3.13

7zip/Compress/RangeCoder/RangeCoderBit.h

@@ -0,0 +1,107 @@
+// Compress/RangeCoder/RangeCoderBit.h
+
+// #pragma once
+
+#ifndef __COMPRESS_RANGECODER_BIT_TREE_H
+#define __COMPRESS_RANGECODER_BIT_TREE_H
+
+#include "RangeCoder.h"
+
+namespace NCompress {
+namespace NRangeCoder {
+
+const int kNumBitModelTotalBits  = 11;
+const UINT32 kBitModelTotal = (1 << kNumBitModelTotalBits);
+
+const int kNumMoveReducingBits = 2;
+
+const int kNumBitPriceShiftBits = 6;
+const UINT32 kBitPrice = 1 << kNumBitPriceShiftBits;
+
+class CPriceTables
+{
+public:
+  UINT32 StatePrices[kBitModelTotal >> kNumMoveReducingBits];
+  CPriceTables();
+};
+
+extern CPriceTables g_PriceTables;
+
+
+/////////////////////////////
+// CBitModel
+
+template <int aNumMoveBits>
+class CBitModel
+{
+public:
+  UINT32 Probability;
+  void UpdateModel(UINT32 symbol)
+  {
+    /*
+    Probability -= (Probability + ((symbol - 1) & ((1 << aNumMoveBits) - 1))) >> aNumMoveBits;
+    Probability += (1 - symbol) << (kNumBitModelTotalBits - aNumMoveBits);
+    */
+    if (symbol == 0)
+      Probability += (kBitModelTotal - Probability) >> aNumMoveBits;
+    else
+      Probability -= (Probability) >> aNumMoveBits;
+  }
+public:
+  void Init() { Probability = kBitModelTotal / 2; }
+};
+
+template <int aNumMoveBits>
+class CBitEncoder: public CBitModel<aNumMoveBits>
+{
+public:
+  void Encode(CEncoder *encoder, UINT32 symbol)
+  {
+    encoder->EncodeBit(Probability, kNumBitModelTotalBits, symbol);
+    UpdateModel(symbol);
+  }
+  UINT32 GetPrice(UINT32 symbol) const
+  {
+    return g_PriceTables.StatePrices[
+      (((Probability - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];
+  }
+};
+
+
+template <int aNumMoveBits>
+class CBitDecoder: public CBitModel<aNumMoveBits>
+{
+public:
+  UINT32 Decode(CDecoder *decoder)
+  {
+    UINT32 newBound = (decoder->Range >> kNumBitModelTotalBits) * Probability;
+    if (decoder->Code < newBound)
+    {
+      decoder->Range = newBound;
+      Probability += (kBitModelTotal - Probability) >> aNumMoveBits;
+      if (decoder->Range < kTopValue)
+      {
+        decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();
+        decoder->Range <<= 8;
+      }
+      return 0;
+    }
+    else
+    {
+      decoder->Range -= newBound;
+      decoder->Code -= newBound;
+      Probability -= (Probability) >> aNumMoveBits;
+      if (decoder->Range < kTopValue)
+      {
+        decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();
+        decoder->Range <<= 8;
+      }
+      return 1;
+    }
+  }
+};
+
+}}
+
+
+#endif