| <!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="Yes, but what is it really ?"><meta name="keywords" content="rust, rustlang, rust-lang, fastdivide"><title>fastdivide - 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="../crates.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 crate"><!--[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="../fastdivide/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="../fastdivide/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate fastdivide</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 0.4.0</li><li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#enums">Enums</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">Crate <a class="mod" href="#">fastdivide</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/fastdivide/lib.rs.html#1-250">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"><h2 id="yes-but-what-is-it-really-"><a href="#yes-but-what-is-it-really-">Yes, but what is it really ?</a></h2> |
| <p>Division is a very costly operation for your CPU (probably between 10 |
| and 40 cycles).</p> |
| <p>You may have noticed that when the divisor is known at compile time, |
| your compiler transforms the operations into a cryptic combination of |
| a multiplication and bitshift.</p> |
| <p>Fastdivide is about doing the same trick your compiler uses but |
| when the divisor is unknown at compile time. |
| Of course, it requires preprocessing a datastructure that is |
| specific to your divisor, and using it only makes sense if |
| this preprocessing is amortized by a high number of division (with the |
| same divisor).</p> |
| <h2 id="when-is-it-useful-"><a href="#when-is-it-useful-">When is it useful ?</a></h2> |
| <p>You should probably use <code>fastdivide</code>, if you do a lot (> 10) of division with the same divisor ; |
| and these divisions are a bottleneck in your program.</p> |
| <p>This is for instance useful to compute histograms.</p> |
| <h2 id="example"><a href="#example">Example</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>fastdivide::DividerU64; |
| |
| <span class="kw">fn </span>histogram(vals: <span class="kw-2">&</span>[u64], min: u64, interval: u64, output: <span class="kw-2">&mut </span>[usize]) { |
| |
| <span class="comment">// Preprocessing a datastructure dedicated |
| // to dividing `u64` by `interval`. |
| // |
| // This preprocessing is not cheap. |
| </span><span class="kw">let </span>divide = DividerU64::divide_by(interval); |
| |
| <span class="comment">// We reuse the same `Divider` for all of the |
| // values in vals. |
| </span><span class="kw">for </span><span class="kw-2">&</span>val <span class="kw">in </span>vals { |
| <span class="kw">if </span>val < min { |
| <span class="kw">continue</span>; |
| } |
| <span class="kw">let </span>bucket_id = divide.divide(val - min) <span class="kw">as </span>usize; |
| <span class="kw">if </span>bucket_id < output.len() { |
| output[bucket_id <span class="kw">as </span>usize] += <span class="number">1</span>; |
| } |
| } |
| } |
| |
| </code></pre></div> |
| </div></details><h2 id="enums" class="small-section-header"><a href="#enums">Enums</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="enum" href="enum.DividerU64.html" title="fastdivide::DividerU64 enum">DividerU64</a></div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="fastdivide" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
