deflaterengine.cs

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		/// <summary>
		/// Find the best (longest) string in the window matching the 
		/// string starting at strstart.
		///
		/// Preconditions:
		/// <code>
		/// strstart + MAX_MATCH &lt;= window.length.</code>
		/// </summary>
		/// <param name="curMatch"></param>
		/// <returns>True if a match greater than the minimum length is found</returns>
		bool FindLongestMatch(int curMatch) 
		{
			int chainLength = this.max_chain;
			int niceLength  = this.niceLength;
			short[] prev    = this.prev;
			int scan        = this.strstart;
			int match;
			int best_end = this.strstart + matchLen;
			int best_len = Math.Max(matchLen, MIN_MATCH - 1);
			
			int limit = Math.Max(strstart - MAX_DIST, 0);
			
			int strend = strstart + MAX_MATCH - 1;
			byte scan_end1 = window[best_end - 1];
			byte scan_end  = window[best_end];
			
			/* Do not waste too much time if we already have a good match: */
			if (best_len >= this.goodLength) {
				chainLength >>= 2;
			}
			
			/* Do not look for matches beyond the end of the input. This is necessary
			* to make deflate deterministic.
			*/
			if (niceLength > lookahead) {
				niceLength = lookahead;
			}
			
/*
			if (DeflaterConstants.DEBUGGING && strstart > 2 * WSIZE - MIN_LOOKAHEAD) {
				throw new InvalidOperationException("need lookahead");
			}
*/			
			do {
/*
				if (DeflaterConstants.DEBUGGING && curMatch >= strstart) {
					throw new InvalidOperationException("future match");
				}
*/            
				if (window[curMatch + best_len] != scan_end      || 
					window[curMatch + best_len - 1] != scan_end1 || 
					window[curMatch] != window[scan]             || 
					window[curMatch + 1] != window[scan + 1]) {
					continue;
				}
				
				match = curMatch + 2;
				scan += 2;
				
				/* We check for insufficient lookahead only every 8th comparison;
				* the 256th check will be made at strstart + 258.
				*/
			while (window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && 
				window[++scan] == window[++match] && scan < strend) ;
				
				if (scan > best_end) {
/*
					if (DeflaterConstants.DEBUGGING && ins_h == 0)
						System.err.println("Found match: "+curMatch+"-"+(scan-strstart));
*/
					matchStart = curMatch;
					best_end = scan;
					best_len = scan - strstart;
					
					if (best_len >= niceLength) {
						break;
					}
					
					scan_end1  = window[best_end - 1];
					scan_end   = window[best_end];
				}
				scan = strstart;
			} while ((curMatch = (prev[curMatch & WMASK] & 0xffff)) > limit && --chainLength != 0);
			
			matchLen = Math.Min(best_len, lookahead);
			return matchLen >= MIN_MATCH;
		}
		
		/// <summary>
		/// Set compression dictionary
		/// </summary>
		public void SetDictionary(byte[] buffer, int offset, int length) 
		{
/*
			if (DeflaterConstants.DEBUGGING && strstart != 1) {
				throw new InvalidOperationException("strstart not 1");
			}
*/
			adler.Update(buffer, offset, length);
			if (length < MIN_MATCH) {
				return;
			}
			if (length > MAX_DIST) {
				offset += length - MAX_DIST;
				length = MAX_DIST;
			}
			
			System.Array.Copy(buffer, offset, window, strstart, length);
			
			UpdateHash();
			--length;
			while (--length > 0) {
				InsertString();
				strstart++;
			}
			strstart += 2;
			blockStart = strstart;
		}
		
		bool DeflateStored(bool flush, bool finish)
		{
			if (!flush && lookahead == 0) {
				return false;
			}
			
			strstart += lookahead;
			lookahead = 0;
			
			int storedLen = strstart - blockStart;
			
			if ((storedLen >= DeflaterConstants.MAX_BLOCK_SIZE) || /* Block is full */
				(blockStart < WSIZE && storedLen >= MAX_DIST) ||   /* Block may move out of window */
				flush) {
				bool lastBlock = finish;
				if (storedLen > DeflaterConstants.MAX_BLOCK_SIZE) {
					storedLen = DeflaterConstants.MAX_BLOCK_SIZE;
					lastBlock = false;
				}
				
