// CRC32.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2011 Dino Chiesa.
// All rights reserved.
//
// This code module is part of DotNetZip, a zipfile class library.
//
// ------------------------------------------------------------------
//
// This code is licensed under the Microsoft Public License.
// See the file License.txt for the license details.
// More info on: http://dotnetzip.codeplex.com
//
// ------------------------------------------------------------------
//
// Last Saved: <2011-August-02 18:25:54>
//
// ------------------------------------------------------------------
//
// This module defines the CRC32 class, which can do the CRC32 algorithm, using
// arbitrary starting polynomials, and bit reversal. The bit reversal is what
// distinguishes this CRC-32 used in BZip2 from the CRC-32 that is used in PKZIP
// files, or GZIP files. This class does both.
//
// ------------------------------------------------------------------


using System;
using Interop = System.Runtime.InteropServices;

namespace Ionic.Crc
{
	/// <summary>
	///   Computes a CRC-32. The CRC-32 algorithm is parameterized - you
	///   can set the polynomial and enable or disable bit
	///   reversal. This can be used for GZIP, BZip2, or ZIP.
	/// </summary>
	/// <remarks>
	///   This type is used internally by DotNetZip; it is generally not used
	///   directly by applications wishing to create, read, or manipulate zip
	///   archive files.
	/// </remarks>

	[Interop.GuidAttribute("ebc25cf6-9120-4283-b972-0e5520d0000C")]
	[Interop.ComVisible(true)]
#if !NETCF
	[Interop.ClassInterface(Interop.ClassInterfaceType.AutoDispatch)]
#endif
	internal class CRC32
	{
		/// <summary>
		///   Indicates the total number of bytes applied to the CRC.
		/// </summary>
		public Int64 TotalBytesRead
		{
			get
			{
				return _TotalBytesRead;
			}
		}

		/// <summary>
		/// Indicates the current CRC for all blocks slurped in.
		/// </summary>
		public Int32 Crc32Result
		{
			get
			{
				return unchecked((Int32)(~_register));
			}
		}

		/// <summary>
		/// Returns the CRC32 for the specified stream.
		/// </summary>
		/// <param name="input">The stream over which to calculate the CRC32</param>
		/// <returns>the CRC32 calculation</returns>
		public Int32 GetCrc32(System.IO.Stream input)
		{
			return GetCrc32AndCopy(input, null);
		}

		/// <summary>
		/// Returns the CRC32 for the specified stream, and writes the input into the
		/// output stream.
		/// </summary>
		/// <param name="input">The stream over which to calculate the CRC32</param>
		/// <param name="output">The stream into which to deflate the input</param>
		/// <returns>the CRC32 calculation</returns>
		public Int32 GetCrc32AndCopy(System.IO.Stream input, System.IO.Stream output)
		{
			if (input == null)
				throw new Exception("The input stream must not be null.");

			unchecked
			{
				byte[] buffer = new byte[BUFFER_SIZE];
				int readSize = BUFFER_SIZE;

				_TotalBytesRead = 0;
				int count = input.Read(buffer, 0, readSize);
				if (output != null) output.Write(buffer, 0, count);
				_TotalBytesRead += count;
				while (count > 0)
				{
					SlurpBlock(buffer, 0, count);
					count = input.Read(buffer, 0, readSize);
					if (output != null) output.Write(buffer, 0, count);
					_TotalBytesRead += count;
				}

				return (Int32)(~_register);
			}
		}


		/// <summary>
		///   Get the CRC32 for the given (word,byte) combo.  This is a
		///   computation defined by PKzip for PKZIP 2.0 (weak) encryption.
		/// </summary>
		/// <param name="W">The word to start with.</param>
		/// <param name="B">The byte to combine it with.</param>
		/// <returns>The CRC-ized result.</returns>
		public Int32 ComputeCrc32(Int32 W, byte B)
		{
			return _InternalComputeCrc32((UInt32)W, B);
		}

		internal Int32 _InternalComputeCrc32(UInt32 W, byte B)
		{
			return (Int32)(crc32Table[(W ^ B) & 0xFF] ^ (W >> 8));
		}


		/// <summary>
		/// Update the value for the running CRC32 using the given block of bytes.
		/// This is useful when using the CRC32() class in a Stream.
		/// </summary>
		/// <param name="block">block of bytes to slurp</param>
		/// <param name="offset">starting point in the block</param>
		/// <param name="count">how many bytes within the block to slurp</param>
		public void SlurpBlock(byte[] block, int offset, int count)
		{
			if (block == null)
				throw new Exception("The data buffer must not be null.");

			// bzip algorithm
			for (int i = 0; i < count; i++)
			{
				int x = offset + i;
				byte b = block[x];
				if (this.reverseBits)
				{
					UInt32 temp = (_register >> 24) ^ b;
					_register = (_register << 8) ^ crc32Table[temp];
				}
				else
				{
					UInt32 temp = (_register & 0x000000FF) ^ b;
					_register = (_register >> 8) ^ crc32Table[temp];
				}
			}
			_TotalBytesRead += count;
		}


		/// <summary>
		///   Process one byte in the CRC.
		/// </summary>
		/// <param name = "b">the byte to include into the CRC .  </param>
		public void UpdateCRC(byte b)
		{
			if (this.reverseBits)
			{
				UInt32 temp = (_register >> 24) ^ b;
				_register = (_register << 8) ^ crc32Table[temp];
			}
			else
			{
				UInt32 temp = (_register & 0x000000FF) ^ b;
				_register = (_register >> 8) ^ crc32Table[temp];
			}
		}

		/// <summary>
		///   Process a run of N identical bytes into the CRC.
		/// </summary>
		/// <remarks>
		///   <para>
		///     This method serves as an optimization for updating the CRC when a
		///     run of identical bytes is found. Rather than passing in a buffer of
		///     length n, containing all identical bytes b, this method accepts the
		///     byte value and the length of the (virtual) buffer - the length of
		///     the run.
		///   </para>
		/// </remarks>
		/// <param name = "b">the byte to include into the CRC.  </param>
		/// <param name = "n">the number of times that byte should be repeated. </param>
		public void UpdateCRC(byte b, int n)
		{
			while (n-- > 0)
			{
				if (this.reverseBits)
				{
					uint temp = (_register >> 24) ^ b;
					_register = (_register << 8) ^ crc32Table[(temp >= 0)
																										? temp
																										: (temp + 256)];
				}
				else
				{
					UInt32 temp = (_register & 0x000000FF) ^ b;
					_register = (_register >> 8) ^ crc32Table[(temp >= 0)
																										? temp
																										: (temp + 256)];

				}
			}
		}



		private static uint ReverseBits(uint data)
		{
			unchecked
			{
				uint ret = data;
				ret = (ret & 0x55555555) << 1 | (ret >> 1) & 0x55555555;
				ret = (ret & 0x33333333) << 2 | (ret >> 2) & 0x33333333;
				ret = (ret & 0x0F0F0F0F) << 4 | (ret >> 4) & 0x0F0F0F0F;
				ret = (ret << 24) | ((ret & 0xFF00) << 8) | ((ret >> 8) & 0xFF00) | (ret >> 24);
				return ret;
			}
		}

		private static byte ReverseBits(byte data)
		{
			unchecked
			{
				uint u = (uint)data * 0x00020202;
				uint m = 0x01044010;
				uint s = u & m;
				uint t = (u << 2) & (m << 1);
				return (byte)((0x01001001 * (s + t)) >> 24);
			}
		}



		private void GenerateLookupTable()
		{
			crc32Table = new UInt32[256];
			unchecked
			{
				UInt32 dwCrc;
				byte i = 0;
				do
				{
					dwCrc = i;
					for (byte j = 8; j > 0; j--)
					{
						if ((dwCrc & 1) == 1)
						{
							dwCrc = (dwCrc >> 1) ^ dwPolynomial;
						}
						else
						{
							dwCrc >>= 1;
						}
					}
					if (reverseBits)
					{
						crc32Table[ReverseBits(i)] = ReverseBits(dwCrc);
					}
					else
					{
						crc32Table[i] = dwCrc;
					}
					i++;
				} while (i != 0);
			}

