<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="An implementation of the Two-Way substring search algorithm."><title>memchr::arch::all::twoway - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../../../../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../../../../static.files/rustdoc-5bc39a1768837dd0.css"><metaname="rustdoc-vars"data-root-path="../../../../"data-static-root-path="../../../../static.files/"data-current-crate="memchr"data-themes=""data-resource-suffix=""data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)"data-channel="1.77.0"data-search-js="search-dd67cee4cfa65049.js"data-settings-js="settings-4313503d2e1961c2.js"><scriptsrc="../../../../static.files/storage-4c98445ec4002617.js"></script><scriptdefersrc="../sidebar-items.js"></script><scriptdefersrc="../../../../static.files/main-48f368f3872407c8.js"></script><noscript><linkrel="stylesheet"href="../../../../static.files/noscript-04d5337699b92874.css"></noscript><linkrel="alternate icon"type="image/png"href="../../../../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../../../../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../../../../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle"title="show sidebar"></button></nav><navclass="sidebar"><divclass="sidebar-crate"><h2><ahref="../../../../memchr/index.html">memchr</a><spanclass="version">2.7.1</span></h2></div><h2class="location"><ahref="#">Module twoway</a></h2><divclass="sidebar-elems"><section><ulclass="block"><li><ahref="#structs">Structs</a></li></ul></section><h2><ahref="../index.html">In memchr::arch::all</a></h2></div></nav><divclass="sidebar-resizer"></div>
<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../../../../memchr/all.html"title="show sidebar"></a></div><inputclass="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"><divid="help-button"tabindex="-1"><ahref="../../../../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../../../../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../../../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Module <ahref="../../../index.html">memchr</a>::<wbr><ahref="../../index.html">arch</a>::<wbr><ahref="../index.html">all</a>::<wbr><aclass="mod"href="#">twoway</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../../../../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../../../../src/memchr/arch/all/twoway.rs.html#1-877">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>An implementation of the <ahref="https://en.wikipedia.org/wiki/Two-way_string-matching_algorithm">Two-Way substring search algorithm</a>.</p>
<p><ahref="struct.Finder.html"title="struct memchr::arch::all::twoway::Finder"><code>Finder</code></a> can be built for forward searches, while <ahref="struct.FinderRev.html"title="struct memchr::arch::all::twoway::FinderRev"><code>FinderRev</code></a> can be built
for reverse searches.</p>
<p>Two-Way makes for a nice general purpose substring search algorithm because of
its time and space complexity properties. It also performs well in practice.
Namely, with <code>m = len(needle)</code> and <code>n = len(haystack)</code>, Two-Way takes <code>O(m)</code>
time to create a finder, <code>O(1)</code> space and <code>O(n)</code> search time. In other words,
the preprocessing step is quick, doesn’t require any heap memory and the worst
case search time is guaranteed to be linear in the haystack regardless of the
size of the needle.</p>
<p>While vector algorithms will usually beat Two-Way handedly, vector algorithms
also usually have pathological or edge cases that are better handled by Two-Way.
Moreover, not all targets support vector algorithms or implementations for them
simply may not exist yet.</p>
<p>Two-Way can be found in the <code>memmem</code> implementations in at least <ahref="https://www.gnu.org/software/libc/">GNU libc</a> and