/*
				if (DeflaterConstants.DEBUGGING) {
				   Console.WriteLine("storedBlock["+storedLen+","+lastBlock+"]");
				}
*/
	
				huffman.FlushStoredBlock(window, blockStart, storedLen, lastBlock);
				blockStart += storedLen;
				return !lastBlock;
			}
			return true;
		}
		
		private bool DeflateFast(bool flush, bool finish)
		{
			if (lookahead < MIN_LOOKAHEAD && !flush) {
				return false;
			}
			
			while (lookahead >= MIN_LOOKAHEAD || flush) {
				if (lookahead == 0) {
					/* We are flushing everything */
					huffman.FlushBlock(window, blockStart, strstart - blockStart, finish);
					blockStart = strstart;
					return false;
				}
				
				if (strstart > 2 * WSIZE - MIN_LOOKAHEAD) {
					/* slide window, as findLongestMatch needs this.
					 * This should only happen when flushing and the window
					 * is almost full.
					 */
					SlideWindow();
				}
				
				int hashHead;
				if (lookahead >= MIN_MATCH && 
					(hashHead = InsertString()) != 0 && 
					strategy != DeflateStrategy.HuffmanOnly &&
					strstart - hashHead <= MAX_DIST && 
					FindLongestMatch(hashHead)) {
					/* longestMatch sets matchStart and matchLen */
/*
					if (DeflaterConstants.DEBUGGING) {
						for (int i = 0 ; i < matchLen; i++) {
							if (window[strstart+i] != window[matchStart + i]) {
								throw new SharpZipBaseException("Match failure");
							}
						}
					}
*/					
					// -jr- Hak hak hak this stops problems with fast/low compression and index out of range
					if (huffman.TallyDist(strstart - matchStart, matchLen)) {
						bool lastBlock = finish && lookahead == 0;
						huffman.FlushBlock(window, blockStart, strstart - blockStart, lastBlock);
						blockStart = strstart;
					}
					
					lookahead -= matchLen;
					if (matchLen <= max_lazy && lookahead >= MIN_MATCH) {
						while (--matchLen > 0) {
							++strstart;
							InsertString();
						}
						++strstart;
					} else {
						strstart += matchLen;
						if (lookahead >= MIN_MATCH - 1) {
							UpdateHash();
						}
					}
					matchLen = MIN_MATCH - 1;
					continue;
				} else {
					/* No match found */
					huffman.TallyLit(window[strstart] & 0xff);
					++strstart;
					--lookahead;
				}
				
				if (huffman.IsFull()) {
					bool lastBlock = finish && lookahead == 0;
					huffman.FlushBlock(window, blockStart, strstart - blockStart, lastBlock);
					blockStart = strstart;
					return !lastBlock;
				}
			}
			return true;
		}
		
		bool DeflateSlow(bool flush, bool finish)
		{
			if (lookahead < MIN_LOOKAHEAD && !flush) {
				return false;
			}
			
			while (lookahead >= MIN_LOOKAHEAD || flush) {
				if (lookahead == 0) {
					if (prevAvailable) {
						huffman.TallyLit(window[strstart-1] & 0xff);
					}
					prevAvailable = false;
					
