| <!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/crc32fast-1.3.2/src/combine.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>combine.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="../../crc32fast/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="../../crc32fast/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="kw">const </span>GF2_DIM: usize = <span class="number">32</span>; |
| |
| <span class="kw">fn </span>gf2_matrix_times(mat: <span class="kw-2">&</span>[u32; GF2_DIM], <span class="kw-2">mut </span>vec: u32) -> u32 { |
| <span class="kw">let </span><span class="kw-2">mut </span>sum = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>idx = <span class="number">0</span>; |
| <span class="kw">while </span>vec > <span class="number">0 </span>{ |
| <span class="kw">if </span>vec & <span class="number">1 </span>== <span class="number">1 </span>{ |
| sum ^= mat[idx]; |
| } |
| vec >>= <span class="number">1</span>; |
| idx += <span class="number">1</span>; |
| } |
| <span class="kw">return </span>sum; |
| } |
| |
| <span class="kw">fn </span>gf2_matrix_square(square: <span class="kw-2">&mut </span>[u32; GF2_DIM], mat: <span class="kw-2">&</span>[u32; GF2_DIM]) { |
| <span class="kw">for </span>n <span class="kw">in </span><span class="number">0</span>..GF2_DIM { |
| square[n] = gf2_matrix_times(mat, mat[n]); |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>combine(<span class="kw-2">mut </span>crc1: u32, crc2: u32, <span class="kw-2">mut </span>len2: u64) -> u32 { |
| <span class="kw">let </span><span class="kw-2">mut </span>row: u32; |
| <span class="kw">let </span><span class="kw-2">mut </span>even = [<span class="number">0u32</span>; GF2_DIM]; <span class="comment">/* even-power-of-two zeros operator */ |
| </span><span class="kw">let </span><span class="kw-2">mut </span>odd = [<span class="number">0u32</span>; GF2_DIM]; <span class="comment">/* odd-power-of-two zeros operator */ |
| |
| /* degenerate case (also disallow negative lengths) */ |
| </span><span class="kw">if </span>len2 <= <span class="number">0 </span>{ |
| <span class="kw">return </span>crc1; |
| } |
| |
| <span class="comment">/* put operator for one zero bit in odd */ |
| </span>odd[<span class="number">0</span>] = <span class="number">0xedb88320</span>; <span class="comment">/* CRC-32 polynomial */ |
| </span>row = <span class="number">1</span>; |
| <span class="kw">for </span>n <span class="kw">in </span><span class="number">1</span>..GF2_DIM { |
| odd[n] = row; |
| row <<= <span class="number">1</span>; |
| } |
| |
| <span class="comment">/* put operator for two zero bits in even */ |
| </span>gf2_matrix_square(<span class="kw-2">&mut </span>even, <span class="kw-2">&</span>odd); |
| |
| <span class="comment">/* put operator for four zero bits in odd */ |
| </span>gf2_matrix_square(<span class="kw-2">&mut </span>odd, <span class="kw-2">&</span>even); |
| |
| <span class="comment">/* apply len2 zeros to crc1 (first square will put the operator for one |
| zero byte, eight zero bits, in even) */ |
| </span><span class="kw">loop </span>{ |
| <span class="comment">/* apply zeros operator for this bit of len2 */ |
| </span>gf2_matrix_square(<span class="kw-2">&mut </span>even, <span class="kw-2">&</span>odd); |
| <span class="kw">if </span>len2 & <span class="number">1 </span>== <span class="number">1 </span>{ |
| crc1 = gf2_matrix_times(<span class="kw-2">&</span>even, crc1); |
| } |
| len2 >>= <span class="number">1</span>; |
| |
| <span class="comment">/* if no more bits set, then done */ |
| </span><span class="kw">if </span>len2 == <span class="number">0 </span>{ |
| <span class="kw">break</span>; |
| } |
| |
| <span class="comment">/* another iteration of the loop with odd and even swapped */ |
| </span>gf2_matrix_square(<span class="kw-2">&mut </span>odd, <span class="kw-2">&</span>even); |
| <span class="kw">if </span>len2 & <span class="number">1 </span>== <span class="number">1 </span>{ |
| crc1 = gf2_matrix_times(<span class="kw-2">&</span>odd, crc1); |
| } |
| len2 >>= <span class="number">1</span>; |
| |
| <span class="comment">/* if no more bits set, then done */ |
| </span><span class="kw">if </span>len2 == <span class="number">0 </span>{ |
| <span class="kw">break</span>; |
| } |
| } |
| |
| <span class="comment">/* return combined crc */ |
| </span>crc1 ^= crc2; |
| <span class="kw">return </span>crc1; |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="crc32fast" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |