| <!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/regex-1.8.3/src/backtrack.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>backtrack.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="../../regex/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="../../regex/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="comment">// This is the backtracking matching engine. It has the same exact capability |
| // as the full NFA simulation, except it is artificially restricted to small |
| // regexes on small inputs because of its memory requirements. |
| // |
| // In particular, this is a *bounded* backtracking engine. It retains worst |
| // case linear time by keeping track of the states that it has visited (using a |
| // bitmap). Namely, once a state is visited, it is never visited again. Since a |
| // state is keyed by `(instruction index, input index)`, we have that its time |
| // complexity is `O(mn)` (i.e., linear in the size of the search text). |
| // |
| // The backtracking engine can beat out the NFA simulation on small |
| // regexes/inputs because it doesn't have to keep track of multiple copies of |
| // the capture groups. In benchmarks, the backtracking engine is roughly twice |
| // as fast as the full NFA simulation. Note though that its performance doesn't |
| // scale, even if you're willing to live with the memory requirements. Namely, |
| // the bitset has to be zeroed on each execution, which becomes quite expensive |
| // on large bitsets. |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::exec::ProgramCache; |
| <span class="kw">use </span><span class="kw">crate</span>::input::{Input, InputAt}; |
| <span class="kw">use </span><span class="kw">crate</span>::prog::{InstPtr, Program}; |
| <span class="kw">use </span><span class="kw">crate</span>::re_trait::Slot; |
| |
| <span class="kw">type </span>Bits = u32; |
| |
| <span class="kw">const </span>BIT_SIZE: usize = <span class="number">32</span>; |
| <span class="kw">const </span>MAX_SIZE_BYTES: usize = <span class="number">256 </span>* (<span class="number">1 </span><< <span class="number">10</span>); <span class="comment">// 256 KB |
| |
| </span><span class="doccomment">/// Returns true iff the given regex and input should be executed by this |
| /// engine with reasonable memory usage. |
| </span><span class="kw">pub fn </span>should_exec(num_insts: usize, text_len: usize) -> bool { |
| <span class="comment">// Total memory usage in bytes is determined by: |
| // |
| // ((len(insts) * (len(input) + 1) + bits - 1) / bits) * (size_of(u32)) |
| // |
| // The actual limit picked is pretty much a heuristic. |
| // See: https://github.com/rust-lang/regex/issues/215 |
| </span><span class="kw">let </span>size = ((num_insts * (text_len + <span class="number">1</span>) + BIT_SIZE - <span class="number">1</span>) / BIT_SIZE) * <span class="number">4</span>; |
| size <= MAX_SIZE_BYTES |
| } |
| |
| <span class="doccomment">/// A backtracking matching engine. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Bounded<<span class="lifetime">'a</span>, <span class="lifetime">'m</span>, <span class="lifetime">'r</span>, <span class="lifetime">'s</span>, I> { |
| prog: <span class="kw-2">&</span><span class="lifetime">'r </span>Program, |
| input: I, |
| matches: <span class="kw-2">&</span><span class="lifetime">'m </span><span class="kw-2">mut </span>[bool], |
| slots: <span class="kw-2">&</span><span class="lifetime">'s </span><span class="kw-2">mut </span>[Slot], |
| m: <span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>Cache, |
| } |
| |
| <span class="doccomment">/// Shared cached state between multiple invocations of a backtracking engine |
| /// in the same thread. |
| </span><span class="attribute">#[derive(Clone, Debug)] |
| </span><span class="kw">pub struct </span>Cache { |
| jobs: Vec<Job>, |
| visited: Vec<Bits>, |
| } |
| |
| <span class="kw">impl </span>Cache { |
| <span class="doccomment">/// Create new empty cache for the backtracking engine. |
| </span><span class="kw">pub fn </span>new(_prog: <span class="kw-2">&</span>Program) -> <span class="self">Self </span>{ |
| Cache { jobs: <span class="macro">vec!</span>[], visited: <span class="macro">vec!</span>[] } |
| } |
| } |
| |
| <span class="doccomment">/// A job is an explicit unit of stack space in the backtracking engine. |
| /// |
| /// The "normal" representation is a single state transition, which corresponds |
| /// to an NFA state and a character in the input. However, the backtracking |
| /// engine must keep track of old capture group values. We use the explicit |
| /// stack to do it. |
| </span><span class="attribute">#[derive(Clone, Copy, Debug)] |
| </span><span class="kw">enum </span>Job { |
| Inst { ip: InstPtr, at: InputAt }, |
| SaveRestore { slot: usize, old_pos: <span class="prelude-ty">Option</span><usize> }, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, <span class="lifetime">'m</span>, <span class="lifetime">'r</span>, <span class="lifetime">'s</span>, I: Input> Bounded<<span class="lifetime">'a</span>, <span class="lifetime">'m</span>, <span class="lifetime">'r</span>, <span class="lifetime">'s</span>, I> { |
| <span class="doccomment">/// Execute the backtracking matching engine. |
