From 3e900bb687f0ed8b34f6425e9ad7bdca7e1f6d39 Mon Sep 17 00:00:00 2001
From: Pavel Nikitin <pavel.nikitin@jetbrains.com>
Date: Fri, 19 May 2017 14:39:44 +0200
Subject: [PATCH] optimize MathUtil.integerLogarithm

---
 .../java/jetbrains/exodus/util/MathUtil.java  | 23 ++----------
 .../java/jetbrains/exodus/util/MathTest.java  | 35 +++++++++++++++++++
 2 files changed, 38 insertions(+), 20 deletions(-)
 create mode 100644 utils/src/test/java/jetbrains/exodus/util/MathTest.java

diff --git a/utils/src/main/java/jetbrains/exodus/util/MathUtil.java b/utils/src/main/java/jetbrains/exodus/util/MathUtil.java
index c65897c10..6fb563563 100644
--- a/utils/src/main/java/jetbrains/exodus/util/MathUtil.java
+++ b/utils/src/main/java/jetbrains/exodus/util/MathUtil.java
@@ -15,33 +15,16 @@
  */
 package jetbrains.exodus.util;
 
-import java.util.Arrays;
-
 public class MathUtil {
 
-    private static final int POWERS_OF_2[];
-
-    static {
-        POWERS_OF_2 = new int[31];
-        int power = 1;
-        for (int i = 0; i < POWERS_OF_2.length; ++i) {
-            POWERS_OF_2[i] = power;
-            power <<= 1;
-        }
-    }
-
-    private MathUtil() {
-    }
-
     /**
      * @param i integer
      * @return discrete logarithm of specified integer base 2
      */
     public static int integerLogarithm(final int i) {
-        int result = Arrays.binarySearch(POWERS_OF_2, i);
-        if (result < 0) {
-            result = ~result;
+        if (i <= 0) {
+            return 0;
         }
-        return result;
+        return Integer.SIZE - Integer.numberOfLeadingZeros(i - 1);
     }
 }
diff --git a/utils/src/test/java/jetbrains/exodus/util/MathTest.java b/utils/src/test/java/jetbrains/exodus/util/MathTest.java
new file mode 100644
index 000000000..483881f28
--- /dev/null
+++ b/utils/src/test/java/jetbrains/exodus/util/MathTest.java
@@ -0,0 +1,35 @@
+/**
+ * Copyright 2010 - 2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package jetbrains.exodus.util;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MathTest {
+
+    @Test
+    public void testLog() {
+        int power = 1;
+        int expected = 0;
+        for (int i = 0; i < 10000; i++) {
+            Assert.assertEquals(expected, MathUtil.integerLogarithm(i));
+            if (i == power) {
+                power <<= 1;
+                expected++;
+            }
+        }
+    }
+}