| <!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/snap-0.2.5/src/crc32.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>crc32.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="../../snap/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="../../snap/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="comment">// Sadly, all of the crc crates in Rust appear to be insufficient for high |
| // performance algorithms. In fact, the implementation here is insufficient! |
| // The best implementation uses the CRC32 instruction from SSE 4.2, but using |
| // specialty instructions on stable Rust is an absolute nightmare at the |
| // moment. The only way I can think to do it is to write some Assembly in a |
| // separate source file and run an Assembler from build.rs. But we'd need to be |
| // careful to only do this on platforms that support the CRC32 instruction, |
| // which means we'd need to query CPUID. There are a couple Rust crates for |
| // that, but of course, they only work on unstable Rust so we'd need to hand |
| // roll that too. |
| // |
| // As a stopgap, we implement the fastest (slicing-by-16) algorithm described |
| // here: http://create.stephan-brumme.com/crc32/ |
| // (Actually, slicing-by-16 doesn't seem to be measurably faster than |
| // slicing-by-8 on my i7-6900K, so use slicing-by-8.) |
| // |
| // For Snappy, we only care about CRC32C (32 bit, Castagnoli). |
| // |
| // ---AG |
| |
| // We have a bunch of different implementations of crc32 below that seem |
| // somewhat useful to leave around for easy benchmarking. |
| </span><span class="attribute">#![allow(dead_code)] |
| |
| </span><span class="kw">use </span>byteorder::{ByteOrder, LittleEndian <span class="kw">as </span>LE}; |
| |
| <span class="kw">const </span>CASTAGNOLI_POLY: u32 = <span class="number">0x82f63b78</span>; |
| |
| <span class="macro">lazy_static! </span>{ |
| <span class="kw">static </span><span class="kw-2">ref </span>TABLE: [u32; <span class="number">256</span>] = make_table(CASTAGNOLI_POLY); |
| <span class="kw">static </span><span class="kw-2">ref </span>TABLE16: [[u32; <span class="number">256</span>]; <span class="number">16</span>] = { |
| <span class="kw">let </span><span class="kw-2">mut </span>tab = [[<span class="number">0</span>; <span class="number">256</span>]; <span class="number">16</span>]; |
| tab[<span class="number">0</span>] = make_table(CASTAGNOLI_POLY); |
| <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">256 </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>crc = tab[<span class="number">0</span>][i]; |
| <span class="kw">for </span>j <span class="kw">in </span><span class="number">1</span>..<span class="number">16 </span>{ |
| crc = (crc >> <span class="number">8</span>) ^ tab[<span class="number">0</span>][crc <span class="kw">as </span>u8 <span class="kw">as </span>usize]; |
| tab[j][i] = crc; |
| } |
| } |
| tab |
| }; |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">pub fn </span>crc32c(buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="comment">// I can't measure any difference between slice8 and slice16. |
| </span>crc32c_slice8(buf) |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">fn </span>crc32c_slice16(<span class="kw-2">mut </span>buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="kw">let </span>tab = <span class="kw-2">&*</span>TABLE; |
| <span class="kw">let </span>tab16 = <span class="kw-2">&*</span>TABLE16; |
| <span class="kw">let </span><span class="kw-2">mut </span>crc: u32 = !<span class="number">0</span>; |
| <span class="kw">while </span>buf.len() >= <span class="number">16 </span>{ |
| crc ^= LE::read_u32(<span class="kw-2">&</span>buf[<span class="number">0</span>..<span class="number">4</span>]); |
| crc = tab16[<span class="number">0</span>][buf[<span class="number">15</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">1</span>][buf[<span class="number">14</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">2</span>][buf[<span class="number">13</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">3</span>][buf[<span class="number">12</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">4</span>][buf[<span class="number">11</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">5</span>][buf[<span class="number">10</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">6</span>][buf[<span class="number">9</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">7</span>][buf[<span class="number">8</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">8</span>][buf[<span class="number">7</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">9</span>][buf[<span class="number">6</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">10</span>][buf[<span class="number">5</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">11</span>][buf[<span class="number">4</span>] <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">12</span>][(crc >> <span class="number">24</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">13</span>][(crc >> <span class="number">16</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">14</span>][(crc >> <span class="number">8 </span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab16[<span class="number">15</span>][(crc ) <span class="kw">as </span>u8 <span class="kw">as </span>usize]; |
| buf = <span class="kw-2">&</span>buf[<span class="number">16</span>..]; |
| } |
| <span class="kw">for </span><span class="kw-2">&</span>b <span class="kw">in </span>buf { |