| /// |
| /// If there's a match, `exec` returns `true` and populates the given |
| /// captures accordingly. |
| </span><span class="kw">pub fn </span>exec( |
| prog: <span class="kw-2">&</span><span class="lifetime">'r </span>Program, |
| cache: <span class="kw-2">&</span>ProgramCache, |
| matches: <span class="kw-2">&</span><span class="lifetime">'m </span><span class="kw-2">mut </span>[bool], |
| slots: <span class="kw-2">&</span><span class="lifetime">'s </span><span class="kw-2">mut </span>[Slot], |
| input: I, |
| start: usize, |
| end: usize, |
| ) -> bool { |
| <span class="kw">let </span><span class="kw-2">mut </span>cache = cache.borrow_mut(); |
| <span class="kw">let </span>cache = <span class="kw-2">&mut </span>cache.backtrack; |
| <span class="kw">let </span>start = input.at(start); |
| <span class="kw">let </span><span class="kw-2">mut </span>b = Bounded { prog, input, matches, slots, m: cache }; |
| b.exec_(start, end) |
| } |
| |
| <span class="doccomment">/// Clears the cache such that the backtracking engine can be executed |
| /// on some input of fixed length. |
| </span><span class="kw">fn </span>clear(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="comment">// Reset the job memory so that we start fresh. |
| </span><span class="self">self</span>.m.jobs.clear(); |
| |
| <span class="comment">// Now we need to clear the bit state set. |
| // We do this by figuring out how much space we need to keep track |
| // of the states we've visited. |
| // Then we reset all existing allocated space to 0. |
| // Finally, we request more space if we need it. |
| // |
| // This is all a little circuitous, but doing this using unchecked |
| // operations doesn't seem to have a measurable impact on performance. |
| // (Probably because backtracking is limited to such small |
| // inputs/regexes in the first place.) |
| </span><span class="kw">let </span>visited_len = |
| (<span class="self">self</span>.prog.len() * (<span class="self">self</span>.input.len() + <span class="number">1</span>) + BIT_SIZE - <span class="number">1</span>) |
| / BIT_SIZE; |
| <span class="self">self</span>.m.visited.truncate(visited_len); |
| <span class="kw">for </span>v <span class="kw">in </span><span class="kw-2">&mut </span><span class="self">self</span>.m.visited { |
| <span class="kw-2">*</span>v = <span class="number">0</span>; |
| } |
| <span class="kw">if </span>visited_len > <span class="self">self</span>.m.visited.len() { |
| <span class="kw">let </span>len = <span class="self">self</span>.m.visited.len(); |
| <span class="self">self</span>.m.visited.reserve_exact(visited_len - len); |
| <span class="kw">for _ in </span><span class="number">0</span>..(visited_len - len) { |
| <span class="self">self</span>.m.visited.push(<span class="number">0</span>); |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Start backtracking at the given position in the input, but also look |
| /// for literal prefixes. |
| </span><span class="kw">fn </span>exec_(<span class="kw-2">&mut </span><span class="self">self</span>, <span class="kw-2">mut </span>at: InputAt, end: usize) -> bool { |
| <span class="self">self</span>.clear(); |
| <span class="comment">// If this is an anchored regex at the beginning of the input, then |
| // we're either already done or we only need to try backtracking once. |
| </span><span class="kw">if </span><span class="self">self</span>.prog.is_anchored_start { |
| <span class="kw">return if </span>!at.is_start() { <span class="bool-val">false </span>} <span class="kw">else </span>{ <span class="self">self</span>.backtrack(at) }; |
| } |
| <span class="kw">let </span><span class="kw-2">mut </span>matched = <span class="bool-val">false</span>; |
| <span class="kw">loop </span>{ |
| <span class="kw">if </span>!<span class="self">self</span>.prog.prefixes.is_empty() { |
| at = <span class="kw">match </span><span class="self">self</span>.input.prefix_at(<span class="kw-2">&</span><span class="self">self</span>.prog.prefixes, at) { |
| <span class="prelude-val">None </span>=> <span class="kw">break</span>, |
| <span class="prelude-val">Some</span>(at) => at, |
| }; |
| } |
| matched = <span class="self">self</span>.backtrack(at) || matched; |
| <span class="kw">if </span>matched && <span class="self">self</span>.prog.matches.len() == <span class="number">1 </span>{ |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| <span class="kw">if </span>at.pos() >= end { |
| <span class="kw">break</span>; |
| } |
| at = <span class="self">self</span>.input.at(at.next_pos()); |
| } |
| matched |
| } |
| |
| <span class="doccomment">/// The main backtracking loop starting at the given input position. |
| </span><span class="kw">fn </span>backtrack(<span class="kw-2">&mut </span><span class="self">self</span>, start: InputAt) -> bool { |
| <span class="comment">// N.B. We use an explicit stack to avoid recursion. |
| // To avoid excessive pushing and popping, most transitions are handled |
| // in the `step` helper function, which only pushes to the stack when |
| // there's a capture or a branch. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>matched = <span class="bool-val">false</span>; |
| <span class="self">self</span>.m.jobs.push(Job::Inst { ip: <span class="number">0</span>, at: start }); |
