deflaterhuffman.cs

用C#實現能產生PDF格式文件的源碼

			/// <returns>Encoded length, the sum of frequencies * lengths</returns>
			public int GetEncodedLength()
			{
				int len = 0;
				for (int i = 0; i < freqs.Length; i++) {
					len += freqs[i] * length[i];
				}
				return len;
			}
			
			/// <summary>
			/// Not documented
			/// </summary>
			public void CalcBLFreq(Tree blTree) 
			{
				int max_count;               /* max repeat count */
				int min_count;               /* min repeat count */
				int count;                   /* repeat count of the current code */
				int curlen = -1;             /* length of current code */
				
				int i = 0;
				while (i < numCodes) {
					count = 1;
					int nextlen = length[i];
					if (nextlen == 0) {
						max_count = 138;
						min_count = 3;
					} else {
						max_count = 6;
						min_count = 3;
						if (curlen != nextlen) {
							blTree.freqs[nextlen]++;
							count = 0;
						}
					}
					curlen = nextlen;
					i++;
					
					while (i < numCodes && curlen == length[i]) {
						i++;
						if (++count >= max_count) {
							break;
						}
					}
					
					if (count < min_count) {
						blTree.freqs[curlen] += (short)count;
					} else if (curlen != 0) {
						blTree.freqs[REP_3_6]++;
					} else if (count <= 10) {
						blTree.freqs[REP_3_10]++;
					} else {
						blTree.freqs[REP_11_138]++;
					}
				}
			}
		
			/// <summary>
			/// Write tree values
			/// </summary>
			/// <param name="blTree">Tree to write</param>
			public void WriteTree(Tree blTree)
			{
				int max_count;               /* max repeat count */
				int min_count;               /* min repeat count */
				int count;                   /* repeat count of the current code */
				int curlen = -1;             /* length of current code */
				
				int i = 0;
				while (i < numCodes) {
					count = 1;
					int nextlen = length[i];
					if (nextlen == 0) {
						max_count = 138;
						min_count = 3;
					} else {
						max_count = 6;
						min_count = 3;
						if (curlen != nextlen) {
							blTree.WriteSymbol(nextlen);
							count = 0;
						}
					}
					curlen = nextlen;
					i++;
					
					while (i < numCodes && curlen == length[i]) {
						i++;
						if (++count >= max_count) {
							break;
						}
					}
					
					if (count < min_count) {
						while (count-- > 0) {
							blTree.WriteSymbol(curlen);
						}
					} else if (curlen != 0) {
						blTree.WriteSymbol(REP_3_6);
						dh.pending.WriteBits(count - 3, 2);
					} else if (count <= 10) {
						blTree.WriteSymbol(REP_3_10);
						dh.pending.WriteBits(count - 3, 3);
					} else {
						blTree.WriteSymbol(REP_11_138);
						dh.pending.WriteBits(count - 11, 7);
					}
				}
			}
		}
		
		/// <summary>
		/// Pending buffer to use
		/// </summary>
		public DeflaterPending pending;
		
		Tree literalTree, distTree, blTree;
		
		short[] d_buf;
		byte[]  l_buf;
		int last_lit;
		int extra_bits;
		
		static short[] staticLCodes;
		static byte[]  staticLLength;
		static short[] staticDCodes;
		static byte[]  staticDLength;
		
		/// <summary>
		/// Reverse the bits of a 16 bit value.
		/// </summary>
		/// <param name="toReverse">Value to reverse bits</param>
		/// <returns>Value with bits reversed</returns>
		public static short BitReverse(int toReverse) 
		{
			return (short) (bit4Reverse[toReverse & 0xF] << 12 | 
			                bit4Reverse[(toReverse >> 4) & 0xF] << 8 | 
			                bit4Reverse[(toReverse >> 8) & 0xF] << 4 |
			                bit4Reverse[toReverse >> 12]);
		}
		
		
		static DeflaterHuffman() 
		{
			/* See RFC 1951 3.2.6 */
			/* Literal codes */
			staticLCodes = new short[LITERAL_NUM];
			staticLLength = new byte[LITERAL_NUM];
			int i = 0;
			while (i < 144) {
				staticLCodes[i] = BitReverse((0x030 + i) << 8);
				staticLLength[i++] = 8;
			}
			while (i < 256) {
				staticLCodes[i] = BitReverse((0x190 - 144 + i) << 7);
				staticLLength[i++] = 9;
			}
			while (i < 280) {
				staticLCodes[i] = BitReverse((0x000 - 256 + i) << 9);
				staticLLength[i++] = 7;
			}
			while (i < LITERAL_NUM) {
				staticLCodes[i] = BitReverse((0x0c0 - 280 + i)  << 8);
				staticLLength[i++] = 8;
			}
			
			/* Distant codes */
			staticDCodes = new short[DIST_NUM];
			staticDLength = new byte[DIST_NUM];
			for (i = 0; i < DIST_NUM; i++) {
				staticDCodes[i] = BitReverse(i << 11);
				staticDLength[i] = 5;
			}
		}
		
		/// <summary>
		/// Construct instance with pending buffer
		/// </summary>
		/// <param name="pending">Pending buffer to use</param>
		public DeflaterHuffman(DeflaterPending pending)
		{
			this.pending = pending;
			
			literalTree = new Tree(this, LITERAL_NUM, 257, 15);
			distTree    = new Tree(this, DIST_NUM, 1, 15);
			blTree      = new Tree(this, BITLEN_NUM, 4, 7);
			
			d_buf = new short[BUFSIZE];
			l_buf = new byte [BUFSIZE];
		}

		/// <summary>
		/// Reset internal state
		/// </summary>		
		public void Reset() 
		{
			last_lit = 0;
			extra_bits = 0;
			literalTree.Reset();
			distTree.Reset();
			blTree.Reset();
		}
		
		int Lcode(int len) 
		{
			if (len == 255) {
				return 285;
			}
			
			int code = 257;
			while (len >= 8) {
				code += 4;
				len >>= 1;
			}
			return code + len;
		}
		
		int Dcode(int distance) 
		{
			int code = 0;
			while (distance >= 4) {
				code += 2;
				distance >>= 1;
			}
			return code + distance;
		}

		/// <summary>
		/// Write all trees to pending buffer
		/// </summary>		
		public void SendAllTrees(int blTreeCodes)
		{
			blTree.BuildCodes();
			literalTree.BuildCodes();
			distTree.BuildCodes();
			pending.WriteBits(literalTree.numCodes - 257, 5);
			pending.WriteBits(distTree.numCodes - 1, 5);
			pending.WriteBits(blTreeCodes - 4, 4);
			for (int rank = 0; rank < blTreeCodes; rank++) {
				pending.WriteBits(blTree.length[BL_ORDER[rank]], 3);
			}
			literalTree.WriteTree(blTree);
			distTree.WriteTree(blTree);
			//			if (DeflaterConstants.DEBUGGING) {
			//				blTree.CheckEmpty();
			//			}
		}

		/// <summary>
		/// Compress current buffer writing data to pending buffer
		/// </summary>
		public void CompressBlock()
		{
			for (int i = 0; i < last_lit; i++) {
				int litlen = l_buf[i] & 0xff;
				int dist = d_buf[i];
				if (dist-- != 0) {
					//					if (DeflaterConstants.DEBUGGING) {
					//						Console.Write("["+(dist+1)+","+(litlen+3)+"]: ");
					//					}
					
					int lc = Lcode(litlen);
					literalTree.WriteSymbol(lc);
					
					int bits = (lc - 261) / 4;
					if (bits > 0 && bits <= 5) {
						pending.WriteBits(litlen & ((1 << bits) - 1), bits);
					}
					
					int dc = Dcode(dist);
					distTree.WriteSymbol(dc);
					
					bits = dc / 2 - 1;
					if (bits > 0) {
						pending.WriteBits(dist & ((1 << bits) - 1), bits);
					}
				} else {
					//					if (DeflaterConstants.DEBUGGING) {
					//						if (litlen > 32 && litlen < 127) {
					//							Console.Write("("+(char)litlen+"): ");
					//						} else {
					//							Console.Write("{"+litlen+"}: ");
					//						}
					//					}
					literalTree.WriteSymbol(litlen);
				}
			}
			//			if (DeflaterConstants.DEBUGGING) {
			//				Console.Write("EOF: ");
			//			}
			literalTree.WriteSymbol(EOF_SYMBOL);
			//			if (DeflaterConstants.DEBUGGING) {
			//				literalTree.CheckEmpty();
			//				distTree.CheckEmpty();
			//			}
		}
		
		/// <summary>
		/// Flush block to output with no compression
		/// </summary>
		/// <param name="stored">Data to write</param>
		/// <param name="storedOffset">Index of first byte to write</param>
		/// <param name="storedLength">Count of bytes to write</param>
		/// <param name="lastBlock">True if this is the last block</param>
		public void FlushStoredBlock(byte[] stored, int storedOffset, int storedLength, bool lastBlock)
		{
			//			if (DeflaterConstants.DEBUGGING) {
			//				//Console.WriteLine("Flushing stored block "+ storedLength);
			//			}
			pending.WriteBits((DeflaterConstants.STORED_BLOCK << 1) + (lastBlock ? 1 : 0), 3);
			pending.AlignToByte();
			pending.WriteShort(storedLength);
			pending.WriteShort(~storedLength);
			pending.WriteBlock(stored, storedOffset, storedLength);
			Reset();
		}

