Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 1 | /*! |
| 2 | The DFA matching engine. |
| 3 | |
| 4 | A DFA provides faster matching because the engine is in exactly one state at |
| 5 | any point in time. In the NFA, there may be multiple active states, and |
| 6 | considerable CPU cycles are spent shuffling them around. In finite automata |
| 7 | speak, the DFA follows epsilon transitions in the regex far less than the NFA. |
| 8 | |
| 9 | A DFA is a classic trade off between time and space. The NFA is slower, but |
| 10 | its memory requirements are typically small and predictable. The DFA is faster, |
| 11 | but given the right regex and the right input, the number of states in the |
| 12 | DFA can grow exponentially. To mitigate this space problem, we do two things: |
| 13 | |
| 14 | 1. We implement an *online* DFA. That is, the DFA is constructed from the NFA |
| 15 | during a search. When a new state is computed, it is stored in a cache so |
| 16 | that it may be reused. An important consequence of this implementation |
| 17 | is that states that are never reached for a particular input are never |
| 18 | computed. (This is impossible in an "offline" DFA which needs to compute |
| 19 | all possible states up front.) |
| 20 | 2. If the cache gets too big, we wipe it and continue matching. |
| 21 | |
| 22 | In pathological cases, a new state can be created for every byte of input. |
| 23 | (e.g., The regex `(a|b)*a(a|b){20}` on a long sequence of a's and b's.) |
| 24 | In this case, performance regresses to slightly slower than the full NFA |
| 25 | simulation, in large part because the cache becomes useless. If the cache |
| 26 | is wiped too frequently, the DFA quits and control falls back to one of the |
| 27 | NFA simulations. |
| 28 | |
| 29 | Because of the "lazy" nature of this DFA, the inner matching loop is |
| 30 | considerably more complex than one might expect out of a DFA. A number of |
| 31 | tricks are employed to make it fast. Tread carefully. |
| 32 | |
| 33 | N.B. While this implementation is heavily commented, Russ Cox's series of |
| 34 | articles on regexes is strongly recommended: https://swtch.com/~rsc/regexp/ |
| 35 | (As is the DFA implementation in RE2, which heavily influenced this |
| 36 | implementation.) |
| 37 | */ |
| 38 | |
| 39 | use std::collections::HashMap; |
| 40 | use std::fmt; |
| 41 | use std::iter::repeat; |
| 42 | use std::mem; |
| 43 | use std::sync::Arc; |
| 44 | |
| 45 | use exec::ProgramCache; |
| 46 | use prog::{Inst, Program}; |
| 47 | use sparse::SparseSet; |
| 48 | |
| 49 | /// Return true if and only if the given program can be executed by a DFA. |
| 50 | /// |
| 51 | /// Generally, a DFA is always possible. A pathological case where it is not |
| 52 | /// possible is if the number of NFA states exceeds `u32::MAX`, in which case, |
| 53 | /// this function will return false. |
| 54 | /// |
| 55 | /// This function will also return false if the given program has any Unicode |
| 56 | /// instructions (Char or Ranges) since the DFA operates on bytes only. |
| 57 | pub fn can_exec(insts: &Program) -> bool { |
| 58 | use prog::Inst::*; |
| 59 | // If for some reason we manage to allocate a regex program with more |
| 60 | // than i32::MAX instructions, then we can't execute the DFA because we |
| 61 | // use 32 bit instruction pointer deltas for memory savings. |
| 62 | // If i32::MAX is the largest positive delta, |
| 63 | // then -i32::MAX == i32::MIN + 1 is the largest negative delta, |
| 64 | // and we are OK to use 32 bits. |
| 65 | if insts.dfa_size_limit == 0 || insts.len() > ::std::i32::MAX as usize { |
| 66 | return false; |
| 67 | } |
| 68 | for inst in insts { |
| 69 | match *inst { |
| 70 | Char(_) | Ranges(_) => return false, |
| 71 | EmptyLook(_) | Match(_) | Save(_) | Split(_) | Bytes(_) => {} |
| 72 | } |
