| <!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/git/checkouts/incubator-teaclave-crates-c8106113f74feefc/ede1f68/image/./src/codecs/jpeg/entropy.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>entropy.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="../../../../image/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="../../../../image/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">/// Given an array containing the number of codes of each code length, |
| /// this function generates the huffman codes lengths and their respective |
| /// code lengths as specified by the JPEG spec. |
| </span><span class="kw">fn </span>derive_codes_and_sizes(bits: <span class="kw-2">&</span>[u8; <span class="number">16</span>]) -> ([u8; <span class="number">256</span>], [u16; <span class="number">256</span>]) { |
| <span class="kw">let </span><span class="kw-2">mut </span>huffsize = [<span class="number">0u8</span>; <span class="number">256</span>]; |
| <span class="kw">let </span><span class="kw-2">mut </span>huffcode = [<span class="number">0u16</span>; <span class="number">256</span>]; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>k = <span class="number">0</span>; |
| |
| <span class="comment">// Annex C.2 |
| // Figure C.1 |
| // Generate table of individual code lengths |
| </span><span class="kw">for </span>i <span class="kw">in </span><span class="number">0u8</span>..<span class="number">16 </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>j = <span class="number">0</span>; |
| |
| <span class="kw">while </span>j < bits[usize::from(i)] { |
| huffsize[k] = i + <span class="number">1</span>; |
| k += <span class="number">1</span>; |
| j += <span class="number">1</span>; |
| } |
| } |
| |
| huffsize[k] = <span class="number">0</span>; |
| |
| <span class="comment">// Annex C.2 |
| // Figure C.2 |
| // Generate table of huffman codes |
| </span>k = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>code = <span class="number">0u16</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>size = huffsize[<span class="number">0</span>]; |
| |
| <span class="kw">while </span>huffsize[k] != <span class="number">0 </span>{ |
| huffcode[k] = code; |
| code += <span class="number">1</span>; |
| k += <span class="number">1</span>; |
| |
| <span class="kw">if </span>huffsize[k] == size { |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="comment">// FIXME there is something wrong with this code |
| </span><span class="kw">let </span>diff = huffsize[k].wrapping_sub(size); |
| code = <span class="kw">if </span>diff < <span class="number">16 </span>{ code << diff <span class="kw">as </span>usize } <span class="kw">else </span>{ <span class="number">0 </span>}; |
| |
| size = size.wrapping_add(diff); |
| } |
| |
| (huffsize, huffcode) |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>build_huff_lut(bits: <span class="kw-2">&</span>[u8; <span class="number">16</span>], huffval: <span class="kw-2">&</span>[u8]) -> [(u8, u16); <span class="number">256</span>] { |
| <span class="kw">let </span><span class="kw-2">mut </span>lut = [(<span class="number">17u8</span>, <span class="number">0u16</span>); <span class="number">256</span>]; |
| <span class="kw">let </span>(huffsize, huffcode) = derive_codes_and_sizes(bits); |
| |
| <span class="kw">for </span>(i, <span class="kw-2">&</span>v) <span class="kw">in </span>huffval.iter().enumerate() { |
| lut[v <span class="kw">as </span>usize] = (huffsize[i], huffcode[i]); |
| } |
| |
| lut |
| } |
| </code></pre></div> |
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