<!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/huffman_lengths.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>huffman_lengths.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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</pre><pre class="rust">
<span class="kw">use</span> <span class="ident">length_encode</span>::{<span class="ident">EncodedLength</span>, <span class="ident">encode_lengths_m</span>, <span class="ident">huffman_lengths_from_frequency_m</span>,
<span class="ident">COPY_PREVIOUS</span>, <span class="ident">REPEAT_ZERO_3_BITS</span>, <span class="ident">REPEAT_ZERO_7_BITS</span>};
<span class="kw">use</span> <span class="ident">huffman_table</span>::{<span class="ident">HuffmanTable</span>, <span class="ident">create_codes_in_place</span>, <span class="ident">num_extra_bits_for_length_code</span>,
<span class="ident">num_extra_bits_for_distance_code</span>, <span class="ident">NUM_LITERALS_AND_LENGTHS</span>,
<span class="ident">NUM_DISTANCE_CODES</span>, <span class="ident">MAX_CODE_LENGTH</span>, <span class="ident">FIXED_CODE_LENGTHS</span>, <span class="ident">LENGTH_BITS_START</span>};
<span class="kw">use</span> <span class="ident">bitstream::LsbWriter</span>;
<span class="kw">use</span> <span class="ident">output_writer::FrequencyType</span>;
<span class="kw">use</span> <span class="ident">stored_block::MAX_STORED_BLOCK_LENGTH</span>;
<span class="kw">use</span> <span class="ident">deflate_state::LengthBuffers</span>;
<span class="kw">use</span> <span class="ident">std::cmp</span>;
<span class="comment">// The minimum number of literal/length values</span>
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">MIN_NUM_LITERALS_AND_LENGTHS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">257</span>;
<span class="comment">// The minimum number of distances</span>
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">MIN_NUM_DISTANCES</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span>;
<span class="kw">const</span> <span class="ident">NUM_HUFFMAN_LENGTHS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">19</span>;
<span class="comment">// The output ordering of the lengths for the huffman codes used to encode the lengths</span>
<span class="comment">// used to build the full huffman tree for length/literal codes.</span>
<span class="comment">// http://www.gzip.org/zlib/rfc-deflate.html#dyn</span>
<span class="kw">const</span> <span class="ident">HUFFMAN_LENGTH_ORDER</span>: [<span class="ident">u8</span>; <span class="ident">NUM_HUFFMAN_LENGTHS</span>] <span class="op">=</span> [
<span class="number">16</span>,
<span class="number">17</span>,
<span class="number">18</span>,
<span class="number">0</span>,
<span class="number">8</span>,
<span class="number">7</span>,
<span class="number">9</span>,
<span class="number">6</span>,
<span class="number">10</span>,
<span class="number">5</span>,
<span class="number">11</span>,
<span class="number">4</span>,
<span class="number">12</span>,
<span class="number">3</span>,
<span class="number">13</span>,
<span class="number">2</span>,
<span class="number">14</span>,
<span class="number">1</span>,
<span class="number">15</span>,
];
<span class="comment">// Number of bits used for the values specifying the number of codes</span>
<span class="kw">const</span> <span class="ident">HLIT_BITS</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">5</span>;
<span class="kw">const</span> <span class="ident">HDIST_BITS</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">5</span>;
<span class="kw">const</span> <span class="ident">HCLEN_BITS</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">4</span>;
<span class="comment">// The longest a huffman code describing another huffman length can be</span>
<span class="kw">const</span> <span class="ident">MAX_HUFFMAN_CODE_LENGTH</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">7</span>;
<span class="comment">// How many bytes (not including padding and the 3-bit block type) the stored block header takes up.</span>
<span class="kw">const</span> <span class="ident">STORED_BLOCK_HEADER_LENGTH</span>: <span class="ident">u64</span> <span class="op">=</span> <span class="number">4</span>;
<span class="kw">const</span> <span class="ident">BLOCK_MARKER_LENGTH</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">3</span>;
<span class="doccomment">/// Creates a new slice from the input slice that stops at the final non-zero value</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">remove_trailing_zeroes</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">From</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span> <span class="op">+</span> <span class="ident">PartialEq</span><span class="op">></span>(<span class="ident">input</span>: <span class="kw-2">&</span>[<span class="ident">T</span>], <span class="ident">min_length</span>: <span class="ident">usize</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span>[<span class="ident">T</span>] {
