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</pre><pre class="rust">
<span class="doccomment">//! This module contains the various options to tweak how compression is performed.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Note that due to the nature of the `DEFLATE` format, lower compression levels</span>
<span class="doccomment">//! may for some data compress better than higher compression levels.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! For applications where a maximum level of compression (irrespective of compression</span>
<span class="doccomment">//! speed) is required, consider using the [`Zopfli`](https://crates.io/crates/zopfli)</span>
<span class="doccomment">//! compressor, which uses a specialised (but slow) algorithm to figure out the maximum</span>
<span class="doccomment">//! of compression for the provided data.</span>
<span class="doccomment">//!</span>
<span class="kw">use</span> <span class="ident">lz77::MatchingType</span>;
<span class="kw">use</span> <span class="ident">std::convert::From</span>;
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">HIGH_MAX_HASH_CHECKS</span>: <span class="ident">u16</span> <span class="op">=</span> <span class="number">1768</span>;
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">HIGH_LAZY_IF_LESS_THAN</span>: <span class="ident">u16</span> <span class="op">=</span> <span class="number">128</span>;
<span class="doccomment">/// The maximum number of hash checks that make sense as this is the length</span>
<span class="doccomment">/// of the hash chain.</span>
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">MAX_HASH_CHECKS</span>: <span class="ident">u16</span> <span class="op">=</span> <span class="number">32</span> <span class="op">*</span> <span class="number">1024</span>;
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">DEFAULT_MAX_HASH_CHECKS</span>: <span class="ident">u16</span> <span class="op">=</span> <span class="number">128</span>;
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">DEFAULT_LAZY_IF_LESS_THAN</span>: <span class="ident">u16</span> <span class="op">=</span> <span class="number">32</span>;
<span class="doccomment">/// An enum describing the level of compression to be used by the encoder</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Higher compression ratios will take longer to encode.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is a simplified interface to specify a compression level.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [See also `CompressionOptions`](./struct.CompressionOptions.html) which provides for</span>
<span class="doccomment">/// tweaking the settings more finely.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>, <span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">Ord</span>, <span class="ident">PartialOrd</span>, <span class="ident">Hash</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Compression</span> {
<span class="doccomment">/// Fast minimal compression (`CompressionOptions::fast()`).</span>
<span class="ident">Fast</span>,
<span class="doccomment">/// Default level (`CompressionOptions::default()`).</span>
<span class="ident">Default</span>,
<span class="doccomment">/// Higher compression level (`CompressionOptions::high()`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Best in this context isn't actually the highest possible level</span>
<span class="doccomment">/// the encoder can do, but is meant to emulate the `Best` setting in the `Flate2`</span>
<span class="doccomment">/// library.</span>
<span class="ident">Best</span>,
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">Compression</span> {
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="ident">Compression</span> {
<span class="ident">Compression::Default</span>
}
}
<span class="doccomment">/// Enum allowing some special options (not implemented yet)!</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>, <span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">Hash</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SpecialOptions</span> {
<span class="doccomment">/// Compress normally.</span>
<span class="ident">Normal</span>,
<span class="doccomment">/// Force fixed huffman tables. (Unimplemented!).</span>
<span class="ident">_ForceFixed</span>,
<span class="doccomment">/// Force stored (uncompressed) blocks only. (Unimplemented!).</span>
<span class="ident">_ForceStored</span>,
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">SpecialOptions</span> {
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="ident">SpecialOptions</span> {
<span class="ident">SpecialOptions::Normal</span>
}
}
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">DEFAULT_OPTIONS</span>: <span class="ident">CompressionOptions</span> <span class="op">=</span> <span class="ident">CompressionOptions</span> {
<span class="ident">max_hash_checks</span>: <span class="ident">DEFAULT_MAX_HASH_CHECKS</span>,
<span class="ident">lazy_if_less_than</span>: <span class="ident">DEFAULT_LAZY_IF_LESS_THAN</span>,
<span class="ident">matching_type</span>: <span class="ident">MatchingType::Lazy</span>,
<span class="ident">special</span>: <span class="ident">SpecialOptions::Normal</span>,
};
<span class="doccomment">/// A struct describing the options for a compressor or compression function.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// These values are not stable and still subject to change!</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">Hash</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">CompressionOptions</span> {
<span class="doccomment">/// The maximum number of checks to make in the hash table for matches.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Higher numbers mean slower, but better compression. Very high (say `>1024`) values</span>
<span class="doccomment">/// will impact compression speed a lot. The maximum match length is 2^15, so values higher than</span>
<span class="doccomment">/// this won't make any difference, and will be truncated to 2^15 by the compression</span>
<span class="doccomment">/// function/writer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Default value: `128`</span>
<span class="kw">pub</span> <span class="ident">max_hash_checks</span>: <span class="ident">u16</span>,
<span class="comment">// pub _window_size: u16,</span>
<span class="doccomment">/// Only lazy match if we have a length less than this value.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Higher values degrade compression slightly, but improve compression speed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `0`: Never lazy match. (Same effect as setting MatchingType to greedy, but may be slower).</span>
<span class="doccomment">/// * `1...257`: Only check for a better match if the first match was shorter than this value.</span>
