<!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="Prefilter controls whether heuristics are used to accelerate searching."><title>Prefilter in memchr::memmem - 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-ac92e1bbe349e143.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="1.76.0 (07dca489a 2024-02-04)"data-channel="1.76.0"data-search-js="search-2b6ce74ff89ae146.js"data-settings-js="settings-4313503d2e1961c2.js"><scriptsrc="../../static.files/storage-f2adc0d6ca4d09fb.js"></script><scriptdefersrc="sidebar-items.js"></script><scriptdefersrc="../../static.files/main-305769736d49e732.js"></script><noscript><linkrel="stylesheet"href="../../static.files/noscript-feafe1bb7466e4bd.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 enum"><!--[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">☰</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="#">Prefilter</a></h2><divclass="sidebar-elems"><section><h3><ahref="#variants">Variants</a></h3><ulclass="block variant"><li><ahref="#variant.Auto">Auto</a></li><li><ahref="#variant.None">None</a></li></ul><h3><ahref="#trait-implementations">Trait Implementations</a></h3><ulclass="block trait-implementation"><li><ahref="#impl-Clone-for-PrefilterConfig">Clone</a></li><li><ahref="#impl-Copy-for-PrefilterConfig">Copy</a></li><li><ahref="#impl-Debug-for-PrefilterConfig">Debug</a></li><li><ahref="#impl-Default-for-PrefilterConfig">Default</a></li></ul><h3><ahref="#synthetic-implementations">Auto Trait Implementations</a></h3><ulclass="block synthetic-implementation"><li><ahref="#impl-RefUnwindSafe-for-PrefilterConfig">RefUnwindSafe</a></li><li><ahref="#impl-Send-for-PrefilterConfig">Send</a></li><li><ahref="#impl-Sync-for-PrefilterConfig">Sync</a></li><li><ahref="#impl-Unpin-for-PrefilterConfig">Unpin</a></li><li><ahref="#impl-UnwindSafe-for-PrefilterConfig">UnwindSafe</a></li></ul><h3><ahref="#blanket-implementations">Blanket Implementations</a></h3><ulclass="block blanket-implementation"><li><ahref="#impl-Any-for-T">Any</a></li><li><ahref="#impl-Borrow%3CT%3E-for-T">Borrow<T></a></li><li><ahref="#impl-BorrowMut%3CT%3E-for-T">BorrowMut<T></a></li><li><ahref="#impl-From%3CT%3E-for-T">From<T></a></li><li><ahref="#impl-Into%3CU%3E-for-T">Into<U></a></li><li><ahref="#impl-ToOwned-for-T">ToOwned</a></li><li><ahref="#impl-TryFrom%3CU%3E-for-T">TryFrom<U></a></li><li><ahref="#impl-TryInto%3CU%3E-for-T">TryInto<U></a></li></ul></secti
<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>Enum <ahref="../index.html">memchr</a>::<wbr><ahref="index.html">memmem</a>::<wbr><aclass="enum"href="#">Prefilter</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/memmem/searcher.rs.html#544-551">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code><divclass="code-attribute">#[non_exhaustive]</div>pub enum Prefilter {
None,
Auto,
}</code></pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>Prefilter controls whether heuristics are used to accelerate searching.</p>
<p>A prefilter refers to the idea of detecting candidate matches very quickly,
and then confirming whether those candidates are full matches. This
idea can be quite effective since it’s often the case that looking for
candidates can be a lot faster than running a complete substring search
over the entire input. Namely, looking for candidates can be done with
extremely fast vectorized code.</p>
<p>The downside of a prefilter is that it assumes false positives (which are
candidates generated by a prefilter that aren’t matches) are somewhat rare
relative to the frequency of full matches. That is, if a lot of false
positives are generated, then it’s possible for search time to be worse
than if the prefilter wasn’t enabled in the first place.</p>
<p>Another downside of a prefilter is that it can result in highly variable
performance, where some cases are extraordinarily fast and others aren’t.
Typically, variable performance isn’t a problem, but it may be for your use
case.</p>
<p>The use of prefilters in this implementation does use a heuristic to detect
when a prefilter might not be carrying its weight, and will dynamically
disable its use. Nevertheless, this configuration option gives callers
the ability to disable prefilters if you have knowledge that they won’t be
useful.</p>
</div></details><h2id="variants"class="variants section-header">Variants (Non-exhaustive)<ahref="#variants"class="anchor">§</a></h2><detailsclass="toggle non-exhaustive"><summaryclass="hideme"><span>This enum is marked as non-exhaustive</span></summary><divclass="docblock">Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.</div></details><divclass="variants"><sectionid="variant.None"class="variant"><ahref="#variant.None"class="anchor">§</a><h3class="code-header">None</h3></section><divclass="docblock"><p>Never used a prefilter in substring search.</p>
</div><sectionid="variant.Auto"class="variant"><ahref="#variant.Auto"class="anchor">§</a><h3class="code-header">Auto</h3></section><divclass="docblock"><p>Automatically detect whether a heuristic prefilter should be used. If
it is used, then heuristics will be used to dynamically disable the
prefilter if it is believed to not be carrying its weight.</p>
<p>That is, this conversion is whatever the implementation of
<code><ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.From.html"title="trait core::convert::From">From</a><T> for U</code> chooses to do.</p>
</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-ToOwned-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#83-85">source</a><ahref="#impl-ToOwned-for-T"class="anchor">§</a><h3class="code-header">impl<T><aclass="trait"href="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html"title="trait alloc::borrow::ToOwned">ToOwned</a> for T<divclass="where">where
T: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/clone/trait.Clone.html"title="trait core::clone::Clone">Clone</a>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Owned"class="associatedtype trait-impl"><ahref="#associatedtype.Owned"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#associatedtype.Owned"class="associatedtype">Owned</a> = T</h4></section></summary><divclass='docblock'>The resulting type after obtaining ownership.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.to_owned"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#88">source</a><ahref="#method.to_owned"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#tymethod.to_owned"class="fn">to_owned</a>(&self) -> T</h4></section></summary><divclass='docblock'>Creates owned data from borrowed data, usually by cloning. <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#tymethod.to_owned">Read more</a></div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.clone_into"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#92">source</a><ahref="#method.clone_into"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#method.clone_into"class="fn">clone_into</a>(&self, target: <aclass="primitive"href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&mut T</a>)</h4></section></summary><divclass='docblock'>Uses borrowed data to replace owned data, usually by cloning. <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#method.clone_into">Read more</a></div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryFrom%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#803-805">source</a><ahref="#impl-TryFrom%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.Into.html"title="trait core::convert::Into">Into</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error"class="associatedtype trait-impl"><ahref="#associatedtype.Error"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"class="associatedtype">Error</a> = <aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/convert/enum.Infallible.html"title="enum core::convert::Infallible">Infallible</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_from"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#810">source</a><ahref="#method.try_from"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#tymethod.try_from"class="fn">try_from</a>(value: U) -><aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><T, <T as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryInto%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#788-790">source</a><ahref="#impl-TryInto%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html"title="trait core::convert::TryInto">TryInto</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error-1"class="associatedtype trait-impl"><ahref="#associatedtype.Error-1"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html#associatedtype.Error"class="associatedtype">Error</a> = <U as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_into"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#795">source</a><ahref="#method.try_into"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html#tymethod.try_into"class="fn">try_into</a>(self) -><aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><U, <U as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details></div></section></div></main></body></html>
