// DeflaterHuffman.cs
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//
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// Copyright (C) 2001 Mike Krueger
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// Copyright (C) 2004 John Reilly
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//
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// This file was translated from java, it was part of the GNU Classpath
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// Copyright (C) 2001 Free Software Foundation, Inc.
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License
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// as published by the Free Software Foundation; either version 2
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// of the License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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//
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// Linking this library statically or dynamically with other modules is
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// making a combined work based on this library. Thus, the terms and
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// conditions of the GNU General Public License cover the whole
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// combination.
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//
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// As a special exception, the copyright holders of this library give you
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// permission to link this library with independent modules to produce an
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// executable, regardless of the license terms of these independent
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// modules, and to copy and distribute the resulting executable under
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// terms of your choice, provided that you also meet, for each linked
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// independent module, the terms and conditions of the license of that
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// module. An independent module is a module which is not derived from
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// or based on this library. If you modify this library, you may extend
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// this exception to your version of the library, but you are not
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// obligated to do so. If you do not wish to do so, delete this
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// exception statement from your version.
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using System;
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namespace ICSharpCode.SharpZipLib.Zip.Compression
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{
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/// <summary>
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/// This is the DeflaterHuffman class.
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///
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/// This class is <i>not</i> thread safe. This is inherent in the API, due
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/// to the split of Deflate and SetInput.
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///
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/// author of the original java version : Jochen Hoenicke
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/// </summary>
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public class DeflaterHuffman
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{
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const int BUFSIZE = 1 << (DeflaterConstants.DEFAULT_MEM_LEVEL + 6);
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const int LITERAL_NUM = 286;
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// Number of distance codes
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const int DIST_NUM = 30;
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// Number of codes used to transfer bit lengths
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const int BITLEN_NUM = 19;
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// repeat previous bit length 3-6 times (2 bits of repeat count)
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const int REP_3_6 = 16;
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// repeat a zero length 3-10 times (3 bits of repeat count)
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const int REP_3_10 = 17;
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// repeat a zero length 11-138 times (7 bits of repeat count)
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const int REP_11_138 = 18;
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const int EOF_SYMBOL = 256;
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// The lengths of the bit length codes are sent in order of decreasing
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// probability, to avoid transmitting the lengths for unused bit length codes.
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static readonly int[] BL_ORDER = { 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };
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static readonly byte[] bit4Reverse = {
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0,
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8,
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4,
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12,
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2,
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10,
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6,
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14,
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1,
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9,
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5,
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13,
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3,
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11,
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7,
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15
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};
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static short[] staticLCodes;
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static byte[] staticLLength;
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static short[] staticDCodes;
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static byte[] staticDLength;
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class Tree
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{
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#region Instance Fields
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public short[] freqs;
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public byte[] length;
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public int minNumCodes;
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public int numCodes;
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short[] codes;
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int[] bl_counts;
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int maxLength;
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DeflaterHuffman dh;
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#endregion
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#region Constructors
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public Tree(DeflaterHuffman dh, int elems, int minCodes, int maxLength)
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{
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this.dh = dh;
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this.minNumCodes = minCodes;
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this.maxLength = maxLength;
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freqs = new short[elems];
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bl_counts = new int[maxLength];
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}
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#endregion
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/// <summary>
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/// Resets the internal state of the tree
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/// </summary>
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public void Reset()
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{
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for (int i = 0; i < freqs.Length; i++) {
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freqs[i] = 0;
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}
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codes = null;
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length = null;
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}
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public void WriteSymbol(int code)
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{
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// if (DeflaterConstants.DEBUGGING) {
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// freqs[code]--;
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// // Console.Write("writeSymbol("+freqs.length+","+code+"): ");
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// }
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dh.pending.WriteBits(codes[code] & 0xffff, length[code]);
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}
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/// <summary>
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/// Check that all frequencies are zero
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/// </summary>
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/// <exception cref="SharpZipBaseException">
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/// At least one frequency is non-zero
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/// </exception>
