deflaterengine.cs

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// DeflaterEngine.cs
//
// Copyright (C) 2001 Mike Krueger
// Copyright (C) 2004 John Reilly
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

using ICSharpCode.SharpZipLib.Checksums;

namespace ICSharpCode.SharpZipLib.Zip.Compression 
{
	
	/// <summary>
	/// Strategies for deflater
	/// </summary>
	public enum DeflateStrategy 
	{
		/// <summary>
		/// The default strategy
		/// </summary>
		Default  = 0,
		
		/// <summary>
		/// This strategy will only allow longer string repetitions.  It is
		/// useful for random data with a small character set.
		/// </summary>
		Filtered = 1,

			
		/// <summary>
		/// This strategy will not look for string repetitions at all.  It
		/// only encodes with Huffman trees (which means, that more common
		/// characters get a smaller encoding.
		/// </summary>
		HuffmanOnly = 2
	}

	// DEFLATE ALGORITHM:
	// 
	// The uncompressed stream is inserted into the window array.  When
	// the window array is full the first half is thrown away and the
	// second half is copied to the beginning.
	//
	// The head array is a hash table.  Three characters build a hash value
	// and they the value points to the corresponding index in window of 
	// the last string with this hash.  The prev array implements a
	// linked list of matches with the same hash: prev[index & WMASK] points
	// to the previous index with the same hash.
	// 

	
	/// <summary>
	/// Low level compression engine for deflate algorithm which uses a 32K sliding window
	/// with secondary compression from Huffman/Shannon-Fano codes.
	/// </summary>
	public class DeflaterEngine : DeflaterConstants 
	{
		static int TOO_FAR = 4096;
		
		int ins_h;

		/// <summary>
		/// Hashtable, hashing three characters to an index for window, so
		/// that window[index]..window[index+2] have this hash code.  
		/// Note that the array should really be unsigned short, so you need
		/// to and the values with 0xffff.
		/// </summary>
		short[] head;

		/// <summary>
		/// <code>prev[index &amp; WMASK]</code> points to the previous index that has the
		/// same hash code as the string starting at index.  This way 
		/// entries with the same hash code are in a linked list.
		/// Note that the array should really be unsigned short, so you need
		/// to and the values with 0xffff.
		/// </summary>
		short[] prev;
		
		int    matchStart;
		int    matchLen;
		bool   prevAvailable;
		int    blockStart;

		/// <summary>
		/// Points to the current character in the window.
		/// </summary>
		int    strstart;

		/// <summary>
		/// lookahead is the number of characters starting at strstart in
		/// window that are valid.
		/// So window[strstart] until window[strstart+lookahead-1] are valid
		/// characters.
		/// </summary>
		int    lookahead;

		/// <summary>
		/// This array contains the part of the uncompressed stream that 
		/// is of relevance.  The current character is indexed by strstart.
		/// </summary>
		byte[] window;
		
		DeflateStrategy strategy;
		int max_chain, max_lazy, niceLength, goodLength;
		
		/// <summary>
		/// The current compression function.
		/// </summary>
		int comprFunc;
		
		/// <summary>
		/// The input data for compression.
		/// </summary>
		byte[] inputBuf;
		
		/// <summary>
		/// The total bytes of input read.
		/// </summary>
		int totalIn;
		
		/// <summary>
		/// The offset into inputBuf, where input data starts.
		/// </summary>
		int inputOff;
		
		/// <summary>
		/// The end offset of the input data.
		/// </summary>
		int inputEnd;
		
		DeflaterPending pending;
		DeflaterHuffman huffman;
		
		/// <summary>
		/// The adler checksum
		/// </summary>
		Adler32 adler;
		
		/// <summary>
		/// Construct instance with pending buffer
		/// </summary>
		/// <param name="pending">
		/// Pending buffer to use
		/// </param>>
		public DeflaterEngine(DeflaterPending pending) 
		{
			this.pending = pending;
			huffman = new DeflaterHuffman(pending);
			adler = new Adler32();
			
			window = new byte[2 * WSIZE];
			head   = new short[HASH_SIZE];
			prev   = new short[WSIZE];
			
			// We start at index 1, to avoid an implementation deficiency, that
		   // we cannot build a repeat pattern at index 0.
			blockStart = strstart = 1;
		}

		/// <summary>
		/// Reset internal state
		/// </summary>		
		public void Reset()
		{
			huffman.Reset();
			adler.Reset();
			blockStart = strstart = 1;
			lookahead = 0;
			totalIn   = 0;
			prevAvailable = false;
			matchLen = MIN_MATCH - 1;
			
			for (int i = 0; i < HASH_SIZE; i++) {
				head[i] = 0;
			}
			
			for (int i = 0; i < WSIZE; i++) {
				prev[i] = 0;
			}
		}

		/// <summary>
		/// Reset Adler checksum
		/// </summary>		
		public void ResetAdler()
		{
			adler.Reset();
		}

		/// <summary>
		/// Get current value of Adler checksum
		/// </summary>		
		public int Adler {
			get {
				return (int)adler.Value;
			}
		}