#if VERBOSE
            Console.WriteLine();
            Console.WriteLine("private static readonly UInt32[] crc32Table = {");
            for (int i = 0; i < crc32Table.Length; i+=4)
            {
                Console.Write("   ");
                for (int j=0; j < 4; j++)
                {
                    Console.Write(" 0x{0:X8}U,", crc32Table[i+j]);
                }
                Console.WriteLine();
            }
            Console.WriteLine("};");
            Console.WriteLine();
#endif
		}


		private uint gf2_matrix_times(uint[] matrix, uint vec)
		{
			uint sum = 0;
			int i = 0;
			while (vec != 0)
			{
				if ((vec & 0x01) == 0x01)
					sum ^= matrix[i];
				vec >>= 1;
				i++;
			}
			return sum;
		}

		private void gf2_matrix_square(uint[] square, uint[] mat)
		{
			for (int i = 0; i < 32; i++)
				square[i] = gf2_matrix_times(mat, mat[i]);
		}



		/// <summary>
		///   Combines the given CRC32 value with the current running total.
		/// </summary>
		/// <remarks>
		///   This is useful when using a divide-and-conquer approach to
		///   calculating a CRC.  Multiple threads can each calculate a
		///   CRC32 on a segment of the data, and then combine the
		///   individual CRC32 values at the end.
		/// </remarks>
		/// <param name="crc">the crc value to be combined with this one</param>
		/// <param name="length">the length of data the CRC value was calculated on</param>
		public void Combine(int crc, int length)
		{
			uint[] even = new uint[32];     // even-power-of-two zeros operator
			uint[] odd = new uint[32];      // odd-power-of-two zeros operator

			if (length == 0)
				return;

			uint crc1 = ~_register;
			uint crc2 = (uint)crc;

			// put operator for one zero bit in odd
			odd[0] = this.dwPolynomial;  // the CRC-32 polynomial
			uint row = 1;
			for (int i = 1; i < 32; i++)
			{
				odd[i] = row;
				row <<= 1;
			}

			// put operator for two zero bits in even
			gf2_matrix_square(even, odd);

			// put operator for four zero bits in odd
			gf2_matrix_square(odd, even);

			uint len2 = (uint)length;

			// apply len2 zeros to crc1 (first square will put the operator for one
			// zero byte, eight zero bits, in even)
			do
			{
				// apply zeros operator for this bit of len2
				gf2_matrix_square(even, odd);

				if ((len2 & 1) == 1)
					crc1 = gf2_matrix_times(even, crc1);
				len2 >>= 1;

				if (len2 == 0)
					break;

				// another iteration of the loop with odd and even swapped
				gf2_matrix_square(odd, even);
				if ((len2 & 1) == 1)
					crc1 = gf2_matrix_times(odd, crc1);
				len2 >>= 1;


			} while (len2 != 0);

			crc1 ^= crc2;

			_register = ~crc1;

			//return (int) crc1;
			return;
		}


		/// <summary>
		///   Create an instance of the CRC32 class using the default settings: no
		///   bit reversal, and a polynomial of 0xEDB88320.
		/// </summary>
		public CRC32() : this(false)
		{
		}

		/// <summary>
		///   Create an instance of the CRC32 class, specifying whether to reverse
		///   data bits or not.
		/// </summary>
		/// <param name='reverseBits'>
		///   specify true if the instance should reverse data bits.
		/// </param>
		/// <remarks>
		///   <para>
		///     In the CRC-32 used by BZip2, the bits are reversed. Therefore if you
		///     want a CRC32 with compatibility with BZip2, you should pass true
		///     here. In the CRC-32 used by GZIP and PKZIP, the bits are not
		///     reversed; Therefore if you want a CRC32 with compatibility with
		///     those, you should pass false.
		///   </para>
		/// </remarks>
		public CRC32(bool reverseBits) :
				this(unchecked((int)0xEDB88320), reverseBits)
		{
		}


		/// <summary>
		///   Create an instance of the CRC32 class, specifying the polynomial and
		///   whether to reverse data bits or not.
		/// </summary>
		/// <param name='polynomial'>
		///   The polynomial to use for the CRC, expressed in the reversed (LSB)
		///   format: the highest ordered bit in the polynomial value is the
		///   coefficient of the 0th power; the second-highest order bit is the
		///   coefficient of the 1 power, and so on. Expressed this way, the
		///   polynomial for the CRC-32C used in IEEE 802.3, is 0xEDB88320.
		/// </param>
		/// <param name='reverseBits'>
		///   specify true if the instance should reverse data bits.
		/// </param>
		///
		/// <remarks>
		///   <para>
		///     In the CRC-32 used by BZip2, the bits are reversed. Therefore if you
		///     want a CRC32 with compatibility with BZip2, you should pass true
		///     here for the <c>reverseBits</c> parameter. In the CRC-32 used by
		///     GZIP and PKZIP, the bits are not reversed; Therefore if you want a
		///     CRC32 with compatibility with those, you should pass false for the
		///     <c>reverseBits</c> parameter.
		///   </para>
		/// </remarks>
		public CRC32(int polynomial, bool reverseBits)
		{
			this.reverseBits = reverseBits;
			this.dwPolynomial = (uint)polynomial;
			this.GenerateLookupTable();
		}

		/// <summary>
		///   Reset the CRC-32 class - clear the CRC "remainder register."
		/// </summary>
		/// <remarks>
		///   <para>
		///     Use this when employing a single instance of this class to compute
		///     multiple, distinct CRCs on multiple, distinct data blocks.
		///   </para>
		/// </remarks>
		public void Reset()
		{
			_register = 0xFFFFFFFFU;
		}

		// private member vars
		private UInt32 dwPolynomial;
		private Int64 _TotalBytesRead;
		private bool reverseBits;
		private UInt32[] crc32Table;
		private const int BUFFER_SIZE = 8192;
		private UInt32 _register = 0xFFFFFFFFU;
	}

	/// <summary>
	/// A Stream that calculates a CRC32 (a checksum) on all bytes read,
	/// or on all bytes written.
	/// </summary>
	///
	/// <remarks>
	/// <para>
	/// This class can be used to verify the CRC of a ZipEntry when
	/// reading from a stream, or to calculate a CRC when writing to a
	/// stream.  The stream should be used to either read, or write, but
	/// not both.  If you intermix reads and writes, the results are not
	/// defined.
	/// </para>
	///
	/// <para>
	/// This class is intended primarily for use internally by the
	/// DotNetZip library.
	/// </para>
	/// </remarks>
	internal class CrcCalculatorStream : System.IO.Stream, System.IDisposable
	{
		private static readonly Int64 UnsetLengthLimit = -99;

		internal System.IO.Stream _innerStream;
		private CRC32 _Crc32;
		private Int64 _lengthLimit = -99;
		private bool _leaveOpen;

		/// <summary>
		/// The default constructor.
		/// </summary>
		/// <remarks>
		///   <para>
		///     Instances returned from this constructor will leave the underlying
		///     stream open upon Close().  The stream uses the default CRC32
		///     algorithm, which implies a polynomial of 0xEDB88320.
		///   </para>
		/// </remarks>
		/// <param name="stream">The underlying stream</param>
		public CrcCalculatorStream(System.IO.Stream stream)
				: this(true, CrcCalculatorStream.UnsetLengthLimit, stream, null)
		{
		}

		/// <summary>
		///   The constructor allows the caller to specify how to handle the
		///   underlying stream at close.
		/// </summary>
		/// <remarks>
		///   <para>
		///     The stream uses the default CRC32 algorithm, which implies a
		///     polynomial of 0xEDB88320.
		///   </para>
		/// </remarks>
		/// <param name="stream">The underlying stream</param>
		/// <param name="leaveOpen">true to leave the underlying stream
		/// open upon close of the <c>CrcCalculatorStream</c>; false otherwise.</param>
		public CrcCalculatorStream(System.IO.Stream stream, bool leaveOpen)
				: this(leaveOpen, CrcCalculatorStream.UnsetLengthLimit, stream, null)
		{
		}

