1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a 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 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.hardware.camera2.utils; 18 19 /** 20 * Provide hashing functions using the Modified Bernstein hash 21 */ 22 public final class HashCodeHelpers { 23 24 /** 25 * Hash every element uniformly using the Modified Bernstein hash. 26 * 27 * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p> 28 * 29 * @param array a non-{@code null} array of integers 30 * 31 * @return the numeric hash code 32 */ 33 public static int hashCode(int[] array) { 34 if (array == null) { 35 return 0; 36 } 37 38 /* 39 * Note that we use 31 here instead of 33 since it's preferred in Effective Java 40 * and used elsewhere in the runtime (e.g. Arrays#hashCode) 41 * 42 * That being said 33 and 31 are nearly identical in terms of their usefulness 43 * according to http://svn.apache.org/repos/asf/apr/apr/trunk/tables/apr_hash.c 44 */ 45 int h = 1; 46 for (int x : array) { 47 // Strength reduction; in case the compiler has illusions about divisions being faster 48 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 49 } 50 51 return h; 52 } 53 54 /** 55 * Hash every element uniformly using the Modified Bernstein hash. 56 * 57 * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p> 58 * 59 * @param array a non-{@code null} array of floats 60 * 61 * @return the numeric hash code 62 */ 63 public static int hashCode(float[] array) { 64 if (array == null) { 65 return 0; 66 } 67 68 int h = 1; 69 for (float f : array) { 70 int x = Float.floatToIntBits(f); 71 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 72 } 73 74 return h; 75 } 76 77 /** 78 * Hash every element uniformly using the Modified Bernstein hash. 79 * 80 * <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p> 81 * 82 * @param array a non-{@code null} array of objects 83 * 84 * @return the numeric hash code 85 */ 86 public static <T> int hashCode(T[] array) { 87 if (array == null) { 88 return 0; 89 } 90 91 int h = 1; 92 for (T o : array) { 93 int x = (o == null) ? 0 : o.hashCode(); 94 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 95 } 96 97 return h; 98 } 99 100 public static <T> int hashCode(T a) { 101 return (a == null) ? 0 : a.hashCode(); 102 } 103 104 public static <T> int hashCode(T a, T b) { 105 int h = hashCode(a); 106 107 int x = (b == null) ? 0 : b.hashCode(); 108 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 109 110 return h; 111 } 112 113 public static <T> int hashCode(T a, T b, T c) { 114 int h = hashCode(a, b); 115 116 int x = (c == null) ? 0 : c.hashCode(); 117 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 118 119 return h; 120 } 121 122 public static <T> int hashCode(T a, T b, T c, T d) { 123 int h = hashCode(a, b, c); 124 125 int x = (d == null) ? 0 : d.hashCode(); 126 h = ((h << 5) - h) ^ x; // (h * 31) XOR x 127 128 return h; 129 } 130 131 public static int hashCode(int x) { 132 return hashCode(new int[] { x } ); 133 } 134 135 public static int hashCode(int x, int y) { 136 return hashCode(new int[] { x, y } ); 137 } 138 139 public static int hashCode(int x, int y, int z) { 140 return hashCode(new int[] { x, y, z } ); 141 } 142 143 public static int hashCode(int x, int y, int z, int w) { 144 return hashCode(new int[] { x, y, z, w } ); 145 } 146 147 public static int hashCode(int x, int y, int z, int w, int t) { 148 return hashCode(new int[] { x, y, z, w, t } ); 149 } 150 151 152 } 153