| <!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/integer-encoding-1.1.7/src/varint.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>varint.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="../../integer_encoding/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="../../integer_encoding/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">/// Most-significant byte, == 0x80 |
| </span><span class="kw">pub const </span>MSB: u8 = <span class="number">0b1000_0000</span>; |
| <span class="kw">const </span>DROP_MSB: u8 = <span class="number">0b0111_1111</span>; |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>required_encoded_space_unsigned(<span class="kw-2">mut </span>v: u64) -> usize { |
| <span class="kw">if </span>v == <span class="number">0 </span>{ |
| <span class="kw">return </span><span class="number">1</span>; |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>logcounter = <span class="number">0</span>; |
| <span class="kw">while </span>v > <span class="number">0 </span>{ |
| logcounter += <span class="number">1</span>; |
| v >>= <span class="number">7</span>; |
| } |
| logcounter |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>required_encoded_space_signed(v: i64) -> usize { |
| required_encoded_space_unsigned(zigzag_encode(v)) |
| } |
| |
| <span class="doccomment">/// Varint (variable length integer) encoding, as described in |
| /// https://developers.google.com/protocol-buffers/docs/encoding. |
| /// Uses zigzag encoding (also described there) for signed integer representation. |
| </span><span class="kw">pub trait </span>VarInt: Sized + Copy { |
| <span class="doccomment">/// Returns the number of bytes this number needs in its encoded form. Note: This varies |
| /// depending on the actual number you want to encode. |
| </span><span class="kw">fn </span>required_space(<span class="self">self</span>) -> usize; |
| <span class="doccomment">/// Decode a value from the slice. Returns the value and the number of bytes read from the |
| /// slice (can be used to read several consecutive values from a big slice) |
| </span><span class="kw">fn </span>decode_var(src: <span class="kw-2">&</span>[u8]) -> (<span class="self">Self</span>, usize); |
| <span class="doccomment">/// Encode a value into the slice. The slice must be at least `required_space()` bytes long. |
| /// The number of bytes taken by the encoded integer is returned. |
| </span><span class="kw">fn </span>encode_var(<span class="self">self</span>, src: <span class="kw-2">&mut </span>[u8]) -> usize; |
| |
| <span class="doccomment">/// Helper: Encode a value and return the encoded form as Vec. The Vec must be at least |
| /// `required_space()` bytes long. |
| </span><span class="kw">fn </span>encode_var_vec(<span class="self">self</span>) -> Vec<u8> { |
| <span class="kw">let </span><span class="kw-2">mut </span>v = Vec::new(); |
| v.resize(<span class="self">self</span>.required_space(), <span class="number">0</span>); |
| <span class="self">self</span>.encode_var(<span class="kw-2">&mut </span>v); |
| v |
| } |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>zigzag_encode(from: i64) -> u64 { |
| ((from << <span class="number">1</span>) ^ (from >> <span class="number">63</span>)) <span class="kw">as </span>u64 |
| } |
| |
| <span class="comment">// see: http://stackoverflow.com/a/2211086/56332 |
| // casting required because operations like unary negation |
| // cannot be performed on unsigned integers |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>zigzag_decode(from: u64) -> i64 { |
| ((from >> <span class="number">1</span>) ^ (-((from & <span class="number">1</span>) <span class="kw">as </span>i64)) <span class="kw">as </span>u64) <span class="kw">as </span>i64 |
| } |
| |
| <span class="macro">macro_rules! </span>impl_varint { |
| (<span class="macro-nonterminal">$t</span>:ty, unsigned) => { |
| <span class="kw">impl </span>VarInt <span class="kw">for </span><span class="macro-nonterminal">$t </span>{ |
| <span class="kw">fn </span>required_space(<span class="self">self</span>) -> usize { |
| required_encoded_space_unsigned(<span class="self">self </span><span class="kw">as </span>u64) |
| } |
| |
| <span class="kw">fn </span>decode_var(src: <span class="kw-2">&</span>[u8]) -> (<span class="self">Self</span>, usize) { |
| <span class="kw">let </span>(n, s) = u64::decode_var(src); |
| (n <span class="kw">as </span><span class="self">Self</span>, s) |
| } |
| |
| <span class="kw">fn </span>encode_var(<span class="self">self</span>, dst: <span class="kw-2">&mut </span>[u8]) -> usize { |
| (<span class="self">self </span><span class="kw">as </span>u64).encode_var(dst) |
| } |
| } |
| }; |
| (<span class="macro-nonterminal">$t</span>:ty, signed) => { |
| <span class="kw">impl </span>VarInt <span class="kw">for </span><span class="macro-nonterminal">$t </span>{ |
| <span class="kw">fn </span>required_space(<span class="self">self</span>) -> usize { |
| required_encoded_space_signed(<span class="self">self </span><span class="kw">as </span>i64) |
| } |
| |