<span class="kw">let</span> <span class="ident">num_zeroes</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">iter</span>().<span class="ident">rev</span>().<span class="ident">take_while</span>(<span class="op">|</span><span class="kw-2">&</span><span class="ident">a</span><span class="op">|</span> <span class="kw-2">*</span><span class="ident">a</span> <span class="op">=</span><span class="op">=</span> <span class="ident">T::from</span>(<span class="number">0</span>)).<span class="ident">count</span>();
<span class="kw-2">&</span><span class="ident">input</span>[<span class="number">0</span>..<span class="ident">cmp::max</span>(<span class="ident">input</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="ident">num_zeroes</span>, <span class="ident">min_length</span>)]
}
<span class="doccomment">/// How many extra bits the huffman length code uses to represent a value.</span>
<span class="kw">fn</span> <span class="ident">extra_bits_for_huffman_length_code</span>(<span class="ident">code</span>: <span class="ident">u8</span>) <span class="op">-</span><span class="op">></span> <span class="ident">u8</span> {
<span class="kw">match</span> <span class="ident">code</span> {
<span class="number">16</span>...<span class="number">17</span> <span class="op">=</span><span class="op">></span> <span class="number">3</span>,
<span class="number">18</span> <span class="op">=</span><span class="op">></span> <span class="number">7</span>,
<span class="kw">_</span> <span class="op">=</span><span class="op">></span> <span class="number">0</span>,
}
}
<span class="doccomment">/// Calculate how many bits the huffman-encoded huffman lengths will use.</span>
<span class="kw">fn</span> <span class="ident">calculate_huffman_length</span>(<span class="ident">frequencies</span>: <span class="kw-2">&</span>[<span class="ident">FrequencyType</span>], <span class="ident">code_lengths</span>: <span class="kw-2">&</span>[<span class="ident">u8</span>]) <span class="op">-</span><span class="op">></span> <span class="ident">u64</span> {
<span class="ident">frequencies</span>.<span class="ident">iter</span>().<span class="ident">zip</span>(<span class="ident">code_lengths</span>).<span class="ident">enumerate</span>().<span class="ident">fold</span>(
<span class="number">0</span>,
<span class="op">|</span><span class="ident">acc</span>, (<span class="ident">n</span>, (<span class="kw-2">&</span><span class="ident">f</span>, <span class="kw-2">&</span><span class="ident">l</span>))<span class="op">|</span> {
<span class="ident">acc</span> <span class="op">+</span>
(<span class="ident">u64::from</span>(<span class="ident">f</span>) <span class="op">*</span>
(<span class="ident">u64::from</span>(<span class="ident">l</span>) <span class="op">+</span> <span class="ident">u64::from</span>(<span class="ident">extra_bits_for_huffman_length_code</span>(<span class="ident">n</span> <span class="kw">as</span> <span class="ident">u8</span>))))
},
)
}
<span class="doccomment">/// Calculate how many bits data with the given frequencies will use when compressed with dynamic</span>
<span class="doccomment">/// code lengths (first return value) and static code lengths (second return value).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Parameters:</span>
<span class="doccomment">/// Frequencies, length of dynamic codes, and a function to get how many extra bits in addition</span>
<span class="doccomment">/// to the length of the huffman code the symbol will use.</span>
<span class="kw">fn</span> <span class="ident">calculate_block_length</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(
<span class="ident">frequencies</span>: <span class="kw-2">&</span>[<span class="ident">FrequencyType</span>],
<span class="ident">dyn_code_lengths</span>: <span class="kw-2">&</span>[<span class="ident">u8</span>],
<span class="ident">get_num_extra_bits</span>: <span class="kw-2">&</span><span class="ident">F</span>,
) <span class="op">-</span><span class="op">></span> (<span class="ident">u64</span>, <span class="ident">u64</span>)
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">Fn</span>(<span class="ident">usize</span>) <span class="op">-</span><span class="op">></span> <span class="ident">u64</span>,
{
<span class="comment">// Length of data represented by dynamic codes.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">d_ll_length</span> <span class="op">=</span> <span class="number">0u64</span>;
