| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/memchr-2.5.0/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs - source</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="../../source-script.js"></script><script defer src="../../source-files.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 source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../memchr/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../memchr/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="doccomment">/*! |
| This library provides heavily optimized routines for string search primitives. |
| |
| # Overview |
| |
| This section gives a brief high level overview of what this crate offers. |
| |
| * The top-level module provides routines for searching for 1, 2 or 3 bytes |
| in the forward or reverse direction. When searching for more than one byte, |
| positions are considered a match if the byte at that position matches any |
| of the bytes. |
| * The [`memmem`] sub-module provides forward and reverse substring search |
| routines. |
| |
| In all such cases, routines operate on `&[u8]` without regard to encoding. This |
| is exactly what you want when searching either UTF-8 or arbitrary bytes. |
| |
| # Example: using `memchr` |
| |
| This example shows how to use `memchr` to find the first occurrence of `z` in |
| a haystack: |
| |
| ``` |
| use memchr::memchr; |
| |
| let haystack = b"foo bar baz quuz"; |
| assert_eq!(Some(10), memchr(b'z', haystack)); |
| ``` |
| |
| # Example: matching one of three possible bytes |
| |
| This examples shows how to use `memrchr3` to find occurrences of `a`, `b` or |
| `c`, starting at the end of the haystack. |
| |
| ``` |
| use memchr::memchr3_iter; |
| |
| let haystack = b"xyzaxyzbxyzc"; |
| |
| let mut it = memchr3_iter(b'a', b'b', b'c', haystack).rev(); |
| assert_eq!(Some(11), it.next()); |
| assert_eq!(Some(7), it.next()); |
| assert_eq!(Some(3), it.next()); |
| assert_eq!(None, it.next()); |
| ``` |
| |
| # Example: iterating over substring matches |
| |
| This example shows how to use the [`memmem`] sub-module to find occurrences of |
| a substring in a haystack. |
| |
| ``` |
| use memchr::memmem; |
| |
| let haystack = b"foo bar foo baz foo"; |
| |
| let mut it = memmem::find_iter(haystack, "foo"); |
| assert_eq!(Some(0), it.next()); |
| assert_eq!(Some(8), it.next()); |
| assert_eq!(Some(16), it.next()); |
| assert_eq!(None, it.next()); |
| ``` |
| |
| # Example: repeating a search for the same needle |
| |
| It may be possible for the overhead of constructing a substring searcher to be |
| measurable in some workloads. In cases where the same needle is used to search |
| many haystacks, it is possible to do construction once and thus to avoid it for |
| subsequent searches. This can be done with a [`memmem::Finder`]: |
| |
| ``` |
| use memchr::memmem; |
| |
| let finder = memmem::Finder::new("foo"); |
| |
| assert_eq!(Some(4), finder.find(b"baz foo quux")); |
| assert_eq!(None, finder.find(b"quux baz bar")); |
| ``` |
| |
| # Why use this crate? |
| |
| At first glance, the APIs provided by this crate might seem weird. Why provide |
| a dedicated routine like `memchr` for something that could be implemented |
| clearly and trivially in one line: |
| |
| ``` |
| fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> { |
| haystack.iter().position(|&b| b == needle) |
| } |
| ``` |
| |
| Or similarly, why does this crate provide substring search routines when Rust's |
| core library already provides them? |
| |
| ``` |
| fn search(haystack: &str, needle: &str) -> Option<usize> { |
| haystack.find(needle) |
| } |
| ``` |
| |
| The primary reason for both of them to exist is performance. When it comes to |
| performance, at a high level at least, there are two primary ways to look at |
| it: |
| |
| * **Throughput**: For this, think about it as, "given some very large haystack |
| and a byte that never occurs in that haystack, how long does it take to |
| search through it and determine that it, in fact, does not occur?" |
| * **Latency**: For this, think about it as, "given a tiny haystack---just a |
| few bytes---how long does it take to determine if a byte is in it?" |
| |
| The `memchr` routine in this crate has _slightly_ worse latency than the |
| solution presented above, however, its throughput can easily be over an |
| order of magnitude faster. This is a good general purpose trade off to make. |
| You rarely lose, but often gain big. |
| |
| **NOTE:** The name `memchr` comes from the corresponding routine in libc. A key |
| advantage of using this library is that its performance is not tied to its |
| quality of implementation in the libc you happen to be using, which can vary |
| greatly from platform to platform. |
| |
| But what about substring search? This one is a bit more complicated. The |
| primary reason for its existence is still indeed performance, but it's also |
| useful because Rust's core library doesn't actually expose any substring |
| search routine on arbitrary bytes. The only substring search routine that |
| exists works exclusively on valid UTF-8. |
| |
| So if you have valid UTF-8, is there a reason to use this over the standard |
| library substring search routine? Yes. This routine is faster on almost every |
| metric, including latency. The natural question then, is why isn't this |
| implementation in the standard library, even if only for searching on UTF-8? |
| The reason is that the implementation details for using SIMD in the standard |
| library haven't quite been worked out yet. |
| |
| **NOTE:** Currently, only `x86_64` targets have highly accelerated |
| implementations of substring search. For `memchr`, all targets have |
| somewhat-accelerated implementations, while only `x86_64` targets have highly |
| accelerated implementations. This limitation is expected to be lifted once the |
| standard library exposes a platform independent SIMD API. |
| |
| # Crate features |
| |
| * **std** - When enabled (the default), this will permit this crate to use |
| features specific to the standard library. Currently, the only thing used |
| from the standard library is runtime SIMD CPU feature detection. This means |
| that this feature must be enabled to get AVX accelerated routines. When |
| `std` is not enabled, this crate will still attempt to use SSE2 accelerated |
| routines on `x86_64`. |
| * **libc** - When enabled (**not** the default), this library will use your |
| platform's libc implementation of `memchr` (and `memrchr` on Linux). This |
| can be useful on non-`x86_64` targets where the fallback implementation in |
| this crate is not as good as the one found in your libc. All other routines |
| (e.g., `memchr[23]` and substring search) unconditionally use the |
| implementation in this crate. |
| */ |
| |
| </span><span class="attribute">#![deny(missing_docs)] |
| #![cfg_attr(not(feature = <span class="string">"std"</span>), no_std)] |
| </span><span class="comment">// It's not worth trying to gate all code on just miri, so turn off relevant |
| // dead code warnings. |
| </span><span class="attribute">#![cfg_attr(miri, allow(dead_code, unused_macros))] |
| |
| </span><span class="comment">// Supporting 8-bit (or others) would be fine. If you need it, please submit a |
| // bug report at https://github.com/BurntSushi/memchr |
| </span><span class="attribute">#[cfg(not(any( |
| target_pointer_width = <span class="string">"16"</span>, |
| target_pointer_width = <span class="string">"32"</span>, |
| target_pointer_width = <span class="string">"64" |
| </span>)))] |
| </span><span class="macro">compile_error!</span>(<span class="string">"memchr currently not supported on non-{16,32,64}"</span>); |
| |
| <span class="kw">pub use </span><span class="kw">crate</span>::memchr::{ |
| memchr, memchr2, memchr2_iter, memchr3, memchr3_iter, memchr_iter, |
| memrchr, memrchr2, memrchr2_iter, memrchr3, memrchr3_iter, memrchr_iter, |
| Memchr, Memchr2, Memchr3, |
| }; |
| |
| <span class="kw">mod </span>cow; |
| <span class="kw">mod </span>memchr; |
| <span class="kw">pub mod </span>memmem; |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests; |
| </code></pre></div> |
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