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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Provides direct access to NFA implementations of Aho-Corasick."><title>aho_corasick::nfa - Rust</title><script> if (window.location.protocol !== "file:") document.write(`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2">`)</script><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-e935ef01ae1c1829.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="aho_corasick" data-themes="" data-resource-suffix="" data-rustdoc-version="1.78.0 (9b00956e5 2024-04-29)" data-channel="1.78.0" data-search-js="search-42d8da7a6b9792c2.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-4c98445ec4002617.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../static.files/main-12cf3b4f4f9dc36d.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-04d5337699b92874.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../aho_corasick/index.html">aho_corasick</a><span class="version">1.1.3</span></h2></div><h2 class="location"><a href="#">Module nfa</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#modules">Modules</a></li></ul></section><h2><a href="../index.html">In crate aho_corasick</a></h2></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../aho_corasick/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Module <a href="../index.html">aho_corasick</a>::<wbr><a class="mod" href="#">nfa</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/aho_corasick/nfa/mod.rs.html#1-40">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Provides direct access to NFA implementations of Aho-Corasick.</p>
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<p>The principle characteristic of an NFA in this crate is that it may
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transition through multiple states per byte of haystack. In Aho-Corasick
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parlance, NFAs follow failure transitions during a search. In contrast,
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a <a href="../dfa/struct.DFA.html" title="struct aho_corasick::dfa::DFA"><code>DFA</code></a> pre-computes all failure transitions during
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compilation at the expense of a much bigger memory footprint.</p>
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<p>Currently, there are two NFA implementations provided: noncontiguous and
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contiguous. The names reflect their internal representation, and consequently,
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the trade offs associated with them:</p>
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<ul>
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<li>A <a href="noncontiguous/struct.NFA.html" title="struct aho_corasick::nfa::noncontiguous::NFA"><code>noncontiguous::NFA</code></a> uses a separate allocation for every NFA state to
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represent its transitions in a sparse format. This is ideal for building an
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NFA, since it cheaply permits different states to have a different number of
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transitions. A noncontiguous NFA is where the main Aho-Corasick construction
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algorithm is implemented. All other Aho-Corasick implementations are built by
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first constructing a noncontiguous NFA.</li>
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<li>A <a href="contiguous/struct.NFA.html" title="struct aho_corasick::nfa::contiguous::NFA"><code>contiguous::NFA</code></a> is uses a single allocation to represent all states,
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while still encoding most states as sparse states but permitting states near
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the starting state to have a dense representation. The dense representation
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uses more memory, but permits computing transitions during a search more
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quickly. By only making the most active states dense (the states near the
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starting state), a contiguous NFA better balances memory usage with search
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speed. The single contiguous allocation also uses less overhead per state and
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enables compression tricks where most states only use 8 bytes of heap memory.</li>
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</ul>
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<p>When given the choice between these two, you almost always want to pick a
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contiguous NFA. It takes only a little longer to build, but both its memory
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usage and search speed are typically much better than a noncontiguous NFA. A
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noncontiguous NFA is useful when prioritizing build times, or when there are
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so many patterns that a contiguous NFA could not be built. (Currently, because
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of both memory and search speed improvements, a contiguous NFA has a smaller
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internal limit on the total number of NFA states it can represent. But you
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would likely need to have hundreds of thousands or even millions of patterns
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before you hit this limit.)</p>
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</div></details><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="mod" href="contiguous/index.html" title="mod aho_corasick::nfa::contiguous">contiguous</a></div><div class="desc docblock-short">Provides a contiguous NFA implementation of Aho-Corasick.</div></li><li><div class="item-name"><a class="mod" href="noncontiguous/index.html" title="mod aho_corasick::nfa::noncontiguous">noncontiguous</a></div><div class="desc docblock-short">Provides a noncontiguous NFA implementation of Aho-Corasick.</div></li></ul></section></div></main></body></html> |