/Utilities/Compression/Streams/StreamManipulator.cs

// Based on Mike Krueger's SharpZipLib, Copyright (C) 2001 (GNU license).

// Authors of the original java version: Jochen Hoenicke, John Leuner

// See http://www.ISeeSharpCode.com for more information.



using System;



namespace Delta.Utilities.Compression.Streams

{

	/// <summary>

	/// This class allows us to retrieve a specified amount of bits from

	/// the input buffer, as well as copy big byte blocks.

	///

	/// It uses an int buffer to store up to 31 bits for direct

	/// manipulation. This guarantees that we can get at least 16 bits,

	/// but we only need at most 15, so this is all safe.

	///

	/// There are some optimizations in this class, for example, you must

	/// never peek more then 8 bits more than needed, and you must first

	/// peek bits before you may drop them. This is not a general purpose

	/// class but optimized for the behavior of the Inflater.

	/// </summary>

	public class StreamManipulator

	{

		#region AvailableBits (Public)

		/// <summary>

		/// Gets the number of bits available in the bit buffer.  This must be

		/// only called when a previous peekBits() returned -1.

		/// </summary>

		/// <returns>The number of bits available.</returns>

		public int AvailableBits

		{

			get

			{

				return bitsInBuffer;

			} // get

		}

		#endregion



		#region AvailableBytes (Public)

		/// <summary>

		/// Gets the number of bytes available.

		/// </summary>

		/// <returns>The number of bytes available.</returns>

		public int AvailableBytes

		{

			get

			{

				return windowEnd - windowStart + (bitsInBuffer >> 3);

			} // get

		}

		#endregion



		#region IsNeedingInput (Public)

		/// <summary>

		/// Is needing input

		/// </summary>

		/// <returns>

		/// True if we need input, false if the start window is already at the end.

		/// </returns>

		public bool IsNeedingInput

		{

			get

			{

				return windowStart == windowEnd;

			} // get

		}

		#endregion



		#region Private



		#region window (Private)

		/// <summary>

		/// Window

		/// </summary>

		private byte[] window;

		#endregion



		#region windowStart (Private)

		/// <summary>

		/// Window start

		/// </summary>

		private int windowStart;

		#endregion



		#region windowEnd (Private)

		/// <summary>

		/// Window end

		/// </summary>

		private int windowEnd;

		#endregion



		#region buffer (Private)

		/// <summary>

		/// Buffer

		/// </summary>

		private uint buffer;

		#endregion



		#region bitsInBuffer (Private)

		/// <summary>

		/// Bits in buffer

		/// </summary>

		private int bitsInBuffer;

		#endregion



		#endregion



		#region PeekBits (Public)

		/// <summary>

		/// Get the next n bits but don't increase input pointer.  n must be

		/// less or equal 16 and if you if this call succeeds, you must drop

		/// at least n-8 bits in the next call.

		/// </summary>

		/// <returns>

		/// the value of the bits, or -1 if not enough bits available.  */

		/// </returns>

		public int PeekBits(int n)

		{

			if (bitsInBuffer < n)

			{

				if (windowStart == windowEnd)

				{

					return -1; // ok

				} // if (windowStart)

				buffer |= (uint)((window[windowStart++] & 0xff |

				                  (window[windowStart++] & 0xff) << 8) << bitsInBuffer);

				bitsInBuffer += 16;

			} // if (bitsInBuffer)

			return (int)(buffer & ((1 << n) - 1));

		}

		#endregion



		#region DropBits (Public)

		/// <summary>

		/// Drops the next n bits from the input.  You should have called peekBits

		/// with a bigger or equal n before, to make sure that enough bits are in

		/// the bit buffer.

		/// </summary>

		public void DropBits(int n)

		{

			buffer >>= n;

			bitsInBuffer -= n;

		}

		#endregion



		#region GetBits (Public)

		/// <summary>

		/// Gets the next n bits and increases input pointer.  This is equivalent

		/// to peekBits followed by dropBits, except for correct error handling.

		/// </summary>

		/// <returns>

		/// the value of the bits, or -1 if not enough bits available.

		/// </returns>

		public int GetBits(int n)

		{

			int bits = PeekBits(n);

			if (bits >= 0)

			{

				DropBits(n);

			} // if (bits)

			return bits;

		}

		#endregion



		#region SkipToByteBoundary (Public)

		/// <summary>

		/// Skips to the next byte boundary.

		/// </summary>

		public void SkipToByteBoundary()

		{

			buffer >>= (bitsInBuffer & 7);

			bitsInBuffer &= ~7;

		}

		#endregion



		#region CopyBytes (Public)

		/// <summary>

		/// Copies length bytes from input buffer to output buffer starting

		/// at output[offset].  You have to make sure, that the buffer is

		/// byte aligned.  If not enough bytes are available, copies fewer

		/// bytes.

		/// </summary>

		/// <param name="output">The buffer.</param>

		/// <param name="offset">The offset in the buffer.</param>

		/// <param name="length">the length to copy, 0 is allowed.</param>

		/// <returns>The number of bytes copied, 0 if no byte is available.

		/// </returns>

		public int CopyBytes(byte[] output, int offset, int length)

		{

			if (length < 0)

			{

				throw new ArgumentOutOfRangeException("length negative");

			} // if (length)

			if ((bitsInBuffer & 7) != 0)

			{

				// bitsInBuffer may only be 0 or 8

				throw new InvalidOperationException("Bit buffer is not aligned!");

			} // if (bitsInBuffer)



			int count = 0;

			while (bitsInBuffer > 0 &&

			       length > 0)

			{

				output[offset++] = (byte)buffer;

				buffer >>= 8;

				bitsInBuffer -= 8;

				length--;

				count++;

			} // while (bitsInBuffer)

			if (length == 0)

			{

				return count;

			} // if (length)



			int avail = windowEnd - windowStart;

			if (length > avail)

			{

				length = avail;

			} // if (length)

			Array.Copy(window, windowStart, output, offset, length);

			windowStart += length;



			if (((windowStart - windowEnd) & 1) != 0)

			{

				// We always want an even number of bytes in input, see peekBits

				buffer = (uint)(window[windowStart++] & 0xff);

				bitsInBuffer = 8;

			} // if (windowStart)

			return count + length;

		}

		#endregion



		#region Reset (Public)

		/// <summary>

		/// Reset

		/// </summary>

		public void Reset()

		{

			buffer = (uint)(windowStart = windowEnd = bitsInBuffer = 0);

		}

		#endregion



		#region SetInput (Public)

		/// <summary>

		/// Set input

		/// </summary>

		/// <param name="buf">Buf</param>

		/// <param name="off">Off</param>

		/// <param name="len">Len</param>

		public void SetInput(byte[] buf, int off, int len)

		{

			if (windowStart < windowEnd)

			{

				throw new InvalidOperationException(

					"Old input was not completely processed");

			} // if (windowStart)



			int end = off + len;



			// We want to throw an ArrayIndexOutOfBoundsException early.

			// The check is very tricky: it also handles integer wrap around.

			if (0 > off || off > end || end > buf.Length)

			{

				throw new ArgumentOutOfRangeException();

			} // if (0)



			if ((len & 1) != 0)

			{

				// We always want an even number of bytes in input, see peekBits

				buffer |= (uint)((buf[off++] & 0xff) << bitsInBuffer);

				bitsInBuffer += 8;

			} // if (len)



			window = buf;

			windowStart = off;

			windowEnd = end;

		}

		#endregion

	}

}