| crc = tab[((crc <span class="kw">as </span>u8) ^ b) <span class="kw">as </span>usize] ^ (crc >> <span class="number">8</span>); |
| } |
| !crc |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">fn </span>crc32c_slice8(<span class="kw-2">mut </span>buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="kw">let </span>tab = <span class="kw-2">&*</span>TABLE; |
| <span class="kw">let </span>tab8 = <span class="kw-2">&*</span>TABLE16; |
| <span class="kw">let </span><span class="kw-2">mut </span>crc: u32 = !<span class="number">0</span>; |
| <span class="kw">while </span>buf.len() >= <span class="number">8 </span>{ |
| crc ^= LE::read_u32(<span class="kw-2">&</span>buf[<span class="number">0</span>..<span class="number">4</span>]); |
| crc = tab8[<span class="number">0</span>][buf[<span class="number">7</span>] <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">1</span>][buf[<span class="number">6</span>] <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">2</span>][buf[<span class="number">5</span>] <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">3</span>][buf[<span class="number">4</span>] <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">4</span>][(crc >> <span class="number">24</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">5</span>][(crc >> <span class="number">16</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">6</span>][(crc >> <span class="number">8 </span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab8[<span class="number">7</span>][(crc ) <span class="kw">as </span>u8 <span class="kw">as </span>usize]; |
| buf = <span class="kw-2">&</span>buf[<span class="number">8</span>..]; |
| } |
| <span class="kw">for </span><span class="kw-2">&</span>b <span class="kw">in </span>buf { |
| crc = tab[((crc <span class="kw">as </span>u8) ^ b) <span class="kw">as </span>usize] ^ (crc >> <span class="number">8</span>); |
| } |
| !crc |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">fn </span>crc32c_slice4(<span class="kw-2">mut </span>buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="kw">let </span>tab = <span class="kw-2">&*</span>TABLE; |
| <span class="kw">let </span>tab4 = <span class="kw-2">&*</span>TABLE16; |
| <span class="kw">let </span><span class="kw-2">mut </span>crc: u32 = !<span class="number">0</span>; |
| <span class="kw">while </span>buf.len() >= <span class="number">4 </span>{ |
| crc ^= LE::read_u32(<span class="kw-2">&</span>buf[<span class="number">0</span>..<span class="number">4</span>]); |
| crc = tab4[<span class="number">0</span>][(crc >> <span class="number">24</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab4[<span class="number">1</span>][(crc >> <span class="number">16</span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab4[<span class="number">2</span>][(crc >> <span class="number">8 </span>) <span class="kw">as </span>u8 <span class="kw">as </span>usize] |
| ^ tab4[<span class="number">3</span>][(crc ) <span class="kw">as </span>u8 <span class="kw">as </span>usize]; |
| buf = <span class="kw-2">&</span>buf[<span class="number">4</span>..]; |
| } |
| <span class="kw">for </span><span class="kw-2">&</span>b <span class="kw">in </span>buf { |
| crc = tab[((crc <span class="kw">as </span>u8) ^ b) <span class="kw">as </span>usize] ^ (crc >> <span class="number">8</span>); |
| } |
| !crc |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">fn </span>crc32c_multiple(buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="kw">let </span>tab = <span class="kw-2">&*</span>TABLE; |
| <span class="kw">let </span><span class="kw-2">mut </span>crc: u32 = !<span class="number">0</span>; |
| <span class="kw">for </span><span class="kw-2">&</span>b <span class="kw">in </span>buf { |
| crc = tab[((crc <span class="kw">as </span>u8) ^ b) <span class="kw">as </span>usize] ^ (crc >> <span class="number">8</span>); |
| } |
| !crc |
| } |
| |
| <span class="doccomment">/// Returns the CRC32 checksum of `buf` using the Castagnoli polynomial. |
| </span><span class="kw">fn </span>crc32c_bitwise(buf: <span class="kw-2">&</span>[u8]) -> u32 { |
| <span class="kw">let </span><span class="kw-2">mut </span>crc: u32 = !<span class="number">0</span>; |
| <span class="kw">for </span><span class="kw-2">&</span>b <span class="kw">in </span>buf { |
| crc ^= b <span class="kw">as </span>u32; |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">8 </span>{ |
| crc = (crc >> <span class="number">1</span>) ^ ((crc & <span class="number">1</span>) * CASTAGNOLI_POLY); |
| } |
| } |
| !crc |
| } |
| |
| <span class="kw">fn </span>make_table(poly: u32) -> [u32; <span class="number">256</span>] { |
| <span class="kw">let </span><span class="kw-2">mut </span>tab = [<span class="number">0</span>; <span class="number">256</span>]; |
| <span class="kw">for </span>i <span class="kw">in </span><span class="number">0u32</span>..<span class="number">256u32 </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>crc = i; |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">8 </span>{ |
| <span class="kw">if </span>crc & <span class="number">1 </span>== <span class="number">1 </span>{ |
| crc = (crc >> <span class="number">1</span>) ^ poly; |
| } <span class="kw">else </span>{ |
| crc >>= <span class="number">1</span>; |
| } |
| } |
| tab[i <span class="kw">as </span>usize] = crc; |
| } |
| tab |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="snap" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