<span class="comment">// length of data represented by static codes.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">s_ll_length</span> <span class="op">=</span> <span class="number">0u64</span>;
<span class="kw">let</span> <span class="ident">iter</span> <span class="op">=</span> <span class="ident">frequencies</span>
.<span class="ident">iter</span>()
.<span class="ident">zip</span>(<span class="ident">dyn_code_lengths</span>.<span class="ident">iter</span>().<span class="ident">zip</span>(<span class="ident">FIXED_CODE_LENGTHS</span>.<span class="ident">iter</span>()))
.<span class="ident">enumerate</span>();
<span class="comment">// This could maybe be optimised a bit by splitting the iteration of codes using extra bits and</span>
<span class="comment">// codes not using extra bits, but the extra complexity may not be worth it.</span>
<span class="kw">for</span> (<span class="ident">c</span>, (<span class="kw-2">&</span><span class="ident">f</span>, (<span class="kw-2">&</span><span class="ident">l</span>, <span class="kw-2">&</span><span class="ident">fl</span>))) <span class="kw">in</span> <span class="ident">iter</span> {
<span class="comment">// Frequency</span>
<span class="kw">let</span> <span class="ident">f</span> <span class="op">=</span> <span class="ident">u64::from</span>(<span class="ident">f</span>);
<span class="comment">// How many extra bits the current code number needs.</span>
<span class="kw">let</span> <span class="ident">extra_bits_for_code</span> <span class="op">=</span> <span class="ident">get_num_extra_bits</span>(<span class="ident">c</span>);
<span class="ident">d_ll_length</span> <span class="op">+</span><span class="op">=</span> <span class="ident">f</span> <span class="op">*</span> (<span class="ident">u64::from</span>(<span class="ident">l</span>) <span class="op">+</span> <span class="ident">extra_bits_for_code</span>);
<span class="ident">s_ll_length</span> <span class="op">+</span><span class="op">=</span> <span class="ident">f</span> <span class="op">*</span> (<span class="ident">u64::from</span>(<span class="ident">fl</span>) <span class="op">+</span> <span class="ident">extra_bits_for_code</span>);
}
(<span class="ident">d_ll_length</span>, <span class="ident">s_ll_length</span>)
}
<span class="doccomment">/// Get how extra padding bits after a block start header a stored block would use.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">/// Panics if `pending_bits > 8`</span>
<span class="kw">fn</span> <span class="ident">stored_padding</span>(<span class="ident">pending_bits</span>: <span class="ident">u8</span>) <span class="op">-</span><span class="op">></span> <span class="ident">u64</span> {
<span class="macro">assert!</span>(<span class="ident">pending_bits</span> <span class="op"><</span><span class="op">=</span> <span class="number">8</span>);
<span class="kw">let</span> <span class="ident">free_space</span> <span class="op">=</span> <span class="number">8</span> <span class="op">-</span> <span class="ident">pending_bits</span>;
<span class="kw">if</span> <span class="ident">free_space</span> <span class="op">></span><span class="op">=</span> <span class="ident">BLOCK_MARKER_LENGTH</span> {
<span class="comment">// There is space in the current byte for the header.</span>
<span class="ident">free_space</span> <span class="op">-</span> <span class="ident">BLOCK_MARKER_LENGTH</span>
} <span class="kw">else</span> {
<span class="comment">// The header will require an extra byte.</span>
<span class="number">8</span> <span class="op">-</span> (<span class="ident">BLOCK_MARKER_LENGTH</span> <span class="op">-</span> <span class="ident">free_space</span>)
}.<span class="ident">into</span>()
}
<span class="doccomment">/// Calculate the number of bits storing the data in stored blocks will take up, excluding the</span>
<span class="doccomment">/// first block start code and potential padding bits. As stored blocks have a maximum length,</span>
<span class="doccomment">/// (as opposed to fixed and dynamic ones), multiple blocks may have to be utilised.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">/// Panics if `input_bytes` is 0.</span>
<span class="kw">fn</span> <span class="ident">stored_length</span>(<span class="ident">input_bytes</span>: <span class="ident">u64</span>) <span class="op">-</span><span class="op">></span> <span class="ident">u64</span> {
<span class="comment">// Check how many stored blocks these bytes would take up.</span>
<span class="comment">// (Integer divison rounding up.)</span>
<span class="kw">let</span> <span class="ident">num_blocks</span> <span class="op">=</span> (<span class="ident">input_bytes</span>
