<!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="This trait allows the user to customize the heuristic used to determine the relative frequency of a given byte in the dataset being searched."><title>HeuristicFrequencyRank in memchr::arch::all::packedpair - 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 trait"><!--[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="#">HeuristicFrequencyRank</a></h2><divclass="sidebar-elems"><section><h3><ahref="#required-methods">Required Methods</a></h3><ulclass="block"><li><ahref="#tymethod.rank">rank</a></li></ul><h3><ahref="#foreign-impls">Implementations on Foreign Types</a></h3><ulclass="block"><li><ahref="#impl-HeuristicFrequencyRank-for-%26R">&'a R</a></li></ul><h3><ahref="#implementors">Implementors</a></h3></section><h2><ahref="index.html">In memchr::arch::all::packedpair</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>Trait <ahref="../../../index.html">memchr</a>::<wbr><ahref="../../index.html">arch</a>::<wbr><ahref="../index.html">all</a>::<wbr><ahref="index.html">packedpair</a>::<wbr><aclass="trait"href="#">HeuristicFrequencyRank</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/packedpair/mod.rs.html#309-318">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code>pub trait HeuristicFrequencyRank {
}</code></pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>This trait allows the user to customize the heuristic used to determine the
relative frequency of a given byte in the dataset being searched.</p>
<p>The use of this trait can have a dramatic impact on performance depending
on the type of data being searched. The details of why are explained in the
docs of <ahref="../../../memmem/enum.Prefilter.html"title="enum memchr::memmem::Prefilter"><code>crate::memmem::Prefilter</code></a>. To summarize, the core algorithm uses
a prefilter to quickly identify candidate matches that are later verified
more slowly. This prefilter is implemented in terms of trying to find
<code>rare</code> bytes at specific offsets that will occur less frequently in the
dataset. While the concept of a <code>rare</code> byte is similar for most datasets,
there are some specific datasets (like binary executables) that have
dramatically different byte distributions. For these datasets customizing
the byte frequency heuristic can have a massive impact on performance, and
might even need to be done at runtime.</p>
<p>The default implementation of <code>HeuristicFrequencyRank</code> reads from the
static frequency table defined in <code>src/memmem/byte_frequencies.rs</code>. This
is optimal for most inputs, so if you are unsure of the impact of using a
custom <code>HeuristicFrequencyRank</code> you should probably just use the default.</p>
</div></details><h2id="required-methods"class="section-header">Required Methods<ahref="#required-methods"class="anchor">§</a></h2><divclass="methods"><detailsclass="toggle method-toggle"open><summary><sectionid="tymethod.rank"class="method"><aclass="src rightside"href="../../../../src/memchr/arch/all/packedpair/mod.rs.html#317">source</a><h4class="code-header">fn <ahref="#tymethod.rank"class="fn">rank</a>(&self, byte: <aclass="primitive"href="https://doc.rust-lang.org/1.76.0/std/primitive.u8.html">u8</a>) -><aclass="primitive"href="https://doc.rust-lang.org/1.76.0/std/primitive.u8.html">u8</a></h4></section></summary><divclass="docblock"><p>Return the heuristic frequency rank of the given byte. A lower rank
R: <aclass="trait"href="trait.HeuristicFrequencyRank.html"title="trait memchr::arch::all::packedpair::HeuristicFrequencyRank">HeuristicFrequencyRank</a>,</div></h3></section></summary><divclass="docblock"><p>This permits passing any implementation of <code>HeuristicFrequencyRank</code> as a
