vcs.maemo.org Git - physicsfs/blob - lzma/Java/SevenZip/Compression/RangeCoder/Decoder.java

   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 }