| <span class="kw">while let </span><span class="prelude-val">Some</span>(job) = <span class="self">self</span>.m.jobs.pop() { |
| <span class="kw">match </span>job { |
| Job::Inst { ip, at } => { |
| <span class="kw">if </span><span class="self">self</span>.step(ip, at) { |
| <span class="comment">// Only quit if we're matching one regex. |
| // If we're matching a regex set, then mush on and |
| // try to find other matches (if we want them). |
| </span><span class="kw">if </span><span class="self">self</span>.prog.matches.len() == <span class="number">1 </span>{ |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| matched = <span class="bool-val">true</span>; |
| } |
| } |
| Job::SaveRestore { slot, old_pos } => { |
| <span class="kw">if </span>slot < <span class="self">self</span>.slots.len() { |
| <span class="self">self</span>.slots[slot] = old_pos; |
| } |
| } |
| } |
| } |
| matched |
| } |
| |
| <span class="kw">fn </span>step(<span class="kw-2">&mut </span><span class="self">self</span>, <span class="kw-2">mut </span>ip: InstPtr, <span class="kw-2">mut </span>at: InputAt) -> bool { |
| <span class="kw">use </span><span class="kw">crate</span>::prog::Inst::<span class="kw-2">*</span>; |
| <span class="kw">loop </span>{ |
| <span class="comment">// This loop is an optimization to avoid constantly pushing/popping |
| // from the stack. Namely, if we're pushing a job only to run it |
| // next, avoid the push and just mutate `ip` (and possibly `at`) |
| // in place. |
| </span><span class="kw">if </span><span class="self">self</span>.has_visited(ip, at) { |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| <span class="kw">match </span><span class="self">self</span>.prog[ip] { |
| Match(slot) => { |
| <span class="kw">if </span>slot < <span class="self">self</span>.matches.len() { |
| <span class="self">self</span>.matches[slot] = <span class="bool-val">true</span>; |
| } |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| Save(<span class="kw-2">ref </span>inst) => { |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">&</span>old_pos) = <span class="self">self</span>.slots.get(inst.slot) { |
| <span class="comment">// If this path doesn't work out, then we save the old |
| // capture index (if one exists) in an alternate |
| // job. If the next path fails, then the alternate |
| // job is popped and the old capture index is restored. |
| </span><span class="self">self</span>.m.jobs.push(Job::SaveRestore { |
| slot: inst.slot, |
| old_pos, |
| }); |
| <span class="self">self</span>.slots[inst.slot] = <span class="prelude-val">Some</span>(at.pos()); |
| } |
| ip = inst.goto; |
| } |
| Split(<span class="kw-2">ref </span>inst) => { |
| <span class="self">self</span>.m.jobs.push(Job::Inst { ip: inst.goto2, at }); |
| ip = inst.goto1; |
| } |
| EmptyLook(<span class="kw-2">ref </span>inst) => { |
| <span class="kw">if </span><span class="self">self</span>.input.is_empty_match(at, inst) { |
| ip = inst.goto; |
| } <span class="kw">else </span>{ |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| Char(<span class="kw-2">ref </span>inst) => { |
| <span class="kw">if </span>inst.c == at.char() { |
| ip = inst.goto; |
| at = <span class="self">self</span>.input.at(at.next_pos()); |
| } <span class="kw">else </span>{ |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| Ranges(<span class="kw-2">ref </span>inst) => { |
| <span class="kw">if </span>inst.matches(at.char()) { |
| ip = inst.goto; |
| at = <span class="self">self</span>.input.at(at.next_pos()); |
| } <span class="kw">else </span>{ |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| Bytes(<span class="kw-2">ref </span>inst) => { |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(b) = at.byte() { |
| <span class="kw">if </span>inst.matches(b) { |
| ip = inst.goto; |
| at = <span class="self">self</span>.input.at(at.next_pos()); |
| <span class="kw">continue</span>; |
| } |
| } |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| } |
| } |
| |
| <span class="kw">fn </span>has_visited(<span class="kw-2">&mut </span><span class="self">self</span>, ip: InstPtr, at: InputAt) -> bool { |
| <span class="kw">let </span>k = ip * (<span class="self">self</span>.input.len() + <span class="number">1</span>) + at.pos(); |
| <span class="kw">let </span>k1 = k / BIT_SIZE; |
| <span class="kw">let </span>k2 = usize_to_u32(<span class="number">1 </span><< (k & (BIT_SIZE - <span class="number">1</span>))); |
| <span class="kw">if </span><span class="self">self</span>.m.visited[k1] & k2 == <span class="number">0 </span>{ |
| <span class="self">self</span>.m.visited[k1] |= k2; |
| <span class="bool-val">false |
| </span>} <span class="kw">else </span>{ |
| <span class="bool-val">true |
| </span>} |
| } |
| } |
| |
| <span class="kw">fn </span>usize_to_u32(n: usize) -> u32 { |
| <span class="kw">if </span>(n <span class="kw">as </span>u64) > (::std::u32::MAX <span class="kw">as </span>u64) { |
| <span class="macro">panic!</span>(<span class="string">"BUG: {} is too big to fit into u32"</span>, n) |
| } |
| n <span class="kw">as </span>u32 |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="regex" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |