13 @@ defineSuite([
         expect(CesiumMath.isPowerOfTwo(12)).toEqual(false);
     });
 
+    it('nextPowerOfTwo finds next power of two', function() {
+        expect(CesiumMath.nextPowerOfTwo(0)).toEqual(0);
+        expect(CesiumMath.nextPowerOfTwo(257)).toEqual(512);
+        expect(CesiumMath.nextPowerOfTwo(512)).toEqual(512);
+        expect(CesiumMath.nextPowerOfTwo(1023)).toEqual(1024);
+    });
+
     it('factorial throws for non-numbers', function() {
         expect(function() {
             CesiumMath.factorial({});
@@ -185,4 +192,21 @@ defineSuite([
         }).toThrow();
     });
 
+    it('nextPowerOfTwo throws for non-numbers', function() {
+        expect(function() {
+            CesiumMath.nextPowerOfTwo({});
+        }).toThrow();
+    });
+
+    it('nextPowerOfTwo throws for negative numbers', function() {
+        expect(function() {
+            CesiumMath.nextPowerOfTwo(-1);
+        }).toThrow();
+    });
+
+    it('nextPowerOfTwo throws for undefined', function() {
+        expect(function() {
+            CesiumMath.nextPowerOfTwo();
+        }).toThrow();
+    });
 });