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Diffstat (limited to 'vendor/regex-automata/src/dfa/dense.rs')
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diff --git a/vendor/regex-automata/src/dfa/dense.rs b/vendor/regex-automata/src/dfa/dense.rs new file mode 100644 index 000000000..07c135098 --- /dev/null +++ b/vendor/regex-automata/src/dfa/dense.rs @@ -0,0 +1,4470 @@ +/*! +Types and routines specific to dense DFAs. + +This module is the home of [`dense::DFA`](DFA). + +This module also contains a [`dense::Builder`](Builder) and a +[`dense::Config`](Config) for configuring and building a dense DFA. +*/ + +#[cfg(feature = "alloc")] +use core::cmp; +use core::{convert::TryFrom, fmt, iter, mem::size_of, slice}; + +#[cfg(feature = "alloc")] +use alloc::{ + collections::{BTreeMap, BTreeSet}, + vec, + vec::Vec, +}; + +#[cfg(feature = "alloc")] +use crate::{ + dfa::{ + accel::Accel, determinize, error::Error, minimize::Minimizer, sparse, + }, + nfa::thompson, + util::alphabet::ByteSet, + MatchKind, +}; +use crate::{ + dfa::{ + accel::Accels, + automaton::{fmt_state_indicator, Automaton}, + special::Special, + DEAD, + }, + util::{ + alphabet::{self, ByteClasses}, + bytes::{self, DeserializeError, Endian, SerializeError}, + id::{PatternID, StateID}, + start::Start, + }, +}; + +/// The label that is pre-pended to a serialized DFA. +const LABEL: &str = "rust-regex-automata-dfa-dense"; + +/// The format version of dense regexes. This version gets incremented when a +/// change occurs. A change may not necessarily be a breaking change, but the +/// version does permit good error messages in the case where a breaking change +/// is made. +const VERSION: u32 = 2; + +/// The configuration used for compiling a dense DFA. +/// +/// A dense DFA configuration is a simple data object that is typically used +/// with [`dense::Builder::configure`](self::Builder::configure). +/// +/// The default configuration guarantees that a search will _never_ return a +/// [`MatchError`](crate::MatchError) for any haystack or pattern. Setting a +/// quit byte with [`Config::quit`] or enabling heuristic support for Unicode +/// word boundaries with [`Config::unicode_word_boundary`] can in turn cause a +/// search to return an error. See the corresponding configuration options for +/// more details on when those error conditions arise. +#[cfg(feature = "alloc")] +#[derive(Clone, Copy, Debug, Default)] +pub struct Config { + // As with other configuration types in this crate, we put all our knobs + // in options so that we can distinguish between "default" and "not set." + // This makes it possible to easily combine multiple configurations + // without default values overwriting explicitly specified values. See the + // 'overwrite' method. + // + // For docs on the fields below, see the corresponding method setters. + anchored: Option<bool>, + accelerate: Option<bool>, + minimize: Option<bool>, + match_kind: Option<MatchKind>, + starts_for_each_pattern: Option<bool>, + byte_classes: Option<bool>, + unicode_word_boundary: Option<bool>, + quit: Option<ByteSet>, + dfa_size_limit: Option<Option<usize>>, + determinize_size_limit: Option<Option<usize>>, +} + +#[cfg(feature = "alloc")] +impl Config { + /// Return a new default dense DFA compiler configuration. + pub fn new() -> Config { + Config::default() + } + + /// Set whether matching must be anchored at the beginning of the input. + /// + /// When enabled, a match must begin at the start of a search. When + /// disabled, the DFA will act as if the pattern started with a `(?s:.)*?`, + /// which enables a match to appear anywhere. + /// + /// Note that if you want to run both anchored and unanchored + /// searches without building multiple automatons, you can enable the + /// [`Config::starts_for_each_pattern`] configuration instead. This will + /// permit unanchored any-pattern searches and pattern-specific anchored + /// searches. See the documentation for that configuration for an example. + /// + /// By default this is disabled. + /// + /// **WARNING:** this is subtly different than using a `^` at the start of + /// your regex. A `^` forces a regex to match exclusively at the start of + /// input, regardless of where you begin your search. In contrast, enabling + /// this option will allow your regex to match anywhere in your input, + /// but the match must start at the beginning of a search. (Most of the + /// higher level convenience search routines make "start of input" and + /// "start of search" equivalent, but some routines allow treating these as + /// orthogonal.) + /// + /// For example, consider the haystack `aba` and the following searches: + /// + /// 1. The regex `^a` is compiled with `anchored=false` and searches + /// `aba` starting at position `2`. Since `^` requires the match to + /// start at the beginning of the input and `2 > 0`, no match is found. + /// 2. The regex `a` is compiled with `anchored=true` and searches `aba` + /// starting at position `2`. This reports a match at `[2, 3]` since + /// the match starts where the search started. Since there is no `^`, + /// there is no requirement for the match to start at the beginning of + /// the input. + /// 3. The regex `a` is compiled with `anchored=true` and searches `aba` + /// starting at position `1`. Since `b` corresponds to position `1` and + /// since the regex is anchored, it finds no match. + /// 4. The regex `a` is compiled with `anchored=false` and searches `aba` + /// startting at position `1`. Since the regex is neither anchored nor + /// starts with `^`, the regex is compiled with an implicit `(?s:.)*?` + /// prefix that permits it to match anywhere. Thus, it reports a match + /// at `[2, 3]`. + /// + /// # Example + /// + /// This demonstrates the differences between an anchored search and + /// a pattern that begins with `^` (as described in the above warning + /// message). + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// let haystack = "aba".as_bytes(); + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().anchored(false)) // default + /// .build(r"^a")?; + /// let got = dfa.find_leftmost_fwd_at(None, None, haystack, 2, 3)?; + /// // No match is found because 2 is not the beginning of the haystack, + /// // which is what ^ requires. + /// let expected = None; + /// assert_eq!(expected, got); + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().anchored(true)) + /// .build(r"a")?; + /// let got = dfa.find_leftmost_fwd_at(None, None, haystack, 2, 3)?; + /// // An anchored search can still match anywhere in the haystack, it just + /// // must begin at the start of the search which is '2' in this case. + /// let expected = Some(HalfMatch::must(0, 3)); + /// assert_eq!(expected, got); + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().anchored(true)) + /// .build(r"a")?; + /// let got = dfa.find_leftmost_fwd_at(None, None, haystack, 1, 3)?; + /// // No match is found since we start searching at offset 1 which + /// // corresponds to 'b'. Since there is no '(?s:.)*?' prefix, no match + /// // is found. + /// let expected = None; + /// assert_eq!(expected, got); + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().anchored(false)) // default + /// .build(r"a")?; + /// let got = dfa.find_leftmost_fwd_at(None, None, haystack, 1, 3)?; + /// // Since anchored=false, an implicit '(?s:.)*?' prefix was added to the + /// // pattern. Even though the search starts at 'b', the 'match anything' + /// // prefix allows the search to match 'a'. + /// let expected = Some(HalfMatch::must(0, 3)); + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn anchored(mut self, yes: bool) -> Config { + self.anchored = Some(yes); + self + } + + /// Enable state acceleration. + /// + /// When enabled, DFA construction will analyze each state to determine + /// whether it is eligible for simple acceleration. Acceleration typically + /// occurs when most of a state's transitions loop back to itself, leaving + /// only a select few bytes that will exit the state. When this occurs, + /// other routines like `memchr` can be used to look for those bytes which + /// may be much faster than traversing the DFA. + /// + /// Callers may elect to disable this if consistent performance is more + /// desirable than variable performance. Namely, acceleration can sometimes + /// make searching slower than it otherwise would be if the transitions + /// that leave accelerated states are traversed frequently. + /// + /// See [`Automaton::accelerator`](crate::dfa::Automaton::accelerator) for + /// an example. + /// + /// This is enabled by default. + pub fn accelerate(mut self, yes: bool) -> Config { + self.accelerate = Some(yes); + self + } + + /// Minimize the DFA. + /// + /// When enabled, the DFA built will be minimized such that it is as small + /// as possible. + /// + /// Whether one enables minimization or not depends on the types of costs + /// you're willing to pay and how much you care about its benefits. In + /// particular, minimization has worst case `O(n*k*logn)` time and `O(k*n)` + /// space, where `n` is the number of DFA states and `k` is the alphabet + /// size. In practice, minimization can be quite costly in terms of both + /// space and time, so it should only be done if you're willing to wait + /// longer to produce a DFA. In general, you might want a minimal DFA in + /// the following circumstances: + /// + /// 1. You would like to optimize for the size of the automaton. This can + /// manifest in one of two ways. Firstly, if you're converting the + /// DFA into Rust code (or a table embedded in the code), then a minimal + /// DFA will translate into a corresponding reduction in code size, and + /// thus, also the final compiled binary size. Secondly, if you are + /// building many DFAs and putting them on the heap, you'll be able to + /// fit more if they are smaller. Note though that building a minimal + /// DFA itself requires additional space; you only realize the space + /// savings once the minimal DFA is constructed (at which point, the + /// space used for minimization is freed). + /// 2. You've observed that a smaller DFA results in faster match + /// performance. Naively, this isn't guaranteed since there is no + /// inherent difference between matching with a bigger-than-minimal + /// DFA and a minimal DFA. However, a smaller DFA may make use of your + /// CPU's cache more efficiently. + /// 3. You are trying to establish an equivalence between regular + /// languages. The standard method for this is to build a minimal DFA + /// for each language and then compare them. If the DFAs are equivalent + /// (up to state renaming), then the languages are equivalent. + /// + /// Typically, minimization only makes sense as an offline process. That + /// is, one might minimize a DFA before serializing it to persistent + /// storage. In practical terms, minimization can take around an order of + /// magnitude more time than compiling the initial DFA via determinization. + /// + /// This option is disabled by default. + pub fn minimize(mut self, yes: bool) -> Config { + self.minimize = Some(yes); + self + } + + /// Set the desired match semantics. + /// + /// The default is [`MatchKind::LeftmostFirst`], which corresponds to the + /// match semantics of Perl-like regex engines. That is, when multiple + /// patterns would match at the same leftmost position, the pattern that + /// appears first in the concrete syntax is chosen. + /// + /// Currently, the only other kind of match semantics supported is + /// [`MatchKind::All`]. This corresponds to classical DFA construction + /// where all possible matches are added to the DFA. + /// + /// Typically, `All` is used when one wants to execute an overlapping + /// search and `LeftmostFirst` otherwise. In particular, it rarely makes + /// sense to use `All` with the various "leftmost" find routines, since the + /// leftmost routines depend on the `LeftmostFirst` automata construction + /// strategy. Specifically, `LeftmostFirst` adds dead states to the DFA + /// as a way to terminate the search and report a match. `LeftmostFirst` + /// also supports non-greedy matches using this strategy where as `All` + /// does not. + /// + /// # Example: overlapping search + /// + /// This example shows the typical use of `MatchKind::All`, which is to + /// report overlapping matches. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, OverlappingState, dense}, + /// HalfMatch, MatchKind, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().match_kind(MatchKind::All)) + /// .build_many(&[r"\w+$", r"\S+$"])?; + /// let haystack = "@foo".as_bytes(); + /// let mut state = OverlappingState::start(); + /// + /// let expected = Some(HalfMatch::must(1, 4)); + /// let got = dfa.find_overlapping_fwd(haystack, &mut state)?; + /// assert_eq!(expected, got); + /// + /// // The first pattern also matches at the same position, so re-running + /// // the search will yield another match. Notice also that the first + /// // pattern is returned after the second. This is because the second + /// // pattern begins its match before the first, is therefore an earlier + /// // match and is thus reported first. + /// let expected = Some(HalfMatch::must(0, 4)); + /// let got = dfa.find_overlapping_fwd(haystack, &mut state)?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: reverse automaton to find start of match + /// + /// Another example for using `MatchKind::All` is for constructing a + /// reverse automaton to find the start of a match. `All` semantics are + /// used for this in order to find the longest possible match, which + /// corresponds to the leftmost starting position. + /// + /// Note that if you need the starting position then + /// [`dfa::regex::Regex`](crate::dfa::regex::Regex) will handle this for + /// you, so it's usually not necessary to do this yourself. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, MatchKind}; + /// + /// let haystack = "123foobar456".as_bytes(); + /// let pattern = r"[a-z]+"; + /// + /// let dfa_fwd = dense::DFA::new(pattern)?; + /// let dfa_rev = dense::Builder::new() + /// .configure(dense::Config::new() + /// .anchored(true) + /// .match_kind(MatchKind::All) + /// ) + /// .build(pattern)?; + /// let expected_fwd = HalfMatch::must(0, 9); + /// let expected_rev = HalfMatch::must(0, 3); + /// let got_fwd = dfa_fwd.find_leftmost_fwd(haystack)?.unwrap(); + /// // Here we don't specify the pattern to search for since there's only + /// // one pattern and we're doing a leftmost search. But if this were an + /// // overlapping search, you'd need to specify the pattern that matched + /// // in the forward direction. (Otherwise, you might wind up finding the + /// // starting position of a match of some other pattern.) That in turn + /// // requires building the reverse automaton with starts_for_each_pattern + /// // enabled. Indeed, this is what Regex does internally. + /// let got_rev = dfa_rev.find_leftmost_rev_at( + /// None, haystack, 0, got_fwd.offset(), + /// )?.unwrap(); + /// assert_eq!(expected_fwd, got_fwd); + /// assert_eq!(expected_rev, got_rev); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn match_kind(mut self, kind: MatchKind) -> Config { + self.match_kind = Some(kind); + self + } + + /// Whether to compile a separate start state for each pattern in the + /// automaton. + /// + /// When enabled, a separate **anchored** start state is added for each + /// pattern in the DFA. When this start state is used, then the DFA will + /// only search for matches for the pattern specified, even if there are + /// other patterns in the DFA. + /// + /// The main downside of this option is that it can potentially increase + /// the size of the DFA and/or increase the time it takes to build the DFA. + /// + /// There are a few reasons one might want to enable this (it's disabled + /// by default): + /// + /// 1. When looking for the start of an overlapping match (using a + /// reverse DFA), doing it correctly requires starting the reverse search + /// using the starting state of the pattern that matched in the forward + /// direction. Indeed, when building a [`Regex`](crate::dfa::regex::Regex), + /// it will automatically enable this option when building the reverse DFA + /// internally. + /// 2. When you want to use a DFA with multiple patterns to both search + /// for matches of any pattern or to search for anchored matches of one + /// particular pattern while using the same DFA. (Otherwise, you would need + /// to compile a new DFA for each pattern.) + /// 3. Since the start states added for each pattern are anchored, if you + /// compile an unanchored DFA with one pattern while also enabling this + /// option, then you can use the same DFA to perform anchored or unanchored + /// searches. The latter you get with the standard search APIs. The former + /// you get from the various `_at` search methods that allow you specify a + /// pattern ID to search for. + /// + /// By default this is disabled. + /// + /// # Example + /// + /// This example shows how to use this option to permit the same DFA to + /// run both anchored and unanchored searches for a single pattern. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, PatternID, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().starts_for_each_pattern(true)) + /// .build(r"foo[0-9]+")?; + /// let haystack = b"quux foo123"; + /// + /// // Here's a normal unanchored search. Notice that we use 'None' for the + /// // pattern ID. Since the DFA was built as an unanchored machine, it + /// // use its default unanchored starting state. + /// let expected = HalfMatch::must(0, 11); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd_at( + /// None, None, haystack, 0, haystack.len(), + /// )?); + /// // But now if we explicitly specify the pattern to search ('0' being + /// // the only pattern in the DFA), then it will use the starting state + /// // for that specific pattern which is always anchored. Since the + /// // pattern doesn't have a match at the beginning of the haystack, we + /// // find nothing. + /// assert_eq!(None, dfa.find_leftmost_fwd_at( + /// None, Some(PatternID::must(0)), haystack, 0, haystack.len(), + /// )?); + /// // And finally, an anchored search is not the same as putting a '^' at + /// // beginning of the pattern. An anchored search can only match at the + /// // beginning of the *search*, which we can change: + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd_at( + /// None, Some(PatternID::must(0)), haystack, 5, haystack.len(), + /// )?