| 73 | } |
| 74 | true |
| 75 | } |
| 76 | |
| 77 | /// A reusable cache of DFA states. |
| 78 | /// |
| 79 | /// This cache is reused between multiple invocations of the same regex |
| 80 | /// program. (It is not shared simultaneously between threads. If there is |
| 81 | /// contention, then new caches are created.) |
| 82 | #[derive(Debug)] |
| 83 | pub struct Cache { |
| 84 | /// Group persistent DFA related cache state together. The sparse sets |
| 85 | /// listed below are used as scratch space while computing uncached states. |
| 86 | inner: CacheInner, |
| 87 | /// qcur and qnext are ordered sets with constant time |
| 88 | /// addition/membership/clearing-whole-set and linear time iteration. They |
| 89 | /// are used to manage the sets of NFA states in DFA states when computing |
| 90 | /// cached DFA states. In particular, the order of the NFA states matters |
| 91 | /// for leftmost-first style matching. Namely, when computing a cached |
| 92 | /// state, the set of NFA states stops growing as soon as the first Match |
| 93 | /// instruction is observed. |
| 94 | qcur: SparseSet, |
| 95 | qnext: SparseSet, |
| 96 | } |
| 97 | |
| 98 | /// `CacheInner` is logically just a part of Cache, but groups together fields |
| 99 | /// that aren't passed as function parameters throughout search. (This split |
| 100 | /// is mostly an artifact of the borrow checker. It is happily paid.) |
| 101 | #[derive(Debug)] |
| 102 | struct CacheInner { |
| 103 | /// A cache of pre-compiled DFA states, keyed by the set of NFA states |
| 104 | /// and the set of empty-width flags set at the byte in the input when the |
| 105 | /// state was observed. |
| 106 | /// |
| 107 | /// A StatePtr is effectively a `*State`, but to avoid various inconvenient |
| 108 | /// things, we just pass indexes around manually. The performance impact of |
| 109 | /// this is probably an instruction or two in the inner loop. However, on |
| 110 | /// 64 bit, each StatePtr is half the size of a *State. |
| 111 | compiled: StateMap, |
| 112 | /// The transition table. |
| 113 | /// |
| 114 | /// The transition table is laid out in row-major order, where states are |
| 115 | /// rows and the transitions for each state are columns. At a high level, |
| 116 | /// given state `s` and byte `b`, the next state can be found at index |
| 117 | /// `s * 256 + b`. |
| 118 | /// |
| 119 | /// This is, of course, a lie. A StatePtr is actually a pointer to the |
| 120 | /// *start* of a row in this table. When indexing in the DFA's inner loop, |
| 121 | /// this removes the need to multiply the StatePtr by the stride. Yes, it |
| 122 | /// matters. This reduces the number of states we can store, but: the |
| 123 | /// stride is rarely 256 since we define transitions in terms of |
| 124 | /// *equivalence classes* of bytes. Each class corresponds to a set of |
| 125 | /// bytes that never discriminate a distinct path through the DFA from each |
| 126 | /// other. |
| 127 | trans: Transitions, |
| 128 | /// A set of cached start states, which are limited to the number of |
| 129 | /// permutations of flags set just before the initial byte of input. (The |
| 130 | /// index into this vec is a `EmptyFlags`.) |
| 131 | /// |
| 132 | /// N.B. A start state can be "dead" (i.e., no possible match), so we |
| 133 | /// represent it with a StatePtr. |
| 134 | start_states: Vec<StatePtr>, |
| 135 | /// Stack scratch space used to follow epsilon transitions in the NFA. |
| 136 | /// (This permits us to avoid recursion.) |
| 137 | /// |
| 138 | /// The maximum stack size is the number of NFA states. |
| 139 | stack: Vec<InstPtr>, |
| 140 | /// The total number of times this cache has been flushed by the DFA |
| 141 | /// because of space constraints. |
| 142 | flush_count: u64, |
| 143 | /// The total heap size of the DFA's cache. We use this to determine when |
