misc/libphysfs/lzma/CS/7zip/Compress/LZ/LzInWindow.cs
author nemo
Mon, 10 Apr 2017 12:06:43 -0400
changeset 12218 bb5522e88ab2
permissions -rw-r--r--
bulk copy of latest physfs to our misc/libphysfs since this seems to fix an off-by-1 error reliably hit in readln read of 1 byte probably introduced in the addition of the buffered read. Whether this is excessive or whether libphysfs should even be maintained by us is another matter. But at least we shouldn't crash

// LzInWindow.cs

using System;

namespace SevenZip.Compression.LZ
{
	public class InWindow
	{
		public Byte[] _bufferBase = null; // pointer to buffer with data
		System.IO.Stream _stream;
		UInt32 _posLimit; // offset (from _buffer) of first byte when new block reading must be done
		bool _streamEndWasReached; // if (true) then _streamPos shows real end of stream

		UInt32 _pointerToLastSafePosition;

		public UInt32 _bufferOffset;

		public UInt32 _blockSize; // Size of Allocated memory block
		public UInt32 _pos; // offset (from _buffer) of curent byte
		UInt32 _keepSizeBefore; // how many BYTEs must be kept in buffer before _pos
		UInt32 _keepSizeAfter; // how many BYTEs must be kept buffer after _pos
		public UInt32 _streamPos; // offset (from _buffer) of first not read byte from Stream

		public void MoveBlock()
		{
			UInt32 offset = (UInt32)(_bufferOffset) + _pos - _keepSizeBefore;
			// we need one additional byte, since MovePos moves on 1 byte.
			if (offset > 0)
				offset--;
			
			UInt32 numBytes = (UInt32)(_bufferOffset) + _streamPos - offset;

			// check negative offset ????
			for (UInt32 i = 0; i < numBytes; i++)
				_bufferBase[i] = _bufferBase[offset + i];
			_bufferOffset -= offset;
		}

		public virtual void ReadBlock()
		{
			if (_streamEndWasReached)
				return;
			while (true)
			{
				int size = (int)((0 - _bufferOffset) + _blockSize - _streamPos);
				if (size == 0)
					return;
				int numReadBytes = _stream.Read(_bufferBase, (int)(_bufferOffset + _streamPos), size);
				if (numReadBytes == 0)
				{
					_posLimit = _streamPos;
					UInt32 pointerToPostion = _bufferOffset + _posLimit;
					if (pointerToPostion > _pointerToLastSafePosition)
						_posLimit = (UInt32)(_pointerToLastSafePosition - _bufferOffset);

					_streamEndWasReached = true;
					return;
				}
				_streamPos += (UInt32)numReadBytes;
				if (_streamPos >= _pos + _keepSizeAfter)
					_posLimit = _streamPos - _keepSizeAfter;
			}
		}

		void Free() { _bufferBase = null; }

		public void Create(UInt32 keepSizeBefore, UInt32 keepSizeAfter, UInt32 keepSizeReserv)
		{
			_keepSizeBefore = keepSizeBefore;
			_keepSizeAfter = keepSizeAfter;
			UInt32 blockSize = keepSizeBefore + keepSizeAfter + keepSizeReserv;
			if (_bufferBase == null || _blockSize != blockSize)
			{
				Free();
				_blockSize = blockSize;
				_bufferBase = new Byte[_blockSize];
			}
			_pointerToLastSafePosition = _blockSize - keepSizeAfter;
		}

		public void SetStream(System.IO.Stream stream) { _stream = stream; }
		public void ReleaseStream() { _stream = null; }

		public void Init()
		{
			_bufferOffset = 0;
			_pos = 0;
			_streamPos = 0;
			_streamEndWasReached = false;
			ReadBlock();
		}

		public void MovePos()
		{
			_pos++;
			if (_pos > _posLimit)
			{
				UInt32 pointerToPostion = _bufferOffset + _pos;
				if (pointerToPostion > _pointerToLastSafePosition)
					MoveBlock();
				ReadBlock();
			}
		}

		public Byte GetIndexByte(Int32 index) { return _bufferBase[_bufferOffset + _pos + index]; }

		// index + limit have not to exceed _keepSizeAfter;
		public UInt32 GetMatchLen(Int32 index, UInt32 distance, UInt32 limit)
		{
			if (_streamEndWasReached)
				if ((_pos + index) + limit > _streamPos)
					limit = _streamPos - (UInt32)(_pos + index);
			distance++;
			// Byte *pby = _buffer + (size_t)_pos + index;
			UInt32 pby = _bufferOffset + _pos + (UInt32)index;

			UInt32 i;
			for (i = 0; i < limit && _bufferBase[pby + i] == _bufferBase[pby + i - distance]; i++);
			return i;
		}

		public UInt32 GetNumAvailableBytes() { return _streamPos - _pos; }

		public void ReduceOffsets(Int32 subValue)
		{
			_bufferOffset += (UInt32)subValue;
			_posLimit -= (UInt32)subValue;
			_pos -= (UInt32)subValue;
			_streamPos -= (UInt32)subValue;
		}
	}
}