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn starts_for_each_pattern(mut self, yes: bool) -> Config { + self.starts_for_each_pattern = Some(yes); + self + } + + /// Whether to attempt to shrink the size of the DFA's alphabet or not. + /// + /// This option is enabled by default and should never be disabled unless + /// one is debugging a generated DFA. + /// + /// When enabled, the DFA will use a map from all possible bytes to their + /// corresponding equivalence class. Each equivalence class represents a + /// set of bytes that does not discriminate between a match and a non-match + /// in the DFA. For example, the pattern `[ab]+` has at least two + /// equivalence classes: a set containing `a` and `b` and a set containing + /// every byte except for `a` and `b`. `a` and `b` are in the same + /// equivalence classes because they never discriminate between a match + /// and a non-match. + /// + /// The advantage of this map is that the size of the transition table + /// can be reduced drastically from `#states * 256 * sizeof(StateID)` to + /// `#states * k * sizeof(StateID)` where `k` is the number of equivalence + /// classes (rounded up to the nearest power of 2). As a result, total + /// space usage can decrease substantially. Moreover, since a smaller + /// alphabet is used, DFA compilation becomes faster as well. + /// + /// **WARNING:** This is only useful for debugging DFAs. Disabling this + /// does not yield any speed advantages. Namely, even when this is + /// disabled, a byte class map is still used while searching. The only + /// difference is that every byte will be forced into its own distinct + /// equivalence class. This is useful for debugging the actual generated + /// transitions because it lets one see the transitions defined on actual + /// bytes instead of the equivalence classes. + pub fn byte_classes(mut self, yes: bool) -> Config { + self.byte_classes = Some(yes); + self + } + + /// Heuristically enable Unicode word boundaries. + /// + /// When set, this will attempt to implement Unicode word boundaries as if + /// they were ASCII word boundaries. This only works when the search input + /// is ASCII only. If a non-ASCII byte is observed while searching, then a + /// [`MatchError::Quit`](crate::MatchError::Quit) error is returned. + /// + /// A possible alternative to enabling this option is to simply use an + /// ASCII word boundary, e.g., via `(?-u:\b)`. The main reason to use this + /// option is if you absolutely need Unicode support. This option lets one + /// use a fast search implementation (a DFA) for some potentially very + /// common cases, while providing the option to fall back to some other + /// regex engine to handle the general case when an error is returned. + /// + /// If the pattern provided has no Unicode word boundary in it, then this + /// option has no effect. (That is, quitting on a non-ASCII byte only + /// occurs when this option is enabled _and_ a Unicode word boundary is + /// present in the pattern.) + /// + /// This is almost equivalent to setting all non-ASCII bytes to be quit + /// bytes. The only difference is that this will cause non-ASCII bytes to + /// be quit bytes _only_ when a Unicode word boundary is present in the + /// pattern. + /// + /// When enabling this option, callers _must_ be prepared to handle + /// a [`MatchError`](crate::MatchError) error during search. + /// When using a [`Regex`](crate::dfa::regex::Regex), this corresponds + /// to using the `try_` suite of methods. Alternatively, if + /// callers can guarantee that their input is ASCII only, then a + /// [`MatchError::Quit`](crate::MatchError::Quit) error will never be + /// returned while searching. + /// + /// This is disabled by default. + /// + /// # Example + /// + /// This example shows how to heuristically enable Unicode word boundaries + /// in a pattern. It also shows what happens when a search comes across a + /// non-ASCII byte. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, MatchError, MatchKind, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().unicode_word_boundary(true)) + /// .build(r"\b[0-9]+\b")?; + /// + /// // The match occurs before the search ever observes the snowman + /// // character, so no error occurs. + /// let haystack = "foo 123 ☃".as_bytes(); + /// let expected = Some(HalfMatch::must(0, 7)); + /// let got = dfa.find_leftmost_fwd(haystack)?; + /// assert_eq!(expected, got); + /// + /// // Notice that this search fails, even though the snowman character + /// // occurs after the ending match offset. This is because search + /// // routines read one byte past the end of the search to account for + /// // look-around, and indeed, this is required here to determine whether + /// // the trailing \b matches. + /// let haystack = "foo 123☃".as_bytes(); + /// let expected = MatchError::Quit { byte: 0xE2, offset: 7 }; + /// let got = dfa.find_leftmost_fwd(haystack); + /// assert_eq!(Err(expected), got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn unicode_word_boundary(mut self, yes: bool) -> Config { + // We have a separate option for this instead of just setting the + // appropriate quit bytes here because we don't want to set quit bytes + // for every regex. We only want to set them when the regex contains a + // Unicode word boundary. + self.unicode_word_boundary = Some(yes); + self + } + + /// Add a "quit" byte to the DFA. + /// + /// When a quit byte is seen during search time, then search will return + /// a [`MatchError::Quit`](crate::MatchError::Quit) error indicating the + /// offset at which the search stopped. + /// + /// A quit byte will always overrule any other aspects of a regex. For + /// example, if the `x` byte is added as a quit byte and the regex `\w` is + /// used, then observing `x` will cause the search to quit immediately + /// despite the fact that `x` is in the `\w` class. + /// + /// This mechanism is primarily useful for heuristically enabling certain + /// features like Unicode word boundaries in a DFA. Namely, if the input + /// to search is ASCII, then a Unicode word boundary can be implemented + /// via an ASCII word boundary with no change in semantics. Thus, a DFA + /// can attempt to match a Unicode word boundary but give up as soon as it + /// observes a non-ASCII byte. Indeed, if callers set all non-ASCII bytes + /// to be quit bytes, then Unicode word boundaries will be permitted when + /// building DFAs. Of course, callers should enable + /// [`Config::unicode_word_boundary`] if they want this behavior instead. + /// (The advantage being that non-ASCII quit bytes will only be added if a + /// Unicode word boundary is in the pattern.) + /// + /// When enabling this option, callers _must_ be prepared to handle a + /// [`MatchError`](crate::MatchError) error during search. When using a + /// [`Regex`](crate::dfa::regex::Regex), this corresponds to using the + /// `try_` suite of methods. + /// + /// By default, there are no quit bytes set. + /// + /// # Panics + /// + /// This panics if heuristic Unicode word boundaries are enabled and any + /// non-ASCII byte is removed from the set of quit bytes. Namely, enabling + /// Unicode word boundaries requires setting every non-ASCII byte to a quit + /// byte. So if the caller attempts to undo any of that, then this will + /// panic. + /// + /// # Example + /// + /// This example shows how to cause a search to terminate if it sees a + /// `\n` byte. This could be useful if, for example, you wanted to prevent + /// a user supplied pattern from matching across a line boundary. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, MatchError, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().quit(b'\n', true)) + /// .build(r"foo\p{any}+bar")?; + /// + /// let haystack = "foo\nbar".as_bytes(); + /// // Normally this would produce a match, since \p{any} contains '\n'. + /// // But since we instructed the automaton to enter a quit state if a + /// // '\n' is observed, this produces a match error instead. + /// let expected = MatchError::Quit { byte: 0x0A, offset: 3 }; + /// let got = dfa.find_leftmost_fwd(haystack).unwrap_err(); + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn quit(mut self, byte: u8, yes: bool) -> Config { + if self.get_unicode_word_boundary() && !byte.is_ascii() && !yes { + panic!( + "cannot set non-ASCII byte to be non-quit when \ + Unicode word boundaries are enabled" + ); + } + if self.quit.is_none() { + self.quit = Some(ByteSet::empty()); + } + if yes { + self.quit.as_mut().unwrap().add(byte); + } else { + self.quit.as_mut().unwrap().remove(byte); + } + self + } + + /// Set a size limit on the total heap used by a DFA. + /// + /// This size limit is expressed in bytes and is applied during + /// determinization of an NFA into a DFA. If the DFA's heap usage, and only + /// the DFA, exceeds this configured limit, then determinization is stopped + /// and an error is returned. + /// + /// This limit does not apply to auxiliary storage used during + /// determinization that isn't part of the generated DFA. + /// + /// This limit is only applied during determinization. Currently, there is + /// no way to post-pone this check to after minimization if minimization + /// was enabled. + /// + /// The total limit on heap used during determinization is the sum of the + /// DFA and determinization size limits. + /// + /// The default is no limit. + /// + /// # Example + /// + /// This example shows a DFA that fails to build because of a configured + /// size limit. This particular example also serves as a cautionary tale + /// demonstrating just how big DFAs with large Unicode character classes + /// can get. + /// + /// ``` + /// use regex_automata::dfa::{dense, Automaton}; + /// + /// // 3MB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new().dfa_size_limit(Some(3_000_000))) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 4MB probably is! + /// // (Note that DFA sizes aren't necessarily stable between releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().dfa_size_limit(Some(4_000_000))) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// assert!(dfa.find_leftmost_fwd(&haystack)?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// While one needs a little more than 3MB to represent `\w{20}`, it + /// turns out that you only need a little more than 4KB to represent + /// `(?-u:\w{20})`. So only use Unicode if you need it! + pub fn dfa_size_limit(mut self, bytes: Option<usize>) -> Config { + self.dfa_size_limit = Some(bytes); + self + } + + /// Set a size limit on the total heap used by determinization. + /// + /// This size limit is expressed in bytes and is applied during + /// determinization of an NFA into a DFA. If the heap used for auxiliary + /// storage during determinization (memory that is not in the DFA but + /// necessary for building the DFA) exceeds this configured limit, then + /// determinization is stopped and an error is returned. + /// + /// This limit does not apply to heap used by the DFA itself. + /// + /// The total limit on heap used during determinization is the sum of the + /// DFA and determinization size limits. + /// + /// The default is no limit. + /// + /// # Example + /// + /// This example shows a DFA that fails to build because of a + /// configured size limit on the amount of heap space used by + /// determinization. This particular example complements the example for + /// [`Config::dfa_size_limit`] by demonstrating that not only does Unicode + /// potentially make DFAs themselves big, but it also results in more + /// auxiliary storage during determinization. (Although, auxiliary storage + /// is still not as much as the DFA itself.) + /// + /// ``` + /// use regex_automata::dfa::{dense, Automaton}; + /// + /// // 300KB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(300_000)) + /// ) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 400KB probably is! + /// // (Note that auxiliary storage sizes aren't necessarily stable between + /// // releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(400_000)) + /// ) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// assert!(dfa.find_leftmost_fwd(&haystack)?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn determinize_size_limit(mut self, bytes: Option<usize>) -> Config { + self.determinize_size_limit = Some(bytes); + self + } + + /// Returns whether this configuration has enabled anchored searches. + pub fn get_anchored(&self) -> bool { + self.anchored.unwrap_or(false) + } + + /// Returns whether this configuration has enabled simple state + /// acceleration. + pub fn get_accelerate(&self) -> bool { + self.accelerate.unwrap_or(true) + } + + /// Returns whether this configuration has enabled the expensive process + /// of minimizing a DFA. + pub fn get_minimize(&self) -> bool { + self.minimize.unwrap_or(false) + } + + /// Returns the match semantics set in this configuration. + pub fn get_match_kind(&self) -> MatchKind { + self.match_kind.unwrap_or(MatchKind::LeftmostFirst) + } + + /// Returns whether this configuration has enabled anchored starting states + /// for every pattern in the DFA. + pub fn get_starts_for_each_pattern(&self) -> bool { + self.starts_for_each_pattern.unwrap_or(false) + } + + /// Returns whether this configuration has enabled byte classes or not. + /// This is typically a debugging oriented option, as disabling it confers + /// no speed benefit. + pub fn get_byte_classes(&self) -> bool { + self.byte_classes.unwrap_or(true) + } + + /// Returns whether this configuration has enabled heuristic Unicode word + /// boundary support. When enabled, it is possible for a search to return + /// an error. + pub fn get_unicode_word_boundary(&self) -> bool { + self.unicode_word_boundary.unwrap_or(false) + } + + /// Returns whether this configuration will instruct the DFA to enter a + /// quit state whenever the given byte is seen during a search. When at + /// least one byte has this enabled, it is possible for a search to return + /// an error. + pub fn get_quit(&self, byte: u8) -> bool { + self.quit.map_or(false, |q| q.contains(byte)) + } + + /// Returns the DFA size limit of this configuration if one was set. + /// The size limit is total number of bytes on the heap that a DFA is + /// permitted to use. If the DFA exceeds this limit during construction, + /// then construction is stopped and an error is returned. + pub fn get_dfa_size_limit(&self) -> Option<usize> { + self.dfa_size_limit.unwrap_or(None) + } + + /// Returns the determinization size limit of this configuration if one + /// was set. The size limit is total number of bytes on the heap that + /// determinization is permitted to use. If determinization exceeds this + /// limit during construction, then construction is stopped and an error is + /// returned. + /// + /// This is different from the DFA size limit in that this only applies to + /// the auxiliary storage used during determinization. Once determinization + /// is complete, this memory is freed. + /// + /// The limit on the total heap memory used is the sum of the DFA and + /// determinization size limits. + pub fn get_determinize_size_limit(&self) -> Option<usize> { + self.determinize_size_limit.unwrap_or(None) + } + + /// Overwrite the default configuration such that the options in `o` are + /// always used. If an option in `o` is not set, then the corresponding + /// option in `self` is used. If it's not set in `self` either, then it + /// remains not set. + pub(crate) fn overwrite(self, o: Config) -> Config { + Config { + anchored: o.anchored.or(self.anchored), + accelerate: o.accelerate.or(self.accelerate), + minimize: o.minimize.or(self.minimize), + match_kind: o.match_kind.or(self.match_kind), + starts_for_each_pattern: o + .starts_for_each_pattern + .or(self.starts_for_each_pattern), + byte_classes: o.byte_classes.or(self.byte_classes), + unicode_word_boundary: o + .unicode_word_boundary + .or(self.unicode_word_boundary), + quit: o.quit.or(self.quit), + dfa_size_limit: o.dfa_size_limit.or(self.dfa_size_limit), + determinize_size_limit: o + .determinize_size_limit + .or(self.determinize_size_limit), + } + } +} + +/// A builder for constructing a deterministic finite automaton from regular +/// expressions. +/// +/// This builder provides two main things: +/// +/// 1. It provides a few different `build` routines for actually constructing +/// a DFA from different kinds of inputs. The most convenient is +/// [`Builder::build`], which builds a DFA directly from a pattern string. The +/// most flexible is [`Builder::build_from_nfa`], which builds a DFA straight +/// from an NFA. +/// 2. The builder permits configuring a number of things. +/// [`Builder::configure`] is used with [`Config`] to configure aspects of +/// the DFA and the construction process itself. [`Builder::syntax`] and +/// [`Builder::thompson`] permit configuring the regex parser and Thompson NFA +/// construction, respectively. The syntax and thompson configurations only +/// apply when building from a pattern string. +/// +/// This builder always constructs a *single* DFA. As such, this builder +/// can only be used to construct regexes that either detect the presence +/// of a match or find the end location of a match. A single DFA cannot +/// produce both the start and end of a match. For that information, use a +/// [`Regex`](crate::dfa::regex::Regex), which can be similarly configured +/// using [`regex::Builder`](crate::dfa::regex::Builder). The main reason to +/// use a DFA directly is if the end location of a match is enough for your use +/// case. Namely, a `Regex` will construct two DFAs instead of one, since a +/// second reverse DFA is needed to find the start of a match. +/// +/// Note that if one wants to build a sparse DFA, you must first build a dense +/// DFA and convert that to a sparse DFA. There is no way to build a sparse +/// DFA without first building a dense DFA. +/// +/// # Example +/// +/// This example shows how to build a minimized DFA that completely disables +/// Unicode. That is: +/// +/// * Things such as `\w`, `.` and `\b` are no longer Unicode-aware. `\w` +/// and `\b` are ASCII-only while `.` matches any byte except for `\n` +/// (instead of any UTF-8 encoding of a Unicode scalar value except for +/// `\n`). Things that are Unicode only, such as `\pL`, are not allowed. +/// * The pattern itself is permitted to match invalid UTF-8. For example, +/// things like `[^a]` that match any byte except for `a` are permitted. +/// * Unanchored patterns can search through invalid UTF-8. That is, for +/// unanchored patterns, the implicit prefix is `(?s-u:.)*?` instead of +/// `(?s:.)*?`. +/// +/// ``` +/// use regex_automata::{ +/// dfa::{Automaton, dense}, +/// nfa::thompson, +/// HalfMatch, SyntaxConfig, +/// }; +/// +/// let dfa = dense::Builder::new() +/// .configure(dense::Config::new().minimize(false)) +/// .syntax(SyntaxConfig::new().unicode(false).utf8(false)) +/// .thompson(thompson::Config::new().utf8(false)) +/// .build(r"foo[^b]ar.*")?; +/// +/// let haystack = b"\xFEfoo\xFFar\xE2\x98\xFF\n"; +/// let expected = Some(HalfMatch::must(0, 10)); +/// let got = dfa.find_leftmost_fwd(haystack)?; +/// assert_eq!(expected, got); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[cfg(feature = "alloc")] +#[derive(Clone, Debug)] +pub struct Builder { + config: Config, + thompson: thompson::Builder, +} + +#[cfg(feature = "alloc")] +impl Builder { + /// Create a new dense DFA builder with the default configuration. + pub fn new() -> Builder { + Builder { + config: Config::default(), + thompson: thompson::Builder::new(), + } + } + + /// Build a DFA from the given pattern. + /// + /// If there was a problem parsing or compiling the pattern, then an error + /// is returned. + pub fn build(&self, pattern: &str) -> Result<OwnedDFA, Error> { + self.build_many(&[pattern]) + } + + /// Build a DFA from the given patterns. + /// + /// When matches are returned, the pattern ID corresponds to the index of + /// the pattern in the slice given. + pub fn build_many<P: AsRef<str>>( + &self, + patterns: &[P], + ) -> Result<OwnedDFA, Error> { + let nfa = self.thompson.build_many(patterns).map_err(Error::nfa)?; + self.build_from_nfa(&nfa) + } + + /// Build a DFA from the given NFA. + /// + /// # Example + /// + /// This example shows how to build a DFA if you already have an NFA in + /// hand. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// nfa::thompson, + /// HalfMatch, + /// }; + /// + /// let haystack = "foo123bar".as_bytes(); + /// + /// // This shows how to set non-default options for building an NFA. + /// let nfa = thompson::Builder::new() + /// .configure(thompson::Config::new().shrink(false)) + /// .build(r"[0-9]+")?; + /// let dfa = dense::Builder::new().build_from_nfa(&nfa)?; + /// let expected = Some(HalfMatch::must(0, 6)); + /// let got = dfa.find_leftmost_fwd(haystack)?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn build_from_nfa( + &self, + nfa: &thompson::NFA, + ) -> Result<OwnedDFA, Error> { + let mut quit = self.config.quit.unwrap_or(ByteSet::empty()); + if self.config.get_unicode_word_boundary() + && nfa.has_word_boundary_unicode() + { + for b in 0x80..=0xFF { + quit.add(b); + } + } + let classes = if !self.config.get_byte_classes() { + // DFAs will always use the equivalence class map, but enabling + // this option is useful for debugging. Namely, this will cause all + // transitions to be defined over their actual bytes instead of an + // opaque equivalence class identifier. The former is much easier + // to grok as a human. + ByteClasses::singletons() + } else { + let mut set = nfa.byte_class_set().clone(); + // It is important to distinguish any "quit" bytes from all other + // bytes. Otherwise, a non-quit byte may end up in the same class + // as a quit byte, and thus cause the DFA stop when it shouldn't. + if !quit.is_empty() { + set.add_set(&quit); + } + set.byte_classes() + }; + + let mut dfa = DFA::initial( + classes, + nfa.pattern_len(), + self.config.get_starts_for_each_pattern(), + )?; + determinize::Config::new() + .anchored(self.config.get_anchored()) + .match_kind(self.config.get_match_kind()) + .quit(quit) + .dfa_size_limit(self.config.get_dfa_size_limit()) + .determinize_size_limit(self.config.get_determinize_size_limit()) + .run(nfa, &mut dfa)?; + if self.config.get_minimize() { + dfa.minimize(); + } + if self.config.get_accelerate() { + dfa.accelerate(); + } + Ok(dfa) + } + + /// Apply the given dense DFA configuration options to this builder. + pub fn configure(&mut self, config: Config) -> &mut Builder { + self.config = self.config.overwrite(config); + self + } + + /// Set the syntax configuration for this builder using + /// [`SyntaxConfig`](crate::SyntaxConfig). + /// + /// This permits setting things like case insensitivity, Unicode and multi + /// line mode. + /// + /// These settings only apply when constructing a DFA directly from a + /// pattern. + pub fn syntax( + &mut self, + config: crate::util::syntax::SyntaxConfig, + ) -> &mut Builder { + self.thompson.syntax(config); + self + } + + /// Set the Thompson NFA configuration for this builder using + /// [`nfa::thompson::Config`](crate::nfa::thompson::Config). + /// + /// This permits setting things like whether the DFA should match the regex + /// in reverse or if additional time should be spent shrinking the size of + /// the NFA. + /// + /// These settings only apply when constructing a DFA directly from a + /// pattern. + pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder { + self.thompson.configure(config); + self + } +} + +#[cfg(feature = "alloc")] +impl Default for Builder { + fn default() -> Builder { + Builder::new() + } +} + +/// A convenience alias for an owned DFA. We use this particular instantiation +/// a lot in this crate, so it's worth giving it a name. This instantiation +/// is commonly used for mutable APIs on the DFA while building it. The main +/// reason for making DFAs generic is no_std support, and more generally, +/// making it possible to load a DFA from an arbitrary slice of bytes. +#[cfg(feature = "alloc")] +pub(crate) type OwnedDFA = DFA<Vec<u32>>; + +/// A dense table-based deterministic finite automaton (DFA). +/// +/// All dense DFAs have one or more start states, zero or more match states +/// and a transition table that maps the current state and the current byte +/// of input to the next state. A DFA can use this information to implement +/// fast searching. In particular, the use of a dense DFA generally makes the +/// trade off that match speed is the most valuable characteristic, even if +/// building the DFA may take significant time *and* space. (More concretely, +/// building a DFA takes time and space that is exponential in the size of the +/// pattern in the worst case.) As such, the processing of every byte of input +/// is done with a small constant number of operations that does not vary with +/// the pattern, its size or the size of the alphabet. If your needs don't line +/// up with this trade off, then a dense DFA may not be an adequate solution to +/// your problem. +/// +/// In contrast, a [`sparse::DFA`] makes the opposite +/// trade off: it uses less space but will execute a variable number of +/// instructions per byte at match time, which makes it slower for matching. +/// (Note that space usage is still exponential in the size of the pattern in +/// the worst case.) +/// +/// A DFA can be built using the default configuration via the +/// [`DFA::new`] constructor. Otherwise, one can +/// configure various aspects via [`dense::Builder`](Builder). +/// +/// A single DFA fundamentally supports the following operations: +/// +/// 1. Detection of a match. +/// 2. Location of the end of a match. +/// 3. In the case of a DFA with multiple patterns, which pattern matched is +/// reported as well. +/// +/// A notable absence from the above list of capabilities is the location of +/// the *start* of a match. In order to provide both the start and end of +/// a match, *two* DFAs are required. This functionality is provided by a +/// [`Regex`](crate::dfa::regex::Regex). +/// +/// # Type parameters +/// +/// A `DFA` has one type parameter, `T`, which is used to represent state IDs, +/// pattern IDs and accelerators. `T` is typically a `Vec<u32>` or a `&[u32]`. +/// +/// # The `Automaton` trait +/// +/// This type implements the [`Automaton`] trait, which means it can be used +/// for searching. For example: +/// +/// ``` +/// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; +/// +/// let dfa = DFA::new("foo[0-9]+")?; +/// let expected = HalfMatch::must(0, 8); +/// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone)] +pub struct DFA<T> { + /// The transition table for this DFA. This includes the transitions + /// themselves, along with the stride, number of states and the equivalence + /// class mapping. + tt: TransitionTable<T>, + /// The set of starting state identifiers for this DFA. The starting state + /// IDs act as pointers into the transition table. The specific starting + /// state chosen for each search is dependent on the context at which the + /// search begins. + st: StartTable<T>, + /// The set of match states and the patterns that match for each + /// corresponding match state. + /// + /// This structure is technically only needed because of support for + /// multi-regexes. Namely, multi-regexes require answering not just whether + /// a match exists, but _which_ patterns match. So we need to store the + /// matching pattern IDs for each match state. We do this even when there + /// is only one pattern for the sake of simplicity. In practice, this uses + /// up very little space for the case of on pattern. + ms: MatchStates<T>, + /// Information about which states are "special." Special states are states + /// that are dead, quit, matching, starting or accelerated. For more info, + /// see the docs for `Special`. + special: Special, + /// The accelerators for this DFA. + /// + /// If a state is accelerated, then there exist only a small number of + /// bytes that can cause the DFA to leave the state. This permits searching + /// to use optimized routines to find those specific bytes instead of using + /// the transition table. + /// + /// All accelerated states exist in a contiguous range in the DFA's + /// transition table. See dfa/special.rs for more details on how states are + /// arranged. + accels: Accels<T>, +} + +#[cfg(feature = "alloc")] +impl OwnedDFA { + /// Parse the given regular expression using a default configuration and + /// return the corresponding DFA. + /// + /// If you want a non-default configuration, then use the + /// [`dense::Builder`](Builder) to set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// let dfa = dense::DFA::new("foo[0-9]+bar")?; + /// let expected = HalfMatch::must(0, 11); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345bar")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn new(pattern: &str) -> Result<OwnedDFA, Error> { + Builder::new().build(pattern) + } + + /// Parse the given regular expressions using a default configuration and + /// return the corresponding multi-DFA. + /// + /// If you want a non-default configuration, then use the + /// [`dense::Builder`](Builder) to set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// let dfa = dense::DFA::new_many(&["[0-9]+", "[a-z]+"])?; + /// let expected = HalfMatch::must(1, 3); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345bar")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn new_many<P: AsRef<str>>(patterns: &[P]) -> Result<OwnedDFA, Error> { + Builder::new().build_many(patterns) + } +} + +#[cfg(feature = "alloc")] +impl OwnedDFA { + /// Create a new DFA that matches every input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// let dfa = dense::DFA::always_match()?; + /// + /// let expected = HalfMatch::must(0, 0); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"")?); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn always_match() -> Result<OwnedDFA, Error> { + let nfa = thompson::NFA::always_match(); + Builder::new().build_from_nfa(&nfa) + } + + /// Create a new DFA that never matches any input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::dfa::{Automaton, dense}; + /// + /// let dfa = dense::DFA::never_match()?; + /// assert_eq!(None, dfa.find_leftmost_fwd(b"")?); + /// assert_eq!(None, dfa.find_leftmost_fwd(b"foo")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn never_match() -> Result<OwnedDFA, Error> { + let nfa = thompson::NFA::never_match(); + Builder::new().build_from_nfa(&nfa) + } + + /// Create an initial DFA with the given equivalence classes, pattern count + /// and whether anchored starting states are enabled for each pattern. An + /// initial DFA can be further mutated via determinization. + fn initial( + classes: ByteClasses, + pattern_count: usize, + starts_for_each_pattern: bool, + ) -> Result<OwnedDFA, Error> { + let start_pattern_count = + if starts_for_each_pattern { pattern_count } else { 0 }; + Ok(DFA { + tt: TransitionTable::minimal(classes), + st: StartTable::dead(start_pattern_count)?, + ms: MatchStates::empty(pattern_count), + special: Special::new(), + accels: Accels::empty(), + }) + } +} + +impl<T: AsRef<[u32]>> DFA<T> { + /// Cheaply return a borrowed version of this dense DFA. Specifically, + /// the DFA returned always uses `&[u32]` for its transition table. + pub fn as_ref(&self) -> DFA<&'_ [u32]> { + DFA { + tt: self.tt.as_ref(), + st: self.st.as_ref(), + ms: self.ms.as_ref(), + special: self.special, + accels: self.accels(), + } + } + + /// Return an owned version of this sparse DFA. Specifically, the DFA + /// returned always uses `Vec<u32>` for its transition table. + /// + /// Effectively, this returns a dense DFA whose transition table lives on + /// the heap. + #[cfg(feature = "alloc")] + pub fn to_owned(&self) -> OwnedDFA { + DFA { + tt: self.tt.to_owned(), + st: self.st.to_owned(), + ms: self.ms.to_owned(), + special: self.special, + accels: self.accels().to_owned(), + } + } + + /// Returns true only if this DFA has starting states for each pattern. + /// + /// When a DFA has starting states for each pattern, then a search with the + /// DFA can be configured to only look for anchored matches of a specific + /// pattern. Specifically, APIs like [`Automaton::find_earliest_fwd_at`] + /// can accept a non-None `pattern_id` if and only if this method returns + /// true. Otherwise, calling `find_earliest_fwd_at` will panic. + /// + /// Note that if the DFA has no patterns, this always returns false. + pub fn has_starts_for_each_pattern(&self) -> bool { + self.st.patterns > 0 + } + + /// Returns the total number of elements in the alphabet for this DFA. + /// + /// That is, this returns the total number of transitions that each state + /// in this DFA must have. Typically, a normal byte oriented DFA would + /// always have an alphabet size of 256, corresponding to the number of + /// unique values in a single byte. However, this implementation has two + /// peculiarities that impact the alphabet length: + /// + /// * Every state has a special "EOI" transition that is only followed + /// after the end of some haystack is reached. This EOI transition is + /// necessary to account for one byte of look-ahead when implementing + /// things like `\b` and `$`. + /// * Bytes are grouped into equivalence classes such that no two bytes in + /// the same class can distinguish a match from a non-match. For example, + /// in the regex `^[a-z]+$`, the ASCII bytes `a-z` could all be in the + /// same equivalence class. This leads to a massive space savings. + /// + /// Note though that the alphabet length does _not_ necessarily equal the + /// total stride space taken up by a single DFA state in the transition + /// table. Namely, for performance reasons, the stride is always the + /// smallest power of two that is greater than or equal to the alphabet + /// length. For this reason, [`DFA::stride`] or [`DFA::stride2`] are + /// often more useful. The alphabet length is typically useful only for + /// informational purposes. + pub fn alphabet_len(&self) -> usize { + self.tt.alphabet_len() + } + + /// Returns the total stride for every state in this DFA, expressed as the + /// exponent of a power of 2. The stride is the amount of space each state + /// takes up in the transition table, expressed as a number of transitions. + /// (Unused transitions map to dead states.) + /// + /// The stride of a DFA is always equivalent to the smallest power of 2 + /// that is greater than or equal to the DFA's alphabet length. This + /// definition uses extra space, but permits faster translation between + /// premultiplied state identifiers and contiguous indices (by using shifts + /// instead of relying on integer division). + /// + /// For example, if the DFA's stride is 16 transitions, then its `stride2` + /// is `4` since `2^4 = 16`. + /// + /// The minimum `stride2` value is `1` (corresponding to a stride of `2`) + /// while the maximum `stride2` value is `9` (corresponding to a stride of + /// `512`). The maximum is not `8` since the maximum alphabet size is `257` + /// when accounting for the special EOI transition. However, an alphabet + /// length of that size is exceptionally rare since the alphabet is shrunk + /// into equivalence classes. + pub fn stride2(&self) -> usize { + self.tt.stride2 + } + + /// Returns the total stride for every state in this DFA. This corresponds + /// to the total number of transitions used by each state in this DFA's + /// transition table. + /// + /// Please see [`DFA::stride2`] for more information. In particular, this + /// returns the stride as the number of transitions, where as `stride2` + /// returns it as the exponent of a power of 2. + pub fn stride(&self) -> usize { + self.tt.stride() + } + + /// Returns the "universal" start state for this DFA. + /// + /// A universal start state occurs only when all of the starting states + /// for this DFA are precisely the same. This occurs when there are no + /// look-around assertions at the beginning (or end for a reverse DFA) of + /// the pattern. + /// + /// Using this as a starting state for a DFA without a universal starting + /// state has unspecified behavior. This condition is not checked, so the + /// caller must guarantee it themselves. + pub(crate) fn universal_start_state(&self) -> StateID { + // We choose 'NonWordByte' for no particular reason, other than + // the fact that this is the 'main' starting configuration used in + // determinization. But in essence, it doesn't really matter. + // + // Also, we might consider exposing this routine, but it seems + // a little tricky to use correctly. Maybe if we also expose a + // 'has_universal_start_state' method? + self.st.start(Start::NonWordByte, None) + } + + /// Returns the memory usage, in bytes, of this DFA. + /// + /// The memory usage is computed based on the number of bytes used to + /// represent this DFA. + /// + /// This does **not** include the stack size used up by this DFA. To + /// compute that, use `std::mem::size_of::<dense::DFA>()`. + pub fn memory_usage(&self) -> usize { + self.tt.memory_usage() + + self.st.memory_usage() + + self.ms.memory_usage() + + self.accels.memory_usage() + } +} + +/// Routines for converting a dense DFA to other representations, such as +/// sparse DFAs or raw bytes suitable for persistent storage. +impl<T: AsRef<[u32]>> DFA<T> { + /// Convert this dense DFA to a sparse DFA. + /// + /// If a `StateID` is too small to represent all states in the sparse + /// DFA, then this returns an error. In most cases, if a dense DFA is + /// constructable with `StateID` then a sparse DFA will be as well. + /// However, it is not guaranteed. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// let dense = dense::DFA::new("foo[0-9]+")?; + /// let sparse = dense.to_sparse()?; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), sparse.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "alloc")] + pub fn to_sparse(&self) -> Result<sparse::DFA<Vec<u8>>, Error> { + sparse::DFA::from_dense(self) + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in little endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // N.B. We use native endianness here to make the example work, but + /// // using to_bytes_little_endian would work on a little endian target. + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "alloc")] + pub fn to_bytes_little_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<bytes::LE>() + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in big endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // N.B. We use native endianness here to make the example work, but + /// // using to_bytes_big_endian would work on a big endian target. + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "alloc")] + pub fn to_bytes_big_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<bytes::BE>() + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in native endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// Generally speaking, native endian format should only be used when + /// you know that the target you're compiling the DFA for matches the + /// endianness of the target on which you're compiling DFA. For example, + /// if serialization and deserialization happen in the same process or on + /// the same machine. Otherwise, when serializing a DFA for use in a + /// portable environment, you'll almost certainly want to serialize _both_ + /// a little endian and a big endian version and then load the correct one + /// based on the target's configuration. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "alloc")] + pub fn to_bytes_native_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<bytes::NE>() + } + + /// The implementation of the public `to_bytes` serialization methods, + /// which is generic over endianness. + #[cfg(feature = "alloc")] + fn to_bytes<E: Endian>(&self) -> (Vec<u8>, usize) { + let len = self.write_to_len(); + let (mut buf, padding) = bytes::alloc_aligned_buffer::<u32>(len); + // This should always succeed since the only possible serialization + // error is providing a buffer that's too small, but we've ensured that + // `buf` is big enough here. + self.as_ref().write_to::<E>(&mut buf[padding..]).unwrap(); + (buf, padding) + } + + /// Serialize this DFA as raw bytes to the given slice, in little endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. + /// let mut buf = [0u8; 4 * (1<<10)]; + /// // N.B. We use native endianness here to make the example work, but + /// // using write_to_little_endian would work on a little endian target. + /// let written = original_dfa.write_to_native_endian(&mut buf)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf[..written])?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_little_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<bytes::LE>(dst) + } + + /// Serialize this DFA as raw bytes to the given slice, in big endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. + /// let mut buf = [0u8; 4 * (1<<10)]; + /// // N.B. We use native endianness here to make the example work, but + /// // using write_to_big_endian would work on a big endian target. + /// let written = original_dfa.write_to_native_endian(&mut buf)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf[..written])?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_big_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<bytes::BE>(dst) + } + + /// Serialize this DFA as raw bytes to the given slice, in native endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Generally speaking, native endian format should only be used when + /// you know that the target you're compiling the DFA for matches the + /// endianness of the target on which you're compiling DFA. For example, + /// if serialization and deserialization happen in the same process or on + /// the same machine. Otherwise, when serializing a DFA for use in a + /// portable environment, you'll almost certainly want to serialize _both_ + /// a little endian and a big endian version and then load the correct one + /// based on the target's configuration. + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. + /// let mut buf = [0u8; 4 * (1<<10)]; + /// let written = original_dfa.write_to_native_endian(&mut buf)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf[..written])?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_native_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<bytes::NE>(dst) + } + + /// Return the total number of bytes required to serialize this DFA. + /// + /// This is useful for determining the size of the buffer required to pass + /// to one of the serialization routines: + /// + /// * [`DFA::write_to_little_endian`] + /// * [`DFA::write_to_big_endian`] + /// * [`DFA::write_to_native_endian`] + /// + /// Passing a buffer smaller than the size returned by this method will + /// result in a serialization error. Serialization routines are guaranteed + /// to succeed when the buffer is big enough. + /// + /// # Example + /// + /// This example shows how to dynamically allocate enough room to serialize + /// a DFA. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// let mut buf = vec![0; original_dfa.write_to_len()]; + /// let written = original_dfa.write_to_native_endian(&mut buf)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf[..written])?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Note that this example isn't actually guaranteed to work! In + /// particular, if `buf` is not aligned to a 4-byte boundary, then the + /// `DFA::from_bytes` call will fail. If you need this to work, then you + /// either need to deal with adding some initial padding yourself, or use + /// one of the `to_bytes` methods, which will do it for you. + pub fn write_to_len(&self) -> usize { + bytes::write_label_len(LABEL) + + bytes::write_endianness_check_len() + + bytes::write_version_len() + + size_of::<u32>() // unused, intended for future flexibility + + self.tt.write_to_len() + + self.st.write_to_len() + + self.ms.write_to_len() + + self.special.write_to_len() + + self.accels.write_to_len() + } +} + +impl<'a> DFA<&'a [u32]> { + /// Safely deserialize a DFA with a specific state identifier + /// representation. Upon success, this returns both the deserialized DFA + /// and the number of bytes read from the given slice. Namely, the contents + /// of the slice beyond the DFA are not read. + /// + /// Deserializing a DFA using this routine will never allocate heap memory. + /// For safety purposes, the DFA's transition table will be verified such + /// that every transition points to a valid state. If this verification is + /// too costly, then a [`DFA::from_bytes_unchecked`] API is provided, which + /// will always execute in constant time. + /// + /// The bytes given must be generated by one of the serialization APIs + /// of a `DFA` using a semver compatible release of this crate. Those + /// include: + /// + /// * [`DFA::to_bytes_little_endian`] + /// * [`DFA::to_bytes_big_endian`] + /// * [`DFA::to_bytes_native_endian`] + /// * [`DFA::write_to_little_endian`] + /// * [`DFA::write_to_big_endian`] + /// * [`DFA::write_to_native_endian`] + /// + /// The `to_bytes` methods allocate and return a `Vec<u8>` for you, along + /// with handling alignment correctly. The `write_to` methods do not + /// allocate and write to an existing slice (which may be on the stack). + /// Since deserialization always uses the native endianness of the target + /// platform, the serialization API you use should match the endianness of + /// the target platform. (It's often a good idea to generate serialized + /// DFAs for both forms of endianness and then load the correct one based + /// on endianness.) + /// + /// # Errors + /// + /// Generally speaking, it's easier to state the conditions in which an + /// error is _not_ returned. All of the following must be true: + /// + /// * The bytes given must be produced by one of the serialization APIs + /// on this DFA, as mentioned above. + /// * The endianness of the target platform matches the endianness used to + /// serialized the provided DFA. + /// * The slice given must have the same alignment as `u32`. + /// + /// If any of the above are not true, then an error will be returned. + /// + /// # Panics + /// + /// This routine will never panic for any input. + /// + /// # Example + /// + /// This example shows how to serialize a DFA to raw bytes, deserialize it + /// and then use it for searching. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// let (bytes, _) = initial.to_bytes_native_endian(); + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&bytes)?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: dealing with alignment and padding + /// + /// In the above example, we used the `to_bytes_native_endian` method to + /// serialize a DFA, but we ignored part of its return value corresponding + /// to padding added to the beginning of the serialized DFA. This is OK + /// because deserialization will skip this initial padding. What matters + /// is that the address immediately following the padding has an alignment + /// that matches `u32`. That is, the following is an equivalent but + /// alternative way to write the above example: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// // Serialization returns the number of leading padding bytes added to + /// // the returned Vec<u8>. + /// let (bytes, pad) = initial.to_bytes_native_endian(); + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&bytes[pad..])?.0; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// This padding is necessary because Rust's standard library does + /// not expose any safe and robust way of creating a `Vec<u8>` with a + /// guaranteed alignment other than 1. Now, in practice, the underlying + /// allocator is likely to provide a `Vec<u8>` that meets our alignment + /// requirements, which means `pad` is zero in practice most of the time. + /// + /// The purpose of exposing the padding like this is flexibility for the + /// caller. For example, if one wants to embed a serialized DFA into a + /// compiled program, then it's important to guarantee that it starts at a + /// `u32`-aligned address. The simplest way to do this is to discard the + /// padding bytes and set it up so that the serialized DFA itself begins at + /// a properly aligned address. We can show this in two parts. The first + /// part is serializing the DFA to a file: + /// + /// ```no_run + /// use regex_automata::dfa::{Automaton, dense::DFA}; + /// + /// let dfa = DFA::new("foo[0-9]+")?; + /// + /// let (bytes, pad) = dfa.to_bytes_big_endian(); + /// // Write the contents of the DFA *without* the initial padding. + /// std::fs::write("foo.bigendian.dfa", &bytes[pad..])?; + /// + /// // Do it again, but this time for little endian. + /// let (bytes, pad) = dfa.to_bytes_little_endian(); + /// std::fs::write("foo.littleendian.dfa", &bytes[pad..])?; + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And now the second part is embedding the DFA into the compiled program + /// and deserializing it at runtime on first use. We use conditional + /// compilation to choose the correct endianness. + /// + /// ```no_run + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch}; + /// + /// type S = u32; + /// type DFA = dense::DFA<&'static [S]>; + /// + /// fn get_foo() -> &'static DFA { + /// use std::cell::Cell; + /// use std::mem::MaybeUninit; + /// use std::sync::Once; + /// + /// // This struct with a generic B is used to permit unsizing + /// // coercions, specifically, where B winds up being a [u8]. We also + /// // need repr(C) to guarantee that _align comes first, which forces + /// // a correct alignment. + /// #[repr(C)] + /// struct Aligned<B: ?Sized> { + /// _align: [S; 0], + /// bytes: B, + /// } + /// + /// # const _: &str = stringify! { + /// // This assignment is made possible (implicitly) via the + /// // CoerceUnsized trait. + /// static ALIGNED: &Aligned<[u8]> = &Aligned { + /// _align: [], + /// #[cfg(target_endian = "big")] + /// bytes: *include_bytes!("foo.bigendian.dfa"), + /// #[cfg(target_endian = "little")] + /// bytes: *include_bytes!("foo.littleendian.dfa"), + /// }; + /// # }; + /// # static ALIGNED: &Aligned<[u8]> = &Aligned { + /// # _align: [], + /// # bytes: [], + /// # }; + /// + /// struct Lazy(Cell<MaybeUninit<DFA>>); + /// // SAFETY: This is safe because DFA impls Sync. + /// unsafe impl Sync for Lazy {} + /// + /// static INIT: Once = Once::new(); + /// static DFA: Lazy = Lazy(Cell::new(MaybeUninit::uninit())); + /// + /// INIT.call_once(|| { + /// let (dfa, _) = DFA::from_bytes(&ALIGNED.bytes) + /// .expect("serialized DFA should be valid"); + /// // SAFETY: This is guaranteed to only execute once, and all + /// // we do with the pointer is write the DFA to it. + /// unsafe { + /// (*DFA.0.as_ptr()).as_mut_ptr().write(dfa); + /// } + /// }); + /// // SAFETY: DFA is guaranteed to by initialized via INIT and is + /// // stored in static memory. + /// unsafe { + /// let dfa = (*DFA.0.as_ptr()).as_ptr(); + /// std::mem::transmute::<*const DFA, &'static DFA>(dfa) + /// } + /// } + /// + /// let dfa = get_foo(); + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Ok(Some(expected)), dfa.find_leftmost_fwd(b"foo12345")); + /// ``` + /// + /// Alternatively, consider using + /// [`lazy_static`](https://crates.io/crates/lazy_static) + /// or + /// [`once_cell`](https://crates.io/crates/once_cell), + /// which will guarantee safety for you. You will still need to use the + /// `Aligned` trick above to force correct alignment, but this is safe to + /// do and `from_bytes` will return an error if you get it wrong. + pub fn from_bytes( + slice: &'a [u8], + ) -> Result<(DFA<&'a [u32]>, usize), DeserializeError> { + // SAFETY: This is safe because we validate both the transition table, + // start state ID list and the match states below. If either validation + // fails, then we return an error. + let (dfa, nread) = unsafe { DFA::from_bytes_unchecked(slice)? }; + dfa.tt.validate()?; + dfa.st.validate(&dfa.tt)?; + dfa.ms.validate(&dfa)?; + dfa.accels.validate()?; + // N.B. dfa.special doesn't have a way to do unchecked deserialization, + // so it has already been validated. + Ok((dfa, nread)) + } + + /// Deserialize a DFA with a specific state identifier representation in + /// constant time by omitting the verification of the validity of the + /// transition table and other data inside the DFA. + /// + /// This is just like [`DFA::from_bytes`], except it can potentially return + /// a DFA that exhibits undefined behavior if its transition table contains + /// invalid state identifiers. + /// + /// This routine is useful if you need to deserialize a DFA cheaply + /// and cannot afford the transition table validation performed by + /// `from_bytes`. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// let (bytes, _) = initial.to_bytes_native_endian(); + /// // SAFETY: This is guaranteed to be safe since the bytes given come + /// // directly from a compatible serialization routine. + /// let dfa: DFA<&[u32]> = unsafe { DFA::from_bytes_unchecked(&bytes)?.0 }; + /// + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.find_leftmost_fwd(b"foo12345")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub unsafe fn from_bytes_unchecked( + slice: &'a [u8], + ) -> Result<(DFA<&'a [u32]>, usize), DeserializeError> { + let mut nr = 0; + + nr += bytes::skip_initial_padding(slice); + bytes::check_alignment::<StateID>(&slice[nr..])?; + nr += bytes::read_label(&slice[nr..], LABEL)?; + nr += bytes::read_endianness_check(&slice[nr..])?; + nr += bytes::read_version(&slice[nr..], VERSION)?; + + let _unused = bytes::try_read_u32(&slice[nr..], "unused space")?; + nr += size_of::<u32>(); + + let (tt, nread) = TransitionTable::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (st, nread) = StartTable::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (ms, nread) = MatchStates::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (special, nread) = Special::from_bytes(&slice[nr..])?; + nr += nread; + special.validate_state_count(tt.count(), tt.stride2)?; + + let (accels, nread) = Accels::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + Ok((DFA { tt, st, ms, special, accels }, nr)) + } + + /// The implementation of the public `write_to` serialization methods, + /// which is generic over endianness. + /// + /// This is defined only for &[u32] to reduce binary size/compilation time. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("dense DFA")); + } + dst = &mut dst[..nwrite]; + + let mut nw = 0; + nw += bytes::write_label(LABEL, &mut dst[nw..])?; + nw += bytes::write_endianness_check::<E>(&mut dst[nw..])?; + nw += bytes::write_version::<E>(VERSION, &mut dst[nw..])?; + nw += { + // Currently unused, intended for future flexibility + E::write_u32(0, &mut dst[nw..]); + size_of::<u32>() + }; + nw += self.tt.write_to::<E>(&mut dst[nw..])?; + nw += self.st.write_to::<E>(&mut dst[nw..])?; + nw += self.ms.write_to::<E>(&mut dst[nw..])?; + nw += self.special.write_to::<E>(&mut dst[nw..])?; + nw += self.accels.write_to::<E>(&mut dst[nw..])?; + Ok(nw) + } +} + +/// The following methods implement mutable routines on the internal +/// representation of a DFA. As such, we must fix the first type parameter to a +/// `Vec<u32>` since a generic `T: AsRef<[u32]>` does not permit mutation. We +/// can get away with this because these methods are internal to the crate and +/// are exclusively used during construction of the DFA. +#[cfg(feature = "alloc")] +impl OwnedDFA { + /// Add a start state of this DFA. + pub(crate) fn set_start_state( + &mut self, + index: Start, + pattern_id: Option<PatternID>, + id: StateID, + ) { + assert!(self.tt.is_valid(id), "invalid start state"); + self.st.set_start(index, pattern_id, id); + } + + /// Set the given transition to this DFA. Both the `from` and `to` states + /// must already exist. + pub(crate) fn set_transition( + &mut self, + from: StateID, + byte: alphabet::Unit, + to: StateID, + ) { + self.tt.set(from, byte, to); + } + + /// An an empty state (a state where all transitions lead to a dead state) + /// and return its identifier. The identifier returned is guaranteed to + /// not point to any other existing state. + /// + /// If adding a state would exceed `StateID::LIMIT`, then this returns an + /// error. + pub(crate) fn add_empty_state(&mut self) -> Result<StateID, Error> { + self.tt.add_empty_state() + } + + /// Swap the two states given in the transition table. + /// + /// This routine does not do anything to check the correctness of this + /// swap. Callers must ensure that other states pointing to id1 and id2 are + /// updated appropriately. + pub(crate) fn swap_states(&mut self, id1: StateID, id2: StateID) { + self.tt.swap(id1, id2); + } + + /// Truncate the states in this DFA to the given count. + /// + /// This routine does not do anything to check the correctness of this + /// truncation. Callers must ensure that other states pointing to truncated + /// states are updated appropriately. + pub(crate) fn truncate_states(&mut self, count: usize) { + self.tt.truncate(count); + } + + /// Return a mutable representation of the state corresponding to the given + /// id. This is useful for implementing routines that manipulate DFA states + /// (e.g., swapping states). + pub(crate) fn state_mut(&mut self, id: StateID) -> StateMut<'_> { + self.tt.state_mut(id) + } + + /// Minimize this DFA in place using Hopcroft's algorithm. + pub(crate) fn minimize(&mut self) { + Minimizer::new(self).run(); + } + + /// Updates the match state pattern ID map to use the one provided. + /// + /// This is useful when it's convenient to manipulate matching states + /// (and their corresponding pattern IDs) as a map. In particular, the + /// representation used by a DFA for this map is not amenable to mutation, + /// so if things need to be changed (like when shuffling states), it's + /// often easier to work with the map form. + pub(crate) fn set_pattern_map( + &mut self, + map: &BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<(), Error> { + self.ms = self.ms.new_with_map(map)?; + Ok(()) + } + + /// Find states that have a small number of non-loop transitions and mark + /// them as candidates for acceleration during search. + pub(crate) fn accelerate(&mut self) { + // dead and quit states can never be accelerated. + if self.state_count() <= 2 { + return; + } + + // Go through every state and record their accelerator, if possible. + let mut accels = BTreeMap::new(); + // Count the number of accelerated match, start and non-match/start + // states. + let (mut cmatch, mut cstart, mut cnormal) = (0, 0, 0); + for state in self.states() { + if let Some(accel) = state.accelerate(self.byte_classes()) { + accels.insert(state.id(), accel); + if self.is_match_state(state.id()) { + cmatch += 1; + } else if self.is_start_state(state.id()) { + cstart += 1; + } else { + assert!(!self.is_dead_state(state.id())); + assert!