<span class="doccomment">/// * `258`: Always lazy match.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// As the maximum length of a match is `258`, values higher than this will have</span>
<span class="doccomment">/// no further effect.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Default value: `32`</span>
<span class="kw">pub</span> <span class="ident">lazy_if_less_than</span>: <span class="ident">u16</span>,
<span class="comment">// pub _decent_match: u16,</span>
<span class="doccomment">/// Whether to use lazy or greedy matching.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Lazy matching will provide better compression, at the expense of compression speed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// As a special case, if max_hash_checks is set to 0, and matching_type is set to lazy,</span>
<span class="doccomment">/// compression using only run-length encoding (i.e maximum match distance of 1) is performed.</span>
<span class="doccomment">/// (This may be changed in the future but is defined like this at the moment to avoid API</span>
<span class="doccomment">/// breakage.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [See `MatchingType`](./enum.MatchingType.html)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Default value: `MatchingType::Lazy`</span>
<span class="kw">pub</span> <span class="ident">matching_type</span>: <span class="ident">MatchingType</span>,
<span class="doccomment">/// Force fixed/stored blocks (Not implemented yet).</span>
<span class="doccomment">/// * Default value: `SpecialOptions::Normal`</span>
<span class="kw">pub</span> <span class="ident">special</span>: <span class="ident">SpecialOptions</span>,
}
<span class="comment">// Some standard profiles for the compression options.</span>
<span class="comment">// Ord should be implemented at some point, but won't yet until the struct is stabilised.</span>
<span class="kw">impl</span> <span class="ident">CompressionOptions</span> {
<span class="doccomment">/// Returns compression settings rouhgly corresponding to the `HIGH(9)` setting in miniz.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">high</span>() <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="ident">CompressionOptions</span> {
<span class="ident">max_hash_checks</span>: <span class="ident">HIGH_MAX_HASH_CHECKS</span>,
<span class="ident">lazy_if_less_than</span>: <span class="ident">HIGH_LAZY_IF_LESS_THAN</span>,
<span class="ident">matching_type</span>: <span class="ident">MatchingType::Lazy</span>,
<span class="ident">special</span>: <span class="ident">SpecialOptions::Normal</span>,
}
}
<span class="doccomment">/// Returns a fast set of compression settings</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Ideally this should roughly correspond to the `FAST(1)` setting in miniz.</span>
<span class="doccomment">/// However, that setting makes miniz use a somewhat different algorhithm,</span>
<span class="doccomment">/// so currently hte fast level in this library is slower and better compressing</span>
<span class="doccomment">/// than the corresponding level in miniz.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">fast</span>() <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="ident">CompressionOptions</span> {
<span class="ident">max_hash_checks</span>: <span class="number">1</span>,
<span class="ident">lazy_if_less_than</span>: <span class="number">0</span>,
<span class="ident">matching_type</span>: <span class="ident">MatchingType::Greedy</span>,
<span class="ident">special</span>: <span class="ident">SpecialOptions::Normal</span>,
}
}
<span class="doccomment">/// Returns a set of compression settings that makes the compressor only compress using</span>
<span class="doccomment">/// huffman coding. (Ignoring any length/distance matching)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This will normally have the worst compression ratio (besides only using uncompressed data),</span>
<span class="doccomment">/// but may be the fastest method in some cases.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">huffman_only</span>() <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="ident">CompressionOptions</span> {
<span class="ident">max_hash_checks</span>: <span class="number">0</span>,
<span class="ident">lazy_if_less_than</span>: <span class="number">0</span>,
<span class="ident">matching_type</span>: <span class="ident">MatchingType::Greedy</span>,
<span class="ident">special</span>: <span class="ident">SpecialOptions::Normal</span>,
}
}
<span class="doccomment">/// Returns a set of compression settings that makes the compressor compress only using</span>
<span class="doccomment">/// run-length encoding (i.e only looking for matches one byte back).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is very fast, but tends to compress worse than looking for more matches using hash</span>
<span class="doccomment">/// chains that the slower settings do.</span>
<span class="doccomment">/// Works best on data that has runs of equivialent bytes, like binary or simple images,</span>
<span class="doccomment">/// less good for text.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">rle</span>() <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="ident">CompressionOptions</span> {
<span class="ident">max_hash_checks</span>: <span class="number">0</span>,
<span class="ident">lazy_if_less_than</span>: <span class="number">0</span>,
<span class="ident">matching_type</span>: <span class="ident">MatchingType::Lazy</span>,
<span class="ident">special</span>: <span class="ident">SpecialOptions::Normal</span>,
}
}
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">CompressionOptions</span> {
<span class="doccomment">/// Returns the options describing the default compression level.</span>
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="ident">DEFAULT_OPTIONS</span>
}
}
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">Compression</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CompressionOptions</span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">compression</span>: <span class="ident">Compression</span>) <span class="op">-</span><span class="op">></span> <span class="ident">CompressionOptions</span> {
<span class="kw">match</span> <span class="ident">compression</span> {
<span class="ident">Compression::Fast</span> <span class="op">=</span><span class="op">></span> <span class="ident">CompressionOptions::fast</span>(),
<span class="ident">Compression::Default</span> <span class="op">=</span><span class="op">></span> <span class="ident">CompressionOptions::default</span>(),
<span class="ident">Compression::Best</span> <span class="op">=</span><span class="op">></span> <span class="ident">CompressionOptions::high</span>(),
}
}
}
</pre></div>
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