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    1   /*
    2    * Copyright (c) 1994, 1995, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package sun.misc;
   27   
   28   /**
   29    * The CRC-16 class calculates a 16 bit cyclic redundancy check of a set
   30    * of bytes. This error detecting code is used to determine if bit rot
   31    * has occured in a byte stream.
   32    */
   33   
   34   public class CRC16 {
   35   
   36       /** value contains the currently computed CRC, set it to 0 initally */
   37       public int value;
   38   
   39       public CRC16() {
   40           value = 0;
   41       }
   42   
   43       /** update CRC with byte b */
   44       public void update(byte aByte) {
   45           int a, b;
   46   
   47           a = (int) aByte;
   48           for (int count = 7; count >=0; count--) {
   49               a = a << 1;
   50               b = (a >>> 8) & 1;
   51               if ((value & 0x8000) != 0) {
   52                   value = ((value << 1) + b) ^ 0x1021;
   53               } else {
   54                   value = (value << 1) + b;
   55               }
   56           }
   57           value = value & 0xffff;
   58           return;
   59       }
   60   
   61       /** reset CRC value to 0 */
   62       public void reset() {
   63           value = 0;
   64       }
   65   }

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