(!self.is_quit_state(state.id())); + cnormal += 1; + } + } + } + // If no states were able to be accelerated, then we're done. + if accels.is_empty() { + return; + } + let original_accels_len = accels.len(); + + // A remapper keeps track of state ID changes. Once we're done + // shuffling, the remapper is used to rewrite all transitions in the + // DFA based on the new positions of states. + let mut remapper = Remapper::from_dfa(self); + + // As we swap states, if they are match states, we need to swap their + // pattern ID lists too (for multi-regexes). We do this by converting + // the lists to an easily swappable map, and then convert back to + // MatchStates once we're done. + let mut new_matches = self.ms.to_map(self); + + // There is at least one state that gets accelerated, so these are + // guaranteed to get set to sensible values below. + self.special.min_accel = StateID::MAX; + self.special.max_accel = StateID::ZERO; + let update_special_accel = + |special: &mut Special, accel_id: StateID| { + special.min_accel = cmp::min(special.min_accel, accel_id); + special.max_accel = cmp::max(special.max_accel, accel_id); + }; + + // Start by shuffling match states. Any match states that are + // accelerated get moved to the end of the match state range. + if cmatch > 0 && self.special.matches() { + // N.B. special.{min,max}_match do not need updating, since the + // range/number of match states does not change. Only the ordering + // of match states may change. + let mut next_id = self.special.max_match; + let mut cur_id = next_id; + while cur_id >= self.special.min_match { + if let Some(accel) = accels.remove(&cur_id) { + accels.insert(next_id, accel); + update_special_accel(&mut self.special, next_id); + + // No need to do any actual swapping for equivalent IDs. + if cur_id != next_id { + remapper.swap(self, cur_id, next_id); + + // Swap pattern IDs for match states. + let cur_pids = new_matches.remove(&cur_id).unwrap(); + let next_pids = new_matches.remove(&next_id).unwrap(); + new_matches.insert(cur_id, next_pids); + new_matches.insert(next_id, cur_pids); + } + next_id = self.tt.prev_state_id(next_id); + } + cur_id = self.tt.prev_state_id(cur_id); + } + } + + // This is where it gets tricky. Without acceleration, start states + // normally come right after match states. But we want accelerated + // states to be a single contiguous range (to make it very fast + // to determine whether a state *is* accelerated), while also keeping + // match and starting states as contiguous ranges for the same reason. + // So what we do here is shuffle states such that it looks like this: + // + // DQMMMMAAAAASSSSSSNNNNNNN + // | | + // |---------| + // accelerated states + // + // Where: + // D - dead state + // Q - quit state + // M - match state (may be accelerated) + // A - normal state that is accelerated + // S - start state (may be accelerated) + // N - normal state that is NOT accelerated + // + // We implement this by shuffling states, which is done by a sequence + // of pairwise swaps. We start by looking at all normal states to be + // accelerated. When we find one, we swap it with the earliest starting + // state, and then swap that with the earliest normal state. This + // preserves the contiguous property. + // + // Once we're done looking for accelerated normal states, now we look + // for accelerated starting states by moving them to the beginning + // of the starting state range (just like we moved accelerated match + // states to the end of the matching state range). + // + // For a more detailed/different perspective on this, see the docs + // in dfa/special.rs. + if cnormal > 0 { + // our next available starting and normal states for swapping. + let mut next_start_id = self.special.min_start; + let mut cur_id = self.from_index(self.state_count() - 1); + // This is guaranteed to exist since cnormal > 0. + let mut next_norm_id = + self.tt.next_state_id(self.special.max_start); + while cur_id >= next_norm_id { + if let Some(accel) = accels.remove(&cur_id) { + remapper.swap(self, next_start_id, cur_id); + remapper.swap(self, next_norm_id, cur_id); + // Keep our accelerator map updated with new IDs if the + // states we swapped were also accelerated. + if let Some(accel2) = accels.remove(&next_norm_id) { + accels.insert(cur_id, accel2); + } + if let Some(accel2) = accels.remove(&next_start_id) { + accels.insert(next_norm_id, accel2); + } + accels.insert(next_start_id, accel); + update_special_accel(&mut self.special, next_start_id); + // Our start range shifts one to the right now. + self.special.min_start = + self.tt.next_state_id(self.special.min_start); + self.special.max_start = + self.tt.next_state_id(self.special.max_start); + next_start_id = self.tt.next_state_id(next_start_id); + next_norm_id = self.tt.next_state_id(next_norm_id); + } + // This is pretty tricky, but if our 'next_norm_id' state also + // happened to be accelerated, then the result is that it is + // now in the position of cur_id, so we need to consider it + // again. This loop is still guaranteed to terminate though, + // because when accels contains cur_id, we're guaranteed to + // increment next_norm_id even if cur_id remains unchanged. + if !accels.contains_key(&cur_id) { + cur_id = self.tt.prev_state_id(cur_id); + } + } + } + // Just like we did for match states, but we want to move accelerated + // start states to the beginning of the range instead of the end. + if cstart > 0 { + // N.B. special.{min,max}_start do not need updating, since the + // range/number of start states does not change at this point. Only + // the ordering of start states may change. + let mut next_id = self.special.min_start; + let mut cur_id = next_id; + while cur_id <= self.special.max_start { + if let Some(accel) = accels.remove(&cur_id) { + remapper.swap(self, cur_id, next_id); + accels.insert(next_id, accel); + update_special_accel(&mut self.special, next_id); + next_id = self.tt.next_state_id(next_id); + } + cur_id = self.tt.next_state_id(cur_id); + } + } + + // Remap all transitions in our DFA and assert some things. + remapper.remap(self); + // This unwrap is OK because acceleration never changes the number of + // match states or patterns in those match states. Since acceleration + // runs after the pattern map has been set at least once, we know that + // our match states cannot error. + self.set_pattern_map(&new_matches).unwrap(); + self.special.set_max(); + self.special.validate().expect("special state ranges should validate"); + self.special + .validate_state_count(self.state_count(), self.stride2()) + .expect( + "special state ranges should be consistent with state count", + ); + assert_eq!( + self.special.accel_len(self.stride()), + // We record the number of accelerated states initially detected + // since the accels map is itself mutated in the process above. + // If mutated incorrectly, its size may change, and thus can't be + // trusted as a source of truth of how many accelerated states we + // expected there to be. + original_accels_len, + "mismatch with expected number of accelerated states", + ); + + // And finally record our accelerators. We kept our accels map updated + // as we shuffled states above, so the accelerators should now + // correspond to a contiguous range in the state ID space. (Which we + // assert.) + let mut prev: Option<StateID> = None; + for (id, accel) in accels { + assert!(prev.map_or(true, |p| self.tt.next_state_id(p) == id)); + prev = Some(id); + self.accels.add(accel); + } + } + + /// Shuffle the states in this DFA so that starting states, match + /// states and accelerated states are all contiguous. + /// + /// See dfa/special.rs for more details. + pub(crate) fn shuffle( + &mut self, + mut matches: BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<(), Error> { + // The determinizer always adds a quit state and it is always second. + self.special.quit_id = self.from_index(1); + // If all we have are the dead and quit states, then we're done and + // the DFA will never produce a match. + if self.state_count() <= 2 { + self.special.set_max(); + return Ok(()); + } + + // Collect all our start states into a convenient set and confirm there + // is no overlap with match states. In the classicl DFA construction, + // start states can be match states. But because of look-around, we + // delay all matches by a byte, which prevents start states from being + // match states. + let mut is_start: BTreeSet<StateID> = BTreeSet::new(); + for (start_id, _, _) in self.starts() { + // While there's nothing theoretically wrong with setting a start + // state to a dead ID (indeed, it could be an optimization!), the + // shuffling code below assumes that start states aren't dead. If + // this assumption is violated, the dead state could be shuffled + // to a new location, which must never happen. So if we do want + // to allow start states to be dead, then this assert should be + // removed and the code below fixed. + // + // N.B. Minimization can cause start states to be dead, but that + // happens after states are shuffled, so it's OK. Also, start + // states are dead for the DFA that never matches anything, but + // in that case, there are no states to shuffle. + assert_ne!(start_id, DEAD, "start state cannot be dead"); + assert!( + !matches.contains_key(&start_id), + "{:?} is both a start and a match state, which is not allowed", + start_id, + ); + is_start.insert(start_id); + } + + // We implement shuffling by a sequence of pairwise swaps of states. + // Since we have a number of things referencing states via their + // IDs and swapping them changes their IDs, we need to record every + // swap we make so that we can remap IDs. The remapper handles this + // book-keeping for us. + let mut remapper = Remapper::from_dfa(self); + + // Shuffle matching states. + if matches.is_empty() { + self.special.min_match = DEAD; + self.special.max_match = DEAD; + } else { + // The determinizer guarantees that the first two states are the + // dead and quit states, respectively. We want our match states to + // come right after quit. + let mut next_id = self.from_index(2); + let mut new_matches = BTreeMap::new(); + self.special.min_match = next_id; + for (id, pids) in matches { + remapper.swap(self, next_id, id); + new_matches.insert(next_id, pids); + // If we swapped a start state, then update our set. + if is_start.contains(&next_id) { + is_start.remove(&next_id); + is_start.insert(id); + } + next_id = self.tt.next_state_id(next_id); + } + matches = new_matches; + self.special.max_match = cmp::max( + self.special.min_match, + self.tt.prev_state_id(next_id), + ); + } + + // Shuffle starting states. + { + let mut next_id = self.from_index(2); + if self.special.matches() { + next_id = self.tt.next_state_id(self.special.max_match); + } + self.special.min_start = next_id; + for id in is_start { + remapper.swap(self, next_id, id); + next_id = self.tt.next_state_id(next_id); + } + self.special.max_start = cmp::max( + self.special.min_start, + self.tt.prev_state_id(next_id), + ); + } + + // Finally remap all transitions in our DFA. + remapper.remap(self); + self.set_pattern_map(&matches)?; + self.special.set_max(); + self.special.validate().expect("special state ranges should validate"); + self.special + .validate_state_count(self.state_count(), self.stride2()) + .expect( + "special state ranges should be consistent with state count", + ); + Ok(()) + } +} + +/// A variety of generic internal methods for accessing DFA internals. +impl<T: AsRef<[u32]>> DFA<T> { + /// Return the byte classes used by this DFA. + pub(crate) fn byte_classes(&self) -> &ByteClasses { + &self.tt.classes + } + + /// Return the info about special states. + pub(crate) fn special(&self) -> &Special { + &self.special + } + + /// Return the info about special states as a mutable borrow. + #[cfg(feature = "alloc")] + pub(crate) fn special_mut(&mut self) -> &mut Special { + &mut self.special + } + + /// Returns an iterator over all states in this DFA. + /// + /// This iterator yields a tuple for each state. The first element of the + /// tuple corresponds to a state's identifier, and the second element + /// corresponds to the state itself (comprised of its transitions). + pub(crate) fn states(&self) -> StateIter<'_, T> { + self.tt.states() + } + + /// Return the total number of states in this DFA. Every DFA has at least + /// 1 state, even the empty DFA. + pub(crate) fn state_count(&self) -> usize { + self.tt.count() + } + + /// Return an iterator over all pattern IDs for the given match state. + /// + /// If the given state is not a match state, then this panics. + #[cfg(feature = "alloc")] + pub(crate) fn pattern_id_slice(&self, id: StateID) -> &[PatternID] { + assert!(self.is_match_state(id)); + self.ms.pattern_id_slice(self.match_state_index(id)) + } + + /// Return the total number of pattern IDs for the given match state. + /// + /// If the given state is not a match state, then this panics. + pub(crate) fn match_pattern_len(&self, id: StateID) -> usize { + assert!(self.is_match_state(id)); + self.ms.pattern_len(self.match_state_index(id)) + } + + /// Returns the total number of patterns matched by this DFA. + pub(crate) fn pattern_count(&self) -> usize { + self.ms.patterns + } + + /// Returns a map from match state ID to a list of pattern IDs that match + /// in that state. + #[cfg(feature = "alloc")] + pub(crate) fn pattern_map(&self) -> BTreeMap<StateID, Vec<PatternID>> { + self.ms.to_map(self) + } + + /// Returns the ID of the quit state for this DFA. + #[cfg(feature = "alloc")] + pub(crate) fn quit_id(&self) -> StateID { + self.from_index(1) + } + + /// Convert the given state identifier to the state's index. The state's + /// index corresponds to the position in which it appears in the transition + /// table. When a DFA is NOT premultiplied, then a state's identifier is + /// also its index. When a DFA is premultiplied, then a state's identifier + /// is equal to `index * alphabet_len`. This routine reverses that. + pub(crate) fn to_index(&self, id: StateID) -> usize { + self.tt.to_index(id) + } + + /// Convert an index to a state (in the range 0..self.state_count()) to an + /// actual state identifier. + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + #[cfg(feature = "alloc")] + pub(crate) fn from_index(&self, index: usize) -> StateID { + self.tt.from_index(index) + } + + /// Return the table of state IDs for this DFA's start states. + pub(crate) fn starts(&self) -> StartStateIter<'_> { + self.st.iter() + } + + /// Returns the index of the match state for the given ID. If the + /// given ID does not correspond to a match state, then this may + /// panic or produce an incorrect result. + fn match_state_index(&self, id: StateID) -> usize { + debug_assert!(self.is_match_state(id)); + // This is one of the places where we rely on the fact that match + // states are contiguous in the transition table. Namely, that the + // first match state ID always corresponds to dfa.special.min_start. + // From there, since we know the stride, we can compute the overall + // index of any match state given the match state's ID. + let min = self.special().min_match.as_usize(); + // CORRECTNESS: We're allowed to produce an incorrect result or panic, + // so both the subtraction and the unchecked StateID construction is + // OK. + self.to_index(StateID::new_unchecked(id.as_usize() - min)) + } + + /// Returns the index of the accelerator state for the given ID. If the + /// given ID does not correspond to an accelerator state, then this may + /// panic or produce an incorrect result. + fn accelerator_index(&self, id: StateID) -> usize { + let min = self.special().min_accel.as_usize(); + // CORRECTNESS: We're allowed to produce an incorrect result or panic, + // so both the subtraction and the unchecked StateID construction is + // OK. + self.to_index(StateID::new_unchecked(id.as_usize() - min)) + } + + /// Return the accelerators for this DFA. + fn accels(&self) -> Accels<&[u32]> { + self.accels.as_ref() + } + + /// Return this DFA's transition table as a slice. + fn trans(&self) -> &[StateID] { + self.tt.table() + } +} + +impl<T: AsRef<[u32]>> fmt::Debug for DFA<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + writeln!(f, "dense::DFA(")?; + for state in self.states() { + fmt_state_indicator(f, self, state.id())?; + let id = if f.alternate() { + state.id().as_usize() + } else { + self.to_index(state.id()) + }; + write!(f, "{:06?}: ", id)?; + state.fmt(f)?; + write!(f, "\n")?; + } + writeln!(f, "")?; + for (i, (start_id, sty, pid)) in self.starts().enumerate() { + let id = if f.alternate() { + start_id.as_usize() + } else { + self.to_index(start_id) + }; + if i % self.st.stride == 0 { + match pid { + None => writeln!(f, "START-GROUP(ALL)")?, + Some(pid) => { + writeln!(f, "START_GROUP(pattern: {:?})", pid)? + } + } + } + writeln!(f, " {:?} => {:06?}", sty, id)?; + } + if self.pattern_count() > 1 { + writeln!(f, "")?; + for i in 0..self.ms.count() { + let id = self.ms.match_state_id(self, i); + let id = if f.alternate() { + id.as_usize() + } else { + self.to_index(id) + }; + write!(f, "MATCH({:06?}): ", id)?; + for (i, &pid) in self.ms.pattern_id_slice(i).iter().enumerate() + { + if i > 0 { + write!(f, ", ")?; + } + write!(f, "{:?}", pid)?; + } + writeln!(f, "")?; + } + } + writeln!(f, "state count: {:?}", self.state_count())?; + writeln!(f, "pattern count: {:?}", self.pattern_count())?; + writeln!