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public void CheckEmpty()
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{
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bool empty = true;
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for (int i = 0; i < freqs.Length; i++) {
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if (freqs[i] != 0) {
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//Console.WriteLine("freqs[" + i + "] == " + freqs[i]);
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empty = false;
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}
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}
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if (!empty) {
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throw new SharpZipBaseException("!Empty");
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}
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}
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/// <summary>
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/// Set static codes and length
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/// </summary>
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/// <param name="staticCodes">new codes</param>
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/// <param name="staticLengths">length for new codes</param>
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public void SetStaticCodes(short[] staticCodes, byte[] staticLengths)
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{
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codes = staticCodes;
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length = staticLengths;
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}
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/// <summary>
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/// Build dynamic codes and lengths
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/// </summary>
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public void BuildCodes()
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{
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int numSymbols = freqs.Length;
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int[] nextCode = new int[maxLength];
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int code = 0;
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codes = new short[freqs.Length];
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// if (DeflaterConstants.DEBUGGING) {
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// //Console.WriteLine("buildCodes: "+freqs.Length);
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// }
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for (int bits = 0; bits < maxLength; bits++) {
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nextCode[bits] = code;
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code += bl_counts[bits] << (15 - bits);
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// if (DeflaterConstants.DEBUGGING) {
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// //Console.WriteLine("bits: " + ( bits + 1) + " count: " + bl_counts[bits]
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// +" nextCode: "+code);
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// }
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}
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#if DebugDeflation
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if ( DeflaterConstants.DEBUGGING && (code != 65536) )
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{
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throw new SharpZipBaseException("Inconsistent bl_counts!");
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}
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#endif
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for (int i=0; i < numCodes; i++) {
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int bits = length[i];
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if (bits > 0) {
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// if (DeflaterConstants.DEBUGGING) {
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// //Console.WriteLine("codes["+i+"] = rev(" + nextCode[bits-1]+"),
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// +bits);
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// }
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codes[i] = BitReverse(nextCode[bits-1]);
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nextCode[bits-1] += 1 << (16 - bits);
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}
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}
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}
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public void BuildTree()
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{
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int numSymbols = freqs.Length;
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/* heap is a priority queue, sorted by frequency, least frequent
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* nodes first. The heap is a binary tree, with the property, that
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* the parent node is smaller than both child nodes. This assures
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* that the smallest node is the first parent.
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*
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* The binary tree is encoded in an array: 0 is root node and
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* the nodes 2*n+1, 2*n+2 are the child nodes of node n.
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*/
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int[] heap = new int[numSymbols];
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int heapLen = 0;
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int maxCode = 0;
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for (int n = 0; n < numSymbols; n++) {
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int freq = freqs[n];
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if (freq != 0) {
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// Insert n into heap
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int pos = heapLen++;
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int ppos;
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while (pos > 0 && freqs[heap[ppos = (pos - 1) / 2]] > freq) {
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heap[pos] = heap[ppos];
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pos = ppos;
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}
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heap[pos] = n;
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maxCode = n;
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}
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}
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/* We could encode a single literal with 0 bits but then we
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* don't see the literals. Therefore we force at least two
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* literals to avoid this case. We don't care about order in
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* this case, both literals get a 1 bit code.
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*/
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while (heapLen < 2) {
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int node = maxCode < 2 ? ++maxCode : 0;
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heap[heapLen++] = node;
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}
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numCodes = Math.Max(maxCode + 1, minNumCodes);
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int numLeafs = heapLen;
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int[] childs = new int[4 * heapLen - 2];
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int[] values = new int[2 * heapLen - 1];
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int numNodes = numLeafs;
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for (int i = 0; i < heapLen; i++) {
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int node = heap[i];
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childs[2 * i] = node;
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childs[2 * i + 1] = -1;
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values[i] = freqs[node] << 8;
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heap[i] = i;
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}
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/* Construct the Huffman tree by repeatedly combining the least two
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* frequent nodes.
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*/
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do {
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int first = heap[0];
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int last = heap[--heapLen];
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// Propagate the hole to the leafs of the heap
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int ppos = 0;
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int path = 1;
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while (path < heapLen) {
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if (path + 1 < heapLen && values[heap[path]] > values[heap[path+1]]) {
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path++;
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}
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heap[ppos] = heap[path];
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ppos = path;
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path = path * 2 + 1;
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}
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/* Now propagate the last element down along path. Normally
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* it shouldn't go too deep.
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*/
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int lastVal = values[last];
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while ((path = ppos) > 0 && values[heap[ppos = (path - 1)/2]] > lastVal) {
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heap[path] = heap[ppos];
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}
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heap[path] = last;
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int second = heap[0];
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// Create a new node father of first and second
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last = numNodes++;
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childs[2 * last] = first;
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childs[2 * last + 1] = second;
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int mindepth = Math.Min(values[first] & 0xff, values[second] & 0xff);
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values[last] = lastVal = values[first] + values[second] - mindepth + 1;
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// Again, propagate the hole to the leafs
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ppos = 0;
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path = 1;
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while (path < heapLen) {
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if (path + 1 < heapLen && values[heap[path]] > values[heap[path+1]]) {
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path++;
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}
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heap[ppos] = heap[path];
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ppos = path;
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path = ppos * 2 + 1;
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}
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// Now propagate the new element down along path
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while ((path = ppos) > 0 && values[heap[ppos = (path - 1)/2]] > lastVal) {
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heap[path] = heap[ppos];
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}
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heap[path] = last;
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} while (heapLen > 1);
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if (heap[0] != childs.Length / 2 - 1) {
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throw new SharpZipBaseException("Heap invariant violated");
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}
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BuildLength(childs);
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}
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/// <summary>
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/// Get encoded length
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/// </summary>
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/// <returns>Encoded length, the sum of frequencies * lengths</returns>
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public int GetEncodedLength()
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{
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int len = 0;
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for (int i = 0; i < freqs.Length; i++) {
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len += freqs[i] * length[i];
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}
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return len;
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}
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/// <summary>
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/// Scan a literal or distance tree to determine the frequencies of the codes
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/// in the bit length tree.
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/// </summary>
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public void CalcBLFreq(Tree blTree)
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{
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int max_count; /* max repeat count */
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int min_count; /* min repeat count */
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int count; /* repeat count of the current code */
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int curlen = -1; /* length of current code */
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int i = 0;
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while (i < numCodes) {
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count = 1;
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int nextlen = length[i];
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if (nextlen == 0) {
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max_count = 138;
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min_count = 3;
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} else {
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max_count = 6;
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min_count = 3;
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if (curlen != nextlen) {
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blTree.freqs[nextlen]++;
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count = 0;
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}
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}
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curlen = nextlen;
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i++;
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while (i < numCodes && curlen == length[i]) {
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i++;
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if (++count >= max_count) {
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break;
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}
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}
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if (count < min_count) {
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blTree.freqs[curlen] += (short)count;
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} else if (curlen != 0) {
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blTree.freqs[REP_3_6]++;
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} else if (count <= 10) {
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blTree.freqs[REP_3_10]++;
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} else {
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blTree.freqs[REP_11_138]++;
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}
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}
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}
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/// <summary>
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/// Write tree values
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/// </summary>
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/// <param name="blTree">Tree to write</param>
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public void WriteTree(Tree blTree)
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{
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int max_count; // max repeat count
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int min_count; // min repeat count
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int count; // repeat count of the current code
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int curlen = -1; // length of current code
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int i = 0;
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while (i < numCodes) {
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count = 1;
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int nextlen = length[i];
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if (nextlen == 0) {
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max_count = 138;
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min_count = 3;
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} else {
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max_count = 6;
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min_count = 3;
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if (curlen != nextlen) {
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blTree.WriteSymbol(nextlen);
