1 | #region License Information
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2 | /* HeuristicLab
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3 | * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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4 | *
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5 | * This file is part of HeuristicLab.
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6 | *
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7 | * HeuristicLab is free software: you can redistribute it and/or modify
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8 | * it under the terms of the GNU General Public License as published by
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9 | * the Free Software Foundation, either version 3 of the License, or
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10 | * (at your option) any later version.
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11 | *
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12 | * HeuristicLab is distributed in the hope that it will be useful,
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13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 | * GNU General Public License for more details.
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16 | *
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17 | * You should have received a copy of the GNU General Public License
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18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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19 | */
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20 | #endregion
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21 |
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22 | using System;
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23 | using System.Collections.Generic;
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24 |
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25 | namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
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26 | public static class SymbolicExpressionHashExtensions {
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27 | public sealed class HashNode<T> : IComparable<HashNode<T>>, IEquatable<HashNode<T>> where T : class {
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28 | public T Data;
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29 | public int Arity;
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30 | public int Size;
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31 | public bool IsCommutative;
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32 |
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33 | public bool Enabled;
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34 | public ulong HashValue; // the initial (fixed) hash value for this individual node/data
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35 | public ulong CalculatedHashValue; // the calculated hash value (taking into account the children hash values)
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36 |
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37 | public Action<HashNode<T>[], int> Simplify;
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38 | public IComparer<T> Comparer;
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39 |
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40 | public bool IsLeaf => Arity == 0;
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41 |
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42 | public HashNode(IComparer<T> comparer) {
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43 | Comparer = comparer;
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44 | }
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45 |
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46 | private HashNode() { }
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47 |
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48 | public int CompareTo(HashNode<T> other) {
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49 | var res = Comparer.Compare(Data, other.Data);
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50 | return res == 0 ? CalculatedHashValue.CompareTo(other.CalculatedHashValue) : res;
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51 | }
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52 |
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53 | public override string ToString() {
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54 | return $"{Data} {Arity} {Size} {CalculatedHashValue} {Enabled}";
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55 | }
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56 |
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57 | public bool Equals(HashNode<T> other) {
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58 | return CalculatedHashValue.Equals(other.CalculatedHashValue);
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59 | }
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60 |
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61 | public override bool Equals(object obj) {
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62 | var other = obj as HashNode<T>;
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63 | if (other != null)
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64 | return Equals(other);
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65 | return base.Equals(obj);
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66 | }
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67 |
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68 | public override int GetHashCode() {
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69 | return (int)CalculatedHashValue;
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70 | }
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71 |
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72 | public static bool operator ==(HashNode<T> a, HashNode<T> b) {
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73 | return a.Equals(b);
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74 | }
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75 |
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76 | public static bool operator !=(HashNode<T> a, HashNode<T> b) {
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77 | return !a.Equals(b);
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78 | }
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79 | }
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80 |
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81 | public static ulong ComputeHash<T>(this HashNode<T>[] nodes, int i, Func<byte[], ulong> hashFunction) where T : class {
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82 | var node = nodes[i];
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83 | const int size = sizeof(ulong);
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84 | var hashes = new ulong[node.Arity + 1];
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85 | var bytes = new byte[(node.Arity + 1) * size];
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86 |
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87 | for (int j = i - 1, k = 0; k < node.Arity; ++k, j -= 1 + nodes[j].Size) {
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88 | hashes[k] = nodes[j].CalculatedHashValue;
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89 | }
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90 | hashes[node.Arity] = node.HashValue;
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91 | Buffer.BlockCopy(hashes, 0, bytes, 0, bytes.Length);
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92 | return hashFunction(bytes);
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93 | }
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94 |
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95 | // set the enabled state for the whole subtree rooted at this node
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96 | public static void SetEnabled<T>(this HashNode<T>[] nodes, int i, bool enabled) where T : class {
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97 | nodes[i].Enabled = enabled;
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98 | for (int j = i - nodes[i].Size; j < i; ++j)
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99 | nodes[j].Enabled = enabled;
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100 | }
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101 |
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102 | public static HashNode<T>[] Simplify<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {
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103 | var reduced = nodes.UpdateNodeSizes().Reduce().Sort(hashFunction);
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104 |
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105 | for (int i = 0; i < reduced.Length; ++i) {
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106 | var node = reduced[i];
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107 | if (node.IsLeaf) {
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108 | continue;
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109 | }
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110 | node.Simplify?.Invoke(reduced, i);
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111 | }
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112 | // detect if anything was simplified
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113 | var count = 0;
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114 | foreach (var node in reduced) {
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115 | if (!node.Enabled) { ++count; }
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116 | }
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117 | if (count == 0) {
