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1   /*
2    * Copyright 2015 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License, version 2.0 (the
5    * "License"); you may not use this file except in compliance with the License. You may obtain a
6    * copy of the License at:
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software distributed under the License
11   * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
12   * or implied. See the License for the specific language governing permissions and limitations under
13   * the License.
14   */
15  package io.netty.util.internal;
16  
17  /**
18   * Math utility methods.
19   */
20  public final class MathUtil {
21  
22      private MathUtil() {
23      }
24  
25      /**
26       * Fast method of finding the next power of 2 greater than or equal to the supplied value.
27       *
28       * <p>If the value is {@code <= 0} then 1 will be returned.
29       * This method is not suitable for {@link Integer#MIN_VALUE} or numbers greater than 2^30.
30       *
31       * @param value from which to search for next power of 2
32       * @return The next power of 2 or the value itself if it is a power of 2
33       */
34      public static int findNextPositivePowerOfTwo(final int value) {
35          assert value > Integer.MIN_VALUE && value < 0x40000000;
36          return 1 << (32 - Integer.numberOfLeadingZeros(value - 1));
37      }
38  
39      /**
40       * Fast method of finding the next power of 2 greater than or equal to the supplied value.
41       * <p>This method will do runtime bounds checking and call {@link #findNextPositivePowerOfTwo(int)} if within a
42       * valid range.
43       * @param value from which to search for next power of 2
44       * @return The next power of 2 or the value itself if it is a power of 2.
45       * <p>Special cases for return values are as follows:
46       * <ul>
47       *     <li>{@code <= 0} -> 1</li>
48       *     <li>{@code >= 2^30} -> 2^30</li>
49       * </ul>
50       */
51      public static int safeFindNextPositivePowerOfTwo(final int value) {
52          return value <= 0 ? 1 : value >= 0x40000000 ? 0x40000000 : findNextPositivePowerOfTwo(value);
53      }
54  
55      /**
56       * Determine if the requested {@code index} and {@code length} will fit within {@code capacity}.
57       * @param index The starting index.
58       * @param length The length which will be utilized (starting from {@code index}).
59       * @param capacity The capacity that {@code index + length} is allowed to be within.
60       * @return {@code true} if the requested {@code index} and {@code length} will fit within {@code capacity}.
61       * {@code false} if this would result in an index out of bounds exception.
62       */
63      public static boolean isOutOfBounds(int index, int length, int capacity) {
64          return (index | length | (index + length) | (capacity - (index + length))) < 0;
65      }
66  
67      /**
68       * Compares two {@code int} values.
69       *
70       * @param  x the first {@code int} to compare
71       * @param  y the second {@code int} to compare
72       * @return the value {@code 0} if {@code x == y};
73       *         {@code -1} if {@code x < y}; and
74       *         {@code 1} if {@code x > y}
75       */
76      public static int compare(final int x, final int y) {
77          // do not subtract for comparison, it could overflow
78          return x < y ? -1 : (x > y ? 1 : 0);
79      }
80  
81      /**
82       * Compare two {@code long} values.
83       * @param x the first {@code long} to compare.
84       * @param y the second {@code long} to compare.
85       * @return
86       * <ul>
87       * <li>0 if {@code x == y}</li>
88       * <li>{@code > 0} if {@code x > y}</li>
89       * <li>{@code < 0} if {@code x < y}</li>
90       * </ul>
91       */
92      public static int compare(long x, long y) {
93          return (x < y) ? -1 : (x > y) ? 1 : 0;
94      }
95  }