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/*
 * $Id$
 *

 Copyright (c) 2000-2007 Board of Trustees of Leland Stanford Jr. University,
 all rights reserved.

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 STANFORD UNIVERSITY BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
 IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

 Except as contained in this notice, the name of Stanford University shall not
 be used in advertising or otherwise to promote the sale, use or other dealings
 in this Software without prior written authorization from Stanford University.

*/

package org.lockss.util;

/**
 * CRC-8 calculation utility.
 */
public class Crc8 {

  /* 
   * Lookup table for CRC-8, by far the fastest way to deal with 
   * an 1-byte CRC.
   * 
   * These values are generated based on the CRC-8-ATM polynomial
   * x^8 + x^2 + x^1 + 1, 100000111 base 2, 0x107 base 16.
   */

  private static final byte[] CRC8_TABLE =
    new byte[] {
      (byte)0x00,(byte)0x07,(byte)0x0E,(byte)0x09,(byte)0x1C,(byte)0x1B,
      (byte)0x12,(byte)0x15,(byte)0x38,(byte)0x3F,(byte)0x36,(byte)0x31,
      (byte)0x24,(byte)0x23,(byte)0x2A,(byte)0x2D,(byte)0x70,(byte)0x77,
      (byte)0x7E,(byte)0x79,(byte)0x6C,(byte)0x6B,(byte)0x62,(byte)0x65,
      (byte)0x48,(byte)0x4F,(byte)0x46,(byte)0x41,(byte)0x54,(byte)0x53,
      (byte)0x5A,(byte)0x5D,(byte)0xE0,(byte)0xE7,(byte)0xEE,(byte)0xE9,
      (byte)0xFC,(byte)0xFB,(byte)0xF2,(byte)0xF5,(byte)0xD8,(byte)0xDF,
      (byte)0xD6,(byte)0xD1,(byte)0xC4,(byte)0xC3,(byte)0xCA,(byte)0xCD,
      (byte)0x90,(byte)0x97,(byte)0x9E,(byte)0x99,(byte)0x8C,(byte)0x8B,
      (byte)0x82,(byte)0x85,(byte)0xA8,(byte)0xAF,(byte)0xA6,(byte)0xA1,
      (byte)0xB4,(byte)0xB3,(byte)0xBA,(byte)0xBD,(byte)0xC7,(byte)0xC0,
      (byte)0xC9,(byte)0xCE,(byte)0xDB,(byte)0xDC,(byte)0xD5,(byte)0xD2,
      (byte)0xFF,(byte)0xF8,(byte)0xF1,(byte)0xF6,(byte)0xE3,(byte)0xE4,
      (byte)0xED,(byte)0xEA,(byte)0xB7,(byte)0xB0,(byte)0xB9,(byte)0xBE,
      (byte)0xAB,(byte)0xAC,(byte)0xA5,(byte)0xA2,(byte)0x8F,(byte)0x88,
      (byte)0x81,(byte)0x86,(byte)0x93,(byte)0x94,(byte)0x9D,(byte)0x9A,
      (byte)0x27,(byte)0x20,(byte)0x29,(byte)0x2E,(byte)0x3B,(byte)0x3C,
      (byte)0x35,(byte)0x32,(byte)0x1F,(byte)0x18,(byte)0x11,(byte)0x16,
      (byte)0x03,(byte)0x04,(byte)0x0D,(byte)0x0A,(byte)0x57,(byte)0x50,
      (byte)0x59,(byte)0x5E,(byte)0x4B,(byte)0x4C,(byte)0x45,(byte)0x42,
      (byte)0x6F,(byte)0x68,(byte)0x61,(byte)0x66,(byte)0x73,(byte)0x74,
      (byte)0x7D,(byte)0x7A,(byte)0x89,(byte)0x8E,(byte)0x87,(byte)0x80,
      (byte)0x95,(byte)0x92,(byte)0x9B,(byte)0x9C,(byte)0xB1,(byte)0xB6,
      (byte)0xBF,(byte)0xB8,(byte)0xAD,(byte)0xAA,(byte)0xA3,(byte)0xA4,
      (byte)0xF9,(byte)0xFE,(byte)0xF7,(byte)0xF0,(byte)0xE5,(byte)0xE2,
      (byte)0xEB,(byte)0xEC,(byte)0xC1,(byte)0xC6,(byte)0xCF,(byte)0xC8,
      (byte)0xDD,(byte)0xDA,(byte)0xD3,(byte)0xD4,(byte)0x69,(byte)0x6E,
      (byte)0x67,(byte)0x60,(byte)0x75,(byte)0x72,(byte)0x7B,(byte)0x7C,
      (byte)0x51,(byte)0x56,(byte)0x5F,(byte)0x58,(byte)0x4D,(byte)0x4A,
      (byte)0x43,(byte)0x44,(byte)0x19,(byte)0x1E,(byte)0x17,(byte)0x10,
      (byte)0x05,(byte)0x02,(byte)0x0B,(byte)0x0C,(byte)0x21,(byte)0x26,
      (byte)0x2F,(byte)0x28,(byte)0x3D,(byte)0x3A,(byte)0x33,(byte)0x34,
      (byte)0x4E,(byte)0x49,(byte)0x40,(byte)0x47,(byte)0x52,(byte)0x55,
      (byte)0x5C,(byte)0x5B,(byte)0x76,(byte)0x71,(byte)0x78,(byte)0x7F,
      (byte)0x6A,(byte)0x6D,(byte)0x64,(byte)0x63,(byte)0x3E,(byte)0x39,
      (byte)0x30,(byte)0x37,(byte)0x22,(byte)0x25,(byte)0x2C,(byte)0x2B,
      (byte)0x06,(byte)0x01,(byte)0x08,(byte)0x0F,(byte)0x1A,(byte)0x1D,
      (byte)0x14,(byte)0x13,(byte)0xAE,(byte)0xA9,(byte)0xA0,(byte)0xA7,
      (byte)0xB2,(byte)0xB5,(byte)0xBC,(byte)0xBB,(byte)0x96,(byte)0x91,
      (byte)0x98,(byte)0x9F,(byte)0x8A,(byte)0x8D,(byte)0x84,(byte)0x83,
      (byte)0xDE,(byte)0xD9,(byte)0xD0,(byte)0xD7,(byte)0xC2,(byte)0xC5,
      (byte)0xCC,(byte)0xCB,(byte)0xE6,(byte)0xE1,(byte)0xE8,(byte)0xEF,
      (byte)0xFA,(byte)0xFD,(byte)0xF4,(byte)0xF3
    };


  private byte crc;
  private long length;

  /** Construct a new CRC-8 object. */
  public Crc8() {
    reset();
  }
  
  /** Reset the CRC to initial values. */
  public void reset() {
    crc = 0;
    length = 0;
  }
  
  /**
   * Update the CRC from a byte.
   *
   * @param data The data to read.
   */
  public void update(byte data) {
    crc = CRC8_TABLE[(crc ^ data) & 0xff];
    length++;
  }
  
  /**
   * Update the CRC from an array of bytes.
   * 
   * @param data The data to read.
   */
  public void update(byte[] data) {
    for (int i = 0; i < data.length; i++) {
      update(data[i]);
    }
    
  }
  
  /**
   * Return the current value of the CRC.
   * @return
   */
  public byte getValue() {
    return crc;
  }
  
}