(f, ")")?; + Ok(()) + } +} + +unsafe impl<T: AsRef<[u32]>> Automaton for DFA<T> { + #[inline] + fn is_special_state(&self, id: StateID) -> bool { + self.special.is_special_state(id) + } + + #[inline] + fn is_dead_state(&self, id: StateID) -> bool { + self.special.is_dead_state(id) + } + + #[inline] + fn is_quit_state(&self, id: StateID) -> bool { + self.special.is_quit_state(id) + } + + #[inline] + fn is_match_state(&self, id: StateID) -> bool { + self.special.is_match_state(id) + } + + #[inline] + fn is_start_state(&self, id: StateID) -> bool { + self.special.is_start_state(id) + } + + #[inline] + fn is_accel_state(&self, id: StateID) -> bool { + self.special.is_accel_state(id) + } + + #[inline] + fn next_state(&self, current: StateID, input: u8) -> StateID { + let input = self.byte_classes().get(input); + let o = current.as_usize() + usize::from(input); + self.trans()[o] + } + + #[inline] + unsafe fn next_state_unchecked( + &self, + current: StateID, + input: u8, + ) -> StateID { + let input = self.byte_classes().get_unchecked(input); + let o = current.as_usize() + usize::from(input); + *self.trans().get_unchecked(o) + } + + #[inline] + fn next_eoi_state(&self, current: StateID) -> StateID { + let eoi = self.byte_classes().eoi().as_usize(); + let o = current.as_usize() + eoi; + self.trans()[o] + } + + #[inline] + fn pattern_count(&self) -> usize { + self.ms.patterns + } + + #[inline] + fn match_count(&self, id: StateID) -> usize { + self.match_pattern_len(id) + } + + #[inline] + fn match_pattern(&self, id: StateID, match_index: usize) -> PatternID { + // This is an optimization for the very common case of a DFA with a + // single pattern. This conditional avoids a somewhat more costly path + // that finds the pattern ID from the state machine, which requires + // a bit of slicing/pointer-chasing. This optimization tends to only + // matter when matches are frequent. + if self.ms.patterns == 1 { + return PatternID::ZERO; + } + let state_index = self.match_state_index(id); + self.ms.pattern_id(state_index, match_index) + } + + #[inline] + fn start_state_forward( + &self, + pattern_id: Option<PatternID>, + bytes: &[u8], + start: usize, + end: usize, + ) -> StateID { + let index = Start::from_position_fwd(bytes, start, end); + self.st.start(index, pattern_id) + } + + #[inline] + fn start_state_reverse( + &self, + pattern_id: Option<PatternID>, + bytes: &[u8], + start: usize, + end: usize, + ) -> StateID { + let index = Start::from_position_rev(bytes, start, end); + self.st.start(index, pattern_id) + } + + #[inline(always)] + fn accelerator(&self, id: StateID) -> &[u8] { + if !self.is_accel_state(id) { + return &[]; + } + self.accels.needles(self.accelerator_index(id)) + } +} + +/// The transition table portion of a dense DFA. +/// +/// The transition table is the core part of the DFA in that it describes how +/// to move from one state to another based on the input sequence observed. +#[derive(Clone)] +pub(crate) struct TransitionTable<T> { + /// A contiguous region of memory representing the transition table in + /// row-major order. The representation is dense. That is, every state + /// has precisely the same number of transitions. The maximum number of + /// transitions per state is 257 (256 for each possible byte value, plus 1 + /// for the special EOI transition). If a DFA has been instructed to use + /// byte classes (the default), then the number of transitions is usually + /// substantially fewer. + /// + /// In practice, T is either `Vec<u32>` or `&[u32]`. + table: T, + /// A set of equivalence classes, where a single equivalence class + /// represents a set of bytes that never discriminate between a match + /// and a non-match in the DFA. Each equivalence class corresponds to a + /// single character in this DFA's alphabet, where the maximum number of + /// characters is 257 (each possible value of a byte plus the special + /// EOI transition). Consequently, the number of equivalence classes + /// corresponds to the number of transitions for each DFA state. Note + /// though that the *space* used by each DFA state in the transition table + /// may be larger. The total space used by each DFA state is known as the + /// stride. + /// + /// The only time the number of equivalence classes is fewer than 257 is if + /// the DFA's kind uses byte classes (which is the default). Equivalence + /// classes should generally only be disabled when debugging, so that + /// the transitions themselves aren't obscured. Disabling them has no + /// other benefit, since the equivalence class map is always used while + /// searching. In the vast majority of cases, the number of equivalence + /// classes is substantially smaller than 257, particularly when large + /// Unicode classes aren't used. + classes: ByteClasses, + /// The stride of each DFA state, expressed as a power-of-two exponent. + /// + /// The stride of a DFA corresponds to the total amount of space used by + /// each DFA state in the transition table. This may be bigger than the + /// size of a DFA's alphabet, since the stride is always the smallest + /// power of two greater than or equal to the alphabet size. + /// + /// While this wastes space, this avoids the need for integer division + /// to convert between premultiplied state IDs and their corresponding + /// indices. Instead, we can use simple bit-shifts. + /// + /// See the docs for the `stride2` method for more details. + /// + /// The minimum `stride2` value is `1` (corresponding to a stride of `2`) + /// while the maximum `stride2` value is `9` (corresponding to a stride of + /// `512`). The maximum is not `8` since the maximum alphabet size is `257` + /// when accounting for the special EOI transition. However, an alphabet + /// length of that size is exceptionally rare since the alphabet is shrunk + /// into equivalence classes. + stride2: usize, +} + +impl<'a> TransitionTable<&'a [u32]> { + /// Deserialize a transition table starting at the beginning of `slice`. + /// Upon success, return the total number of bytes read along with the + /// transition table. + /// + /// If there was a problem deserializing any part of the transition table, + /// then this returns an error. Notably, if the given slice does not have + /// the same alignment as `StateID`, then this will return an error (among + /// other possible errors). + /// + /// This is guaranteed to execute in constant time. + /// + /// # Safety + /// + /// This routine is not safe because it does not check the valdity of the + /// transition table itself. In particular, the transition table can be + /// quite large, so checking its validity can be somewhat expensive. An + /// invalid transition table is not safe because other code may rely on the + /// transition table being correct (such as explicit bounds check elision). + /// Therefore, an invalid transition table can lead to undefined behavior. + /// + /// Callers that use this function must either pass on the safety invariant + /// or guarantee that the bytes given contain a valid transition table. + /// This guarantee is upheld by the bytes written by `write_to`. + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(TransitionTable<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr() as usize; + + let (count, nr) = bytes::try_read_u32_as_usize(slice, "state count")?; + slice = &slice[nr..]; + + let (stride2, nr) = bytes::try_read_u32_as_usize(slice, "stride2")?; + slice = &slice[nr..]; + + let (classes, nr) = ByteClasses::from_bytes(slice)?; + slice = &slice[nr..]; + + // The alphabet length (determined by the byte class map) cannot be + // bigger than the stride (total space used by each DFA state). + if stride2 > 9 { + return Err(DeserializeError::generic( + "dense DFA has invalid stride2 (too big)", + )); + } + // It also cannot be zero, since even a DFA that never matches anything + // has a non-zero number of states with at least two equivalence + // classes: one for all 256 byte values and another for the EOI + // sentinel. + if stride2 < 1 { + return Err(DeserializeError::generic( + "dense DFA has invalid stride2 (too small)", + )); + } + // This is OK since 1 <= stride2 <= 9. + let stride = + 1usize.checked_shl(u32::try_from(stride2).unwrap()).unwrap(); + if classes.alphabet_len() > stride { + return Err(DeserializeError::generic( + "alphabet size cannot be bigger than transition table stride", + )); + } + + let trans_count = + bytes::shl(count, stride2, "dense table transition count")?; + let table_bytes_len = bytes::mul( + trans_count, + StateID::SIZE, + "dense table state byte count", + )?; + bytes::check_slice_len(slice, table_bytes_len, "transition table")?; + bytes::check_alignment::<StateID>(slice)?; + let table_bytes = &slice[..table_bytes_len]; + slice = &slice[table_bytes_len..]; + // SAFETY: Since StateID is always representable as a u32, all we need + // to do is ensure that we have the proper length and alignment. We've + // checked both above, so the cast below is safe. + // + // N.B. This is the only not-safe code in this function, so we mark + // it explicitly to call it out, even though it is technically + // superfluous. + #[allow(unused_unsafe)] + let table = unsafe { + core::slice::from_raw_parts( + table_bytes.as_ptr() as *const u32, + trans_count, + ) + }; + let tt = TransitionTable { table, classes, stride2 }; + Ok((tt, slice.as_ptr() as usize - slice_start)) + } +} + +#[cfg(feature = "alloc")] +impl TransitionTable<Vec<u32>> { + /// Create a minimal transition table with just two states: a dead state + /// and a quit state. The alphabet length and stride of the transition + /// table is determined by the given set of equivalence classes. + fn minimal(classes: ByteClasses) -> TransitionTable<Vec<u32>> { + let mut tt = TransitionTable { + table: vec![], + classes, + stride2: classes.stride2(), + }; + // Two states, regardless of alphabet size, can always fit into u32. + tt.add_empty_state().unwrap(); // dead state + tt.add_empty_state().unwrap(); // quit state + tt + } + + /// Set a transition in this table. Both the `from` and `to` states must + /// already exist, otherwise this panics. `unit` should correspond to the + /// transition out of `from` to set to `to`. + fn set(&mut self, from: StateID, unit: alphabet::Unit, to: StateID) { + assert!(self.is_valid(from), "invalid 'from' state"); + assert!(self.is_valid(to), "invalid 'to' state"); + self.table[from.as_usize() + self.classes.get_by_unit(unit)] = + to.as_u32(); + } + + /// Add an empty state (a state where all transitions lead to a dead state) + /// and return its identifier. The identifier returned is guaranteed to + /// not point to any other existing state. + /// + /// If adding a state would exhaust the state identifier space, then this + /// returns an error. + fn add_empty_state(&mut self) -> Result<StateID, Error> { + // Normally, to get a fresh state identifier, we would just + // take the index of the next state added to the transition + // table. However, we actually perform an optimization here + // that premultiplies state IDs by the stride, such that they + // point immediately at the beginning of their transitions in + // the transition table. This avoids an extra multiplication + // instruction for state lookup at search time. + // + // Premultiplied identifiers means that instead of your matching + // loop looking something like this: + // + // state = dfa.start + // for byte in haystack: + // next = dfa.transitions[state * stride + byte] + // if dfa.is_match(next): + // return true + // return false + // + // it can instead look like this: + // + // state = dfa.start + // for byte in haystack: + // next = dfa.transitions[state + byte] + // if dfa.is_match(next): + // return true + // return false + // + // In other words, we save a multiplication instruction in the + // critical path. This turns out to be a decent performance win. + // The cost of using premultiplied state ids is that they can + // require a bigger state id representation. (And they also make + // the code a bit more complex, especially during minimization and + // when reshuffling states, as one needs to convert back and forth + // between state IDs and state indices.) + // + // To do this, we simply take the index of the state into the + // entire transition table, rather than the index of the state + // itself. e.g., If the stride is 64, then the ID of the 3rd state + // is 192, not 2. + let next = self.table.len(); + let id = StateID::new(next).map_err(|_| Error::too_many_states())?; + self.table.extend(iter::repeat(0).take(self.stride())); + Ok(id) + } + + /// Swap the two states given in this transition table. + /// + /// This routine does not do anything to check the correctness of this + /// swap. Callers must ensure that other states pointing to id1 and id2 are + /// updated appropriately. + /// + /// Both id1 and id2 must point to valid states, otherwise this panics. + fn swap(&mut self, id1: StateID, id2: StateID) { + assert!(self.is_valid(id1), "invalid 'id1' state: {:?}", id1); + assert!(self.is_valid(id2), "invalid 'id2' state: {:?}", id2); + // We only need to swap the parts of the state that are used. So if the + // stride is 64, but the alphabet length is only 33, then we save a lot + // of work. + for b in 0..self.classes.alphabet_len() { + self.table.swap(id1.as_usize() + b, id2.as_usize() + b); + } + } + + /// Truncate the states in this transition table to the given count. + /// + /// This routine does not do anything to check the correctness of this + /// truncation. Callers must ensure that other states pointing to truncated + /// states are updated appropriately. + fn truncate(&mut self, count: usize) { + self.table.truncate(count << self.stride2); + } + + /// Return a mutable representation of the state corresponding to the given + /// id. This is useful for implementing routines that manipulate DFA states + /// (e.g., swapping states). + fn state_mut(&mut self, id: StateID) -> StateMut<'_> { + let alphabet_len = self.alphabet_len(); + let i = id.as_usize(); + StateMut { + id, + stride2: self.stride2, + transitions: &mut self.table_mut()[i..i + alphabet_len], + } + } +} + +impl<T: AsRef<[u32]>> TransitionTable<T> { + /// Writes a serialized form of this transition table to the buffer given. + /// If the buffer is too small, then an error is returned. To determine + /// how big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("transition table")); + } + dst = &mut dst[..nwrite]; + + // write state count + // Unwrap is OK since number of states is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.count()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write state stride (as power of 2) + // Unwrap is OK since stride2 is guaranteed to be <= 9. + E::write_u32(u32::try_from(self.stride2).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write byte class map + let n = self.classes.write_to(dst)?; + dst = &mut dst[n..]; + + // write actual transitions + for &sid in self.table() { + let n = bytes::write_state_id::<E>(sid, &mut dst); + dst = &mut dst[n..]; + } + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of this transition + /// table will use. + fn write_to_len(&self) -> usize { + size_of::<u32>() // state count + + size_of::<u32>() // stride2 + + self.classes.write_to_len() + + (self.table().len() * StateID::SIZE) + } + + /// Validates that every state ID in this transition table is valid. + /// + /// That is, every state ID can be used to correctly index a state in this + /// table. + fn validate(&self) -> Result<(), DeserializeError> { + for state in self.states() { + for (_, to) in state.transitions() { + if !self.is_valid(to) { + return Err(DeserializeError::generic( + "found invalid state ID in transition table", + )); + } + } + } + Ok(()) + } + + /// Converts this transition table to a borrowed value. + fn as_ref(&self) -> TransitionTable<&'_ [u32]> { + TransitionTable { + table: self.table.as_ref(), + classes: self.classes.clone(), + stride2: self.stride2, + } + } + + /// Converts this transition table to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> TransitionTable<Vec<u32>> { + TransitionTable { + table: self.table.as_ref().to_vec(), + classes: self.classes.clone(), + stride2: self.stride2, + } + } + + /// Return the state for the given ID. If the given ID is not valid, then + /// this panics. + fn state(&self, id: StateID) -> State<'_> { + assert!(self.is_valid(id)); + + let i = id.as_usize(); + State { + id, + stride2: self.stride2, + transitions: &self.table()[i..i + self.alphabet_len()], + } + } + + /// Returns an iterator over all states in this transition table. + /// + /// This iterator yields a tuple for each state. The first element of the + /// tuple corresponds to a state's identifier, and the second element + /// corresponds to the state itself (comprised of its transitions). + fn states(&self) -> StateIter<'_, T> { + StateIter { + tt: self, + it: self.table().chunks(self.stride()).enumerate(), + } + } + + /// Convert a state identifier to an index to a state (in the range + /// 0..self.count()). + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + /// + /// If the given ID is not valid, then this may panic or produce an + /// incorrect index. + fn to_index(&self, id: StateID) -> usize { + id.as_usize() >> self.stride2 + } + + /// Convert an index to a state (in the range 0..self.count()) to an actual + /// state identifier. + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + /// + /// If the given index is not in the specified range, then this may panic + /// or produce an incorrect state ID. + fn from_index(&self, index: usize) -> StateID { + // CORRECTNESS: If the given index is not valid, then it is not + // required for this to panic or return a valid state ID. + StateID::new_unchecked(index << self.stride2) + } + + /// Returns the state ID for the state immediately following the one given. + /// + /// This does not check whether the state ID returned is invalid. In fact, + /// if the state ID given is the last state in this DFA, then the state ID + /// returned is guaranteed to be invalid. + #[cfg(feature = "alloc")] + fn next_state_id(&self, id: StateID) -> StateID { + self.from_index(self.to_index(id).checked_add(1).unwrap()) + } + + /// Returns the state ID for the state immediately preceding the one given. + /// + /// If the dead ID given (which is zero), then this panics. + #[cfg(feature = "alloc")] + fn prev_state_id(&self, id: StateID) -> StateID { + self.from_index(self.to_index(id).checked_sub(1).unwrap()) + } + + /// Returns the table as a slice of state IDs. + fn table(&self) -> &[StateID] { + let integers = self.table.as_ref(); + // SAFETY: This is safe because StateID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts( + integers.as_ptr() as *const StateID, + integers.len(), + ) + } + } + + /// Returns the total number of states in this transition table. + /// + /// Note that a DFA always has at least two states: the dead and quit + /// states. In particular, the dead state always has ID 0 and is + /// correspondingly always the first state. The dead state is never a match + /// state. + fn count(&self) -> usize { + self.table().len() >> self.stride2 + } + + /// Returns the total stride for every state in this DFA. This corresponds + /// to the total number of transitions used by each state in this DFA's + /// transition table. + fn stride(&self) -> usize { + 1 << self.stride2 + } + + /// Returns the total number of elements in the alphabet for this + /// transition table. This is always less than or equal to `self.stride()`. + /// It is only equal when the alphabet length is a power of 2. Otherwise, + /// it is always strictly less. + fn alphabet_len(&self) -> usize { + self.classes.alphabet_len() + } + + /// Returns true if and only if the given state ID is valid for this + /// transition table. Validity in this context means that the given ID can + /// be used as a valid offset with `self.stride()` to index this transition + /// table. + fn is_valid(&self, id: StateID) -> bool { + let id = id.as_usize(); + id < self.table().len() && id % self.stride() == 0 + } + + /// Return the memory usage, in bytes, of this transition table. + /// + /// This does not include the size of a `TransitionTable` value itself. + fn memory_usage(&self) -> usize { + self.table().len() * StateID::SIZE + } +} + +#[cfg(feature = "alloc")] +impl<T: AsMut<[u32]>> TransitionTable<T> { + /// Returns the table as a slice of state IDs. + fn table_mut(&mut self) -> &mut [StateID] { + let integers = self.table.as_mut(); + // SAFETY: This is safe because StateID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts_mut( + integers.as_mut_ptr() as *mut StateID, + integers.len(), + ) + } + } +} + +/// The set of all possible starting states in a DFA. +/// +/// The set of starting states corresponds to the possible choices one can make +/// in terms of starting a DFA. That is, before following the first transition, +/// you first need to select the state that you start in. +/// +/// Normally, a DFA converted from an NFA that has a single starting state +/// would itself just have one starting state. However, our support for look +/// around generally requires more starting states. The correct starting state +/// is chosen based on certain properties of the position at which we begin +/// our search. +/// +/// Before listing those properties, we first must define two terms: +/// +/// * `haystack` - The bytes to execute the search. The search always starts +/// at the beginning of `haystack` and ends before or at the end of +/// `haystack`. +/// * `context` - The (possibly empty) bytes surrounding `haystack`. `haystack` +/// must be contained within `context` such that `context` is at least as big +/// as `haystack`. +/// +/// This split is crucial for dealing with look-around. For example, consider +/// the context `foobarbaz`, the haystack `bar` and the regex `^bar$`. This +/// regex should _not_ match the haystack since `bar` does not appear at the +/// beginning of the input. Similarly, the regex `\Bbar\B` should match the +/// haystack because `bar` is not surrounded by word boundaries. But a search +/// that does not take context into account would not permit `\B` to match +/// since the beginning of any string matches a word boundary. Similarly, a +/// search that does not take context into account when searching `^bar$` in +/// the haystack `bar` would produce a match when it shouldn't. +/// +/// Thus, it follows that the starting state is chosen based on the following +/// criteria, derived from the position at which the search starts in the +/// `context` (corresponding to the start of `haystack`): +/// +/// 1. If the search starts at the beginning of `context`, then the `Text` +/// start state is used. (Since `^` corresponds to +/// `hir::Anchor::StartText`.) +/// 2. If the search starts at a position immediately following a line +/// terminator, then the `Line` start state is used. (Since `(?m:^)` +/// corresponds to `hir::Anchor::StartLine`.) +/// 3. If the search starts at a position immediately following a byte +/// classified as a "word" character (`[_0-9a-zA-Z]`), then the `WordByte` +/// start state is used. (Since `(?