<!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="API documentation for the Rust `align_offset` fn in crate `core`."><meta name="keywords" content="rust, rustlang, rust-lang, align_offset"><title>core::intrinsics::align_offset - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc fn"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>intrinsics</a></p><script>window.sidebarCurrent = {name: 'align_offset', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>core</a>::<wbr><a href='index.html'>intrinsics</a>::<wbr><a class="fn" href=''>align_offset</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version '></span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../src/core/intrinsics.rs.html#1399' title='goto source code'>[src]</a></span></h1><pre class='rust fn'>pub unsafe extern "rust-intrinsic" fn align_offset(<br> ptr: *const (), <br> align: usize<br>) -> usize</pre><div class='stability'><div class='stab unstable'><details><summary><span class=microscope>🔬</span> This is a nightly-only experimental API. (<code>core_intrinsics</code>)</summary><p>intrinsics are unlikely to ever be stabilized, instead they should be used through stabilized interfaces in the rest of the standard library</p>
</details></div></div><div class='docblock'><p>Computes the byte offset that needs to be applied to <code>ptr</code> in order to
make it aligned to <code>align</code>.
If it is not possible to align <code>ptr</code>, the implementation returns
<code>usize::max_value()</code>.</p>
<p>There are no guarantees whatsover that offsetting the pointer will not
overflow or go beyond the allocation that <code>ptr</code> points into.
It is up to the caller to ensure that the returned offset is correct
in all terms other than alignment.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Accessing adjacent <code>u8</code> as <code>u16</code></p>
<pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> [<span class="number">5u8</span>, <span class="number">6u8</span>, <span class="number">7u8</span>, <span class="number">8u8</span>, <span class="number">9u8</span>];
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">x</span>[<span class="ident">n</span>] <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">u8</span>;
<span class="kw">let</span> <span class="ident">offset</span> <span class="op">=</span> <span class="ident">align_offset</span>(<span class="ident">ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> (), <span class="ident">align_of</span>::<span class="op"><</span><span class="ident">u16</span><span class="op">></span>());
<span class="kw">if</span> <span class="ident">offset</span> <span class="op"><</span> <span class="ident">x</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="ident">n</span> <span class="op">-</span> <span class="number">1</span> {
<span class="kw">let</span> <span class="ident">u16_ptr</span> <span class="op">=</span> <span class="ident">ptr</span>.<span class="ident">offset</span>(<span class="ident">offset</span> <span class="kw">as</span> <span class="ident">isize</span>) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">u16</span>;
<span class="macro">assert_ne</span><span class="macro">!</span>(<span class="kw-2">*</span><span class="ident">u16_ptr</span>, <span class="number">500</span>);
} <span class="kw">else</span> {
<span class="comment">// while the pointer can be aligned via `offset`, it would point</span>
<span class="comment">// outside the allocation</span>
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0A%23!%5Bfeature(core_intrinsics)%5D%0Aextern%20crate%20core%3B%0Afn%20main()%20%7B%0Afn%20foo(n%3A%20usize)%20%7B%0Ause%20std%3A%3Aintrinsics%3A%3Aalign_offset%3B%0Ause%20std%3A%3Amem%3A%3Aalign_of%3B%0Aunsafe%20%7B%0Alet%20x%20%3D%20%5B5u8%2C%206u8%2C%207u8%2C%208u8%2C%209u8%5D%3B%0Alet%20ptr%20%3D%20%26x%5Bn%5D%20as%20*const%20u8%3B%0Alet%20offset%20%3D%20align_offset(ptr%20as%20*const%20()%2C%20align_of%3A%3A%3Cu16%3E())%3B%0Aif%20offset%20%3C%20x.len()%20-%20n%20-%201%20%7B%0A%20%20%20%20let%20u16_ptr%20%3D%20ptr.offset(offset%20as%20isize)%20as%20*const%20u16%3B%0A%20%20%20%20assert_ne!(*u16_ptr%2C%20500)%3B%0A%7D%20else%20%7B%0A%20%20%20%20%2F%2F%20while%20the%20pointer%20can%20be%20aligned%20via%20%60offset%60%2C%20it%20would%20point%0A%20%20%20%20%2F%2F%20outside%20the%20allocation%0A%7D%0A%7D%20%7D%0A%7D&version=nightly">Run</a></pre>
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