1  #region License Information


2  /* HeuristicLab


3  * Copyright (C) 20022019 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.Linq;


24 


25  namespace HeuristicLab.Problems.DataAnalysis.Symbolic {


26  public static class SymbolicExpressionHashExtensions {


27  /// <summary>


28  /// Holds data that is necessary to handle tree nodes in hashing / simplification.


29  /// </summary>


30  /// <typeparam name="T">The tree node type</typeparam>


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


32  public T Data;


33  public int Arity;


34  public int Size;


35  public bool IsCommutative;


36 


37  public bool Enabled;


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


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


40 


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


42  public SimplifyAction Simplify;


43 


44  public bool IsLeaf => Arity == 0;


45 


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


47  return CalculatedHashValue.CompareTo(other.CalculatedHashValue);


48  }


49 


50  public override string ToString() {


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


52  }


53 


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


55  return CalculatedHashValue.Equals(other.CalculatedHashValue);


56  }


57 


58  public override bool Equals(object obj) {


59  var other = obj as HashNode<T>;


60  if (other != null)


61  return Equals(other);


62  return base.Equals(obj);


63  }


64 


65  public override int GetHashCode() {


66  return (int)CalculatedHashValue;


67  }


68 


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


70  return a.Equals(b);


71  }


72 


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


74  return !a.Equals(b);


75  }


76  }


77 


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


79  var node = nodes[i];


80  const int size = sizeof(ulong);


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


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


83 


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


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


86  }


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


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


89  return hashFunction(bytes);


90  }


91 


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


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


94  nodes[i].Enabled = enabled;


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


96  nodes[j].Enabled = enabled;


97  }


98 


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


100  bool simplified = false;


101  nodes = nodes.UpdateNodeSizes().Reduce().Sort(hashFunction);


102  do {


103  if (simplified) {


104  simplified = false;


105  nodes = nodes.Where(x => x.Enabled).ToArray().UpdateNodeSizes().Reduce().Sort(hashFunction);


106  }


107 


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


109  var node = nodes[i];


110  if (node.IsLeaf) {


111  continue;


112  }


113  node.Simplify?.Invoke(ref nodes, i);


114  for (int j = i  node.Size; j < i; ++j) {


115  // detect if anything was simplified


116  if (!nodes[j].Enabled) {


117  simplified = true;


118  break;


119  }


120  }


121  }


122  } while (simplified);


123  return nodes.UpdateNodeSizes().Sort(hashFunction);


124  }


125 


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


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


128 


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


130  var node = nodes[i];


131 


132  if (node.IsLeaf) {


133  continue;


134  }


135 


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


137  var arity = node.Arity;


138  var size = node.Size;


139 


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


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


142  } else { // i have some nonterminal children


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


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


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


146  indices[k] = j;


147  }


148  Array.Sort(indices, sort);


149 


150  int idx = 0;


151  foreach (var j in indices) {


152  var child = nodes[j];


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


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


155  idx += child.Size;


156  }


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


158  }


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


160  }


161  }


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


163  }


164  return nodes;


165  }


166 


167  /// <summary>


168  /// Get a function node's child indices


169  /// </summary>


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


171  /// <param name="nodes">An array of hash nodes with uptodate node sizes (see UpdateNodeSizes)</param>


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


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


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


175  var node = nodes[i];


176  var arity = node.Arity;


177  var children = new int[arity];


178  var idx = i  1;


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


180  children[j] = idx;


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


182  }


183  return children;


184  }


185 


186  /// <summary>


187  /// Determines size of each branch and sets the results for each node.


188  /// </summary>


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


190  /// <param name="nodes">An array of hash nodes in postfix order.</param>


191  /// <returns>The array with updated node sizes. The array is not copied.</returns>


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


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


194  var node = nodes[i];


195  if (node.IsLeaf) {


196  node.Size = 0;


197  continue;


198  }


199  node.Size = node.Arity;


200  // visit all children and sum up their size (assumes postfix order).


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


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


203  }


204  }


205  return nodes;


206  }


207 


208  // disables duplicate branches and removes the disabled nodes


209  public 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  }

