1  #region License Information


2  /* HeuristicLab


3  * Copyright (C) 20022018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)


4  *


5  * This file is part of HeuristicLab.


6  *


7  * HeuristicLab is free software: you can redistribute it and/or modify


8  * it under the terms of the GNU General Public License as published by


9  * the Free Software Foundation, either version 3 of the License, or


10  * (at your option) any later version.


11  *


12  * HeuristicLab is distributed in the hope that it will be useful,


13  * but WITHOUT ANY WARRANTY; without even the implied warranty of


14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the


15  * GNU General Public License for more details.


16  *


17  * You should have received a copy of the GNU General Public License


18  * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.


19  */


20  #endregion


21 


22  using System;


23  using System.Collections.Generic;


24 


25  namespace HeuristicLab.Problems.DataAnalysis.Symbolic {


26  public static class SymbolicExpressionHashExtensions {


27  public sealed class HashNode<T> : IComparable<HashNode<T>>, IEquatable<HashNode<T>> where T : class {


28  public T Data;


29  public int Arity;


30  public int Size;


31  public bool IsCommutative;


32 


33  public bool Enabled;


34  public ulong HashValue; // the initial (fixed) hash value for this individual node/data


35  public ulong CalculatedHashValue; // the calculated hash value (taking into account the children hash values)


36 


37  public delegate void SimplifyAction(ref HashNode<T>[] nodes, int i);


38  public SimplifyAction Simplify;


39 


40  public IComparer<T> Comparer;


41 


42  public bool IsLeaf => Arity == 0;


43 


44  public HashNode(IComparer<T> comparer) {


45  Comparer = comparer;


46  }


47 


48  private HashNode() { }


49 


50  public int CompareTo(HashNode<T> other) {


51  var res = Comparer.Compare(Data, other.Data);


52  return res == 0 ? CalculatedHashValue.CompareTo(other.CalculatedHashValue) : res;


53  }


54 


55  public override string ToString() {


56  return $"{Data} {Arity} {Size} {CalculatedHashValue} {Enabled}";


57  }


58 


59  public bool Equals(HashNode<T> other) {


60  return CalculatedHashValue.Equals(other.CalculatedHashValue);


61  }


62 


63  public override bool Equals(object obj) {


64  var other = obj as HashNode<T>;


65  if (other != null)


66  return Equals(other);


67  return base.Equals(obj);


68  }


69 


70  public override int GetHashCode() {


71  return (int)CalculatedHashValue;


72  }


73 


74  public static bool operator ==(HashNode<T> a, HashNode<T> b) {


75  return a.Equals(b);


76  }


77 


78  public static bool operator !=(HashNode<T> a, HashNode<T> b) {


79  return !a.Equals(b);


80  }


81  }


82 


83  public static ulong ComputeHash<T>(this HashNode<T>[] nodes, int i, Func<byte[], ulong> hashFunction) where T : class {


84  var node = nodes[i];


85  const int size = sizeof(ulong);


86  var hashes = new ulong[node.Arity + 1];


87  var bytes = new byte[(node.Arity + 1) * size];


88 


89  for (int j = i  1, k = 0; k < node.Arity; ++k, j = 1 + nodes[j].Size) {


90  hashes[k] = nodes[j].CalculatedHashValue;


91  }


92  hashes[node.Arity] = node.HashValue;


93  Buffer.BlockCopy(hashes, 0, bytes, 0, bytes.Length);


94  return hashFunction(bytes);


95  }


96 


97  // set the enabled state for the whole subtree rooted at this node


98  public static void SetEnabled<T>(this HashNode<T>[] nodes, int i, bool enabled) where T : class {


99  nodes[i].Enabled = enabled;


100  for (int j = i  nodes[i].Size; j < i; ++j)


101  nodes[j].Enabled = enabled;


102  }


103 


104  public static HashNode<T>[] Simplify<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {


105  var reduced = nodes.UpdateNodeSizes().Reduce().Sort(hashFunction);


106 


107  for (int i = 0; i < reduced.Length; ++i) {


108  var node = reduced[i];


109  if (node.IsLeaf) {


110  continue;


111  }


112  node.Simplify?.Invoke(ref reduced, i);


113  }


114  // detect if anything was simplified


115  var count = 0;


