crc.java

传感器网络中的嵌入式操作系统源代码

// $Id: Crc.java,v 1.1.4.2 2003/08/18 22:09:45 cssharp Exp $

/*									tab:4
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 * two paragraphs and the author appear in all copies of this software.
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 * IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
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 * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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 * Copyright (c) 2002-2003 Intel Corporation
 * All rights reserved.
 *
 * This file is distributed under the terms in the attached INTEL-LICENSE     
 * file. If you do not find these files, copies can be found by writing to
 * Intel Research Berkeley, 2150 Shattuck Avenue, Suite 1300, Berkeley, CA, 
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 */
package net.tinyos.util;

public class Crc {
    public static int calcByte(int crc, int b) {
      crc = crc ^ (int)b << 8;

      for (int i = 0; i < 8; i++) {
	if ((crc & 0x8000) == 0x8000)
	  crc = crc << 1 ^ 0x1021;
	else
	  crc = crc << 1;
      }

      return crc & 0xffff;
    }

    public static int calc(byte[] packet, int index, int count) {
	int crc = 0;
	int i;

	while (count > 0) {
	    crc = calcByte(crc, packet[index++]);
	    count--;
	}
	return crc;
    }

    public static int calc(byte[] packet, int count) {
	return calc(packet, 0, count);
    }

    public static void set(byte[] packet) {
        int crc = Crc.calc(packet, packet.length - 2);

        packet[packet.length - 2] = (byte) (crc & 0xFF);
        packet[packet.length - 1] = (byte) ((crc >> 8) & 0xFF);
    }
}