Optimize MathUtil.align to avoid modulo/division

jol-core/src/main/java/org/openjdk/jol/util/MathUtil.java

@@ -62,19 +62,27 @@ public static int pow2(int power) {
         return p;
     }
 
-    public static int align(int addr, int align) {
-        if ((addr % align) == 0) {
-            return addr;
-        } else {
-            return ((addr / align) + 1) * align;
-        }
+    /**
+     * Aligns the argument to the given alignment.
+     * Alignment should be a power of two.
+     *
+     * @param v value to align
+     * @param a alignment, should be power of two
+     * @return aligned value
+     */
+    public static int align(int v, int a) {
+        return (v + a - 1) & -a;
     }
 
-    public static long align(long addr, int align) {
-        if ((addr % align) == 0) {
-            return addr;
-        } else {
-            return ((addr / align) + 1) * align;
-        }
+    /**
+     * Aligns the argument to the given alignment.
+     * Alignment should be a power of two.
+     *
+     * @param v value to align
+     * @param a alignment, should be power of two
+     * @return aligned value
+     */
+    public static long align(long v, int a) {
+        return (v + a - 1) & -a;
     }
 }

jol-core/src/test/java/org/openjdk/jol/util/MathUtilTest.java

@@ -0,0 +1,60 @@
+package org.openjdk.jol.util;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MathUtilTest {
+
+    static int slowIntAlign(int v, int a) {
+        if (v % a == 0) {
+            return v;
+        } else {
+            return ((v / a) + 1) * a;
+        }
+    }
+
+    static long slowLongAlign(long v, int a) {
+        if (v % a == 0) {
+            return v;
+        } else {
+            return ((v / a) + 1) * a;
+        }
+    }
+
+    @Test
+    public void alignIntTest() {
+        Assert.assertEquals(0, MathUtil.align(0, 2));
+        Assert.assertEquals(2, MathUtil.align(1, 2));
+        Assert.assertEquals(2, MathUtil.align(2, 2));
+        Assert.assertEquals(4, MathUtil.align(3, 2));
+        Assert.assertEquals(4, MathUtil.align(4, 2));
+
+        for (int v = 0; v < 10; v++) {
+            for (int a = 1; a <= 256; a *= 2) {
+                Assert.assertEquals(slowIntAlign(v, a), MathUtil.align(v, a));
+            }
+        }
+    }
+
+    @Test
+    public void alignLongTest() {
+        Assert.assertEquals(0, MathUtil.align(0L, 2));
+        Assert.assertEquals(2, MathUtil.align(1L, 2));
+        Assert.assertEquals(2, MathUtil.align(2L, 2));
+        Assert.assertEquals(4, MathUtil.align(3L, 2));
+        Assert.assertEquals(4, MathUtil.align(4L, 2));
+
+        for (long v = 0; v < 10; v++) {
+            for (int a = 1; a <= 256; a *= 2) {
+                Assert.assertEquals(slowLongAlign(v, a), MathUtil.align(v, a));
+            }
+        }
+
+        for (long v = Integer.MAX_VALUE; v < Integer.MAX_VALUE + 10L; v++) {
+            for (int a = 1; a <= 256; a *= 2) {
+                Assert.assertEquals(slowLongAlign(v, a), MathUtil.align(v, a));
+            }
+        }
+    }
+
+}