		/// <summary>
		/// Total data processed
		/// </summary>		
		public int TotalIn {
			get {
				return totalIn;
			}
		}

		/// <summary>
		/// Get/set the <see cref="DeflateStrategy">deflate strategy</see>
		/// </summary>		
		public DeflateStrategy Strategy {
			get {
				return strategy;
			}
			set {
				strategy = value;
			}
		}
		
		/// <summary>
		/// Set the deflate level (0-9)
		/// </summary>
		public void SetLevel(int lvl)
		{
			goodLength = DeflaterConstants.GOOD_LENGTH[lvl];
			max_lazy   = DeflaterConstants.MAX_LAZY[lvl];
			niceLength = DeflaterConstants.NICE_LENGTH[lvl];
			max_chain  = DeflaterConstants.MAX_CHAIN[lvl];
			
			if (DeflaterConstants.COMPR_FUNC[lvl] != comprFunc) {
/*
				if (DeflaterConstants.DEBUGGING) {
				   Console.WriteLine("Change from " + comprFunc + " to "
									      + DeflaterConstants.COMPR_FUNC[lvl]);
				}
*/
				switch (comprFunc) {
					case DEFLATE_STORED:
						if (strstart > blockStart) {
							huffman.FlushStoredBlock(window, blockStart,
								strstart - blockStart, false);
							blockStart = strstart;
						}
						UpdateHash();
						break;
					case DEFLATE_FAST:
						if (strstart > blockStart) {
							huffman.FlushBlock(window, blockStart, strstart - blockStart,
								false);
							blockStart = strstart;
						}
						break;
					case DEFLATE_SLOW:
						if (prevAvailable) {
							huffman.TallyLit(window[strstart-1] & 0xff);
						}
						if (strstart > blockStart) {
							huffman.FlushBlock(window, blockStart, strstart - blockStart, false);
							blockStart = strstart;
						}
						prevAvailable = false;
						matchLen = MIN_MATCH - 1;
						break;
				}
				comprFunc = COMPR_FUNC[lvl];
			}
		}
		
		void UpdateHash() 
		{
/*
			if (DEBUGGING) {
				Console.WriteLine("updateHash: "+strstart);
			}
*/
			ins_h = (window[strstart] << HASH_SHIFT) ^ window[strstart + 1];
		}
		
		/// <summary>
		/// Inserts the current string in the head hash and returns the previous
		/// value for this hash.
		/// </summary>
		/// <returns>The previous hash value</returns>
		int InsertString() 
		{
			short match;
			int hash = ((ins_h << HASH_SHIFT) ^ window[strstart + (MIN_MATCH -1)]) & HASH_MASK;
/*
			if (DeflaterConstants.DEBUGGING) {
				if (hash != (((window[strstart] << (2*HASH_SHIFT)) ^ 
							      (window[strstart + 1] << HASH_SHIFT) ^ 
							      (window[strstart + 2])) & HASH_MASK)) {
						throw new SharpZipBaseException("hash inconsistent: " + hash + "/"
									            +window[strstart] + ","
									            +window[strstart+1] + ","
									            +window[strstart+2] + "," + HASH_SHIFT);
					}
			}
*/
			prev[strstart & WMASK] = match = head[hash];
			head[hash] = (short)strstart;
			ins_h = hash;
			return match & 0xffff;
		}
		
		void SlideWindow()
		{
			Array.Copy(window, WSIZE, window, 0, WSIZE);
			matchStart -= WSIZE;
			strstart   -= WSIZE;
			blockStart -= WSIZE;
			
			/* Slide the hash table (could be avoided with 32 bit values
			 * at the expense of memory usage).
			 */
			for (int i = 0; i < HASH_SIZE; ++i) {
				int m = head[i] & 0xffff;
				head[i] = (short)(m >= WSIZE ? (m - WSIZE) : 0);
			}
			
			/* Slide the prev table. */
			for (int i = 0; i < WSIZE; i++) {
				int m = prev[i] & 0xffff;
				prev[i] = (short)(m >= WSIZE ? (m - WSIZE) : 0);
			}
		}
		
		/// <summary>
		/// Fill the window
		/// </summary>
		public void FillWindow()
		{
			/* If the window is almost full and there is insufficient lookahead,
			 * move the upper half to the lower one to make room in the upper half.
			 */
			if (strstart >= WSIZE + MAX_DIST) {
				SlideWindow();
			}
			
			/* If there is not enough lookahead, but still some input left,
			 * read in the input
			 */
			while (lookahead < DeflaterConstants.MIN_LOOKAHEAD && inputOff < inputEnd) {
				int more = 2 * WSIZE - lookahead - strstart;
				
				if (more > inputEnd - inputOff) {
					more = inputEnd - inputOff;
				}
				
				System.Array.Copy(inputBuf, inputOff, window, strstart + lookahead, more);
				adler.Update(inputBuf, inputOff, more);
				
				inputOff += more;
				totalIn  += more;
				lookahead += more;
			}
			
			if (lookahead >= MIN_MATCH) {
				UpdateHash();
			}
		}