<!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 `/home/sangenya/.cargo/registry/src/github.com-1ecc6299db9ec823/deflate-0.7.20/src/zlib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>zlib.rs - source</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="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><script src="../../crates.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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<span class="doccomment">//! This module contains functionality for generating a [zlib](https://tools.ietf.org/html/rfc1950)</span>
<span class="doccomment">//! header.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The Zlib header contains some metadata (a window size and a compression level), and optionally</span>
<span class="doccomment">//! a block of data serving as an extra dictionary for the compressor/decompressor.</span>
<span class="doccomment">//! The dictionary is not implemented in this library.</span>
<span class="doccomment">//! The data in the header aside from the dictionary doesn't actually have any effect on the</span>
<span class="doccomment">//! decompressed data, it only offers some hints for the decompressor on how the data was</span>
<span class="doccomment">//! compressed.</span>
<span class="kw">use</span> <span class="ident">std::io</span>::{<span class="ident">Write</span>, <span class="prelude-ty">Result</span>};
<span class="comment">// CM = 8 means to use the DEFLATE compression method.</span>
<span class="kw">const</span> <span class="ident">DEFAULT_CM</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">8</span>;
<span class="comment">// CINFO = 7 Indicates a 32k window size.</span>
<span class="kw">const</span> <span class="ident">DEFAULT_CINFO</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">7</span> <span class="op"><</span><span class="op"><</span> <span class="number">4</span>;
<span class="kw">const</span> <span class="ident">DEFAULT_CMF</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="ident">DEFAULT_CM</span> <span class="op">|</span> <span class="ident">DEFAULT_CINFO</span>;
<span class="comment">// No dict by default.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">const</span> <span class="ident">DEFAULT_FDICT</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0</span>;
<span class="comment">// FLEVEL = 0 means fastest compression algorithm.</span>
<span class="kw">const</span> <span class="ident">_DEFAULT_FLEVEL</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0</span> <span class="op"><</span><span class="op"><</span> <span class="number">7</span>;
<span class="comment">// The 16-bit value consisting of CMF and FLG must be divisible by this to be valid.</span>
<span class="kw">const</span> <span class="ident">FCHECK_DIVISOR</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">31</span>;
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">dead_code</span>)]</span>
<span class="attribute">#[<span class="ident">repr</span>(<span class="ident">u8</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">CompressionLevel</span> {
<span class="ident">Fastest</span> <span class="op">=</span> <span class="number">0</span> <span class="op"><</span><span class="op"><</span> <span class="number">6</span>,
<span class="ident">Fast</span> <span class="op">=</span> <span class="number">1</span> <span class="op"><</span><span class="op"><</span> <span class="number">6</span>,
<span class="ident">Default</span> <span class="op">=</span> <span class="number">2</span> <span class="op"><</span><span class="op"><</span> <span class="number">6</span>,
<span class="ident">Maximum</span> <span class="op">=</span> <span class="number">3</span> <span class="op"><</span><span class="op"><</span> <span class="number">6</span>,
}
<span class="doccomment">/// Generate FCHECK from CMF and FLG (without FCKECH )so that they are correct according to the</span>
<span class="doccomment">/// specification, i.e (CMF*256 + FCHK) % 31 = 0.</span>
<span class="doccomment">/// Returns flg with the FCHKECK bits added (any existing FCHECK bits are ignored).</span>
<span class="kw">fn</span> <span class="ident">add_fcheck</span>(<span class="ident">cmf</span>: <span class="ident">u8</span>, <span class="ident">flg</span>: <span class="ident">u8</span>) <span class="op">-</span><span class="op">></span> <span class="ident">u8</span> {
<span class="kw">let</span> <span class="ident">rem</span> <span class="op">=</span> ((<span class="ident">usize::from</span>(<span class="ident">cmf</span>) <span class="op">*</span> <span class="number">256</span>) <span class="op">+</span> <span class="ident">usize::from</span>(<span class="ident">flg</span>)) <span class="op">%</span> <span class="ident">usize::from</span>(<span class="ident">FCHECK_DIVISOR</span>);
<span class="comment">// Clear existing FCHECK if any</span>
<span class="kw">let</span> <span class="ident">flg</span> <span class="op">=</span> <span class="ident">flg</span> <span class="op">&</span> <span class="number">0b11100000</span>;
<span class="comment">// Casting is safe as rem can't overflow since it is a value mod 31</span>
<span class="comment">// We can simply add the value to flg as (31 - rem) will never be above 2^5</span>
<span class="ident">flg</span> <span class="op">+</span> (<span class="ident">FCHECK_DIVISOR</span> <span class="op">-</span> <span class="ident">rem</span> <span class="kw">as</span> <span class="ident">u8</span>)
}
<span class="doccomment">/// Write a zlib header with an empty dictionary to the writer using the specified</span>
<span class="doccomment">/// compression level preset.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">write_zlib_header</span><span class="op"><</span><span class="ident">W</span>: <span class="ident">Write</span><span class="op">></span>(<span class="ident">writer</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">W</span>, <span class="ident">level</span>: <span class="ident">CompressionLevel</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>()<span class="op">></span> {
<span class="ident">writer</span>.<span class="ident">write_all</span>(<span class="kw-2">&</span><span class="ident">get_zlib_header</span>(<span class="ident">level</span>))
}
<span class="doccomment">/// Get the zlib header for the `CompressionLevel` level using the default window size and no</span>
<span class="doccomment">/// dictionary.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_zlib_header</span>(<span class="ident">level</span>: <span class="ident">CompressionLevel</span>) <span class="op">-</span><span class="op">></span> [<span class="ident">u8</span>; <span class="number">2</span>] {
<span class="kw">let</span> <span class="ident">cmf</span> <span class="op">=</span> <span class="ident">DEFAULT_CMF</span>;
[<span class="ident">cmf</span>, <span class="ident">add_fcheck</span>(<span class="ident">cmf</span>, <span class="ident">level</span> <span class="kw">as</span> <span class="ident">u8</span>)]
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">test</span> {
<span class="kw">use</span> <span class="kw">super</span><span class="ident">::DEFAULT_CMF</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_gen_fcheck</span>() {
<span class="kw">let</span> <span class="ident">cmf</span> <span class="op">=</span> <span class="ident">DEFAULT_CMF</span>;
<span class="kw">let</span> <span class="ident">flg</span> <span class="op">=</span> <span class="kw">super</span><span class="ident">::add_fcheck</span>(
<span class="ident">DEFAULT_CMF</span>,
<span class="ident">CompressionLevel::Default</span> <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="kw">super</span><span class="ident">::DEFAULT_FDICT</span>,
);
<span class="macro">assert_eq!</span>(((<span class="ident">usize::from</span>(<span class="ident">cmf</span>) <span class="op">*</span> <span class="number">256</span>) <span class="op">+</span> <span class="ident">usize::from</span>(<span class="ident">flg</span>)) <span class="op">%</span> <span class="number">31</span>, <span class="number">0</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">test_header</span>() {
<span class="kw">let</span> <span class="ident">header</span> <span class="op">=</span> <span class="ident">get_zlib_header</span>(<span class="ident">CompressionLevel::Fastest</span>);
<span class="macro">assert_eq!</span>(
((<span class="ident">usize::from</span>(<span class="ident">header</span>[<span class="number">0</span>]) <span class="op">*</span> <span class="number">256</span>) <span class="op">+</span> <span class="ident">usize::from</span>(<span class="ident">header</span>[<span class="number">1</span>])) <span class="op">%</span> <span class="number">31</span>,
<span class="number">0</span>
);
}
}
</pre></div>
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