-u:\b)` corresponds to a word boundary.) +/// 4. Otherwise, if the search starts at a position immediately following +/// a byte that is not classified as a "word" character (`[^_0-9a-zA-Z]`), +/// then the `NonWordByte` start state is used. (Since `(?-u:\B)` +/// corresponds to a not-word-boundary.) +/// +/// (N.B. Unicode word boundaries are not supported by the DFA because they +/// require multi-byte look-around and this is difficult to support in a DFA.) +/// +/// To further complicate things, we also support constructing individual +/// anchored start states for each pattern in the DFA. (Which is required to +/// implement overlapping regexes correctly, but is also generally useful.) +/// Thus, when individual start states for each pattern are enabled, then the +/// total number of start states represented is `4 + (4 * #patterns)`, where +/// the 4 comes from each of the 4 possibilities above. The first 4 represents +/// the starting states for the entire DFA, which support searching for +/// multiple patterns simultaneously (possibly unanchored). +/// +/// If individual start states are disabled, then this will only store 4 +/// start states. Typically, individual start states are only enabled when +/// constructing the reverse DFA for regex matching. But they are also useful +/// for building DFAs that can search for a specific pattern or even to support +/// both anchored and unanchored searches with the same DFA. +/// +/// Note though that while the start table always has either `4` or +/// `4 + (4 * #patterns)` starting state *ids*, the total number of states +/// might be considerably smaller. That is, many of the IDs may be duplicative. +/// (For example, if a regex doesn't have a `\b` sub-pattern, then there's no +/// reason to generate a unique starting state for handling word boundaries. +/// Similarly for start/end anchors.) +#[derive(Clone)] +pub(crate) struct StartTable<T> { + /// The initial start state IDs. + /// + /// In practice, T is either `Vec<u32>` or `&[u32]`. + /// + /// The first `stride` (currently always 4) entries always correspond to + /// the start states for the entire DFA. After that, there are + /// `stride * patterns` state IDs, where `patterns` may be zero in the + /// case of a DFA with no patterns or in the case where the DFA was built + /// without enabling starting states for each pattern. + table: T, + /// The number of starting state IDs per pattern. + stride: usize, + /// The total number of patterns for which starting states are encoded. + /// This may be zero for non-empty DFAs when the DFA was built without + /// start states for each pattern. Thus, one cannot use this field to + /// say how many patterns are in the DFA in all cases. It is specific to + /// how many patterns are represented in this start table. + patterns: usize, +} + +#[cfg(feature = "alloc")] +impl StartTable<Vec<u32>> { + /// Create a valid set of start states all pointing to the dead state. + /// + /// When the corresponding DFA is constructed with start states for each + /// pattern, then `patterns` should be the number of patterns. Otherwise, + /// it should be zero. + /// + /// If the total table size could exceed the allocatable limit, then this + /// returns an error. In practice, this is unlikely to be able to occur, + /// since it's likely that allocation would have failed long before it got + /// to this point. + fn dead(patterns: usize) -> Result<StartTable<Vec<u32>>, Error> { + assert!(patterns <= PatternID::LIMIT); + let stride = Start::count(); + let pattern_starts_len = match stride.checked_mul(patterns) { + Some(x) => x, + None => return Err(Error::too_many_start_states()), + }; + let table_len = match stride.checked_add(pattern_starts_len) { + Some(x) => x, + None => return Err(Error::too_many_start_states()), + }; + if table_len > core::isize::MAX as usize { + return Err(Error::too_many_start_states()); + } + let table = vec![DEAD.as_u32(); table_len]; + Ok(StartTable { table, stride, patterns }) + } +} + +impl<'a> StartTable<&'a [u32]> { + /// Deserialize a table of start state IDs starting at the beginning of + /// `slice`. Upon success, return the total number of bytes read along with + /// the table of starting state IDs. + /// + /// If there was a problem deserializing any part of the starting IDs, + /// then this returns an error. Notably, if the given slice does not have + /// the same alignment as `StateID`, then this will return an error (among + /// other possible errors). + /// + /// This is guaranteed to execute in constant time. + /// + /// # Safety + /// + /// This routine is not safe because it does not check the valdity of the + /// starting state IDs themselves. In particular, the number of starting + /// IDs can be of variable length, so it's possible that checking their + /// validity cannot be done in constant time. An invalid starting state + /// ID is not safe because other code may rely on the starting IDs being + /// correct (such as explicit bounds check elision). Therefore, an invalid + /// start ID can lead to undefined behavior. + /// + /// Callers that use this function must either pass on the safety invariant + /// or guarantee that the bytes given contain valid starting state IDs. + /// This guarantee is upheld by the bytes written by `write_to`. + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(StartTable<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr() as usize; + + let (stride, nr) = + bytes::try_read_u32_as_usize(slice, "start table stride")?; + slice = &slice[nr..]; + + let (patterns, nr) = + bytes::try_read_u32_as_usize(slice, "start table patterns")?; + slice = &slice[nr..]; + + if stride != Start::count() { + return Err(DeserializeError::generic( + "invalid starting table stride", + )); + } + if patterns > PatternID::LIMIT { + return Err(DeserializeError::generic( + "invalid number of patterns", + )); + } + let pattern_table_size = + bytes::mul(stride, patterns, "invalid pattern count")?; + // Our start states always start with a single stride of start states + // for the entire automaton which permit it to match any pattern. What + // follows it are an optional set of start states for each pattern. + let start_state_count = bytes::add( + stride, + pattern_table_size, + "invalid 'any' pattern starts size", + )?; + let table_bytes_len = bytes::mul( + start_state_count, + StateID::SIZE, + "pattern table bytes length", + )?; + bytes::check_slice_len(slice, table_bytes_len, "start ID table")?; + bytes::check_alignment::<StateID>(slice)?; + let table_bytes = &slice[..table_bytes_len]; + slice = &slice[table_bytes_len..]; + // SAFETY: Since StateID is always representable as a u32, all we need + // to do is ensure that we have the proper length and alignment. We've + // checked both above, so the cast below is safe. + // + // N.B. This is the only not-safe code in this function, so we mark + // it explicitly to call it out, even though it is technically + // superfluous. + #[allow(unused_unsafe)] + let table = unsafe { + core::slice::from_raw_parts( + table_bytes.as_ptr() as *const u32, + start_state_count, + ) + }; + let st = StartTable { table, stride, patterns }; + Ok((st, slice.as_ptr() as usize - slice_start)) + } +} + +impl<T: AsRef<[u32]>> StartTable<T> { + /// Writes a serialized form of this start table to the buffer given. If + /// the buffer is too small, then an error is returned. To determine how + /// big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small( + "starting table ids", + )); + } + dst = &mut dst[..nwrite]; + + // write stride + // Unwrap is OK since the stride is always 4 (currently). + E::write_u32(u32::try_from(self.stride).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + // write pattern count + // Unwrap is OK since number of patterns is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.patterns).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + // write start IDs + for &sid in self.table() { + let n = bytes::write_state_id::<E>(sid, &mut dst); + dst = &mut dst[n..]; + } + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of this start ID table + /// will use. + fn write_to_len(&self) -> usize { + size_of::<u32>() // stride + + size_of::<u32>() // # patterns + + (self.table().len() * StateID::SIZE) + } + + /// Validates that every state ID in this start table is valid by checking + /// it against the given transition table (which must be for the same DFA). + /// + /// That is, every state ID can be used to correctly index a state. + fn validate( + &self, + tt: &TransitionTable<T>, + ) -> Result<(), DeserializeError> { + for &id in self.table() { + if !tt.is_valid(id) { + return Err(DeserializeError::generic( + "found invalid starting state ID", + )); + } + } + Ok(()) + } + + /// Converts this start list to a borrowed value. + fn as_ref(&self) -> StartTable<&'_ [u32]> { + StartTable { + table: self.table.as_ref(), + stride: self.stride, + patterns: self.patterns, + } + } + + /// Converts this start list to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> StartTable<Vec<u32>> { + StartTable { + table: self.table.as_ref().to_vec(), + stride: self.stride, + patterns: self.patterns, + } + } + + /// Return the start state for the given start index and pattern ID. If the + /// pattern ID is None, then the corresponding start state for the entire + /// DFA is returned. If the pattern ID is not None, then the corresponding + /// starting state for the given pattern is returned. If this start table + /// does not have individual starting states for each pattern, then this + /// panics. + fn start(&self, index: Start, pattern_id: Option<PatternID>) -> StateID { + let start_index = index.as_usize(); + let index = match pattern_id { + None => start_index, + Some(pid) => { + let pid = pid.as_usize(); + assert!(pid < self.patterns, "invalid pattern ID {:?}", pid); + self.stride + (self.stride * pid) + start_index + } + }; + self.table()[index] + } + + /// Returns an iterator over all start state IDs in this table. + /// + /// Each item is a triple of: start state ID, the start state type and the + /// pattern ID (if any). + fn iter(&self) -> StartStateIter<'_> { + StartStateIter { st: self.as_ref(), i: 0 } + } + + /// Returns the table as a slice of state IDs. + fn table(&self) -> &[StateID] { + let integers = self.table.as_ref(); + // SAFETY: This is safe because StateID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts( + integers.as_ptr() as *const StateID, + integers.len(), + ) + } + } + + /// Return the memory usage, in bytes, of this start list. + /// + /// This does not include the size of a `StartList` value itself. + fn memory_usage(&self) -> usize { + self.table().len() * StateID::SIZE + } +} + +#[cfg(feature = "alloc")] +impl<T: AsMut<[u32]>> StartTable<T> { + /// Set the start state for the given index and pattern. + /// + /// If the pattern ID or state ID are not valid, then this will panic. + fn set_start( + &mut self, + index: Start, + pattern_id: Option<PatternID>, + id: StateID, + ) { + let start_index = index.as_usize(); + let index = match pattern_id { + None => start_index, + Some(pid) => self + .stride + .checked_mul(pid.as_usize()) + .unwrap() + .checked_add(self.stride) + .unwrap() + .checked_add(start_index) + .unwrap(), + }; + self.table_mut()[index] = id; + } + + /// Returns the table as a mutable slice of state IDs. + fn table_mut(&mut self) -> &mut [StateID] { + let integers = self.table.as_mut(); + // SAFETY: This is safe because StateID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts_mut( + integers.as_mut_ptr() as *mut StateID, + integers.len(), + ) + } + } +} + +/// An iterator over start state IDs. +/// +/// This iterator yields a triple of start state ID, the start state type +/// and the pattern ID (if any). The pattern ID is None for start states +/// corresponding to the entire DFA and non-None for start states corresponding +/// to a specific pattern. The latter only occurs when the DFA is compiled with +/// start states for each pattern. +pub(crate) struct StartStateIter<'a> { + st: StartTable<&'a [u32]>, + i: usize, +} + +impl<'a> Iterator for StartStateIter<'a> { + type Item = (StateID, Start, Option<PatternID>); + + fn next(&mut self) -> Option<(StateID, Start, Option<PatternID>)> { + let i = self.i; + let table = self.st.table(); + if i >= table.len() { + return None; + } + self.i += 1; + + // This unwrap is okay since the stride of the starting state table + // must always match the number of start state types. + let start_type = Start::from_usize(i % self.st.stride).unwrap(); + let pid = if i < self.st.stride { + None + } else { + Some( + PatternID::new((i - self.st.stride) / self.st.stride).unwrap(), + ) + }; + Some((table[i], start_type, pid)) + } +} + +/// This type represents that patterns that should be reported whenever a DFA +/// enters a match state. This structure exists to support DFAs that search for +/// matches for multiple regexes. +/// +/// This structure relies on the fact that all match states in a DFA occur +/// contiguously in the DFA's transition table. (See dfa/special.rs for a more +/// detailed breakdown of the representation.) Namely, when a match occurs, we +/// know its state ID. Since we know the start and end of the contiguous region +/// of match states, we can use that to compute the position at which the match +/// state occurs. That in turn is used as an offset into this structure. +#[derive(Clone, Debug)] +struct MatchStates<T> { + /// Slices is a flattened sequence of pairs, where each pair points to a + /// sub-slice of pattern_ids. The first element of the pair is an offset + /// into pattern_ids and the second element of the pair is the number + /// of 32-bit pattern IDs starting at that position. That is, each pair + /// corresponds to a single DFA match state and its corresponding match + /// IDs. The number of pairs always corresponds to the number of distinct + /// DFA match states. + /// + /// In practice, T is either Vec<u32> or &[u32]. + slices: T, + /// A flattened sequence of pattern IDs for each DFA match state. The only + /// way to correctly read this sequence is indirectly via `slices`. + /// + /// In practice, T is either Vec<u32> or &[u32]. + pattern_ids: T, + /// The total number of unique patterns represented by these match states. + patterns: usize, +} + +impl<'a> MatchStates<&'a [u32]> { + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(MatchStates<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr() as usize; + + // Read the total number of match states. + let (count, nr) = + bytes::try_read_u32_as_usize(slice, "match state count")?; + slice = &slice[nr..]; + + // Read the slice start/length pairs. + let pair_count = bytes::mul(2, count, "match state offset pairs")?; + let slices_bytes_len = bytes::mul( + pair_count, + PatternID::SIZE, + "match state slice offset byte length", + )?; + bytes::check_slice_len(slice, slices_bytes_len, "match state slices")?; + bytes::check_alignment::<PatternID>(slice)?; + let slices_bytes = &slice[..slices_bytes_len]; + slice = &slice[slices_bytes_len..]; + // SAFETY: Since PatternID is always representable as a u32, all we + // need to do is ensure that we have the proper length and alignment. + // We've checked both above, so the cast below is safe. + // + // N.B. This is one of the few not-safe snippets in this function, so + // we mark it explicitly to call it out, even though it is technically + // superfluous. + #[allow(unused_unsafe)] + let slices = unsafe { + core::slice::from_raw_parts( + slices_bytes.as_ptr() as *const u32, + pair_count, + ) + }; + + // Read the total number of unique pattern IDs (which is always 1 more + // than the maximum pattern ID in this automaton, since pattern IDs are + // handed out contiguously starting at 0). + let (patterns, nr) = + bytes::try_read_u32_as_usize(slice, "pattern count")?; + slice = &slice[nr..]; + + // Now read the pattern ID count. We don't need to store this + // explicitly, but we need it to know how many pattern IDs to read. + let (idcount, nr) = + bytes::try_read_u32_as_usize(slice, "pattern ID count")?; + slice = &slice[nr..]; + + // Read the actual pattern IDs. + let pattern_ids_len = + bytes::mul(idcount, PatternID::SIZE, "pattern ID byte length")?; + bytes::check_slice_len(slice, pattern_ids_len, "match pattern IDs")?; + bytes::check_alignment::<PatternID>(slice)?; + let pattern_ids_bytes = &slice[..pattern_ids_len]; + slice = &slice[pattern_ids_len..]; + // SAFETY: Since PatternID is always representable as a u32, all we + // need to do is ensure that we have the proper length and alignment. + // We've checked both above, so the cast below is safe. + // + // N.B. This is one of the few not-safe snippets in this function, so + // we mark it explicitly to call it out, even though it is technically + // superfluous. + #[allow(unused_unsafe)] + let pattern_ids = unsafe { + core::slice::from_raw_parts( + pattern_ids_bytes.as_ptr() as *const u32, + idcount, + ) + }; + + let ms = MatchStates { slices, pattern_ids, patterns }; + Ok((ms, slice.as_ptr() as usize - slice_start)) + } +} + +#[cfg(feature = "alloc")] +impl MatchStates<Vec<u32>> { + fn empty(pattern_count: usize) -> MatchStates<Vec<u32>> { + assert!