.<span class="ident">checked_sub</span>(<span class="number">1</span>)
.<span class="ident">expect</span>(<span class="string">"Underflow calculating stored block length!"</span>) <span class="op">/</span>
<span class="ident">MAX_STORED_BLOCK_LENGTH</span> <span class="kw">as</span> <span class="ident">u64</span>) <span class="op">+</span> <span class="number">1</span>;
<span class="comment">// The length will be the input length and the headers for each block. (Excluding the start</span>
<span class="comment">// of block code for the first one)</span>
(<span class="ident">input_bytes</span> <span class="op">+</span> (<span class="ident">STORED_BLOCK_HEADER_LENGTH</span> <span class="kw">as</span> <span class="ident">u64</span> <span class="op">*</span> <span class="ident">num_blocks</span>) <span class="op">+</span> (<span class="ident">num_blocks</span> <span class="op">-</span> <span class="number">1</span>)) <span class="op">*</span> <span class="number">8</span>
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">BlockType</span> {
<span class="ident">Stored</span>,
<span class="ident">Fixed</span>,
<span class="ident">Dynamic</span>(<span class="ident">DynamicBlockHeader</span>),
}
<span class="doccomment">/// A struct containing the different data needed to write the header for a dynamic block.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The code lengths are stored directly in the `HuffmanTable` struct.</span>
<span class="doccomment">/// TODO: Do the same for other things here.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">DynamicBlockHeader</span> {
<span class="doccomment">/// Length of the run-length encoding symbols.</span>
<span class="kw">pub</span> <span class="ident">huffman_table_lengths</span>: <span class="ident">Vec</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>,
<span class="doccomment">/// Number of lengths for values describing the huffman table that encodes the length values</span>
<span class="doccomment">/// of the main huffman tables.</span>
<span class="kw">pub</span> <span class="ident">used_hclens</span>: <span class="ident">usize</span>,
}
<span class="doccomment">/// Generate the lengths of the huffman codes we will be using, using the</span>
<span class="doccomment">/// frequency of the different symbols/lengths/distances, and determine what block type will give</span>
<span class="doccomment">/// the shortest representation.</span>
<span class="doccomment">/// TODO: This needs a test</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">gen_huffman_lengths</span>(
<span class="ident">l_freqs</span>: <span class="kw-2">&</span>[<span class="ident">FrequencyType</span>],
<span class="ident">d_freqs</span>: <span class="kw-2">&</span>[<span class="ident">FrequencyType</span>],
<span class="ident">num_input_bytes</span>: <span class="ident">u64</span>,
<span class="ident">pending_bits</span>: <span class="ident">u8</span>,
<span class="ident">l_lengths</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> [<span class="ident">u8</span>; <span class="number">288</span>],
<span class="ident">d_lengths</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> [<span class="ident">u8</span>; <span class="number">32</span>],
<span class="ident">length_buffers</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">LengthBuffers</span>,
) <span class="op">-</span><span class="op">></span> <span class="ident">BlockType</span> {
<span class="comment">// Avoid corner cases and issues if this is called for an empty block.</span>
<span class="comment">// For blocks this short, a fixed block will be the shortest.</span>
<span class="comment">// TODO: Find the minimum value it's worth doing calculations for.</span>
<span class="kw">if</span> <span class="ident">num_input_bytes</span> <span class="op"><</span><span class="op">=</span> <span class="number">4</span> {
<span class="kw">return</span> <span class="ident">BlockType::Fixed</span>;
};
<span class="kw">let</span> <span class="ident">l_freqs</span> <span class="op">=</span> <span class="ident">remove_trailing_zeroes</span>(<span class="ident">l_freqs</span>, <span class="ident">MIN_NUM_LITERALS_AND_LENGTHS</span>);
<span class="kw">let</span> <span class="ident">d_freqs</span> <span class="op">=</span> <span class="ident">remove_trailing_zeroes</span>(<span class="ident">d_freqs</span>, <span class="ident">MIN_NUM_DISTANCES</span>);
<span class="comment">// The huffman spec allows us to exclude zeroes at the end of the</span>
<span class="comment">// table of huffman lengths.</span>
<span class="comment">// Since a frequency of 0 will give an huffman</span>
<span class="comment">// length of 0. We strip off the trailing zeroes before even</span>
