org.jacoco.core.internal.data.CRC64.java Source code

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Here is the source code for org.jacoco.core.internal.data.CRC64.java

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/*******************************************************************************
 * Copyright (c) 2009, 2019 Mountainminds GmbH & Co. KG and Contributors
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *    Marc R. Hoffmann - initial API and implementation
 *
 *******************************************************************************/
package org.jacoco.core.internal.data;

import org.objectweb.asm.Opcodes;

/**
 * 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;
        }
    }

    /**
     * Updates given checksum by given byte.
     *
     * @param sum
     *            initial checksum value
     * @param b
     *            byte to update the checksum with
     * @return updated checksum value
     */
    private static long update(final long sum, final byte b) {
        final int lookupidx = ((int) sum ^ b) & 0xff;
        return (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
    }

    /**
     * Updates given checksum by bytes from given array.
     *
     * @param sum
     *            initial checksum value
     * @param bytes
     *            byte array to update the checksum with
     * @param fromIndexInclusive
     *            start index in array, inclusive
     * @param toIndexExclusive
     *            end index in array, exclusive
     * @return updated checksum value
     */
    private static long update(long sum, final byte[] bytes, final int fromIndexInclusive,
            final int toIndexExclusive) {
        for (int i = fromIndexInclusive; i < toIndexExclusive; i++) {
            sum = update(sum, bytes[i]);
        }
        return sum;
    }

    /**
     * Calculates class identifier for the given class bytes.
     *
     * @param bytes
     *            class bytes
     * @return class identifier
     */
    public static long classId(final byte[] bytes) {
        if (bytes.length > 7 && bytes[6] == 0x00 && bytes[7] == Opcodes.V9) {
            // To support early versions of Java 9 we did a trick - change of
            // Java 9 class files version on Java 8. Unfortunately this also
            // affected class identifiers.
            long sum = update(0, bytes, 0, 7);
            sum = update(sum, (byte) Opcodes.V1_8);
            return update(sum, bytes, 8, bytes.length);
        }
        return update(0, bytes, 0, bytes.length);
    }

    private CRC64() {
    }

}