| <span class="kw">fn </span>decode_var(src: <span class="kw-2">&</span>[u8]) -> (<span class="self">Self</span>, usize) { |
| <span class="kw">let </span>(n, s) = i64::decode_var(src); |
| (n <span class="kw">as </span><span class="self">Self</span>, s) |
| } |
| |
| <span class="kw">fn </span>encode_var(<span class="self">self</span>, dst: <span class="kw-2">&mut </span>[u8]) -> usize { |
| (<span class="self">self </span><span class="kw">as </span>i64).encode_var(dst) |
| } |
| } |
| }; |
| } |
| |
| <span class="macro">impl_varint!</span>(usize, unsigned); |
| <span class="macro">impl_varint!</span>(u32, unsigned); |
| <span class="macro">impl_varint!</span>(u16, unsigned); |
| <span class="macro">impl_varint!</span>(u8, unsigned); |
| |
| <span class="macro">impl_varint!</span>(isize, signed); |
| <span class="macro">impl_varint!</span>(i32, signed); |
| <span class="macro">impl_varint!</span>(i16, signed); |
| <span class="macro">impl_varint!</span>(i8, signed); |
| |
| <span class="comment">// Below are the "base implementations" doing the actual encodings; all other integer types are |
| // first cast to these biggest types before being encoded. |
| |
| </span><span class="kw">impl </span>VarInt <span class="kw">for </span>u64 { |
| <span class="kw">fn </span>required_space(<span class="self">self</span>) -> usize { |
| required_encoded_space_unsigned(<span class="self">self</span>) |
| } |
| |
| <span class="kw">fn </span>decode_var(src: <span class="kw-2">&</span>[u8]) -> (<span class="self">Self</span>, usize) { |
| <span class="kw">let </span><span class="kw-2">mut </span>result: u64 = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>shift = <span class="number">0</span>; |
| |
| <span class="kw">for </span>b <span class="kw">in </span>src.iter() { |
| <span class="kw">let </span>msb_dropped = b & DROP_MSB; |
| result |= (msb_dropped <span class="kw">as </span>u64) << shift; |
| shift += <span class="number">7</span>; |
| |
| <span class="kw">if </span>b & MSB == <span class="number">0 </span>|| shift > (<span class="number">10 </span>* <span class="number">7</span>) { |
| <span class="kw">break</span>; |
| } |
| } |
| |
| (result, shift / <span class="number">7 </span><span class="kw">as </span>usize) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>encode_var(<span class="self">self</span>, dst: <span class="kw-2">&mut </span>[u8]) -> usize { |
| <span class="macro">assert!</span>(dst.len() >= <span class="self">self</span>.required_space()); |
| <span class="kw">let </span><span class="kw-2">mut </span>n = <span class="self">self</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>i = <span class="number">0</span>; |
| |
| <span class="kw">while </span>n >= <span class="number">0x80 </span>{ |
| dst[i] = MSB | (n <span class="kw">as </span>u8); |
| i += <span class="number">1</span>; |
| n >>= <span class="number">7</span>; |
| } |
| |
| dst[i] = n <span class="kw">as </span>u8; |
| i+<span class="number">1 |
| </span>} |
| } |
| |
| <span class="kw">impl </span>VarInt <span class="kw">for </span>i64 { |
| <span class="kw">fn </span>required_space(<span class="self">self</span>) -> usize { |
| required_encoded_space_signed(<span class="self">self</span>) |
| } |
| |
| <span class="kw">fn </span>decode_var(src: <span class="kw-2">&</span>[u8]) -> (<span class="self">Self</span>, usize) { |
| <span class="kw">let </span><span class="kw-2">mut </span>result: u64 = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>shift = <span class="number">0</span>; |
| |
| <span class="kw">for </span>b <span class="kw">in </span>src.iter() { |
| <span class="kw">let </span>msb_dropped = b & DROP_MSB; |
| result |= (msb_dropped <span class="kw">as </span>u64) << shift; |
| shift += <span class="number">7</span>; |
| |
| <span class="kw">if </span>b & MSB == <span class="number">0 </span>|| shift > (<span class="number">10 </span>* <span class="number">7</span>) { |
| <span class="kw">break</span>; |
| } |
| } |
| |
| (zigzag_decode(result) <span class="kw">as </span><span class="self">Self</span>, shift / <span class="number">7 </span><span class="kw">as </span>usize) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>encode_var(<span class="self">self</span>, dst: <span class="kw-2">&mut </span>[u8]) -> usize { |
| <span class="macro">assert!</span>(dst.len() >= <span class="self">self</span>.required_space()); |
| <span class="kw">let </span><span class="kw-2">mut </span>n: u64 = zigzag_encode(<span class="self">self </span><span class="kw">as </span>i64); |
| <span class="kw">let </span><span class="kw-2">mut </span>i = <span class="number">0</span>; |
| |
| <span class="kw">while </span>n >= <span class="number">0x80 </span>{ |
| dst[i] = MSB | (n <span class="kw">as </span>u8); |
| i += <span class="number">1</span>; |
| n >>= <span class="number">7</span>; |
| } |
| |
| dst[i] = n <span class="kw">as </span>u8; |
| i+<span class="number">1 |
| </span>} |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="integer_encoding" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