<span class="comment">// generating the lengths to save some work.</span>
<span class="comment">// There is however a minimum number of values we have to keep</span>
<span class="comment">// according to the deflate spec.</span>
<span class="comment">// TODO: We could probably compute some of this in parallel.</span>
<span class="ident">huffman_lengths_from_frequency_m</span>(
<span class="ident">l_freqs</span>,
<span class="ident">MAX_CODE_LENGTH</span>,
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">length_buffers</span>.<span class="ident">leaf_buf</span>,
<span class="ident">l_lengths</span>,
);
<span class="ident">huffman_lengths_from_frequency_m</span>(
<span class="ident">d_freqs</span>,
<span class="ident">MAX_CODE_LENGTH</span>,
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">length_buffers</span>.<span class="ident">leaf_buf</span>,
<span class="ident">d_lengths</span>,
);
<span class="kw">let</span> <span class="ident">used_lengths</span> <span class="op">=</span> <span class="ident">l_freqs</span>.<span class="ident">len</span>();
<span class="kw">let</span> <span class="ident">used_distances</span> <span class="op">=</span> <span class="ident">d_freqs</span>.<span class="ident">len</span>();
<span class="comment">// Encode length values</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">freqs</span> <span class="op">=</span> [<span class="number">0u16</span>; <span class="number">19</span>];
<span class="ident">encode_lengths_m</span>(
<span class="ident">l_lengths</span>[..<span class="ident">used_lengths</span>]
.<span class="ident">iter</span>()
.<span class="ident">chain</span>(<span class="kw-2">&</span><span class="ident">d_lengths</span>[..<span class="ident">used_distances</span>]),
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">length_buffers</span>.<span class="ident">length_buf</span>,
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">freqs</span>,
);
<span class="comment">// Create huffman lengths for the length/distance code lengths</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">huffman_table_lengths</span> <span class="op">=</span> <span class="macro">vec!</span>[<span class="number">0</span>; <span class="ident">freqs</span>.<span class="ident">len</span>()];
<span class="ident">huffman_lengths_from_frequency_m</span>(
<span class="kw-2">&</span><span class="ident">freqs</span>,
<span class="ident">MAX_HUFFMAN_CODE_LENGTH</span>,
<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">length_buffers</span>.<span class="ident">leaf_buf</span>,
<span class="ident">huffman_table_lengths</span>.<span class="ident">as_mut_slice</span>(),
);
<span class="comment">// Count how many of these lengths we use.</span>
<span class="kw">let</span> <span class="ident">used_hclens</span> <span class="op">=</span> <span class="ident">HUFFMAN_LENGTH_ORDER</span>.<span class="ident">len</span>() <span class="op">-</span>
<span class="ident">HUFFMAN_LENGTH_ORDER</span>
.<span class="ident">iter</span>()
.<span class="ident">rev</span>()
.<span class="ident">take_while</span>(<span class="op">|</span><span class="op">&&</span><span class="ident">n</span><span class="op">|</span> <span class="ident">huffman_table_lengths</span>[<span class="ident">n</span> <span class="kw">as</span> <span class="ident">usize</span>] <span class="op">=</span><span class="op">=</span> <span class="number">0</span>)
.<span class="ident">count</span>();
<span class="comment">// There has to be at least 4 hclens, so if there isn't, something went wrong.</span>
<span class="macro">debug_assert!</span>(<span class="ident">used_hclens</span> <span class="op">></span><span class="op">=</span> <span class="number">4</span>);
<span class="comment">// Calculate how many bytes of space this block will take up with the different block types</span>
<span class="comment">// (excluding the 3-bit block header since it's used in all block types).</span>
<span class="comment">// Total length of the compressed literals/lengths.</span>
<span class="kw">let</span> (<span class="ident">d_ll_length</span>, <span class="ident">s_ll_length</span>) <span class="op">=</span> <span class="ident">calculate_block_length</span>(<span class="ident">l_freqs</span>, <span class="ident">l_lengths</span>, <span class="kw-2">&</span><span class="op">|</span><span class="ident">c</span><span class="op">|</span> {
<span class="ident">num_extra_bits_for_length_code</span>(<span class="ident">c</span>.<span class="ident">saturating_sub</span>(<span class="ident">LENGTH_BITS_START</span> <span class="kw">as</span> <span class="ident">usize</span>) <span class="kw">as</span> <span class="ident">u8</span>).<span class="ident">into</span>()
});
<span class="comment">// Total length of the compressed distances.</span>
<span class="kw">let</span> (<span class="ident">d_dist_length</span>, <span class="ident">s_dist_length</span>) <span class="op">=</span> <span class="ident">calculate_block_length</span>(<span class="ident">d_freqs</span>, <span class="ident">d_lengths</span>, <span class="kw-2">&</span><span class="op">|</span><span class="ident">c</span><span class="op">|</span> {
<span class="ident">num_extra_bits_for_distance_code</span>(<span class="ident">c</span> <span class="kw">as</span> <span class="ident">u8</span>).<span class="ident">into</span>()
});
<span class="comment">// Total length of the compressed huffman code lengths.</span>
<span class="kw">let</span> <span class="ident">huff_table_length</span> <span class="op">=</span> <span class="ident">calculate_huffman_length</span>(<span class="kw-2">&</span><span class="ident">freqs</span>, <span class="kw-2">&</span><span class="ident">huffman_table_lengths</span>);
<span class="comment">// For dynamic blocks the huffman tables takes up some extra space.</span>
<span class="kw">let</span> <span class="ident">dynamic_length</span> <span class="op">=</span> <span class="ident">d_ll_length</span> <span class="op">+</span> <span class="ident">d_dist_length</span> <span class="op">+</span> <span class="ident">huff_table_length</span> <span class="op">+</span>
(<span class="ident">used_hclens</span> <span class="kw">as</span> <span class="ident">u64</span> <span class="op">*</span> <span class="number">3</span>) <span class="op">+</span> <span class="ident">u64::from</span>(<span class="ident">HLIT_BITS</span>) <span class="op">+</span>
<span class="ident">u64::from</span>(<span class="ident">HDIST_BITS</span>) <span class="op">+</span> <span class="ident">u64::from</span>(<span class="ident">HCLEN_BITS</span>);
<span class="comment">// Static blocks don't have any extra header data.</span>
<span class="kw">let</span> <span class="ident">static_length</span> <span class="op">=</span> <span class="ident">s_ll_length</span> <span class="op">+</span> <span class="ident">s_dist_length</span>;
<span class="comment">// Calculate how many bits it will take to store the data in uncompressed (stored) block(s).</span>
<span class="kw">let</span> <span class="ident">stored_length</span> <span class="op">=</span> <span class="ident">stored_length</span>(<span class="ident">num_input_bytes</span>) <span class="op">+</span> <span class="ident">stored_padding</span>(<span class="ident">pending_bits</span> <span class="op">%</span> <span class="number">8</span>);
<span class="kw">let</span> <span class="ident">used_length</span> <span class="op">=</span> <span class="ident">cmp::min</span>(<span class="ident">cmp::min</span>(<span class="ident">dynamic_length</span>, <span class="ident">static_length</span>), <span class="ident">stored_length</span>);
<span class="comment">// Check if the block is actually compressed. If using a dynamic block</span>
<span class="comment">// increases the length of the block (for instance if the input data is mostly random or</span>
<span class="comment">// already compressed), we want to output a stored(uncompressed) block instead to avoid wasting</span>
<span class="comment">// space.</span>
<span class="kw">if</span> <span class="ident">used_length</span> <span class="op">=</span><span class="op">=</span> <span class="ident">static_length</span> {
<span class="ident">BlockType::Fixed</span>
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">used_length</span> <span class="op">=</span><span class="op">=</span> <span class="ident">stored_length</span> {
<span class="ident">BlockType::Stored</span>
} <span class="kw">else</span> {
<span class="ident">BlockType::Dynamic</span>(<span class="ident">DynamicBlockHeader</span> {
<span class="ident">huffman_table_lengths</span>: <span class="ident">huffman_table_lengths</span>,
<span class="ident">used_hclens</span>: <span class="ident">used_hclens</span>,
})
}
}
<span class="doccomment">/// Write the specified huffman lengths to the bit writer</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">write_huffman_lengths</span>(
<span class="ident">header</span>: <span class="kw-2">&</span><span class="ident">DynamicBlockHeader</span>,
<span class="ident">huffman_table</span>: <span class="kw-2">&</span><span class="ident">HuffmanTable</span>,
<span class="ident">encoded_lengths</span>: <span class="kw-2">&</span>[<span class="ident">EncodedLength</span>],
<span class="ident">writer</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">LsbWriter</span>,
) {
