CRC16.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
 * by Oracle 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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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 occurred 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;
    }
}