P25 audio decoder integration.

Auto-discovers the jmbe ( https://github.com/DSheirer/jmbe ) library at startup and provides decode P25 Phase 1 audio

src/edac/Golay24.java

@@ -0,0 +1,168 @@
+package edac;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import bits.BinaryMessage;
+
+/*******************************************************************************
+ *     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/>
+ *     -----------------------------------------------------------------------
+ *     Galois24 decoder based on Hank Wallace's tutorial/algorithm located at:
+ *     http://www.aqdi.com/golay.htm
+ ******************************************************************************/
+
+/**
+ * Galois 24/12/7 decoder
+ */
+public class Golay24
+{
+	private final static Logger mLog = LoggerFactory.getLogger( Golay24.class );
+
+	/**
+	 * Galois 24/12 checksums generated by:
+	 * 
+	 * CRCUtil.generate( 12, 11, 0xC75, 0x0, true );
+	 */
+	public static final int[] CHECKSUMS = new int[]
+	{
+	    0x63A, 0x31D, 0x7B4, 0x3DA, 0x1ED, 0x6CC, 0x366, 0x1B3, 
+	    0x6E3, 0x54B, 0x49F, 0x475, 0x400, 0x200, 0x100, 0x080, 
+	    0x040, 0x020, 0x010, 0x008, 0x004, 0x002, 0x001 
+	};
+
+	private static int calculateChecksum( BinaryMessage message, int startIndex )
+	{
+		int calculated = 0; //Starting value
+
+		/* Iterate the set bits and XOR running checksum with lookup value */
+		for (int i = message.nextSetBit( startIndex ); 
+				 i >= startIndex && i < startIndex + 12; 
+				 i = message.nextSetBit( i+1 ) ) 
+		{
+			calculated ^= CHECKSUMS[ i - startIndex ];
+		}
+		
+		return calculated;
+	}
+	
+	/**
+	 * Performs error detection and returns a corrected copy of the 24-bit
+	 * message that starts at the start index.
+	 * @param message - source message containing startIndex + 24 bits length
+	 * @param startIndex - start of the 24-bit galois 24 protected bit set
+	 * @return - corrected 24-bit galois value
+	 */
+	public static BinaryMessage checkAndCorrect( BinaryMessage message, int startIndex )
+	{
+		boolean parityError = message.cardinality() % 2 != 0;
+		
+		int syndrome = getSyndrome( message, startIndex );
+		
+		/* No errors */
+		if( syndrome == 0 )
+		{
+			if( parityError )
+			{
+				message.flip( startIndex + 23 );
+			}
+
+			message.setCRC( CRC.PASSED );
+			
+			return message;
+		}
+
+		/* Get original message value */
+		int original = message.getInt( 0, 22 );
+		
+		int index = -1;
+		int syndromeWeight = 3;
+		int errors = 0;
+		
+		while( index < 23 )
+		{
+			if( index != -1 )
+			{
+				/* restore the previous flipped bit */
+				if( index > 0 )
+				{
+					message.flip( index - 1 );
+				}
+				
+				message.flip( index );
+				
+				syndromeWeight = 2;
+			}
+			
+			syndrome = getSyndrome( message, startIndex );
+			
+			if( syndrome > 0 )
+			{
+				for( int i = 0; i < 23; i++ )
+				{
+				
+					errors = Integer.bitCount( syndrome );
+					
+					if( errors <= syndromeWeight )
+					{
+						message.xor( 12, 11, syndrome );
+						
+						message.rotateRight( i, startIndex, startIndex + 22 );
+
+						if( index >= 0 )
+						{
+							errors ++;
+						}
+
+						int corrected = message.getInt( 0, 22 );
+						
+						if( Integer.bitCount( original ^ corrected ) > 3 )
+						{
+							message.setCRC( CRC.FAILED_CRC );
+							
+							return message;
+						}
+						
+						message.setCRC( CRC.PASSED );
+						
+						return message;
+					}
+					else
+					{
+						message.rotateLeft( startIndex, startIndex + 22 );
+						syndrome = getSyndrome( message, startIndex );
+					}
+				}
+				
+				index++;
+			}
+		}
+
+		message.setCRC( CRC.FAILED_CRC );
+		
+		return message;
+	}
+
+	private static int getSyndrome( BinaryMessage message, int startIndex )
+	{
+		int calculated = calculateChecksum( message, startIndex );
+		
+		int checksum = message.getInt( startIndex + 12, startIndex + 22 );
+
+		return ( checksum ^ calculated );
+	}
+}