<span class="comment">// Ignore trailing zero lengths as allowed by the deflate spec.</span>
<span class="kw">let</span> (<span class="ident">literal_len_lengths</span>, <span class="ident">distance_lengths</span>) <span class="op">=</span> <span class="ident">huffman_table</span>.<span class="ident">get_lengths</span>();
<span class="kw">let</span> <span class="ident">literal_len_lengths</span> <span class="op">=</span>
<span class="ident">remove_trailing_zeroes</span>(<span class="ident">literal_len_lengths</span>, <span class="ident">MIN_NUM_LITERALS_AND_LENGTHS</span>);
<span class="kw">let</span> <span class="ident">distance_lengths</span> <span class="op">=</span> <span class="ident">remove_trailing_zeroes</span>(<span class="ident">distance_lengths</span>, <span class="ident">MIN_NUM_DISTANCES</span>);
<span class="kw">let</span> <span class="ident">huffman_table_lengths</span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">header</span>.<span class="ident">huffman_table_lengths</span>;
<span class="kw">let</span> <span class="ident">used_hclens</span> <span class="op">=</span> <span class="ident">header</span>.<span class="ident">used_hclens</span>;
<span class="macro">assert!</span>(<span class="ident">literal_len_lengths</span>.<span class="ident">len</span>() <span class="op"><</span><span class="op">=</span> <span class="ident">NUM_LITERALS_AND_LENGTHS</span>);
<span class="macro">assert!</span>(<span class="ident">literal_len_lengths</span>.<span class="ident">len</span>() <span class="op">></span><span class="op">=</span> <span class="ident">MIN_NUM_LITERALS_AND_LENGTHS</span>);
<span class="macro">assert!</span>(<span class="ident">distance_lengths</span>.<span class="ident">len</span>() <span class="op"><</span><span class="op">=</span> <span class="ident">NUM_DISTANCE_CODES</span>);
<span class="macro">assert!</span>(<span class="ident">distance_lengths</span>.<span class="ident">len</span>() <span class="op">></span><span class="op">=</span> <span class="ident">MIN_NUM_DISTANCES</span>);
<span class="comment">// Number of length codes - 257.</span>
<span class="kw">let</span> <span class="ident">hlit</span> <span class="op">=</span> (<span class="ident">literal_len_lengths</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="ident">MIN_NUM_LITERALS_AND_LENGTHS</span>) <span class="kw">as</span> <span class="ident">u16</span>;
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">hlit</span>, <span class="ident">HLIT_BITS</span>);
<span class="comment">// Number of distance codes - 1.</span>
<span class="kw">let</span> <span class="ident">hdist</span> <span class="op">=</span> (<span class="ident">distance_lengths</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="ident">MIN_NUM_DISTANCES</span>) <span class="kw">as</span> <span class="ident">u16</span>;
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">hdist</span>, <span class="ident">HDIST_BITS</span>);
<span class="comment">// Number of huffman table lengths - 4.</span>
<span class="kw">let</span> <span class="ident">hclen</span> <span class="op">=</span> <span class="ident">used_hclens</span>.<span class="ident">saturating_sub</span>(<span class="number">4</span>);
<span class="comment">// Write HCLEN.</span>
<span class="comment">// Casting to u16 is safe since the length can never be more than the length of</span>
<span class="comment">// `HUFFMAN_LENGTH_ORDER` anyhow.</span>
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">hclen</span> <span class="kw">as</span> <span class="ident">u16</span>, <span class="ident">HCLEN_BITS</span>);
<span class="comment">// Write the lengths for the huffman table describing the huffman table</span>
<span class="comment">// Each length is 3 bits</span>
<span class="kw">for</span> <span class="ident">n</span> <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">HUFFMAN_LENGTH_ORDER</span>[..<span class="ident">used_hclens</span>] {
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">huffman_table_lengths</span>[<span class="ident">usize::from</span>(<span class="kw-2">*</span><span class="ident">n</span>)] <span class="kw">as</span> <span class="ident">u16</span>, <span class="number">3</span>);
}
<span class="comment">// Generate codes for the main huffman table using the lengths we just wrote</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">codes</span> <span class="op">=</span> [<span class="number">0u16</span>; <span class="ident">NUM_HUFFMAN_LENGTHS</span>];
<span class="ident">create_codes_in_place</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">codes</span>[..], <span class="ident">huffman_table_lengths</span>);
<span class="comment">// Write the actual huffman lengths</span>
