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/*******************************************************************************
* Copyright (c) 2009, 2012 Mountainminds GmbH & Co. KG and Contributors
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Marc R. Hoffmann - initial API and implementation
*
*******************************************************************************/
package org.jacoco.core.internal.data;
/**
* CRC64 checksum calculator based on the polynom specified in ISO 3309. The
* implementation is based on the following publications:
*
* <ul>
* <li>http://en.wikipedia.org/wiki/Cyclic_redundancy_check</li>
* <li>http://www.geocities.com/SiliconValley/Pines/8659/crc.htm</li>
* </ul>
*/
public final class CRC64 {
private static final long POLY64REV = 0xd800000000000000L;
private static final long[] LOOKUPTABLE;
static {
LOOKUPTABLE = new long[0x100];
for (int i = 0; i < 0x100; i++) {
long v = i;
for (int j = 0; j < 8; j++) {
if ((v & 1) == 1) {
v = (v >>> 1) ^ POLY64REV;
} else {
v = (v >>> 1);
}
}
LOOKUPTABLE[i] = v;
}
}
/**
* Calculates the CRC64 checksum for the given data array.
*
* @param data
* data to calculate checksum for
* @return checksum value
*/
public static long checksum(final byte[] data) {
long sum = 0;
for (int i = 0; i < data.length; i++) {
final int lookupidx = ((int) sum ^ data[i]) & 0xff;
sum = (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
}
return sum;
}
private CRC64() {
}
}
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