46 lines
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46 lines
7.3 KiB
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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="An implementation of the Fowler–Noll–Vo hash function."><title>fnv - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="fnv" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.svg"></head><body class="rustdoc mod crate"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><rustdoc-topbar><h2><a href="#">Crate fnv</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../fnv/index.html">fnv</a><span class="version">1.0.7</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#about" title="About">About</a></li><li><a href="#using-fnv-in-a-hashmap" title="Using FNV in a `HashMap`">Using FNV in a <code>HashMap</code></a></li><li><a href="#using-fnv-in-a-hashset" title="Using FNV in a `HashSet`">Using FNV in a <code>HashSet</code></a></li></ul><h3><a href="#structs">Crate Items</a></h3><ul class="block"><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#types" title="Type Aliases">Type Aliases</a></li></ul></section><div id="rustdoc-modnav"></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><h1>Crate <span>fnv</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/fnv/lib.rs.html#1-367">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>An implementation of the <a href="http://www.isthe.com/chongo/tech/comp/fnv/index.html">Fowler–Noll–Vo hash function</a>.</p>
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<h3 id="about"><a class="doc-anchor" href="#about">§</a>About</h3>
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<p>The FNV hash function is a custom <code>Hasher</code> implementation that is more
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efficient for smaller hash keys.</p>
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<p><a href="https://www.rust-lang.org/en-US/faq.html#why-are-rusts-hashmaps-slow">The Rust FAQ states that</a> while the default <code>Hasher</code> implementation,
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SipHash, is good in many cases, it is notably slower than other algorithms
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with short keys, such as when you have a map of integers to other values.
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In cases like these, <a href="https://cglab.ca/~abeinges/blah/hash-rs/">FNV is demonstrably faster</a>.</p>
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<p>Its disadvantages are that it performs badly on larger inputs, and
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provides no protection against collision attacks, where a malicious user
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can craft specific keys designed to slow a hasher down. Thus, it is
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important to profile your program to ensure that you are using small hash
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keys, and be certain that your program could not be exposed to malicious
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inputs (including being a networked server).</p>
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<p>The Rust compiler itself uses FNV, as it is not worried about
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denial-of-service attacks, and can assume that its inputs are going to be
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small—a perfect use case for FNV.</p>
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<h3 id="using-fnv-in-a-hashmap"><a class="doc-anchor" href="#using-fnv-in-a-hashmap">§</a>Using FNV in a <code>HashMap</code></h3>
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<p>The <code>FnvHashMap</code> type alias is the easiest way to use the standard library’s
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<code>HashMap</code> with FNV.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>fnv::FnvHashMap;
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<span class="kw">let </span><span class="kw-2">mut </span>map = FnvHashMap::default();
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map.insert(<span class="number">1</span>, <span class="string">"one"</span>);
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map.insert(<span class="number">2</span>, <span class="string">"two"</span>);
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map = FnvHashMap::with_capacity_and_hasher(<span class="number">10</span>, Default::default());
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map.insert(<span class="number">1</span>, <span class="string">"one"</span>);
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map.insert(<span class="number">2</span>, <span class="string">"two"</span>);</code></pre></div>
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<p>Note, the standard library’s <code>HashMap::new</code> and <code>HashMap::with_capacity</code>
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are only implemented for the <code>RandomState</code> hasher, so using <code>Default</code> to
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get the hasher is the next best option.</p>
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<h3 id="using-fnv-in-a-hashset"><a class="doc-anchor" href="#using-fnv-in-a-hashset">§</a>Using FNV in a <code>HashSet</code></h3>
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<p>Similarly, <code>FnvHashSet</code> is a type alias for the standard library’s <code>HashSet</code>
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with FNV.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>fnv::FnvHashSet;
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<span class="kw">let </span><span class="kw-2">mut </span>set = FnvHashSet::default();
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set.insert(<span class="number">1</span>);
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set.insert(<span class="number">2</span>);
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set = FnvHashSet::with_capacity_and_hasher(<span class="number">10</span>, Default::default());
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set.insert(<span class="number">1</span>);
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set.insert(<span class="number">2</span>);</code></pre></div></div></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.FnvHasher.html" title="struct fnv::FnvHasher">FnvHasher</a></dt><dd>An implementation of the Fowler–Noll–Vo hash function.</dd></dl><h2 id="types" class="section-header">Type Aliases<a href="#types" class="anchor">§</a></h2><dl class="item-table"><dt><a class="type" href="type.FnvBuildHasher.html" title="type fnv::FnvBuildHasher">FnvBuild<wbr>Hasher</a></dt><dd>A builder for default FNV hashers.</dd><dt><a class="type" href="type.FnvHashMap.html" title="type fnv::FnvHashMap">FnvHash<wbr>Map</a></dt><dd>A <code>HashMap</code> using a default FNV hasher.</dd><dt><a class="type" href="type.FnvHashSet.html" title="type fnv::FnvHashSet">FnvHash<wbr>Set</a></dt><dd>A <code>HashSet</code> using a default FNV hasher.</dd></dl></section></div></main></body></html> |