<span class="kw">for</span> <span class="ident">v</span> <span class="kw">in</span> <span class="ident">encoded_lengths</span> {
<span class="kw">match</span> <span class="kw-2">*</span><span class="ident">v</span> {
<span class="ident">EncodedLength::Length</span>(<span class="ident">n</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> (<span class="ident">c</span>, <span class="ident">l</span>) <span class="op">=</span> (<span class="ident">codes</span>[<span class="ident">usize::from</span>(<span class="ident">n</span>)], <span class="ident">huffman_table_lengths</span>[<span class="ident">usize::from</span>(<span class="ident">n</span>)]);
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">c</span>, <span class="ident">l</span>);
}
<span class="ident">EncodedLength::CopyPrevious</span>(<span class="ident">n</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> (<span class="ident">c</span>, <span class="ident">l</span>) <span class="op">=</span> (<span class="ident">codes</span>[<span class="ident">COPY_PREVIOUS</span>], <span class="ident">huffman_table_lengths</span>[<span class="ident">COPY_PREVIOUS</span>]);
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">c</span>, <span class="ident">l</span>);
<span class="macro">debug_assert!</span>(<span class="ident">n</span> <span class="op">></span><span class="op">=</span> <span class="number">3</span>);
<span class="macro">debug_assert!</span>(<span class="ident">n</span> <span class="op"><</span><span class="op">=</span> <span class="number">6</span>);
<span class="ident">writer</span>.<span class="ident">write_bits</span>((<span class="ident">n</span> <span class="op">-</span> <span class="number">3</span>).<span class="ident">into</span>(), <span class="number">2</span>);
}
<span class="ident">EncodedLength::RepeatZero3Bits</span>(<span class="ident">n</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> (<span class="ident">c</span>, <span class="ident">l</span>) <span class="op">=</span> (
<span class="ident">codes</span>[<span class="ident">REPEAT_ZERO_3_BITS</span>],
<span class="ident">huffman_table_lengths</span>[<span class="ident">REPEAT_ZERO_3_BITS</span>],
);
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">c</span>, <span class="ident">l</span>);
<span class="macro">debug_assert!</span>(<span class="ident">n</span> <span class="op">></span><span class="op">=</span> <span class="number">3</span>);
<span class="ident">writer</span>.<span class="ident">write_bits</span>((<span class="ident">n</span> <span class="op">-</span> <span class="number">3</span>).<span class="ident">into</span>(), <span class="number">3</span>);
}
<span class="ident">EncodedLength::RepeatZero7Bits</span>(<span class="ident">n</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> (<span class="ident">c</span>, <span class="ident">l</span>) <span class="op">=</span> (
<span class="ident">codes</span>[<span class="ident">REPEAT_ZERO_7_BITS</span>],
<span class="ident">huffman_table_lengths</span>[<span class="ident">REPEAT_ZERO_7_BITS</span>],
);
<span class="ident">writer</span>.<span class="ident">write_bits</span>(<span class="ident">c</span>, <span class="ident">l</span>);
<span class="macro">debug_assert!</span>(<span class="ident">n</span> <span class="op">></span><span class="op">=</span> <span class="number">11</span>);
<span class="macro">debug_assert!</span>(<span class="ident">n</span> <span class="op"><</span><span class="op">=</span> <span class="number">138</span>);
<span class="ident">writer</span>.<span class="ident">write_bits</span>((<span class="ident">n</span> <span class="op">-</span> <span class="number">11</span>).<span class="ident">into</span>(), <span class="number">7</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">::stored_padding</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">padding</span>() {
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">0</span>), <span class="number">5</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">1</span>), <span class="number">4</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">2</span>), <span class="number">3</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">3</span>), <span class="number">2</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">4</span>), <span class="number">1</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">5</span>), <span class="number">0</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">6</span>), <span class="number">7</span>);
<span class="macro">assert_eq!</span>(<span class="ident">stored_padding</span>(<span class="number">7</span>), <span class="number">6</span>);
}
}
</pre></div>
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