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118 | return reduced;
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119 | }
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120 |
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121 | var simplified = new HashNode<T>[reduced.Length - count];
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122 | int j = 0;
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123 | foreach (var node in reduced) {
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124 | if (node.Enabled) {
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125 | simplified[j++] = node;
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126 | }
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127 | }
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128 | return simplified.UpdateNodeSizes().Reduce().Sort(hashFunction);
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129 | }
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130 |
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131 | public static HashNode<T>[] Sort<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {
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132 | int sort(int a, int b) => nodes[a].CompareTo(nodes[b]);
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133 |
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134 | for (int i = 0; i < nodes.Length; ++i) {
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135 | var node = nodes[i];
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136 |
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137 | if (node.IsLeaf) {
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138 | continue;
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139 | }
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140 |
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141 | if (node.IsCommutative) { // only sort when the argument order does not matter
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142 | var arity = node.Arity;
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143 | var size = node.Size;
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144 |
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145 | if (arity == size) { // all child nodes are terminals
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146 | Array.Sort(nodes, i - size, size);
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147 | } else { // i have some non-terminal children
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148 | var sorted = new HashNode<T>[size];
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149 | var indices = new int[node.Arity];
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150 | for (int j = i - 1, k = 0; k < node.Arity; j -= 1 + nodes[j].Size, ++k) {
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151 | indices[k] = j;
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152 | }
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153 | Array.Sort(indices, sort);
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154 |
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155 | int idx = 0;
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156 | foreach (var j in indices) {
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157 | var child = nodes[j];
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158 | if (!child.IsLeaf) { // must copy complete subtree
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159 | Array.Copy(nodes, j - child.Size, sorted, idx, child.Size);
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160 | idx += child.Size;
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161 | }
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162 | sorted[idx++] = nodes[j];
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163 | }
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164 | Array.Copy(sorted, 0, nodes, i - size, size);
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165 | }
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166 | }
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167 | node.CalculatedHashValue = nodes.ComputeHash(i, hashFunction);
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168 | }
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169 | return nodes;
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170 | }
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171 |
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172 | /// <summary>
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173 | /// Get a function node's child indicest
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174 | /// </summary>
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175 | /// <typeparam name="T">The data type encapsulated by a hash node</typeparam>
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176 | /// <param name="nodes">An array of hash nodes with up-to-date node sizes</param>
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177 | /// <param name="i">The index in the array of hash nodes of the node whose children we want to iterate</param>
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178 | /// <returns>An array containing child indices</returns>
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179 | public static int[] IterateChildren<T>(this HashNode<T>[] nodes, int i) where T : class {
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180 | var node = nodes[i];
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181 | var arity = node.Arity;
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182 | var children = new int[arity];
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183 | var idx = i - 1;
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184 | for (int j = 0; j < arity; ++j) {
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185 | children[j] = idx;
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186 | idx -= 1 + nodes[idx].Size;
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187 | }
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188 | return children;
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189 | }
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190 |
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191 | public static HashNode<T>[] UpdateNodeSizes<T>(this HashNode<T>[] nodes) where T : class {
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192 | for (int i = 0; i < nodes.Length; ++i) {
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193 | var node = nodes[i];
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194 | if (node.IsLeaf) {
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195 | node.Size = 0;
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196 | continue;
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197 | }
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198 | node.Size = node.Arity;
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199 |
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200 | for (int j = i - 1, k = 0; k < node.Arity; j -= 1 + nodes[j].Size, ++k) {
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201 | node.Size += nodes[j].Size;
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202 | }
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203 | }
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204 | return nodes;
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205 | }
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206 |
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207 | private static HashNode<T>[] Reduce<T>(this HashNode<T>[] nodes) where T : class {
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208 | int count = 0;
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209 | for (int i = 0; i < nodes.Length; ++i) {
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210 | var node = nodes[i];
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211 | if (node.IsLeaf || !node.IsCommutative) {
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212 | continue;
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213 | }
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214 |
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215 | var arity = node.Arity;
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216 | for (int j = i - 1, k = 0; k < arity; j -= 1 + nodes[j].Size, ++k) {
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217 | if (node.HashValue == nodes[j].HashValue) {
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218 | nodes[j].Enabled = false;
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219 | node.Arity += nodes[j].Arity - 1;
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220 | ++count;
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221 | }
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222 | }
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223 | }
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224 | if (count == 0)
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225 | return nodes;
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226 |
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227 | var reduced = new HashNode<T>[nodes.Length - count];
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228 | var idx = 0;
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229 | foreach (var node in nodes) {
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230 | if (node.Enabled) { reduced[idx++] = node; }
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231 | }
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232 | return reduced.UpdateNodeSizes();
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233 | }
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234 | }
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235 | }
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