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CPP/7zip/Compress/HuffmanDecoder.h

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+// Compress/HuffmanDecoder.h
+
+#ifndef __COMPRESS_HUFFMAN_DECODER_H
+#define __COMPRESS_HUFFMAN_DECODER_H
+
+#include "../../Common/Types.h"
+
+namespace NCompress {
+namespace NHuffman {
+
+const int kNumTableBits = 9;
+
+template <int kNumBitsMax, UInt32 m_NumSymbols>
+class CDecoder
+{
+  UInt32 m_Limits[kNumBitsMax + 1];     // m_Limits[i] = value limit for symbols with length = i
+  UInt32 m_Positions[kNumBitsMax + 1];  // m_Positions[i] = index in m_Symbols[] of first symbol with length = i
+  UInt32 m_Symbols[m_NumSymbols];
+  Byte m_Lengths[1 << kNumTableBits];   // Table oh length for short codes.
+
+public:
+  
+  bool SetCodeLengths(const Byte *codeLengths)
+  {
+    int lenCounts[kNumBitsMax + 1];
+    UInt32 tmpPositions[kNumBitsMax + 1];
+    int i;
+    for(i = 1; i <= kNumBitsMax; i++)
+      lenCounts[i] = 0;
+    UInt32 symbol;
+    for (symbol = 0; symbol < m_NumSymbols; symbol++)
+    {
+      int len = codeLengths[symbol];
+      if (len > kNumBitsMax)
+        return false;
+      lenCounts[len]++;
+      m_Symbols[symbol] = 0xFFFFFFFF;
+    }
+    lenCounts[0] = 0;
+    m_Positions[0] = m_Limits[0] = 0;
+    UInt32 startPos = 0;
+    UInt32 index = 0;
+    const UInt32 kMaxValue = (1 << kNumBitsMax);
+    for (i = 1; i <= kNumBitsMax; i++)
+    {
+      startPos += lenCounts[i] << (kNumBitsMax - i);
+      if (startPos > kMaxValue)
+        return false;
+      m_Limits[i] = (i == kNumBitsMax) ? kMaxValue : startPos;
+      m_Positions[i] = m_Positions[i - 1] + lenCounts[i - 1];
+      tmpPositions[i] = m_Positions[i];
+      if(i <= kNumTableBits)
+      {
+        UInt32 limit = (m_Limits[i] >> (kNumBitsMax - kNumTableBits));
+        for (; index < limit; index++)
+          m_Lengths[index] = (Byte)i;
+      }
+    }
+    for (symbol = 0; symbol < m_NumSymbols; symbol++)
+    {
+      int len = codeLengths[symbol];
+      if (len != 0)
+        m_Symbols[tmpPositions[len]++] = symbol;
+    }
+    return true;
+  }
+
+  template <class TBitDecoder>
+  UInt32 DecodeSymbol(TBitDecoder *bitStream)
+  {
+    int numBits;
+    UInt32 value = bitStream->GetValue(kNumBitsMax);
+    if (value < m_Limits[kNumTableBits])
+      numBits = m_Lengths[value >> (kNumBitsMax - kNumTableBits)];
+    else
+      for (numBits = kNumTableBits + 1; value >= m_Limits[numBits]; numBits++);
+    bitStream->MovePos(numBits);
+    UInt32 index = m_Positions[numBits] +
+      ((value - m_Limits[numBits - 1]) >> (kNumBitsMax - numBits));
+    if (index >= m_NumSymbols)
+      // throw CDecoderException(); // test it
+      return 0xFFFFFFFF;
+    return m_Symbols[index];
+  }
+};
+
+}}
+
+#endif