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count = 0;
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}
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}
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curlen = nextlen;
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i++;
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while (i < numCodes && curlen == length[i]) {
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i++;
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if (++count >= max_count) {
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break;
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}
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}
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if (count < min_count) {
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while (count-- > 0) {
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blTree.WriteSymbol(curlen);
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}
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} else if (curlen != 0) {
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blTree.WriteSymbol(REP_3_6);
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dh.pending.WriteBits(count - 3, 2);
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} else if (count <= 10) {
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blTree.WriteSymbol(REP_3_10);
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dh.pending.WriteBits(count - 3, 3);
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} else {
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blTree.WriteSymbol(REP_11_138);
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dh.pending.WriteBits(count - 11, 7);
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}
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}
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}
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void BuildLength(int[] childs)
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{
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this.length = new byte [freqs.Length];
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int numNodes = childs.Length / 2;
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int numLeafs = (numNodes + 1) / 2;
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int overflow = 0;
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for (int i = 0; i < maxLength; i++) {
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bl_counts[i] = 0;
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}
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// First calculate optimal bit lengths
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int[] lengths = new int[numNodes];
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lengths[numNodes-1] = 0;
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for (int i = numNodes - 1; i >= 0; i--) {
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if (childs[2 * i + 1] != -1) {
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int bitLength = lengths[i] + 1;
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if (bitLength > maxLength) {
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bitLength = maxLength;
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overflow++;
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}
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lengths[childs[2 * i]] = lengths[childs[2 * i + 1]] = bitLength;
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} else {
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// A leaf node
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int bitLength = lengths[i];
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bl_counts[bitLength - 1]++;
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this.length[childs[2*i]] = (byte) lengths[i];
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}
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}
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// if (DeflaterConstants.DEBUGGING) {
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// //Console.WriteLine("Tree "+freqs.Length+" lengths:");
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// for (int i=0; i < numLeafs; i++) {
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// //Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
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// + " len: "+length[childs[2*i]]);
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// }
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// }
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if (overflow == 0) {
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return;
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}
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int incrBitLen = maxLength - 1;
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do {
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// Find the first bit length which could increase:
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while (bl_counts[--incrBitLen] == 0)
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;
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// Move this node one down and remove a corresponding
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// number of overflow nodes.
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do {
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bl_counts[incrBitLen]--;
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bl_counts[++incrBitLen]++;
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overflow -= 1 << (maxLength - 1 - incrBitLen);
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} while (overflow > 0 && incrBitLen < maxLength - 1);
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} while (overflow > 0);
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/* We may have overshot above. Move some nodes from maxLength to
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* maxLength-1 in that case.
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*/
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bl_counts[maxLength-1] += overflow;
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bl_counts[maxLength-2] -= overflow;
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/* Now recompute all bit lengths, scanning in increasing
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* frequency. It is simpler to reconstruct all lengths instead of
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* fixing only the wrong ones. This idea is taken from 'ar'
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* written by Haruhiko Okumura.
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*
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* The nodes were inserted with decreasing frequency into the childs
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* array.
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*/
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int nodePtr = 2 * numLeafs;
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for (int bits = maxLength; bits != 0; bits--) {
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int n = bl_counts[bits-1];
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while (n > 0) {
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int childPtr = 2*childs[nodePtr++];
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if (childs[childPtr + 1] == -1) {
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// We found another leaf
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length[childs[childPtr]] = (byte) bits;
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n--;
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}
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}
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}
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// if (DeflaterConstants.DEBUGGING) {
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// //Console.WriteLine("*** After overflow elimination. ***");
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// for (int i=0; i < numLeafs; i++) {
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// //Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
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// + " len: "+length[childs[2*i]]);
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// }
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// }
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}
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}