		/// <summary>
		/// Flush block to output with compression
		/// </summary>		
		/// <param name="stored">Data to flush</param>
		/// <param name="storedOffset">Index of first byte to flush</param>
		/// <param name="storedLength">Count of bytes to flush</param>
		/// <param name="lastBlock">True if this is the last block</param>
		public void FlushBlock(byte[] stored, int storedOffset, int storedLength, bool lastBlock)
		{
			literalTree.freqs[EOF_SYMBOL]++;
			
			/* Build trees */
			literalTree.BuildTree();
			distTree.BuildTree();
			
			/* Calculate bitlen frequency */
			literalTree.CalcBLFreq(blTree);
			distTree.CalcBLFreq(blTree);
			
			/* Build bitlen tree */
			blTree.BuildTree();
			
			int blTreeCodes = 4;
			for (int i = 18; i > blTreeCodes; i--) {
				if (blTree.length[BL_ORDER[i]] > 0) {
					blTreeCodes = i+1;
				}
			}
			int opt_len = 14 + blTreeCodes * 3 + blTree.GetEncodedLength() + 
				literalTree.GetEncodedLength() + distTree.GetEncodedLength() + 
				extra_bits;
			
			int static_len = extra_bits;
			for (int i = 0; i < LITERAL_NUM; i++) {
				static_len += literalTree.freqs[i] * staticLLength[i];
			}
			for (int i = 0; i < DIST_NUM; i++) {
				static_len += distTree.freqs[i] * staticDLength[i];
			}
			if (opt_len >= static_len) {
				/* Force static trees */
				opt_len = static_len;
			}
			
			if (storedOffset >= 0 && storedLength + 4 < opt_len >> 3) {
				/* Store Block */
				//				if (DeflaterConstants.DEBUGGING) {
				//					//Console.WriteLine("Storing, since " + storedLength + " < " + opt_len
				//					                  + " <= " + static_len);
				//				}
				FlushStoredBlock(stored, storedOffset, storedLength, lastBlock);
			} else if (opt_len == static_len) {
				/* Encode with static tree */
				pending.WriteBits((DeflaterConstants.STATIC_TREES << 1) + (lastBlock ? 1 : 0), 3);
				literalTree.SetStaticCodes(staticLCodes, staticLLength);
				distTree.SetStaticCodes(staticDCodes, staticDLength);
				CompressBlock();
				Reset();
			} else {
				/* Encode with dynamic tree */
				pending.WriteBits((DeflaterConstants.DYN_TREES << 1) + (lastBlock ? 1 : 0), 3);
				SendAllTrees(blTreeCodes);
				CompressBlock();
				Reset();
			}
		}
		
		/// <summary>
		/// Get value indicating if internal buffer is full
		/// </summary>
		/// <returns>true if buffer is full</returns>
		public bool IsFull()
		{
			return last_lit >= BUFSIZE;
		}
		
		/// <summary>
		/// Add literal to buffer
		/// </summary>
		/// <param name="lit"></param>
		/// <returns>Value indicating internal buffer is full</returns>
		public bool TallyLit(int lit)
		{
			//			if (DeflaterConstants.DEBUGGING) {
			//				if (lit > 32 && lit < 127) {
			//					//Console.WriteLine("("+(char)lit+")");
			//				} else {
			//					//Console.WriteLine("{"+lit+"}");
			//				}
			//			}
			d_buf[last_lit] = 0;
			l_buf[last_lit++] = (byte)lit;
			literalTree.freqs[lit]++;
			return IsFull();
		}
		
		/// <summary>
		/// Add distance code and length to literal and distance trees
		/// </summary>
		/// <param name="dist">Distance code</param>
		/// <param name="len">Length</param>
		/// <returns>Value indicating if internal buffer is full</returns>
		public bool TallyDist(int dist, int len)
		{
			//			if (DeflaterConstants.DEBUGGING) {
			//				//Console.WriteLine("["+dist+","+len+"]");
			//			}
			
			d_buf[last_lit]   = (short)dist;
			l_buf[last_lit++] = (byte)(len - 3);
			
			int lc = Lcode(len - 3);
			literalTree.freqs[lc]++;
			if (lc >= 265 && lc < 285) {
				extra_bits += (lc - 261) / 4;
			}
			
			int dc = Dcode(dist - 1);
			distTree.freqs[dc]++;
			if (dc >= 4) {
				extra_bits += dc / 2 - 1;
			}
			return IsFull();
		}
	}
}