1 // LzInWindow.cs
2 
3 using System;
4 
5 namespace SevenZip.Compression.LZ
6 {
7 	public class InWindow
8 	{
9 		public Byte[] _bufferBase = null; // pointer to buffer with data
10 		System.IO.Stream _stream;
11 		UInt32 _posLimit; // offset (from _buffer) of first byte when new block reading must be done
12 		bool _streamEndWasReached; // if (true) then _streamPos shows real end of stream
13 
14 		UInt32 _pointerToLastSafePosition;
15 
16 		public UInt32 _bufferOffset;
17 
18 		public UInt32 _blockSize; // Size of Allocated memory block
19 		public UInt32 _pos; // offset (from _buffer) of curent byte
20 		UInt32 _keepSizeBefore; // how many BYTEs must be kept in buffer before _pos
21 		UInt32 _keepSizeAfter; // how many BYTEs must be kept buffer after _pos
22 		public UInt32 _streamPos; // offset (from _buffer) of first not read byte from Stream
23 
MoveBlock()24 		public void MoveBlock()
25 		{
26 			UInt32 offset = (UInt32)(_bufferOffset) + _pos - _keepSizeBefore;
27 			// we need one additional byte, since MovePos moves on 1 byte.
28 			if (offset > 0)
29 				offset--;
30 
31 			UInt32 numBytes = (UInt32)(_bufferOffset) + _streamPos - offset;
32 
33 			// check negative offset ????
34 			for (UInt32 i = 0; i < numBytes; i++)
35 				_bufferBase[i] = _bufferBase[offset + i];
36 			_bufferOffset -= offset;
37 		}
38 
ReadBlock()39 		public virtual void ReadBlock()
40 		{
41 			if (_streamEndWasReached)
42 				return;
43 			while (true)
44 			{
45 				int size = (int)((0 - _bufferOffset) + _blockSize - _streamPos);
46 				if (size == 0)
47 					return;
48 				int numReadBytes = _stream.Read(_bufferBase, (int)(_bufferOffset + _streamPos), size);
49 				if (numReadBytes == 0)
50 				{
51 					_posLimit = _streamPos;
52 					UInt32 pointerToPostion = _bufferOffset + _posLimit;
53 					if (pointerToPostion > _pointerToLastSafePosition)
54 						_posLimit = (UInt32)(_pointerToLastSafePosition - _bufferOffset);
55 
56 					_streamEndWasReached = true;
57 					return;
58 				}
59 				_streamPos += (UInt32)numReadBytes;
60 				if (_streamPos >= _pos + _keepSizeAfter)
61 					_posLimit = _streamPos - _keepSizeAfter;
62 			}
63 		}
64 
Free()65 		void Free() { _bufferBase = null; }
66 
Create(UInt32 keepSizeBefore, UInt32 keepSizeAfter, UInt32 keepSizeReserv)67 		public void Create(UInt32 keepSizeBefore, UInt32 keepSizeAfter, UInt32 keepSizeReserv)
68 		{
69 			_keepSizeBefore = keepSizeBefore;
70 			_keepSizeAfter = keepSizeAfter;
71 			UInt32 blockSize = keepSizeBefore + keepSizeAfter + keepSizeReserv;
72 			if (_bufferBase == null || _blockSize != blockSize)
73 			{
74 				Free();
75 				_blockSize = blockSize;
76 				_bufferBase = new Byte[_blockSize];
77 			}
78 			_pointerToLastSafePosition = _blockSize - keepSizeAfter;
79 		}
80 
SetStream(System.IO.Stream stream)81 		public void SetStream(System.IO.Stream stream) { _stream = stream; }
ReleaseStream()82 		public void ReleaseStream() { _stream = null; }
83 
Init()84 		public void Init()
85 		{
86 			_bufferOffset = 0;
87 			_pos = 0;
88 			_streamPos = 0;
89 			_streamEndWasReached = false;
90 			ReadBlock();
91 		}
92 
MovePos()93 		public void MovePos()
94 		{
95 			_pos++;
96 			if (_pos > _posLimit)
97 			{
98 				UInt32 pointerToPostion = _bufferOffset + _pos;
99 				if (pointerToPostion > _pointerToLastSafePosition)
100 					MoveBlock();
101 				ReadBlock();
102 			}
103 		}
104 
GetIndexByte(Int32 index)105 		public Byte GetIndexByte(Int32 index) { return _bufferBase[_bufferOffset + _pos + index]; }
106 
107 		// index + limit have not to exceed _keepSizeAfter;
GetMatchLen(Int32 index, UInt32 distance, UInt32 limit)108 		public UInt32 GetMatchLen(Int32 index, UInt32 distance, UInt32 limit)
109 		{
110 			if (_streamEndWasReached)
111 				if ((_pos + index) + limit > _streamPos)
112 					limit = _streamPos - (UInt32)(_pos + index);
113 			distance++;
114 			// Byte *pby = _buffer + (size_t)_pos + index;
115 			UInt32 pby = _bufferOffset + _pos + (UInt32)index;
116 
117 			UInt32 i;
118 			for (i = 0; i < limit && _bufferBase[pby + i] == _bufferBase[pby + i - distance]; i++);
119 			return i;
120 		}
121 
GetNumAvailableBytes()122 		public UInt32 GetNumAvailableBytes() { return _streamPos - _pos; }
123 
ReduceOffsets(Int32 subValue)124 		public void ReduceOffsets(Int32 subValue)
125 		{
126 			_bufferOffset += (UInt32)subValue;
127 			_posLimit -= (UInt32)subValue;
128 			_pos -= (UInt32)subValue;
129 			_streamPos -= (UInt32)subValue;
130 		}
131 	}
132 }
133