					// We are flushing everything
/*
					if (DeflaterConstants.DEBUGGING && !flush) {
						throw new SharpZipBaseException("Not flushing, but no lookahead");
					}
*/               
					huffman.FlushBlock(window, blockStart, strstart - blockStart,
						finish);
					blockStart = strstart;
					return false;
				}
				
				if (strstart >= 2 * WSIZE - MIN_LOOKAHEAD) {
					/* slide window, as findLongestMatch need this.
					 * This should only happen when flushing and the window
					 * is almost full.
					 */
					SlideWindow();
				}
				
				int prevMatch = matchStart;
				int prevLen = matchLen;
				if (lookahead >= MIN_MATCH) {
					int hashHead = InsertString();
					if (strategy != DeflateStrategy.HuffmanOnly && hashHead != 0 && strstart - hashHead <= MAX_DIST && FindLongestMatch(hashHead)) {
						/* longestMatch sets matchStart and matchLen */
							
						/* Discard match if too small and too far away */
						if (matchLen <= 5 && (strategy == DeflateStrategy.Filtered || (matchLen == MIN_MATCH && strstart - matchStart > TOO_FAR))) {
							matchLen = MIN_MATCH - 1;
						}
					}
				}
				
				/* previous match was better */
				if (prevLen >= MIN_MATCH && matchLen <= prevLen) {
/*
					if (DeflaterConstants.DEBUGGING) {
					   for (int i = 0 ; i < matchLen; i++) {
					      if (window[strstart-1+i] != window[prevMatch + i])
					         throw new SharpZipBaseException();
						}
					}
*/               
					huffman.TallyDist(strstart - 1 - prevMatch, prevLen);
					prevLen -= 2;
					do {
						strstart++;
						lookahead--;
						if (lookahead >= MIN_MATCH) {
							InsertString();
						}
					} while (--prevLen > 0);
					strstart ++;
					lookahead--;
					prevAvailable = false;
					matchLen = MIN_MATCH - 1;
				} else {
					if (prevAvailable) {
						huffman.TallyLit(window[strstart-1] & 0xff);
					}
					prevAvailable = true;
					strstart++;
					lookahead--;
				}
				
				if (huffman.IsFull()) {
					int len = strstart - blockStart;
					if (prevAvailable) {
						len--;
					}
					bool lastBlock = (finish && lookahead == 0 && !prevAvailable);
					huffman.FlushBlock(window, blockStart, len, lastBlock);
					blockStart += len;
					return !lastBlock;
				}
			}
			return true;
		}
		
		/// <summary>
		/// Deflate drives actual compression of data
		/// </summary>
		public bool Deflate(bool flush, bool finish)
		{
			bool progress;
			do {
				FillWindow();
				bool canFlush = flush && inputOff == inputEnd;
				//				if (DeflaterConstants.DEBUGGING) {
				//					//Console.WriteLine("window: ["+blockStart+","+strstart+","
				//					                  +lookahead+"], "+comprFunc+","+canFlush);
				//				}
				switch (comprFunc) {
					case DEFLATE_STORED:
						progress = DeflateStored(canFlush, finish);
						break;
					case DEFLATE_FAST:
						progress = DeflateFast(canFlush, finish);
						break;
					case DEFLATE_SLOW:
						progress = DeflateSlow(canFlush, finish);
						break;
					default:
						throw new InvalidOperationException("unknown comprFunc");
				}
			} while (pending.IsFlushed && progress); /* repeat while we have no pending output and progress was made */
			return progress;
		}


		/// <summary>
		/// Sets input data to be deflated.  Should only be called when <code>NeedsInput()</code>
		/// returns true
		/// </summary>
		/// <param name="buf">The buffer containing input data.</param>
		/// <param name="off">The index of the first byte of data.</param>
		/// <param name="len">The number of bytes of data to use as input.</param>
		public void SetInput(byte[] buf, int off, int len)
		{
			if (inputOff < inputEnd) {
				throw new InvalidOperationException("Old input was not completely processed");
			}
			
			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();
			}
			
			inputBuf = buf;
			inputOff = off;
			inputEnd = end;
		}

		/// <summary>
		/// Return true if input is needed via <see cref="SetInput"> SetInput</see>
		/// </summary>		
		public bool NeedsInput()
		{
			return inputEnd == inputOff;
		}
	}
}