1/*
2 * Copyright (c) 2009, 2011, 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
25/**
26 * The {@code ArrayMap} class implements an efficient one-level map which is implemented as an
27 * array. Note that because of the one-level array inside, this data structure performs best when
28 * the range of integer keys is small and densely used. Note that the implementation can handle
29 * arbitrary intervals, including negative numbers, up to intervals of size 2^31 - 1.
30 */
31public class ArrayMap<T> {
32
33    private static final int INITIAL_SIZE = 5; // how big the initial array should be
34    private static final int EXTRA = 2; // how far on the left or right of a new element to grow
35
36    Object[] map;
37    int low;
38
39    /**
40     * Constructs a new {@code ArrayMap} with no initial assumptions.
41     */
42    public ArrayMap() {
43    }
44
45    /**
46     * Constructs a new {@code ArrayMap} that initially covers the specified interval. Note that
47     * this map will automatically expand if necessary later.
48     *
49     * @param low the low index, inclusive
50     * @param high the high index, exclusive
51     */
52    public ArrayMap(int low, int high) {
53        this.low = low;
54        this.map = new Object[high - low + 1];
55    }
56
57    /**
58     * Puts a new value in the map at the specified index.
59     *
60     * @param i the index at which to store the value
61     * @param value the value to store at the specified index
62     */
63    public void put(int i, T value) {
64        int index = i - low;
65        if (map == null) {
66            // no map yet
67            map = new Object[INITIAL_SIZE];
68            low = index - 2;
69            map[INITIAL_SIZE / 2] = value;
70        } else if (index < 0) {
71            // grow backwards
72            growBackward(i, value);
73        } else if (index >= map.length) {
74            // grow forwards
75            growForward(i, value);
76        } else {
77            // no growth necessary
78            map[index] = value;
79        }
80    }
81
82    /**
83     * Gets the value at the specified index in the map.
84     *
85     * @param i the index
86     * @return the value at the specified index; {@code null} if there is no value at the specified
87     *         index, or if the index is out of the currently stored range
88     */
89    public T get(int i) {
90        int index = i - low;
91        if (map == null || index < 0 || index >= map.length) {
92            return null;
93        }
94        Class<T> type = null;
95        return Util.uncheckedCast(type, map[index]);
96    }
97
98    public int length() {
99        return map.length;
100    }
101
102    private void growBackward(int i, T value) {
103        int nlow = i - EXTRA;
104        Object[] nmap = new Object[low - nlow + map.length];
105        System.arraycopy(map, 0, nmap, low - nlow, map.length);
106        map = nmap;
107        low = nlow;
108        map[i - low] = value;
109    }
110
111    private void growForward(int i, T value) {
112        int nlen = i - low + 1 + EXTRA;
113        Object[] nmap = new Object[nlen];
114        System.arraycopy(map, 0, nmap, 0, map.length);
115        map = nmap;
116        map[i - low] = value;
117    }
118}
119