J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1994-1995 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any 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 | } |