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#region Instance Fields
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/// <summary>
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/// Pending buffer to use
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/// </summary>
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public DeflaterPending pending;
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Tree literalTree;
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Tree distTree;
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Tree blTree;
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// Buffer for distances
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short[] d_buf;
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byte[] l_buf;
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int last_lit;
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int extra_bits;
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#endregion
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static DeflaterHuffman()
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{
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// See RFC 1951 3.2.6
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// Literal codes
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staticLCodes = new short[LITERAL_NUM];
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staticLLength = new byte[LITERAL_NUM];
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int i = 0;
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while (i < 144) {
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staticLCodes[i] = BitReverse((0x030 + i) << 8);
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staticLLength[i++] = 8;
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}
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while (i < 256) {
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staticLCodes[i] = BitReverse((0x190 - 144 + i) << 7);
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staticLLength[i++] = 9;
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}
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while (i < 280) {
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staticLCodes[i] = BitReverse((0x000 - 256 + i) << 9);
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staticLLength[i++] = 7;
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}
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while (i < LITERAL_NUM) {
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staticLCodes[i] = BitReverse((0x0c0 - 280 + i) << 8);
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staticLLength[i++] = 8;
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}
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// Distance codes
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staticDCodes = new short[DIST_NUM];
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staticDLength = new byte[DIST_NUM];
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for (i = 0; i < DIST_NUM; i++) {
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staticDCodes[i] = BitReverse(i << 11);
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staticDLength[i] = 5;
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}
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}
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/// <summary>
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/// Construct instance with pending buffer
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/// </summary>
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/// <param name="pending">Pending buffer to use</param>
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public DeflaterHuffman(DeflaterPending pending)
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{
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this.pending = pending;
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literalTree = new Tree(this, LITERAL_NUM, 257, 15);
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distTree = new Tree(this, DIST_NUM, 1, 15);
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blTree = new Tree(this, BITLEN_NUM, 4, 7);
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d_buf = new short[BUFSIZE];
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l_buf = new byte [BUFSIZE];
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}
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|
/// <summary>
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/// Reset internal state
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/// </summary>
|
public void Reset()
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{
|
last_lit = 0;
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extra_bits = 0;
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literalTree.Reset();
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distTree.Reset();
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blTree.Reset();
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}
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|
/// <summary>
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/// Write all trees to pending buffer
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/// </summary>
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/// <param name="blTreeCodes">The number/rank of treecodes to send.</param>
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public void SendAllTrees(int blTreeCodes)
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{
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blTree.BuildCodes();
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literalTree.BuildCodes();
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distTree.BuildCodes();
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pending.WriteBits(literalTree.numCodes - 257, 5);
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pending.WriteBits(distTree.numCodes - 1, 5);
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pending.WriteBits(blTreeCodes - 4, 4);
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for (int rank = 0; rank < blTreeCodes; rank++) {
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pending.WriteBits(blTree.length[BL_ORDER[rank]], 3);
|
}
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literalTree.WriteTree(blTree);
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distTree.WriteTree(blTree);
|
|
#if DebugDeflation
|
if (DeflaterConstants.DEBUGGING) {
|
blTree.CheckEmpty();
|
}
|
#endif
|
}
|
|
/// <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 DebugDeflation
|
if (DeflaterConstants.DEBUGGING) {
|
Console.Write("EOF: ");
|
}
|
#endif
|
literalTree.WriteSymbol(EOF_SYMBOL);
|
|
#if DebugDeflation
|
if (DeflaterConstants.DEBUGGING) {
|
literalTree.CheckEmpty();
|
distTree.CheckEmpty();
|
}
|
#endif
|
}
|
|
/// <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 DebugDeflation
|
// if (DeflaterConstants.DEBUGGING) {
|
// //Console.WriteLine("Flushing stored block "+ storedLength);
|
// }
|
#endif
|
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="literal">Literal value to add to buffer.</param>
|
/// <returns>Value indicating internal buffer is full</returns>
|
public bool TallyLit(int literal)
|
{
|
// 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)literal;
|
literalTree.freqs[literal]++;
|
return IsFull();
|
}
|
|
/// <summary>
|
/// Add distance code and length to literal and distance trees
|
/// </summary>
|
/// <param name="distance">Distance code</param>
|
/// <param name="length">Length</param>
|
/// <returns>Value indicating if internal buffer is full</returns>
|
public bool TallyDist(int distance, int length)
|
{
|
// if (DeflaterConstants.DEBUGGING) {
|
// //Console.WriteLine("[" + distance + "," + length + "]");
|
// }
|
|
d_buf[last_lit] = (short)distance;
|
l_buf[last_lit++] = (byte)(length - 3);
|
|
int lc = Lcode(length - 3);
|
literalTree.freqs[lc]++;
|
if (lc >= 265 && lc < 285) {
|
extra_bits += (lc - 261) / 4;
|
}
|
|
int dc = Dcode(distance - 1);
|
distTree.freqs[dc]++;
|
if (dc >= 4) {
|
extra_bits += dc / 2 - 1;
|
}
|
return IsFull();
|
}
|
|
|
/// <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 int Lcode(int length)
|
{
|
if (length == 255) {
|
return 285;
|
}
|
|
int code = 257;
|
while (length >= 8) {
|
code += 4;
|
length >>= 1;
|
}
|
return code + length;
|
}
|
|
static int Dcode(int distance)
|
{
|
int code = 0;
|
while (distance >= 4) {
|
code += 2;
|
distance >>= 1;
|
}
|
return code + distance;
|
}
|
}
|
}
|
