CRC16.java

/*
 * Copyright 1994-1995 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package sun.misc;

/**
 * The CRC-16 class calculates a 16 bit cyclic redundancy check of a set
 * of bytes. This error detecting code is used to determine if bit rot
 * has occured in a byte stream.
 */

public class CRC16 {

    /** value contains the currently computed CRC, set it to 0 initally */
    public int value;

    public CRC16() {
        value = 0;
    }

    /** update CRC with byte b */
    public void update(byte aByte) {
        int a, b;

        a = (int) aByte;
        for (int count = 7; count >=0; count--) {
            a = a << 1;
            b = (a >>> 8) & 1;
            if ((value & 0x8000) != 0) {
                value = ((value << 1) + b) ^ 0x1021;
            } else {
                value = (value << 1) + b;
            }
        }
        value = value & 0xffff;
        return;
    }

    /** reset CRC value to 0 */
    public void reset() {
        value = 0;
    }
}