116  foreach (var node in reduced) {


117  if (!node.Enabled) { ++count; }


118  }


119  if (count == 0) {


120  return reduced;


121  }


122 


123  var simplified = new HashNode<T>[reduced.Length  count];


124  int j = 0;


125  foreach (var node in reduced) {


126  if (node.Enabled) {


127  simplified[j++] = node;


128  }


129  }


130  return simplified.UpdateNodeSizes().Reduce().Sort(hashFunction);


131  }


132 


133  public static HashNode<T>[] Sort<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {


134  int sort(int a, int b) => nodes[a].CompareTo(nodes[b]);


135 


136  for (int i = 0; i < nodes.Length; ++i) {


137  var node = nodes[i];


138 


139  if (node.IsLeaf) {


140  continue;


141  }


142 


143  if (node.IsCommutative) { // only sort when the argument order does not matter


144  var arity = node.Arity;


145  var size = node.Size;


146 


147  if (arity == size) { // all child nodes are terminals


148  Array.Sort(nodes, i  size, size);


149  } else { // i have some nonterminal children


150  var sorted = new HashNode<T>[size];


151  var indices = new int[node.Arity];


152  for (int j = i  1, k = 0; k < node.Arity; j = 1 + nodes[j].Size, ++k) {


153  indices[k] = j;


154  }


155  Array.Sort(indices, sort);


156 


157  int idx = 0;


158  foreach (var j in indices) {


159  var child = nodes[j];


160  if (!child.IsLeaf) { // must copy complete subtree


161  Array.Copy(nodes, j  child.Size, sorted, idx, child.Size);


162  idx += child.Size;


163  }


164  sorted[idx++] = nodes[j];


165  }


166  Array.Copy(sorted, 0, nodes, i  size, size);


167  }


168  }


169  node.CalculatedHashValue = nodes.ComputeHash(i, hashFunction);


170  }


171  return nodes;


172  }


173 


174  /// <summary>


175  /// Get a function node's child indicest


176  /// </summary>


177  /// <typeparam name="T">The data type encapsulated by a hash node</typeparam>


178  /// <param name="nodes">An array of hash nodes with uptodate node sizes</param>


179  /// <param name="i">The index in the array of hash nodes of the node whose children we want to iterate</param>


180  /// <returns>An array containing child indices</returns>


181  public static int[] IterateChildren<T>(this HashNode<T>[] nodes, int i) where T : class {


182  var node = nodes[i];


183  var arity = node.Arity;


184  var children = new int[arity];


185  var idx = i  1;


186  for (int j = 0; j < arity; ++j) {


187  children[j] = idx;


188  idx = 1 + nodes[idx].Size;


189  }


190  return children;


191  }


192 


193  public static HashNode<T>[] UpdateNodeSizes<T>(this HashNode<T>[] nodes) where T : class {


194  for (int i = 0; i < nodes.Length; ++i) {


195  var node = nodes[i];


196  if (node.IsLeaf) {


197  node.Size = 0;


198  continue;


199  }


200  node.Size = node.Arity;


201 


202  for (int j = i  1, k = 0; k < node.Arity; j = 1 + nodes[j].Size, ++k) {


203  node.Size += nodes[j].Size;


204  }


205  }


206  return nodes;


207  }


208 


209  private static HashNode<T>[] Reduce<T>(this HashNode<T>[] nodes) where T : class {


210  int count = 0;


211  for (int i = 0; i < nodes.Length; ++i) {


212  var node = nodes[i];


213  if (node.IsLeaf  !node.IsCommutative) {


214  continue;


215  }


216 


217  var arity = node.Arity;


218  for (int j = i  1, k = 0; k < arity; j = 1 + nodes[j].Size, ++k) {


219  if (node.HashValue == nodes[j].HashValue) {


220  nodes[j].Enabled = false;


221  node.Arity += nodes[j].Arity  1;


222  ++count;


223  }


224  }


225  }


226  if (count == 0)


227  return nodes;


228 


229  var reduced = new HashNode<T>[nodes.Length  count];


230  var idx = 0;


231  foreach (var node in nodes) {


232  if (node.Enabled) { reduced[idx++] = node; }


233  }


234  return reduced.UpdateNodeSizes();


235  }


236  }


237  }

