3.13

7zip/Common/MSBFDecoder.h

@@ -0,0 +1,73 @@
+// Stream/MSBFDecoder.h
+// the Most Significant Bit of byte is First
+
+#pragma once
+
+#ifndef __STREAM_MSBFDECODER_H
+#define __STREAM_MSBFDECODER_H
+
+namespace NStream {
+namespace NMSBF {
+
+const int kNumBigValueBits = 8 * 4;
+
+const int kNumValueBytes = 3;
+const int kNumValueBits = 8  * kNumValueBytes;
+
+const UINT32 kMask = (1 << kNumValueBits) - 1;
+
+template<class TInByte>
+class CDecoder
+{
+  TInByte m_Stream;
+  UINT32 m_BitPos;
+  UINT32 m_Value;
+
+public:
+  
+  void Init(ISequentialInStream *aStream)
+  {
+    m_Stream.Init(aStream);
+    m_BitPos = kNumBigValueBits; 
+    Normalize();
+  }
+  
+  /*
+  void ReleaseStream()
+  {
+    m_Stream.ReleaseStream();
+  }
+  */
+
+  UINT64 GetProcessedSize() const 
+    { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }
+  
+  void Normalize()
+  {
+    for (;m_BitPos >= 8; m_BitPos -= 8)
+      m_Value = (m_Value << 8) | m_Stream.ReadByte();
+  }
+
+  UINT32 GetValue(UINT32 aNumBits) const
+  {
+    // return (m_Value << m_BitPos) >> (kNumBigValueBits - aNumBits);
+    return ((m_Value >> (8 - m_BitPos)) & kMask) >> (kNumValueBits - aNumBits);
+  }
+  
+  void MovePos(UINT32 aNumBits)
+  {
+    m_BitPos += aNumBits;
+    Normalize();
+  }
+  
+  UINT32 ReadBits(UINT32 aNumBits)
+  {
+    UINT32 aRes = GetValue(aNumBits);
+    MovePos(aNumBits);
+    return aRes;
+  }
+};
+
+}}
+
+#endif