| <!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."><meta name="keywords" content="rust, rustlang, rust-lang, nfa"><title>aho_corasick::nfa - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.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">☰</button><a class="sidebar-logo" href="../../aho_corasick/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../aho_corasick/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><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></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Module <a href="../index.html">aho_corasick</a>::<wbr><a class="mod" href="#">nfa</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../src/aho_corasick/nfa/mod.rs.html#1-40">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-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> |
| <p>The principle characteristic of an NFA in this crate is that it may |
| transition through multiple states per byte of haystack. In Aho-Corasick |
| parlance, NFAs follow failure transitions during a search. In contrast, |
| a <a href="../dfa/struct.DFA.html"><code>DFA</code></a> pre-computes all failure transitions during |
| compilation at the expense of a much bigger memory footprint.</p> |
| <p>Currently, there are two NFA implementations provided: noncontiguous and |
| contiguous. The names reflect their internal representation, and consequently, |
| the trade offs associated with them:</p> |
| <ul> |
| <li>A <a href="noncontiguous/struct.NFA.html" title="noncontiguous::NFA"><code>noncontiguous::NFA</code></a> uses a separate allocation for every NFA state to |
| represent its transitions in a sparse format. This is ideal for building an |
| NFA, since it cheaply permits different states to have a different number of |
| transitions. A noncontiguous NFA is where the main Aho-Corasick construction |
| algorithm is implemented. All other Aho-Corasick implementations are built by |
| first constructing a noncontiguous NFA.</li> |
| <li>A <a href="contiguous/struct.NFA.html" title="contiguous::NFA"><code>contiguous::NFA</code></a> is uses a single allocation to represent all states, |
| while still encoding most states as sparse states but permitting states near |
| the starting state to have a dense representation. The dense representation |
| uses more memory, but permits computing transitions during a search more |
| quickly. By only making the most active states dense (the states near the |
| starting state), a contiguous NFA better balances memory usage with search |
| speed. The single contiguous allocation also uses less overhead per state and |
| enables compression tricks where most states only use 8 bytes of heap memory.</li> |
| </ul> |
| <p>When given the choice between these two, you almost always want to pick a |
| contiguous NFA. It takes only a little longer to build, but both its memory |
| usage and search speed are typically much better than a noncontiguous NFA. A |
| noncontiguous NFA is useful when prioritizing build times, or when there are |
| so many patterns that a contiguous NFA could not be built. (Currently, because |
| of both memory and search speed improvements, a contiguous NFA has a smaller |
| internal limit on the total number of NFA states it can represent. But you |
| would likely need to have hundreds of thousands or even millions of patterns |
| before you hit this limit.)</p> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="contiguous/index.html" title="aho_corasick::nfa::contiguous mod">contiguous</a></div><div class="item-right docblock-short">Provides a contiguous NFA implementation of Aho-Corasick.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="noncontiguous/index.html" title="aho_corasick::nfa::noncontiguous mod">noncontiguous</a></div><div class="item-right docblock-short">Provides a noncontiguous NFA implementation of Aho-Corasick.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="aho_corasick" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
