CRC64.java
1/*******************************************************************************
2 * Copyright (c) 2009, 2010 Mountainminds GmbH & Co. KG and Contributors
3 * All rights reserved. This program and the accompanying materials
4 * are made available under the terms of the Eclipse Public License v1.0
5 * which accompanies this distribution, and is available at
6 * http://www.eclipse.org/legal/epl-v10.html
7 *
8 * Contributors:
9 * Marc R. Hoffmann - initial API and implementation
10 *
11 * $Id: $
12 *******************************************************************************/
13package org.jacoco.core.instr;
14
15/**
16 * CRC64 checksum calculator based on the polynom specified in ISO 3309. The
17 * implementation is based on the following publications:
18 *
19 * <ul>
20 * <li>http://en.wikipedia.org/wiki/Cyclic_redundancy_check</li>
21 * <li>http://www.geocities.com/SiliconValley/Pines/8659/crc.htm</li>
22 * </ul>
23 *
24 * @author Marc R. Hoffmann
25 * @version $Revision: $
26 */
27public final class CRC64 {
28
29 private static final long POLY64REV = 0xd800000000000000L;
30
31 private static final long[] LOOKUPTABLE;
32
33 static {
34 LOOKUPTABLE = new long[0x100];
35 for (int i = 0; i < 0x100; i++) {
36 long v = i;
37 for (int j = 0; j < 8; j++) {
38 if ((v & 1) == 1) {
39 v = (v >>> 1) ^ POLY64REV;
40 } else {
41 v = (v >>> 1);
42 }
43 }
44 LOOKUPTABLE[i] = v;
45 }
46 }
47
48 /**
49 * Calculates the CRC64 checksum for the given data array.
50 *
51 * @param data
52 * data to calculate checksum for
53 * @return checksum value
54 */
55 public static long checksum(final byte[] data) {
56 long sum = 0;
57 for (int i = 0; i < data.length; i++) {
58 final int lookupidx = ((int) sum ^ data[i]) & 0xff;
59 sum = (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
60 }
61 return sum;
62 }
63
64 private CRC64() {
65 }
66
67}