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This package supports the parsing of AIS messages in Java. AIS, the Automatic Identification System, is a system aiming at improving maritime safety by exchanging messages between ships, other vehicles in particular aircraft involved in search-and-rescue (SAR), and (fixed) base stations. To be precise, this package support the ITU-R M.1371-4 AIS standard. See our extensive javadoc and in particular the class AISParser for more information on how to use this package. The parser was used in the Poseidon project, and is improved in the Metis project to better handle uncertain information. Both projects were led by the Embedded Systems Institute. In both projects Thales Nederlands was the carrying industrial partner, and multiple Dutch universities participated.

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package nl.esi.metis.aisparser.impl;

import nl.esi.metis.aisparser.AISMessage08;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;
import cern.colt.bitvector.BitVector;

/** ESI AIS Parser
 * 
 * Copyright 2011/2012 by Pierre van de Laar (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 * @author Pierre van de Laar
 * @author Brian C. Lane
 */


/** AIS Message 8
 * Binary Broadcast Message
 * 
 * Field Nr     Field Name                          NrOf Bits   (from, to )
 * ------------------------------------------------------------------------
 *  1	messageID                               	   6	(   1,   6)
 *  2	repeatIndicator                         	   2	(   7,   8)
 *  3	userID                                  	  30	(   9,  38)
 *  4	spare                                   	   2	(  39,  40)
 *  5	applicationID                           	  16	(  41,  56)
 *  6	applicationBinaryData                   	 952	(  57,1008)
 *                                                      ---- +
 *                           (maximum) number of bits   1008
 */
class AISMessage08Impl extends AISMessageImpl implements AISMessage08 {
	public static final int MINLENGTH = 56;
	public static final int MAXLENGTH = 1008;

	public static boolean validLength(int length)
	{
		return (MINLENGTH <= length && length <= MAXLENGTH);
	}

	/**
	 * Return the difference in available and needed bits to parse this sixbit as an AISMessage
	 * A positive difference indicates that there are more bits available than needed by the standard.
	 * @param sb
	 * @return
	 */
	public static int differenceInBits(Sixbit sb)
	{
		final int available = sb.available();
		if (available > MAXLENGTH)
		{
			return (available - MAXLENGTH);
		}
		else if (available < MINLENGTH)
		{
			return available - MINLENGTH;
		}
		else
		{
			return 0;
		}
	}

	private static final int SPARE_FROM = 39;
	private static final int SPARE_TO = 40;

	private int spare;
	/** spare
	 * @return int value of spare (2 bits [39,40])
	 */
	public int getSpare() { return spare; }


	private static final int APPLICATIONID_FROM = 41;
	private static final int APPLICATIONID_TO = 56;

	private int applicationID;
	/** applicationID
	 * @return int value of applicationID (16 bits [41,56])
	 */
	public int getApplicationID() { return applicationID; }


	private static final int APPLICATIONBINARYDATA_FROM = 57;
	//private static final int APPLICATIONBINARYDATA_TO = 1008;

	private BitVector applicationBinaryData;
	/** applicationBinaryData
	 * @return BitVector value of applicationBinaryData (maximally 952 bits [57,1008])
	 */
	public BitVector getApplicationBinaryData() { return applicationBinaryData; }

	/** AISMessage 8 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==8
	 */
	public AISMessage08Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 8);

		spare = content.getIntFromTo(SPARE_FROM,SPARE_TO);
		if (!UtilsSpare.isSpareSemanticallyCorrect(spare))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare", spare, UtilsSpare.range));
	    }
		applicationID = content.getIntFromTo(APPLICATIONID_FROM,APPLICATIONID_TO);
		applicationBinaryData = content.getBitVectorFromTo(APPLICATIONBINARYDATA_FROM,content.length());
	}
	
	/** Generates a String representing the AIS message. 
	 * Format: all fields are shown in the order as specified by the standard separated by the SEPARATOR string.
	 */
	@Override
	public String toString() {
		return super.toString() + SEPARATOR + Integer.toString(applicationID) 
								+ SEPARATOR + applicationBinaryData.toString();
		
	}
}