		/// <summary>
		///   A constructor allowing the specification of the length of the stream
		///   to read.
		/// </summary>
		/// <remarks>
		///   <para>
		///     The stream uses the default CRC32 algorithm, which implies a
		///     polynomial of 0xEDB88320.
		///   </para>
		///   <para>
		///     Instances returned from this constructor will leave the underlying
		///     stream open upon Close().
		///   </para>
		/// </remarks>
		/// <param name="stream">The underlying stream</param>
		/// <param name="length">The length of the stream to slurp</param>
		public CrcCalculatorStream(System.IO.Stream stream, Int64 length)
				: this(true, length, stream, null)
		{
			if (length < 0)
				throw new ArgumentException("length");
		}

		/// <summary>
		///   A constructor allowing the specification of the length of the stream
		///   to read, as well as whether to keep the underlying stream open upon
		///   Close().
		/// </summary>
		/// <remarks>
		///   <para>
		///     The stream uses the default CRC32 algorithm, which implies a
		///     polynomial of 0xEDB88320.
		///   </para>
		/// </remarks>
		/// <param name="stream">The underlying stream</param>
		/// <param name="length">The length of the stream to slurp</param>
		/// <param name="leaveOpen">true to leave the underlying stream
		/// open upon close of the <c>CrcCalculatorStream</c>; false otherwise.</param>
		public CrcCalculatorStream(System.IO.Stream stream, Int64 length, bool leaveOpen)
				: this(leaveOpen, length, stream, null)
		{
			if (length < 0)
				throw new ArgumentException("length");
		}

		/// <summary>
		///   A constructor allowing the specification of the length of the stream
		///   to read, as well as whether to keep the underlying stream open upon
		///   Close(), and the CRC32 instance to use.
		/// </summary>
		/// <remarks>
		///   <para>
		///     The stream uses the specified CRC32 instance, which allows the
		///     application to specify how the CRC gets calculated.
		///   </para>
		/// </remarks>
		/// <param name="stream">The underlying stream</param>
		/// <param name="length">The length of the stream to slurp</param>
		/// <param name="leaveOpen">true to leave the underlying stream
		/// open upon close of the <c>CrcCalculatorStream</c>; false otherwise.</param>
		/// <param name="crc32">the CRC32 instance to use to calculate the CRC32</param>
		public CrcCalculatorStream(System.IO.Stream stream, Int64 length, bool leaveOpen,
															 CRC32 crc32)
				: this(leaveOpen, length, stream, crc32)
		{
			if (length < 0)
				throw new ArgumentException("length");
		}


		// This ctor is private - no validation is done here.  This is to allow the use
		// of a (specific) negative value for the _lengthLimit, to indicate that there
		// is no length set.  So we validate the length limit in those ctors that use an
		// explicit param, otherwise we don't validate, because it could be our special
		// value.
		private CrcCalculatorStream
				(bool leaveOpen, Int64 length, System.IO.Stream stream, CRC32 crc32)
				: base()
		{
			_innerStream = stream;
			_Crc32 = crc32 ?? new CRC32();
			_lengthLimit = length;
			_leaveOpen = leaveOpen;
		}


		/// <summary>
		///   Gets the total number of bytes run through the CRC32 calculator.
		/// </summary>
		///
		/// <remarks>
		///   This is either the total number of bytes read, or the total number of
		///   bytes written, depending on the direction of this stream.
		/// </remarks>
		public Int64 TotalBytesSlurped
		{
			get { return _Crc32.TotalBytesRead; }
		}

		/// <summary>
		///   Provides the current CRC for all blocks slurped in.
		/// </summary>
		/// <remarks>
		///   <para>
		///     The running total of the CRC is kept as data is written or read
		///     through the stream.  read this property after all reads or writes to
		///     get an accurate CRC for the entire stream.
		///   </para>
		/// </remarks>
		public Int32 Crc
		{
			get { return _Crc32.Crc32Result; }
		}

		/// <summary>
		///   Indicates whether the underlying stream will be left open when the
		///   <c>CrcCalculatorStream</c> is Closed.
		/// </summary>
		/// <remarks>
		///   <para>
		///     Set this at any point before calling <see cref="Close()"/>.
		///   </para>
		/// </remarks>
		public bool LeaveOpen
		{
			get { return _leaveOpen; }
			set { _leaveOpen = value; }
		}

