1 package SevenZip.Compression.RangeCoder;

     2 import java.io.IOException;

     3 

     4 public class Decoder

     5 {

     6 	static final int kTopMask = ~((1 << 24) - 1);

     7 	

     8 	static final int kNumBitModelTotalBits = 11;

     9 	static final int kBitModelTotal = (1 << kNumBitModelTotalBits);

    10 	static final int kNumMoveBits = 5;

    11 	

    12 	int Range;

    13 	int Code;

    14 

    15 	java.io.InputStream Stream;

    16 	

    17 	public final void SetStream(java.io.InputStream stream)

    18 	{ 

    19 		Stream = stream; 

    20 	}

    21 	

    22 	public final void ReleaseStream()

    23 	{ 

    24 		Stream = null; 

    25 	}

    26 	

    27 	public final void Init() throws IOException

    28 	{

    29 		Code = 0;

    30 		Range = -1;

    31 		for (int i = 0; i < 5; i++)

    32 			Code = (Code << 8) | Stream.read();

    33 	}

    34 	

    35 	public final int DecodeDirectBits(int numTotalBits) throws IOException

    36 	{

    37 		int result = 0;

    38 		for (int i = numTotalBits; i != 0; i--)

    39 		{

    40 			Range >>>= 1;

    41 			int t = ((Code - Range) >>> 31);

    42 			Code -= Range & (t - 1);

    43 			result = (result << 1) | (1 - t);

    44 			

    45 			if ((Range & kTopMask) == 0)

    46 			{

    47 				Code = (Code << 8) | Stream.read();

    48 				Range <<= 8;

    49 			}

    50 		}

    51 		return result;

    52 	}

    53 	

    54 	public int DecodeBit(short []probs, int index) throws IOException

    55 	{

    56 		int prob = probs[index];

    57 		int newBound = (Range >>> kNumBitModelTotalBits) * prob;

    58 		if ((Code ^ 0x80000000) < (newBound ^ 0x80000000))

    59 		{

    60 			Range = newBound;

    61 			probs[index] = (short)(prob + ((kBitModelTotal - prob) >>> kNumMoveBits));

    62 			if ((Range & kTopMask) == 0)

    63 			{

    64 				Code = (Code << 8) | Stream.read();

    65 				Range <<= 8;

    66 			}

    67 			return 0;

    68 		}

    69 		else

    70 		{

    71 			Range -= newBound;

    72 			Code -= newBound;

    73 			probs[index] = (short)(prob - ((prob) >>> kNumMoveBits));

    74 			if ((Range & kTopMask) == 0)

    75 			{

    76 				Code = (Code << 8) | Stream.read();

    77 				Range <<= 8;

    78 			}

    79 			return 1;

    80 		}

    81 	}

    82 	

    83 	public static void InitBitModels(short []probs)

    84 	{

    85 		for (int i = 0; i < probs.length; i++)

    86 			probs[i] = (kBitModelTotal >>> 1);

    87 	}

    88 }