(pattern_count <= PatternID::LIMIT); + MatchStates { + slices: vec![], + pattern_ids: vec![], + patterns: pattern_count, + } + } + + fn new( + matches: &BTreeMap<StateID, Vec<PatternID>>, + pattern_count: usize, + ) -> Result<MatchStates<Vec<u32>>, Error> { + let mut m = MatchStates::empty(pattern_count); + for (_, pids) in matches.iter() { + let start = PatternID::new(m.pattern_ids.len()) + .map_err(|_| Error::too_many_match_pattern_ids())?; + m.slices.push(start.as_u32()); + // This is always correct since the number of patterns in a single + // match state can never exceed maximum number of allowable + // patterns. Why? Because a pattern can only appear once in a + // particular match state, by construction. (And since our pattern + // ID limit is one less than u32::MAX, we're guaranteed that the + // length fits in a u32.) + m.slices.push(u32::try_from(pids.len()).unwrap()); + for &pid in pids { + m.pattern_ids.push(pid.as_u32()); + } + } + m.patterns = pattern_count; + Ok(m) + } + + fn new_with_map( + &self, + matches: &BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<MatchStates<Vec<u32>>, Error> { + MatchStates::new(matches, self.patterns) + } +} + +impl<T: AsRef<[u32]>> MatchStates<T> { + /// Writes a serialized form of these match states to the buffer given. If + /// the buffer is too small, then an error is returned. To determine how + /// big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("match states")); + } + dst = &mut dst[..nwrite]; + + // write state ID count + // Unwrap is OK since number of states is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.count()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write slice offset pairs + for &pid in self.slices() { + let n = bytes::write_pattern_id::<E>(pid, &mut dst); + dst = &mut dst[n..]; + } + + // write unique pattern ID count + // Unwrap is OK since number of patterns is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.patterns).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write pattern ID count + // Unwrap is OK since we check at construction (and deserialization) + // that the number of patterns is representable as a u32. + E::write_u32(u32::try_from(self.pattern_ids().len()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write pattern IDs + for &pid in self.pattern_ids() { + let n = bytes::write_pattern_id::<E>(pid, &mut dst); + dst = &mut dst[n..]; + } + + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of this transition + /// table will use. + fn write_to_len(&self) -> usize { + size_of::<u32>() // match state count + + (self.slices().len() * PatternID::SIZE) + + size_of::<u32>() // unique pattern ID count + + size_of::<u32>() // pattern ID count + + (self.pattern_ids().len() * PatternID::SIZE) + } + + /// Valides that the match state info is itself internally consistent and + /// consistent with the recorded match state region in the given DFA. + fn validate(&self, dfa: &DFA<T>) -> Result<(), DeserializeError> { + if self.count() != dfa.special.match_len(dfa.stride()) { + return Err(DeserializeError::generic( + "match state count mismatch", + )); + } + for si in 0..self.count() { + let start = self.slices()[si * 2].as_usize(); + let len = self.slices()[si * 2 + 1].as_usize(); + if start >= self.pattern_ids().len() { + return Err(DeserializeError::generic( + "invalid pattern ID start offset", + )); + } + if start + len > self.pattern_ids().len() { + return Err(DeserializeError::generic( + "invalid pattern ID length", + )); + } + for mi in 0..len { + let pid = self.pattern_id(si, mi); + if pid.as_usize() >= self.patterns { + return Err(DeserializeError::generic( + "invalid pattern ID", + )); + } + } + } + Ok(()) + } + + /// Converts these match states back into their map form. This is useful + /// when shuffling states, as the normal MatchStates representation is not + /// amenable to easy state swapping. But with this map, to swap id1 and + /// id2, all you need to do is: + /// + /// if let Some(pids) = map.remove(&id1) { + /// map.insert(id2, pids); + /// } + /// + /// Once shuffling is done, use MatchStates::new to convert back. + #[cfg(feature = "alloc")] + fn to_map(&self, dfa: &DFA<T>) -> BTreeMap<StateID, Vec<PatternID>> { + let mut map = BTreeMap::new(); + for i in 0..self.count() { + let mut pids = vec![]; + for j in 0..self.pattern_len(i) { + pids.push(self.pattern_id(i, j)); + } + map.insert(self.match_state_id(dfa, i), pids); + } + map + } + + /// Converts these match states to a borrowed value. + fn as_ref(&self) -> MatchStates<&'_ [u32]> { + MatchStates { + slices: self.slices.as_ref(), + pattern_ids: self.pattern_ids.as_ref(), + patterns: self.patterns, + } + } + + /// Converts these match states to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> MatchStates<Vec<u32>> { + MatchStates { + slices: self.slices.as_ref().to_vec(), + pattern_ids: self.pattern_ids.as_ref().to_vec(), + patterns: self.patterns, + } + } + + /// Returns the match state ID given the match state index. (Where the + /// first match state corresponds to index 0.) + /// + /// This panics if there is no match state at the given index. + fn match_state_id(&self, dfa: &DFA<T>, index: usize) -> StateID { + assert!(dfa.special.matches(), "no match states to index"); + // This is one of the places where we rely on the fact that match + // states are contiguous in the transition table. Namely, that the + // first match state ID always corresponds to dfa.special.min_start. + // From there, since we know the stride, we can compute the ID of any + // match state given its index. + let stride2 = u32::try_from(dfa.stride2()).unwrap(); + let offset = index.checked_shl(stride2).unwrap(); + let id = dfa.special.min_match.as_usize().checked_add(offset).unwrap(); + let sid = StateID::new(id).unwrap(); + assert!(dfa.is_match_state(sid)); + sid + } + + /// Returns the pattern ID at the given match index for the given match + /// state. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + /// + /// The match index is the index of the pattern ID for the given state. + /// The index must be less than `self.pattern_len(state_index)`. + fn pattern_id(&self, state_index: usize, match_index: usize) -> PatternID { + self.pattern_id_slice(state_index)[match_index] + } + + /// Returns the number of patterns in the given match state. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + fn pattern_len(&self, state_index: usize) -> usize { + self.slices()[state_index * 2 + 1].as_usize() + } + + /// Returns all of the pattern IDs for the given match state index. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + fn pattern_id_slice(&self, state_index: usize) -> &[PatternID] { + let start = self.slices()[state_index * 2].as_usize(); + let len = self.pattern_len(state_index); + &self.pattern_ids()[start..start + len] + } + + /// Returns the pattern ID offset slice of u32 as a slice of PatternID. + fn slices(&self) -> &[PatternID] { + let integers = self.slices.as_ref(); + // SAFETY: This is safe because PatternID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts( + integers.as_ptr() as *const PatternID, + integers.len(), + ) + } + } + + /// Returns the total number of match states. + fn count(&self) -> usize { + assert_eq!(0, self.slices().len() % 2); + self.slices().len() / 2 + } + + /// Returns the pattern ID slice of u32 as a slice of PatternID. + fn pattern_ids(&self) -> &[PatternID] { + let integers = self.pattern_ids.as_ref(); + // SAFETY: This is safe because PatternID is guaranteed to be + // representable as a u32. + unsafe { + core::slice::from_raw_parts( + integers.as_ptr() as *const PatternID, + integers.len(), + ) + } + } + + /// Return the memory usage, in bytes, of these match pairs. + fn memory_usage(&self) -> usize { + (self.slices().len() + self.pattern_ids().len()) * PatternID::SIZE + } +} + +/// An iterator over all states in a DFA. +/// +/// This iterator yields a tuple for each state. The first element of the +/// tuple corresponds to a state's identifier, and the second element +/// corresponds to the state itself (comprised of its transitions). +/// +/// `'a` corresponding to the lifetime of original DFA, `T` corresponds to +/// the type of the transition table itself. +pub(crate) struct StateIter<'a, T> { + tt: &'a TransitionTable<T>, + it: iter::Enumerate<slice::Chunks<'a, StateID>>, +} + +impl<'a, T: AsRef<[u32]>> Iterator for StateIter<'a, T> { + type Item = State<'a>; + + fn next(&mut self) -> Option<State<'a>> { + self.it.next().map(|(index, _)| { + let id = self.tt.from_index(index); + self.tt.state(id) + }) + } +} + +/// An immutable representation of a single DFA state. +/// +/// `'a` correspondings to the lifetime of a DFA's transition table. +pub(crate) struct State<'a> { + id: StateID, + stride2: usize, + transitions: &'a [StateID], +} + +impl<'a> State<'a> { + /// Return an iterator over all transitions in this state. This yields + /// a number of transitions equivalent to the alphabet length of the + /// corresponding DFA. + /// + /// Each transition is represented by a tuple. The first element is + /// the input byte for that transition and the second element is the + /// transitions itself. + pub(crate) fn transitions(&self) -> StateTransitionIter<'_> { + StateTransitionIter { + len: self.transitions.len(), + it: self.transitions.iter().enumerate(), + } + } + + /// Return an iterator over a sparse representation of the transitions in + /// this state. Only non-dead transitions are returned. + /// + /// The "sparse" representation in this case corresponds to a sequence of + /// triples. The first two elements of the triple comprise an inclusive + /// byte range while the last element corresponds to the transition taken + /// for all bytes in the range. + /// + /// This is somewhat more condensed than the classical sparse + /// representation (where you have an element for every non-dead + /// transition), but in practice, checking if a byte is in a range is very + /// cheap and using ranges tends to conserve quite a bit more space. + pub(crate) fn sparse_transitions(&self) -> StateSparseTransitionIter<'_> { + StateSparseTransitionIter { dense: self.transitions(), cur: None } + } + + /// Returns the identifier for this state. + pub(crate) fn id(&self) -> StateID { + self.id + } + + /// Analyzes this state to determine whether it can be accelerated. If so, + /// it returns an accelerator that contains at least one byte. + #[cfg(feature = "alloc")] + fn accelerate(&self, classes: &ByteClasses) -> Option<Accel> { + // We just try to add bytes to our accelerator. Once adding fails + // (because we've added too many bytes), then give up. + let mut accel = Accel::new(); + for (class, id) in self.transitions() { + if id == self.id() { + continue; + } + for unit in classes.elements(class) { + if let Some(byte) = unit.as_u8() { + if !accel.add(byte) { + return None; + } + } + } + } + if accel.is_empty() { + None + } else { + Some(accel) + } + } +} + +impl<'a> fmt::Debug for State<'a> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + for (i, (start, end, id)) in self.sparse_transitions().enumerate() { + let index = if f.alternate() { + id.as_usize() + } else { + id.as_usize() >> self.stride2 + }; + if i > 0 { + write!(f, ", ")?; + } + if start == end { + write!(f, "{:?} => {:?}", start, index)?; + } else { + write!(f, "{:?}-{:?} => {:?}", start, end, index)?; + } + } + Ok(()) + } +} + +/// A mutable representation of a single DFA state. +/// +/// `'a` correspondings to the lifetime of a DFA's transition table. +#[cfg(feature = "alloc")] +pub(crate) struct StateMut<'a> { + id: StateID, + stride2: usize, + transitions: &'a mut [StateID], +} + +#[cfg(feature = "alloc")] +impl<'a> StateMut<'a> { + /// Return an iterator over all transitions in this state. This yields + /// a number of transitions equivalent to the alphabet length of the + /// corresponding DFA. + /// + /// Each transition is represented by a tuple. The first element is the + /// input byte for that transition and the second element is a mutable + /// reference to the transition itself. + pub(crate) fn iter_mut(&mut self) -> StateTransitionIterMut<'_> { + StateTransitionIterMut { + len: self.transitions.len(), + it: self.transitions.iter_mut().enumerate(), + } + } +} + +#[cfg(feature = "alloc")] +impl<'a> fmt::Debug for StateMut<'a> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt( + &State { + id: self.id, + stride2: self.stride2, + transitions: self.transitions, + }, + f, + ) + } +} + +/// An iterator over all transitions in a single DFA state. This yields +/// a number of transitions equivalent to the alphabet length of the +/// corresponding DFA. +/// +/// Each transition is represented by a tuple. The first element is the input +/// byte for that transition and the second element is the transition itself. +#[derive(Debug)] +pub(crate) struct StateTransitionIter<'a> { + len: usize, + it: iter::Enumerate<slice::Iter<'a, StateID>>, +} + +impl<'a> Iterator for StateTransitionIter<'a> { + type Item = (alphabet::Unit, StateID); + + fn next(&mut self) -> Option<(alphabet::Unit, StateID)> { + self.it.next().map(|(i, &id)| { + let unit = if i + 1 == self.len { + alphabet::Unit::eoi(i) + } else { + let b = u8::try_from(i) + .expect("raw byte alphabet is never exceeded"); + alphabet::Unit::u8(b) + }; + (unit, id) + }) + } +} + +/// A mutable iterator over all transitions in a DFA state. +/// +/// Each transition is represented by a tuple. The first element is the +/// input byte for that transition and the second element is a mutable +/// reference to the transition itself. +#[cfg(feature = "alloc")] +#[derive(Debug)] +pub(crate) struct StateTransitionIterMut<'a> { + len: usize, + it: iter::Enumerate<slice::IterMut<'a, StateID>>, +} + +#[cfg(feature = "alloc")] +impl<'a> Iterator for StateTransitionIterMut<'a> { + type Item = (alphabet::Unit, &'a mut StateID); + + fn next(&mut self) -> Option<(alphabet::Unit, &'a mut StateID)> { + self.it.next().map(|(i, id)| { + let unit = if i + 1 == self.len { + alphabet::Unit::eoi(i) + } else { + let b = u8::try_from(i) + .expect("raw byte alphabet is never exceeded"); + alphabet::Unit::u8(b) + }; + (unit, id) + }) + } +} + +/// An iterator over all non-DEAD transitions in a single DFA state using a +/// sparse representation. +/// +/// Each transition is represented by a triple. The first two elements of the +/// triple comprise an inclusive byte range while the last element corresponds +/// to the transition taken for all bytes in the range. +/// +/// As a convenience, this always returns `alphabet::Unit` values of the same +/// type. That is, you'll never get a (byte, EOI) or a (EOI, byte). Only (byte, +/// byte) and (EOI, EOI) values are yielded. +#[derive(Debug)] +pub(crate) struct StateSparseTransitionIter<'a> { + dense: StateTransitionIter<'a>, + cur: Option<(alphabet::Unit, alphabet::Unit, StateID)>, +} + +impl<'a> Iterator for StateSparseTransitionIter<'a> { + type Item = (alphabet::Unit, alphabet::Unit, StateID); + + fn next(&mut self) -> Option<(alphabet::Unit, alphabet::Unit, StateID)> { + while let Some((unit, next)) = self.dense.next() { + let (prev_start, prev_end, prev_next) = match self.cur { + Some(t) => t, + None => { + self.cur = Some((unit, unit, next)); + continue; + } + }; + if prev_next == next && !unit.is_eoi() { + self.cur = Some((prev_start, unit, prev_next)); + } else { + self.cur = Some((unit, unit, next)); + if prev_next != DEAD { + return Some((prev_start, prev_end, prev_next)); + } + } + } + if let Some((start, end, next)) = self.cur.take() { + if next != DEAD { + return Some((start, end, next)); + } + } + None + } +} + +/// An iterator over pattern IDs for a single match state. +#[derive(Debug)] +pub(crate) struct PatternIDIter<'a>(slice::Iter<'a, PatternID>); + +impl<'a> Iterator for PatternIDIter<'a> { + type Item = PatternID; + + fn next(&mut self) -> Option<PatternID> { + self.0.next().copied() + } +} + +/// Remapper is an abstraction the manages the remapping of state IDs in a +/// dense DFA. This is useful when one wants to shuffle states into different +/// positions in the DFA. +/// +/// One of the key complexities this manages is the ability to correctly move +/// one state multiple times. +/// +/// Once shuffling is complete, `remap` should be called, which will rewrite +/// all pertinent transitions to updated state IDs. +#[cfg(feature = "alloc")] +#[derive(Debug)] +struct Remapper { + /// A map from the index of a state to its pre-multiplied identifier. + /// + /// When a state is swapped with another, then their corresponding + /// locations in this map are also swapped. Thus, its new position will + /// still point to its old pre-multiplied StateID. + /// + /// While there is a bit more to it, this then allows us to rewrite the + /// state IDs in a DFA's transition table in a single pass. This is done + /// by iterating over every ID in this map, then iterating over each + /// transition for the state at that ID and re-mapping the transition from + /// `old_id` to `map[dfa.to_index(old_id)]`. That is, we find the position + /// in this map where `old_id` *started*, and set it to where it ended up + /// after all swaps have been completed. + map: Vec<StateID>, +} + +#[cfg(feature = "alloc")] +impl Remapper { + fn from_dfa(dfa: &OwnedDFA) -> Remapper { + Remapper { + map: (0..dfa.state_count()).map(|i| dfa.from_index(i)).collect(), + } + } + + fn swap(&mut self, dfa: &mut OwnedDFA, id1: StateID, id2: StateID) { + dfa.swap_states(id1, id2); + self.map.swap(dfa.to_index(id1), dfa.to_index(id2)); + } + + fn remap(mut self, dfa: &mut OwnedDFA) { + // Update the map to account for states that have been swapped + // multiple times. For example, if (A, C) and (C, G) are swapped, then + // transitions previously pointing to A should now point to G. But if + // we don't update our map, they will erroneously be set to C. All we + // do is follow the swaps in our map until we see our original state + // ID. + let oldmap = self.map.clone(); + for i in 0..dfa.state_count() { + let cur_id = dfa.from_index(i); + let mut new = oldmap[i]; + if cur_id == new { + continue; + } + loop { + let id = oldmap[dfa.to_index(new)]; + if cur_id == id { + self.map[i] = new; + break; + } + new = id; + } + } + + // To work around the borrow checker for converting state IDs to + // indices. We cannot borrow self while mutably iterating over a + // state's transitions. Otherwise, we'd just use dfa.to_index(..). + let stride2 = dfa.stride2(); + let to_index = |id: StateID| -> usize { id.as_usize() >> stride2 }; + + // Now that we've finished shuffling, we need to remap all of our + // transitions. We don't need to handle re-mapping accelerated states + // since `accels` is only populated after shuffling. + for &id in self.map.iter() { + for (_, next_id) in dfa.state_mut(id).iter_mut() { + *next_id = self.map[to_index(*next_id)]; + } + } + for start_id in dfa.st.table_mut().iter_mut() { + *start_id = self.map[to_index(*start_id)]; + } + } +} + +#[cfg(all(test, feature = "alloc"))] +mod tests { + use super::*; + + #[test] + fn errors_with_unicode_word_boundary() { + let pattern = r"\b"; + assert!(Builder::new().build(pattern).is_err()); + } + + #[test] + fn roundtrip_never_match() { + let dfa = DFA::never_match().unwrap(); + let (buf, _) = dfa.to_bytes_native_endian(); + let dfa: DFA<&[u32]> = DFA::from_bytes(&buf).unwrap().0; + + assert_eq!(None, dfa.find_leftmost_fwd(b"foo12345").unwrap()); + } + + #[test] + fn roundtrip_always_match() { + use crate::HalfMatch; + + let dfa = DFA::always_match().unwrap(); + let (buf, _) = dfa.to_bytes_native_endian(); + let dfa: DFA<&[u32]> = DFA::from_bytes(&buf).unwrap().0; + + assert_eq!( + Some(HalfMatch::must(0, 0)), + dfa.find_leftmost_fwd(b"foo12345").unwrap() + ); + } +} |