FastMath: faster nearestPowerOfTwo and unit test

jme3-core/src/main/java/com/jme3/math/FastMath.java

@@ -87,8 +87,25 @@ final public class FastMath {
         return (number > 0) && (number & (number - 1)) == 0;
     }
 
+    /**
+     * Get the next power of two of the given number.
+     * 
+     * E.g. for an input 100, this returns 128.
+     * Returns 1 for all numbers <= 1.
+     * 
+     * @param number The number to obtain the POT for.
+     * @return The next power of two.
+     */
     public static int nearestPowerOfTwo(int number) {
-        return (int) Math.pow(2, Math.ceil(Math.log(number) / Math.log(2)));
+        number--;
+        number |= number >> 1;
+        number |= number >> 2;
+        number |= number >> 4;
+        number |= number >> 8;
+        number |= number >> 16;
+        number++;
+        number += (number == 0) ? 1 : 0;
+        return number;
     }
 
     /**

jme3-core/src/test/java/com/jme3/math/FastMathTest.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2009-2015 jMonkeyEngine
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of 'jMonkeyEngine' nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.jme3.math;
+
+import org.junit.Test;
+
+/**
+ * Verifies that algorithms in {@link FastMath} are working correctly.
+ * 
+ * @author Kirill Vainer
+ */
+public class FastMathTest {
+    
+    private int nearestPowerOfTwoSlow(int number) {
+        return (int) Math.pow(2, Math.ceil(Math.log(number) / Math.log(2)));
+    }
+    
+    @Test
+    public void testNearestPowerOfTwo() {
+        for (int i = -100; i < 1; i++) {
+            assert FastMath.nearestPowerOfTwo(i) == 1;
+        }
+        for (int i = 1; i < 10000; i++) {
+            int nextPowerOf2 = FastMath.nearestPowerOfTwo(i);
+            assert i <= nextPowerOf2;
+            assert FastMath.isPowerOfTwo(nextPowerOf2);
+            assert nextPowerOf2 == nearestPowerOfTwoSlow(i);
+        }
+    }
+}