FrequencyEncoder.java revision 12651:6ef01bd40ce2 
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 */
23package org.graalvm.compiler.core.common.util;
24
25import java.util.ArrayList;
26import java.util.HashMap;
27import java.util.IdentityHashMap;
28import java.util.List;
29import 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 */
39public 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}
135