		/// <summary>
		/// Read from the stream
		/// </summary>
		/// <param name="buffer">the buffer to read</param>
		/// <param name="offset">the offset at which to start</param>
		/// <param name="count">the number of bytes to read</param>
		/// <returns>the number of bytes actually read</returns>
		public override int Read(byte[] buffer, int offset, int count)
		{
			int bytesToRead = count;

			// Need to limit the # of bytes returned, if the stream is intended to have
			// a definite length.  This is especially useful when returning a stream for
			// the uncompressed data directly to the application.  The app won't
			// necessarily read only the UncompressedSize number of bytes.  For example
			// wrapping the stream returned from OpenReader() into a StreadReader() and
			// calling ReadToEnd() on it, We can "over-read" the zip data and get a
			// corrupt string.  The length limits that, prevents that problem.

			if (_lengthLimit != CrcCalculatorStream.UnsetLengthLimit)
			{
				if (_Crc32.TotalBytesRead >= _lengthLimit) return 0; // EOF
				Int64 bytesRemaining = _lengthLimit - _Crc32.TotalBytesRead;
				if (bytesRemaining < count) bytesToRead = (int)bytesRemaining;
			}
			int n = _innerStream.Read(buffer, offset, bytesToRead);
			if (n > 0) _Crc32.SlurpBlock(buffer, offset, n);
			return n;
		}

		/// <summary>
		/// Write to the stream.
		/// </summary>
		/// <param name="buffer">the buffer from which to write</param>
		/// <param name="offset">the offset at which to start writing</param>
		/// <param name="count">the number of bytes to write</param>
		public override void Write(byte[] buffer, int offset, int count)
		{
			if (count > 0) _Crc32.SlurpBlock(buffer, offset, count);
			_innerStream.Write(buffer, offset, count);
		}

		/// <summary>
		/// Indicates whether the stream supports reading.
		/// </summary>
		public override bool CanRead
		{
			get { return _innerStream.CanRead; }
		}

		/// <summary>
		///   Indicates whether the stream supports seeking.
		/// </summary>
		/// <remarks>
		///   <para>
		///     Always returns false.
		///   </para>
		/// </remarks>
		public override bool CanSeek
		{
			get { return false; }
		}

		/// <summary>
		/// Indicates whether the stream supports writing.
		/// </summary>
		public override bool CanWrite
		{
			get { return _innerStream.CanWrite; }
		}

		/// <summary>
		/// Flush the stream.
		/// </summary>
		public override void Flush()
		{
			_innerStream.Flush();
		}

		/// <summary>
		///   Returns the length of the underlying stream.
		/// </summary>
		public override long Length
		{
			get
			{
				if (_lengthLimit == CrcCalculatorStream.UnsetLengthLimit)
					return _innerStream.Length;
				else return _lengthLimit;
			}
		}

		/// <summary>
		///   The getter for this property returns the total bytes read.
		///   If you use the setter, it will throw
		/// <see cref="NotSupportedException"/>.
		/// </summary>
		public override long Position
		{
			get { return _Crc32.TotalBytesRead; }
			set { throw new NotSupportedException(); }
		}

		/// <summary>
		/// Seeking is not supported on this stream. This method always throws
		/// <see cref="NotSupportedException"/>
		/// </summary>
		/// <param name="offset">N/A</param>
		/// <param name="origin">N/A</param>
		/// <returns>N/A</returns>
		public override long Seek(long offset, System.IO.SeekOrigin origin)
		{
			throw new NotSupportedException();
		}

		/// <summary>
		/// This method always throws
		/// <see cref="NotSupportedException"/>
		/// </summary>
		/// <param name="value">N/A</param>
		public override void SetLength(long value)
		{
			throw new NotSupportedException();
		}


		void IDisposable.Dispose()
		{
			Close();
		}

		/// <summary>
		/// Closes the stream.
		/// </summary>
		public override void Close()
		{
			base.Close();
			if (!_leaveOpen)
				_innerStream.Close();
		}

	}

}