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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head><meta http-equiv="content-type" content="text/html; charset=UTF-8" /><title>BloomFilter64bit xref</title><link type="text/css" rel="stylesheet" href="../../../stylesheet.css" /></head><body><div id="overview"><a href="../../../../apidocs/org/archive/util/BloomFilter64bit.html">View Javadoc</a></div><pre><a name="1" href="#1">1</a> <em class="comment">/*<em class="comment"> BloomFilter</em></em><a name="2" href="#2">2</a> <em class="comment">*</em><a name="3" href="#3">3</a> <em class="comment">* $Id: BloomFilter64bit.java,v 1.2 2005/07/16 03:55:54 gojomo Exp $</em><a name="4" href="#4">4</a> <em class="comment">*</em><a name="5" href="#5">5</a> <em class="comment">* Created on Jun 21, 2005</em><a name="6" href="#6">6</a> <em class="comment">*</em><a name="7" href="#7">7</a> <em class="comment">* Copyright (C) 2005 Internet Archive; a slight adaptation of</em><a name="8" href="#8">8</a> <em class="comment">* LGPL work (C) Sebastiano Vigna</em><a name="9" href="#9">9</a> <em class="comment">*</em><a name="10" href="#10">10</a> <em class="comment">* This file is part of the Heritrix web crawler (crawler.archive.org).</em><a name="11" href="#11">11</a> <em class="comment">*</em><a name="12" href="#12">12</a> <em class="comment">* Heritrix is free software; you can redistribute it and/or modify</em><a name="13" href="#13">13</a> <em class="comment">* it under the terms of the GNU Lesser Public License as published by</em><a name="14" href="#14">14</a> <em class="comment">* the Free Software Foundation; either version 2.1 of the License, or</em><a name="15" href="#15">15</a> <em class="comment">* any later version.</em><a name="16" href="#16">16</a> <em class="comment">*</em><a name="17" href="#17">17</a> <em class="comment">* Heritrix is distributed in the hope that it will be useful,</em><a name="18" href="#18">18</a> <em class="comment">* but WITHOUT ANY WARRANTY; without even the implied warranty of</em><a name="19" href="#19">19</a> <em class="comment">* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the</em><a name="20" href="#20">20</a> <em class="comment">* GNU Lesser Public License for more details.</em><a name="21" href="#21">21</a> <em class="comment">*</em><a name="22" href="#22">22</a> <em class="comment">* You should have received a copy of the GNU Lesser Public License</em><a name="23" href="#23">23</a> <em class="comment">* along with Heritrix; if not, write to the Free Software</em><a name="24" href="#24">24</a> <em class="comment">* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA</em><a name="25" href="#25">25</a> <em class="comment">*/</em><a name="26" href="#26">26</a> <a name="27" href="#27">27</a> <strong>package</strong> <a href="../../../org/archive/util/package-summary.html">org.archive.util</a>;<a name="28" href="#28">28</a> <a name="29" href="#29">29</a> <strong>import</strong> java.io.Serializable;<a name="30" href="#30">30</a> <strong>import</strong> java.security.SecureRandom;<a name="31" href="#31">31</a> <a name="32" href="#32">32</a> <em>/**<em>* A Bloom filter.</em></em><a name="33" href="#33">33</a> <em> *</em><a name="34" href="#34">34</a> <em> * SLIGHTLY ADAPTED VERSION OF MG4J it.unimi.dsi.mg4j.util.BloomFilter</em><a name="35" href="#35">35</a> <em> * </em><a name="36" href="#36">36</a> <em> * <p>KEY CHANGES:</em><a name="37" href="#37">37</a> <em> *</em><a name="38" href="#38">38</a> <em> * <ul></em><a name="39" href="#39">39</a> <em> * <li>NUMBER_OF_WEIGHTS is 2083, to better avoid collisions between </em><a name="40" href="#40">40</a> <em> * similar strings</li></em><a name="41" href="#41">41</a> <em> * <li>Removed dependence on cern.colt MersenneTwister (replaced with</em><a name="42" href="#42">42</a> <em> * SecureRandom) and QuickBitVector (replaced with local methods).</li></em><a name="43" href="#43">43</a> <em> * <li>Adapted to allow long bit indices so long as the index/64 (used </em><a name="44" href="#44">44</a> <em> * an array index in bit vector) fits within Integer.MAX_VALUE</li></em><a name="45" href="#45">45</a> <em> * </ul></em><a name="46" href="#46">46</a> <em> * </em><a name="47" href="#47">47</a> <em> * <hr></em><a name="48" href="#48">48</a> <em> * </em><a name="49" href="#49">49</a> <em> * <P>Instances of this class represent a set of character sequences (with false positives)</em><a name="50" href="#50">50</a> <em> * using a Bloom filter. Because of the way Bloom filters work,</em><a name="51" href="#51">51</a> <em> * you cannot remove elements.</em><a name="52" href="#52">52</a> <em> *</em><a name="53" href="#53">53</a> <em> * <P>Bloom filters have an expected error rate, depending on the number</em><a name="54" href="#54">54</a> <em> * of hash functions used, on the filter size and on the number of elements in the filter. This implementation</em><a name="55" href="#55">55</a> <em> * uses a variable optimal number of hash functions, depending on the expected</em><a name="56" href="#56">56</a> <em> * number of elements. More precisely, a Bloom</em><a name="57" href="#57">57</a> <em> * filter for <var>n</var> character sequences with <var>d</var> hash functions will use</em><a name="58" href="#58">58</a> <em> * ln 2 <var>d</var><var>n</var> &#8776; 1.44 <var>d</var><var>n</var> bits;</em><a name="59" href="#59">59</a> <em> * false positives will happen with probability 2<sup>-<var>d</var></sup>.