InWindow.java

// LZ.InWindow

package SevenZip.Compression.LZ;

import java.io.IOException;

public class InWindow
{
	public byte[] _bufferBase; // pointer to buffer with data
	java.io.InputStream _stream;
	int _posLimit;  // offset (from _buffer) of first byte when new block reading must be done
	boolean _streamEndWasReached; // if (true) then _streamPos shows real end of stream
	
	int _pointerToLastSafePosition;
	
	public int _bufferOffset;
	
	public int _blockSize;  // Size of Allocated memory block
	public int _pos;             // offset (from _buffer) of curent byte
	int _keepSizeBefore;  // how many BYTEs must be kept in buffer before _pos
	int _keepSizeAfter;   // how many BYTEs must be kept buffer after _pos
	public int _streamPos;   // offset (from _buffer) of first not read byte from Stream
	
	public void MoveBlock()
	{
		int offset = _bufferOffset + _pos - _keepSizeBefore;
		// we need one additional byte, since MovePos moves on 1 byte.
		if (offset > 0)
			offset--;

		int numBytes = _bufferOffset + _streamPos - offset;
		
		// check negative offset ????
		for (int i = 0; i < numBytes; i++)
			_bufferBase[i] = _bufferBase[offset + i];
		_bufferOffset -= offset;
	}
	
	public void ReadBlock() throws IOException
	{
		if (_streamEndWasReached)
			return;
		while (true)
		{
			int size = (0 - _bufferOffset) + _blockSize - _streamPos;
			if (size == 0)
				return;
			int numReadBytes = _stream.read(_bufferBase, _bufferOffset + _streamPos, size);
			if (numReadBytes == -1)
			{
				_posLimit = _streamPos;
				int pointerToPostion = _bufferOffset + _posLimit;
				if (pointerToPostion > _pointerToLastSafePosition)
					_posLimit = _pointerToLastSafePosition - _bufferOffset;
				
				_streamEndWasReached = true;
				return;
			}
			_streamPos += numReadBytes;
			if (_streamPos >= _pos + _keepSizeAfter)
				_posLimit = _streamPos - _keepSizeAfter;
		}
	}
	
	void Free() { _bufferBase = null; }
	
	public void Create(int keepSizeBefore, int keepSizeAfter, int keepSizeReserv)
	{
		_keepSizeBefore = keepSizeBefore;
		_keepSizeAfter = keepSizeAfter;
		int blockSize = keepSizeBefore + keepSizeAfter + keepSizeReserv;
		if (_bufferBase == null || _blockSize != blockSize)
		{
			Free();
			_blockSize = blockSize;
			_bufferBase = new byte[_blockSize];
		}
		_pointerToLastSafePosition = _blockSize - keepSizeAfter;
	}
	
	public void SetStream(java.io.InputStream stream) { _stream = stream; 	}
	public void ReleaseStream() { _stream = null; }

	public void Init() throws IOException
	{
		_bufferOffset = 0;
		_pos = 0;
		_streamPos = 0;
		_streamEndWasReached = false;
		ReadBlock();
	}
	
	public void MovePos() throws IOException
	{
		_pos++;
		if (_pos > _posLimit)
		{
			int pointerToPostion = _bufferOffset + _pos;
			if (pointerToPostion > _pointerToLastSafePosition)
				MoveBlock();
			ReadBlock();
		}
	}
	
	public byte GetIndexByte(int index)	{ return _bufferBase[_bufferOffset + _pos + index]; }
	
	// index + limit have not to exceed _keepSizeAfter;
	public int GetMatchLen(int index, int distance, int limit)
	{
		if (_streamEndWasReached)
			if ((_pos + index) + limit > _streamPos)
				limit = _streamPos - (_pos + index);
		distance++;
		// Byte *pby = _buffer + (size_t)_pos + index;
		int pby = _bufferOffset + _pos + index;
		
		int i;
		for (i = 0; i < limit && _bufferBase[pby + i] == _bufferBase[pby + i - distance]; i++);
		return i;
	}
	
	public int GetNumAvailableBytes()	{ return _streamPos - _pos; }
	
	public void ReduceOffsets(int subValue)
	{
		_bufferOffset += subValue;
		_posLimit -= subValue;
		_pos -= subValue;
		_streamPos -= subValue;
	}
}