1 /* 2 * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package org.graalvm.compiler.core.common.util; 24 25 import java.util.ArrayList; 26 import java.util.HashMap; 27 import java.util.IdentityHashMap; 28 import java.util.List; 29 import java.util.Map; 30 31 /** 32 * Creates an array of T objects order by the occurrence frequency of each object. The most 33 * frequently used object is the first one, the least frequently used the last one. If {@code null} 34 * is added, it is always the first element. 35 * 36 * Either object {@link #createIdentityEncoder() identity} or object {@link #createEqualityEncoder() 37 * equality} can be used to build the array and count the frequency. 38 */ 39 public class FrequencyEncoder<T> { 40 41 static class Entry<T> { 42 protected final T object; 43 protected int frequency; 44 protected int index; 45 46 protected Entry(T object) { 47 this.object = object; 48 this.index = -1; 49 } 50 } 51 52 protected final Map<T, Entry<T>> map; 53 protected boolean containsNull; 54 55 /** 56 * Creates an encoder that uses object identity. 57 */ 58 public static <T> FrequencyEncoder<T> createIdentityEncoder() { 59 return new FrequencyEncoder<>(new IdentityHashMap<>()); 60 } 61 62 /** 63 * Creates an encoder that uses {@link Object#equals(Object) object equality}. 64 */ 65 public static <T> FrequencyEncoder<T> createEqualityEncoder() { 66 return new FrequencyEncoder<>(new HashMap<>()); 67 } 68 69 protected FrequencyEncoder(Map<T, Entry<T>> map) { 70 this.map = map; 71 } 72 73 /** 74 * Adds an object to the array. 75 */ 76 public void addObject(T object) { 77 if (object == null) { 78 containsNull = true; 79 return; 80 } 81 82 Entry<T> entry = map.get(object); 83 if (entry == null) { 84 entry = new Entry<>(object); 85 map.put(object, entry); 86 } 87 entry.frequency++; 88 } 89 90 /** 91 * Returns the index of an object in the array. The object must have been 92 * {@link #addObject(Object) added} before. 93 */ 94 public int getIndex(Object object) { 95 if (object == null) { 96 assert containsNull; 97 return 0; 98 } 99 Entry<T> entry = map.get(object); 100 assert entry != null && entry.index >= 0; 101 return entry.index; 102 } 103 104 /** 105 * Returns the number of distinct objects that have been added, i.e., the length of the array. 106 */ 107 public int getLength() { 108 return map.size() + (containsNull ? 1 : 0); 109 } 110 111 /** 112 * Fills the provided array with the added objects. The array must have the {@link #getLength() 113 * correct length}. 114 */ 115 public T[] encodeAll(T[] allObjects) { 116 assert allObjects.length == getLength(); 117 List<Entry<T>> sortedEntries = new ArrayList<>(map.values()); 118 sortedEntries.sort((e1, e2) -> -Integer.compare(e1.frequency, e2.frequency)); 119 120 int offset = 0; 121 if (containsNull) { 122 allObjects[0] = null; 123 offset = 1; 124 } 125 for (int i = 0; i < sortedEntries.size(); i++) { 126 Entry<T> entry = sortedEntries.get(i); 127 int index = i + offset; 128 entry.index = index; 129 allObjects[index] = entry.object; 130 assert entry.object != null; 131 } 132 return allObjects; 133 } 134 }