</em><a name="60" href="#60">60</a> <em> *</em><a name="61" href="#61">61</a> <em> * <P>Hash functions are generated at creation time using universal hashing. Each hash function</em><a name="62" href="#62">62</a> <em> * uses {@link #NUMBER_OF_WEIGHTS} random integers, which are cyclically multiplied by</em><a name="63" href="#63">63</a> <em> * the character codes in a character sequence. The resulting integers are XOR-ed together.</em><a name="64" href="#64">64</a> <em> *</em><a name="65" href="#65">65</a> <em> * <P>This class exports access methods that are very similar to those of {@link java.util.Set},</em><a name="66" href="#66">66</a> <em> * but it does not implement that interface, as too many non-optional methods</em><a name="67" href="#67">67</a> <em> * would be unimplementable (e.g., iterators).</em><a name="68" href="#68">68</a> <em> *</em><a name="69" href="#69">69</a> <em> * @author Sebastiano Vigna</em><a name="70" href="#70">70</a> <em> */</em><a name="71" href="#71">71</a> <strong>public</strong> <strong>class</strong> BloomFilter64bit implements Serializable, <a href="../../../org/archive/util/BloomFilter.html">BloomFilter</a> {<a name="72" href="#72">72</a> <em>/**<em>* The number of weights used to create hash functions. */</em></em><a name="73" href="#73">73</a> <strong>final</strong> <strong>public</strong> <strong>static</strong> <strong>int</strong> NUMBER_OF_WEIGHTS = 2083; <em class="comment">// CHANGED FROM 16</em><a name="74" href="#74">74</a> <em>/**<em>* The number of bits in this filter. */</em></em><a name="75" href="#75">75</a> <strong>final</strong> <strong>public</strong> <strong>long</strong> m;<a name="76" href="#76">76</a> <em>/**<em>* The number of hash functions used by this filter. */</em></em><a name="77" href="#77">77</a> <strong>final</strong> <strong>public</strong> <strong>int</strong> d;<a name="78" href="#78">78</a> <em>/**<em>* The underlying bit vector. */</em></em><a name="79" href="#79">79</a> <strong>final</strong> <strong>private</strong> <strong>long</strong>[] bits;<a name="80" href="#80">80</a> <em>/**<em>* The random integers used to generate the hash functions. */</em></em><a name="81" href="#81">81</a> <strong>final</strong> <strong>private</strong> <strong>long</strong>[][] weight;<a name="82" href="#82">82</a> <a name="83" href="#83">83</a> <em>/**<em>* The number of elements currently in the filter. It may be</em></em><a name="84" href="#84">84</a> <em> * smaller than the actual number of additions of distinct character</em><a name="85" href="#85">85</a> <em> * sequences because of false positives.</em><a name="86" href="#86">86</a> <em> */</em><a name="87" href="#87">87</a> <strong>private</strong> <strong>int</strong> size;<a name="88" href="#88">88</a> <a name="89" href="#89">89</a> <em>/**<em>* The natural logarithm of 2, used in the computation of the number of bits. */</em></em><a name="90" href="#90">90</a> <strong>private</strong> <strong>final</strong> <strong>static</strong> <strong>double</strong> NATURAL_LOG_OF_2 = Math.log( 2 );<a name="91" href="#91">91</a> <a name="92" href="#92">92</a> <strong>private</strong> <strong>final</strong> <strong>static</strong> <strong>boolean</strong> DEBUG = false;<a name="93" href="#93">93</a> <a name="94" href="#94">94</a> <em>/**<em>* Creates a new Bloom filter with given number of hash functions and expected number of elements.</em></em><a name="95" href="#95">95</a> <em> *</em><a name="96" href="#96">96</a> <em> * @param n the expected number of elements.</em><a name="97" href="#97">97</a> <em> * @param d the number of hash functions; if the filter add not more than <code>n</code> elements,</em><a name="98" href="#98">98</a> <em> * false positives will happen with probability 2<sup>-<var>d</var></sup>.</em><a name="99" href="#99">99</a> <em> */</em><a name="100" href="#100">100</a> <strong>public</strong> BloomFilter64bit( <strong>final</strong> <strong>int</strong> n, <strong>final</strong> <strong>int</strong> d ) {<a name="101" href="#101">101</a> <strong>this</strong>.d = d;<a name="102" href="#102">102</a> <strong>int</strong> len = (<strong>int</strong>)Math.ceil( ( (<strong>long</strong>)n * (<strong>long</strong>)d / NATURAL_LOG_OF_2 ) / 64L );<a name="103" href="#103">103</a> <strong>if</strong> ( len/64 > Integer.MAX_VALUE ) <strong>throw</strong> <strong>new</strong> IllegalArgumentException( <span class="string">"This filter would require "</span> + len * 64L + <span class="string">" bits"</span> );<a name="104" href="#104">104</a> bits = <strong>new</strong> <strong>long</strong>[ len ];<a name="105" href="#105">105</a> m = bits.length * 64;<a name="106" href="#106">106</a> <a name="107" href="#107">107</a> <strong>if</strong> ( DEBUG ) System.err.println( <span class="string">"Number of bits: "</span> + m );<a name="108" href="#108">108</a> ⌨️ 快捷键说明
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