001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.codec.digest;
019
020import static java.lang.Integer.rotateLeft;
021
022import java.util.zip.Checksum;
023
024/**
025 * Implementation of the xxhash32 hash algorithm.
026 *
027 * <p>
028 * Copied from Commons Compress 1.14 <a href=
029 * "https://git-wip-us.apache.org/repos/asf?p=commons-compress.git;a=blob;f=src/main/java/org/apache/commons/compress/compressors/lz4/XXHash32.java;h=a406ffc197449be594d46f0d2712b2d4786a1e68;hb=HEAD">https://git-wip-us.apache.org/repos/asf?p=commons-compress.git;a=blob;f=src/main/java/org/apache/commons/compress/compressors/lz4/XXHash32.java;h=a406ffc197449be594d46f0d2712b2d4786a1e68;hb=HEAD</a>
030 * </p>
031 * <p>
032 * NotThreadSafe
033 * </p>
034 *
035 * @see <a href="http://cyan4973.github.io/xxHash/">xxHash</a>
036 * @since 1.11
037 */
038public class XXHash32 implements Checksum {
039
040    private static final int BUF_SIZE = 16;
041    private static final int ROTATE_BITS = 13;
042
043    private static final int PRIME1 = (int) 2654435761l;
044    private static final int PRIME2 = (int) 2246822519l;
045    private static final int PRIME3 = (int) 3266489917l;
046    private static final int PRIME4 =  668265263;
047    private static final int PRIME5 =  374761393;
048
049    private final byte[] oneByte = new byte[1];
050    private final int[] state = new int[4];
051    // Note: the code used to use ByteBuffer but the manual method is 50% faster
052    // See: http://git-wip-us.apache.org/repos/asf/commons-compress/diff/2f56fb5c
053    private final byte[] buffer = new byte[BUF_SIZE];
054    private final int seed;
055
056    private int totalLen;
057    private int pos;
058    /** Set to true when the state array has been updated since the last reset. */
059    private boolean stateUpdated;
060
061    /**
062     * Creates an XXHash32 instance with a seed of 0.
063     */
064    public XXHash32() {
065        this(0);
066    }
067
068    /**
069     * Creates an XXHash32 instance.
070     * @param seed the seed to use
071     */
072    public XXHash32(final int seed) {
073        this.seed = seed;
074        initializeState();
075    }
076
077    @Override
078    public void reset() {
079        initializeState();
080        totalLen = 0;
081        pos = 0;
082        stateUpdated = false;
083    }
084
085    @Override
086    public void update(final int b) {
087        oneByte[0] = (byte) (b & 0xff);
088        update(oneByte, 0, 1);
089    }
090
091    @Override
092    public void update(final byte[] b, int off, final int len) {
093        if (len <= 0) {
094            return;
095        }
096        totalLen += len;
097
098        final int end = off + len;
099
100        // Check if the unprocessed bytes and new bytes can fill a block of 16.
101        // Make this overflow safe in the event that len is Integer.MAX_VALUE.
102        // Equivalent to: (pos + len < BUF_SIZE)
103        if (pos + len - BUF_SIZE < 0) {
104            System.arraycopy(b, off, buffer, pos, len);
105            pos += len;
106            return;
107        }
108
109        // Process left-over bytes with new bytes
110        if (pos > 0) {
111            final int size = BUF_SIZE - pos;
112            System.arraycopy(b, off, buffer, pos, size);
113            process(buffer, 0);
114            off += size;
115        }
116
117        final int limit = end - BUF_SIZE;
118        while (off <= limit) {
119            process(b, off);
120            off += BUF_SIZE;
121        }
122
123        // Handle left-over bytes
124        if (off < end) {
125            pos = end - off;
126            System.arraycopy(b, off, buffer, 0, pos);
127        } else {
128            pos = 0;
129        }
130    }
131
132    @Override
133    public long getValue() {
134        int hash;
135        if (stateUpdated) {
136            // Hash with the state
137            hash =
138                rotateLeft(state[0],  1) +
139                rotateLeft(state[1],  7) +
140                rotateLeft(state[2], 12) +
141                rotateLeft(state[3], 18);
142        } else {
143            // Hash using the original seed from position 2
144            hash = state[2] + PRIME5;
145        }
146        hash += totalLen;
147
148        int idx = 0;
149        final int limit = pos - 4;
150        for (; idx <= limit; idx += 4) {
151            hash = rotateLeft(hash + getInt(buffer, idx) * PRIME3, 17) * PRIME4;
152        }
153        while (idx < pos) {
154            hash = rotateLeft(hash + (buffer[idx++] & 0xff) * PRIME5, 11) * PRIME1;
155        }
156
157        hash ^= hash >>> 15;
158        hash *= PRIME2;
159        hash ^= hash >>> 13;
160        hash *= PRIME3;
161        hash ^= hash >>> 16;
162        return hash & 0xffffffffl;
163    }
164
165    /**
166     * Gets the little-endian int from 4 bytes starting at the specified index.
167     *
168     * @param buffer The data
169     * @param idx The index
170     * @return The little-endian int
171     */
172    private static int getInt(final byte[] buffer, final int idx) {
173        return ((buffer[idx    ] & 0xff)      ) |
174               ((buffer[idx + 1] & 0xff) <<  8) |
175               ((buffer[idx + 2] & 0xff) << 16) |
176               ((buffer[idx + 3] & 0xff) << 24);
177    }
178
179    private void initializeState() {
180        state[0] = seed + PRIME1 + PRIME2;
181        state[1] = seed + PRIME2;
182        state[2] = seed;
183        state[3] = seed - PRIME1;
184    }
185
186    private void process(final byte[] b, final int offset) {
187        // local shadows for performance
188        int s0 = state[0];
189        int s1 = state[1];
190        int s2 = state[2];
191        int s3 = state[3];
192
193        s0 = rotateLeft(s0 + getInt(b, offset) * PRIME2, ROTATE_BITS) * PRIME1;
194        s1 = rotateLeft(s1 + getInt(b, offset + 4) * PRIME2, ROTATE_BITS) * PRIME1;
195        s2 = rotateLeft(s2 + getInt(b, offset + 8) * PRIME2, ROTATE_BITS) * PRIME1;
196        s3 = rotateLeft(s3 + getInt(b, offset + 12) * PRIME2, ROTATE_BITS) * PRIME1;
197
198        state[0] = s0;
199        state[1] = s1;
200        state[2] = s2;
201        state[3] = s3;
202
203        stateUpdated = true;
204    }
205}