context: using System;
  
  namespace ICSharpCode.SharpZipLib.Zip.Compression.Streams
  {
  	/// <summary>
  	/// This class allows us to retrieve a specified number 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 than 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 behaviour of the Inflater.
  	///
  	/// authors of the original java version : John Leuner, Jochen Hoenicke
  	/// </summary>
  	public class StreamManipulator
  	{
  		/// <summary>
  		/// Get the next sequence of bits but don't increase input pointer.  bitCount must be
  		/// less or equal 16 and if this call succeeds, you must drop
  		/// at least n - 8 bits in the next call.
  		/// </summary>
  		/// <param name="bitCount">The number of bits to peek.</param>
  		/// <returns>
  		/// the value of the bits, or -1 if not enough bits available.  */
  		/// </returns>
  		public int PeekBits(int bitCount)
  		{
  			if (bitsInBuffer_ < bitCount) {
  				if (windowStart_ == windowEnd_) {
  					return -1; // ok
  				}
  				buffer_ |= (uint)((window_[windowStart_++] & 0xff |
  								 (window_[windowStart_++] & 0xff) << 8) << bitsInBuffer_);
  				bitsInBuffer_ += 16;
  			}
  			return (int)(buffer_ & ((1 << bitCount) - 1));
  		}
  
  		/// <summary>
  		/// Tries to grab the next <paramref name="bitCount"/> bits from the input and 
  		/// sets <paramref name="output"/> to the value, adding <paramref name="outputOffset"/>.
  		/// </summary>
  		/// <returns>true if enough bits could be read, otherwise false</returns>
  		public bool TryGetBits(int bitCount, ref int output, int outputOffset = 0)
  		{
  			var bits = PeekBits(bitCount);
  			if (bits < 0)
  			{
  				return false;
  			}
  			output = bits + outputOffset;
  			DropBits(bitCount);
  			return true;
  		}
  
  		/// <summary>
  		/// Tries to grab the next <paramref name="bitCount"/> bits from the input and 
  		/// sets <paramref name="output"/> to the value, adding <paramref name="outputOffset"/>.
  		/// </summary>
  		/// <returns>true if enough bits could be read, otherwise false</returns>
  		public bool TryGetBits(int bitCount, ref byte[] array, int index)
  		{
  			var bits = PeekBits(bitCount);
  			if (bits < 0)
  			{
  				return false;
  			}
  			array[index] = (byte)bits;
  			DropBits(bitCount);
  			return true;
  		}
  
  		/// <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>
  		/// <param name="bitCount">The number of bits to drop.</param>
  		public void DropBits(int bitCount)
  		{
  			buffer_ >>= bitCount;
  			bitsInBuffer_ -= bitCount;
  		}
  
  		/// <summary>
  		/// Gets the next n bits and increases input pointer.  This is equivalent
  		/// to <see cref="PeekBits"/> followed by <see cref="DropBits"/>, except for correct error handling.
  		/// </summary>
  		/// <param name="bitCount">The number of bits to retrieve.</param>
  		/// <returns>
  		/// the value of the bits, or -1 if not enough bits available.
  		/// </returns>
  		public int GetBits(int bitCount)
  		{
  			int bits = PeekBits(bitCount);
  			if (bits >= 0) {
  				DropBits(bitCount);
  			}
  			return bits;
  		}
  
  		/// <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_;
  			}
  		}
  
  		/// <summary>
  		/// Gets the number of bytes available.
  		/// </summary>
  		/// <returns>
  		/// The number of bytes available.
  		/// </returns>
  		public int AvailableBytes {
  			get {
  				return windowEnd_ - windowStart_ + (bitsInBuffer_ >> 3);
  			}
  		}
  
  		/// <summary>
  		/// Skips to the next byte boundary.
  		/// </summary>
  		public void SkipToByteBoundary()
  		{
  			buffer_ >>= (bitsInBuffer_ & 7);
  			bitsInBuffer_ &= ~7;
  		}
  
  		/// <summary>
  		/// Returns true when SetInput can be called
  		/// </summary>
  		public bool IsNeedingInput {
  			get {
  				return windowStart_ == windowEnd_;
  			}
  		}
  
  		/// <summary>
  		/// Copies 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 to copy bytes to.
  		/// </param>
  		/// <param name="offset">
  		/// The offset in the buffer at which copying starts
  		/// </param>
  		/// <param name="length">
  		/// The length to copy, 0 is allowed.
  		/// </param>
  		/// <returns>
  		/// The number of bytes copied, 0 if no bytes were available.
  		/// </returns>
  		/// <exception cref="ArgumentOutOfRangeException">
  		/// Length is less than zero
  		/// </exception>
  		/// <exception cref="InvalidOperationException">
  		/// Bit buffer isnt byte aligned
  		/// </exception>
  		public int CopyBytes(byte[] output, int offset, int length)
  		{
  			if (length < 0) {
  				throw new ArgumentOutOfRangeException(nameof(length));
  			}
  
  			if ((bitsInBuffer_ & 7) != 0) {
  				// bits_in_buffer may only be 0 or a multiple of 8
  				throw new InvalidOperationException("Bit buffer is not byte aligned!");
  			}
  
  			int count = 0;
  			while ((bitsInBuffer_ > 0) && (length > 0)) {
  				output[offset++] = (byte)buffer_;
  				buffer_ >>= 8;
  				bitsInBuffer_ -= 8;
  				length--;
  				count++;
  			}
  
  			if (length == 0) {
  				return count;
  			}
  
  			int avail = windowEnd_ - windowStart_;
  			if (length > avail) {
  				length = avail;
  			}
  			System.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;
  			}
  			return count + length;
  		}
  
  		/// <summary>
  		/// Resets state and empties internal buffers
  		/// </summary>
  		public void Reset()
  		{
  			buffer_ = 0;
  			windowStart_ = windowEnd_ = bitsInBuffer_ = 0;
  		}
  
  		/// <summary>
  		/// Add more input for consumption.
  		/// Only call when IsNeedingInput returns true
  		/// </summary>
  		/// <param name="buffer">data to be input</param>
  		/// <param name="offset">offset of first byte of input</param>
  		/// <param name="count">number of bytes of input to add.</param>
  		public void SetInput(byte[] buffer, int offset, int count)
  		{
  			if (buffer == null) {
  				throw new ArgumentNullException(nameof(buffer));
  			}
  
  			if (offset < 0) {
  				throw new ArgumentOutOfRangeException(nameof(offset), "Cannot be negative");
  			}
  
  
gt: 			if (count < 0) {