sdrtrunk/src/crc/CRCUtil.java

/*******************************************************************************
 *     SDR Trunk 
 *     Copyright (C) 2014 Dennis Sheirer
 * 
 *     This program is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 * 
 *     This program is distributed in the hope that it will be useful,
 *     but WITHOUT ANY WARRANTY; without even the implied warranty of
 *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *     GNU General Public License for more details.
 * 
 *     You should have received a copy of the GNU General Public License
 *     along with this program.  If not, see <http://www.gnu.org/licenses/>
 ******************************************************************************/
package crc;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import bits.BitSetBuffer;

public class CRCUtil
{
	private final static Logger mLog = LoggerFactory.getLogger( CRCUtil.class );

	public static long[] generate( int messageSize,
								   int crcSize,
								   long polynomial,
								   long initialFill,
								   boolean includeCRCBitErrors )
	{
		long[] crcTable = new long[ messageSize + 
		                            ( includeCRCBitErrors ? crcSize : 0 ) ];
		
		int[] checksumIndexes = new int[ crcSize ];
		
		for( int x = 0; x < crcSize; x++ )
		{
			checksumIndexes[ x ] = messageSize + x;
		}

		for( int x = 0; x < messageSize; x++ )
		{
			BitSetBuffer message = new BitSetBuffer( messageSize + crcSize );
			
			message.load( messageSize, crcSize, initialFill );
			
			message.set( x );
			
			message = decode( message, 0, messageSize, polynomial, crcSize );
			
			long checksum = message.getLong( checksumIndexes );
			
			crcTable[ x ] = checksum;
		}
		
		if( includeCRCBitErrors )
		{
			for( int x = 0; x < crcSize; x++ )
			{
				crcTable[ messageSize + x ] = Long.rotateLeft( 1, x );
			}
		}
		
		return crcTable;
	}

	/**
	 * Generates the checksum table and treats the final bit of each check value
	 * as a parity bit that complies with the request parity argument.
	 */
	public static long[] generate( int messageSize,
								   int crcSize,
								   long polynomial,
								   long initialFill,
								   boolean includeCRCBitErrors,
								   Parity parity )
	{
		long[] table = generate( messageSize, crcSize, polynomial, initialFill, 
				includeCRCBitErrors );

		if( parity == Parity.NONE )
		{
			return table;
		}
		else
		{
			for( int x = 0; x < table.length; x++ )
			{
				table[ x ] <<= 1;
				
				if( parity( table[ x ] ) != parity )
				{
					table[ x ] ^= 0x1;
				}
			}
			
			return table;
		}
	}
	
	public enum Parity{ EVEN, ODD, NONE };

	/* Determines the parity (number of 1 bits) for the value */
	public static Parity parity( long value ) 
	{ 
		return Long.bitCount( value ) % 2 == 0 ? Parity.EVEN : Parity.ODD;
	} 
	

	/**
	 * Performs binary division of the polynomial into the message for bits
	 * in index 0 to index messageLength - 1, leaving the results in the
	 * checksum filed following the message.
	 * 
	 * IN:   MMMMMMMMMMMMMMMMCCCCCCCCCCC
	 * OUT:  0000000000000000RRRRRRRRRRR
	 * 
	 * M: Message
	 * C: Checksum
	 * R: Remainder
	 * 
	 * @param message - message and crc
	 * @param polynomial - crc polynomial - must be 1 bit longer than the crc width
	 * @param messageSize - message length and start of the checksum
	 * 
	 * @return message with all message bits zeroed out, and the remainder 
	 * placed in the crc field which starts at index messageLength
	 */
	public static BitSetBuffer decode( BitSetBuffer message,
									   int messageStart,
									   int messageSize,
									   long polynomial,
									   int crcSize )
	{
		for (int i = message.nextSetBit( messageStart ); 
				 i >= messageStart && i < messageSize; 
				 i = message.nextSetBit( i+1 ) )
		{
			BitSetBuffer polySet = new BitSetBuffer( crcSize + i + 1 );
			
			polySet.load( i, crcSize + 1, polynomial );
			
			message.xor( polySet );
		}
		
		return message;
	}
	
	public static void main( String[] args )
	{
		mLog.debug( "Starting" );

		long polynomial = 0xC75l;

		long[] table = generate( 12, 11, polynomial, 0x0, true, Parity.NONE );
		mLog.debug( toCodeArray( table ) );
		mLog.debug( "Finished" );
	}
	
	public static String toCodeArray( long[] values )
	{
		boolean integerArray = true;

		/* Determine the correct primitive type: int or long */
		for( long value: values )
		{
			if( value > Integer.MAX_VALUE || value < Integer.MIN_VALUE )
			{
				integerArray = false;
				break;
			}
		}

		StringBuilder sb = new StringBuilder();

		if( integerArray )
		{
			sb.append( "\npublic static final int[] CHECKSUMS = new int[]\n" );
		}
		else
		{
			sb.append( "\npublic static final long[] CHECKSUMS = new long[]\n" );
		}
		sb.append( "{\n" );

		StringBuilder row = new StringBuilder();
		row.append( "    " );
		
		for( long value: values )
		{
			StringBuilder element = new StringBuilder();
			
			element.append( "0x" );
			element.append( Long.toHexString( value ).toUpperCase() );
			
			if( !integerArray )
			{
				element.append( "l" );
			}
			
			element.append( ", " );
			
			if( row.length() + element.length() <= 80 )
			{
				row.append( element.toString() );
			}
			else
			{
				sb.append( row.toString() );
				sb.append( "\n" );
				row = new StringBuilder();
				row.append( "    " );
				
				row.append( element.toString() );
			}
		}
		
		if( row.length() > 4 )
		{
			sb.append( row.toString() );
			sb.append( "\n" );
		}
		
		sb.append( "};\n" );

		return sb.toString();
	}

}