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 *******************************************************************************/
   12package org.jacoco.core.instr;
   13
   14/**
   15 * CRC64 checksum calculator based on the polynom specified in ISO 3309. The
   16 * implementation is based on the following publications:
   17 * 
   18 * <ul>
   19 * <li>http://en.wikipedia.org/wiki/Cyclic_redundancy_check</li>
   20 * <li>http://www.geocities.com/SiliconValley/Pines/8659/crc.htm</li>
   21 * </ul>
   22 * 
   23 * @author Marc R. Hoffmann
   24 * @version 0.4.1.20101007204400
   25 */
   26public final class CRC64 {
   27
   28    private static final long POLY64REV = 0xd800000000000000L;
   29
   30    private static final long[] LOOKUPTABLE;
   31
   32    static {
   33        LOOKUPTABLE = new long[0x100];
   34        for (int i = 0; i < 0x100; i++) {
   35            long v = i;
   36            for (int j = 0; j < 8; j++) {
   37                if ((v & 1) == 1) {
   38                    v = (v >>> 1) ^ POLY64REV;
   39                } else {
   40                    v = (v >>> 1);
   41                }
   42            }
   43            LOOKUPTABLE[i] = v;
   44        }
   45    }
   46
   47    /**
   48     * Calculates the CRC64 checksum for the given data array.
   49     * 
   50     * @param data
   51     *            data to calculate checksum for
   52     * @return checksum value
   53     */
   54    public static long checksum(final byte[] data) {
   55        long sum = 0;
   56        for (int i = 0; i < data.length; i++) {
   57            final int lookupidx = ((int) sum ^ data[i]) & 0xff;
   58            sum = (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
   59        }
   60        return sum;
   61    }
   62
   63    private CRC64() {
   64    }
   65
   66}