1 | #region License Information |
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2 | /* HeuristicLab |
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3 | * Copyright (C) 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 | |
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23 | using System; |
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24 | using System.Security.Cryptography; |
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25 | |
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26 | namespace HeuristicLab.Problems.DataAnalysis.Symbolic { |
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27 | public static class HashUtil { |
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28 | // This class contains some hash functions adapted from http://partow.net/programming/hashfunctions/index.html#AvailableHashFunctions |
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29 | |
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30 | // A simple hash function from Robert Sedgwicks Algorithms in C book.I've added some simple optimizations to the algorithm in order to speed up its hashing process. |
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31 | public static ulong RSHash(byte[] input) { |
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32 | const int b = 378551; |
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33 | ulong a = 63689; |
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34 | ulong hash = 0; |
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35 | |
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36 | foreach (var v in input) { |
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37 | hash = (hash * a) + v; |
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38 | a *= b; |
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39 | } |
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40 | return hash; |
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41 | } |
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42 | |
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43 | // A bitwise hash function written by Justin Sobel |
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44 | public static ulong JSHash(byte[] input) { |
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45 | ulong hash = 1315423911; |
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46 | for (int i = 0; i < input.Length; ++i) |
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47 | hash ^= (hash << 5) + input[i] + (hash >> 2); |
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48 | return hash; |
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49 | } |
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50 | |
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51 | // This hash function comes from Brian Kernighan and Dennis Ritchie's book "The C Programming Language". It is a simple hash function using a strange set of possible seeds which all constitute a pattern of 31....31...31 etc, it seems to be very similar to the DJB hash function. |
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52 | public static ulong BKDRHash(byte[] input) { |
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53 | ulong seed = 131; |
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54 | ulong hash = 0; |
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55 | foreach (var v in input) { |
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56 | hash = (hash * seed) + v; |
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57 | } |
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58 | return hash; |
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59 | } |
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60 | |
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61 | // This is the algorithm of choice which is used in the open source SDBM project. The hash function seems to have a good over-all distribution for many different data sets. It seems to work well in situations where there is a high variance in the MSBs of the elements in a data set. |
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62 | public static ulong SDBMHash(byte[] input) { |
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63 | ulong hash = 0; |
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64 | foreach (var v in input) { |
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65 | hash = v + (hash << 6) + (hash << 16) - hash; |
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66 | } |
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67 | return hash; |
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68 | } |
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69 | |
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70 | // An algorithm produced by Professor Daniel J. Bernstein and shown first to the world on the usenet newsgroup comp.lang.c. It is one of the most efficient hash functions ever published. |
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71 | public static ulong DJBHash(byte[] input) { |
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72 | ulong hash = 5381; |
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73 | foreach (var v in input) { |
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74 | hash = (hash << 5) + hash + v; |
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75 | } |
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76 | return hash; |
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77 | } |
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78 | |
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79 | // An algorithm proposed by Donald E.Knuth in The Art Of Computer Programming Volume 3, under the topic of sorting and search chapter 6.4. |
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80 | public static ulong DEKHash(byte[] input) { |
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81 | ulong hash = (ulong)input.Length; |
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82 | foreach (var v in input) { |
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83 | hash = (hash << 5) ^ (hash >> 27) ^ v; |
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84 | } |
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85 | return hash; |
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86 | } |
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87 | |
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88 | public static ulong CryptoHash(HashAlgorithm ha, byte[] input) { |
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89 | return BitConverter.ToUInt64(ha.ComputeHash(input), 0); |
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90 | } |
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91 | } |
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92 | } |
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