P25 - adds 3/4 rate convolutional decoder for confirmed packet data units.

src/dsp/fsk/Dibit.java

@@ -19,6 +19,60 @@ public enum Dibit
 		mLowValue = lowValue;
 		mHighValue = highValue;
 	}
+
+	/**
+	 * Allowable transition state 1 for trellis coded modulation.  Indicates 
+	 * the dibit that differs from this dibit in the LSB bit position.
+	 */
+	public Dibit getAllowableTransition1()
+	{
+		switch( this )
+		{
+			case D00_PLUS_1:
+				return D01_PLUS_3;
+			case D01_PLUS_3:
+				return D00_PLUS_1;
+			case D10_MINUS_1:
+				return D11_MINUS_3;
+			case D11_MINUS_3:
+				return D10_MINUS_1;
+			default:
+				/* We'll never get here */
+				return D00_PLUS_1;
+		}
+	}
+	
+	/**
+	 * Allowable transition state 2 for trellis coded modulation.  Indicates 
+	 * the dibit that differs from this dibit in the MSB bit position.
+	 */
+	public Dibit getAllowableTransition2()
+	{
+		switch( this )
+		{
+			case D00_PLUS_1:
+				return D10_MINUS_1;
+			case D01_PLUS_3:
+				return D11_MINUS_3;
+			case D10_MINUS_1:
+				return D00_PLUS_1;
+			case D11_MINUS_3:
+				return D01_PLUS_3;
+			default:
+				/* We'll never get here */
+				return D00_PLUS_1;
+		}
+	}
+
+	/**
+	 * Indicates if the trellis coded modulation dibit is allowed to transition 
+	 * to the dibit argument.  
+	 */
+	public boolean isAllowableTransition( Dibit dibit )
+	{
+		return dibit == getAllowableTransition1() ||
+			   dibit == getAllowableTransition2();
+	}
 	
 	public boolean getBit1()
 	{