| 144 | /// we should flush the cache. |
| 145 | size: usize, |
| 146 | /// Scratch space used when building instruction pointer lists for new |
| 147 | /// states. This helps amortize allocation. |
| 148 | insts_scratch_space: Vec<u8>, |
| 149 | } |
| 150 | |
| 151 | /// The transition table. |
| 152 | /// |
| 153 | /// It is laid out in row-major order, with states as rows and byte class |
| 154 | /// transitions as columns. |
| 155 | /// |
| 156 | /// The transition table is responsible for producing valid `StatePtrs`. A |
| 157 | /// `StatePtr` points to the start of a particular row in this table. When |
| 158 | /// indexing to find the next state this allows us to avoid a multiplication |
| 159 | /// when computing an index into the table. |
| 160 | #[derive(Clone)] |
| 161 | struct Transitions { |
| 162 | /// The table. |
| 163 | table: Vec<StatePtr>, |
| 164 | /// The stride. |
| 165 | num_byte_classes: usize, |
| 166 | } |
| 167 | |
| 168 | /// Fsm encapsulates the actual execution of the DFA. |
| 169 | #[derive(Debug)] |
| 170 | pub struct Fsm<'a> { |
| 171 | /// prog contains the NFA instruction opcodes. DFA execution uses either |
| 172 | /// the `dfa` instructions or the `dfa_reverse` instructions from |
| 173 | /// `exec::ExecReadOnly`. (It never uses `ExecReadOnly.nfa`, which may have |
| 174 | /// Unicode opcodes that cannot be executed by the DFA.) |
| 175 | prog: &'a Program, |
| 176 | /// The start state. We record it here because the pointer may change |
| 177 | /// when the cache is wiped. |
| 178 | start: StatePtr, |
| 179 | /// The current position in the input. |
| 180 | at: usize, |
| 181 | /// Should we quit after seeing the first match? e.g., When the caller |
| 182 | /// uses `is_match` or `shortest_match`. |
| 183 | quit_after_match: bool, |
| 184 | /// The last state that matched. |
| 185 | /// |
| 186 | /// When no match has occurred, this is set to STATE_UNKNOWN. |
| 187 | /// |
| 188 | /// This is only useful when matching regex sets. The last match state |
| 189 | /// is useful because it contains all of the match instructions seen, |
| 190 | /// thereby allowing us to enumerate which regexes in the set matched. |
| 191 | last_match_si: StatePtr, |
| 192 | /// The input position of the last cache flush. We use this to determine |
| 193 | /// if we're thrashing in the cache too often. If so, the DFA quits so |
| 194 | /// that we can fall back to the NFA algorithm. |
| 195 | last_cache_flush: usize, |
| 196 | /// All cached DFA information that is persisted between searches. |
| 197 | cache: &'a mut CacheInner, |
| 198 | } |
| 199 | |
| 200 | /// The result of running the DFA. |
| 201 | /// |
| 202 | /// Generally, the result is either a match or not a match, but sometimes the |
| 203 | /// DFA runs too slowly because the cache size is too small. In that case, it |
| 204 | /// gives up with the intent of falling back to the NFA algorithm. |
| 205 | /// |
| 206 | /// The DFA can also give up if it runs out of room to create new states, or if |
| 207 | /// it sees non-ASCII bytes in the presence of a Unicode word boundary. |
| 208 | #[derive(Clone, Debug)] |
| 209 | pub enum Result<T> { |
| 210 | Match(T), |
| 211 | NoMatch(usize), |
| 212 | Quit, |
| 213 | } |
| 214 | |
| 215 | impl<T> Result<T> { |
| 216 | /// Returns true if this result corresponds to a match. |
| 217 | pub fn is_match(&self) -> bool { |
| 218 | match *self { |
| 219 | Result::Match(_) => true, |
| 220 | Result::NoMatch(_) | Result::Quit => false, |
| 221 | } |
| 222 | } |
| 223 | |
| 224 | /// Maps the given function onto T and returns the result. |
| 225 | /// |
| 226 | /// If this isn't a match, then this is a no-op. |
| 227 | #[cfg(feature = "perf-literal")] |
| 228 | pub fn map<U, F: FnMut(T) -> U>(self, mut f: F) -> Result<U> { |
| 229 | match self { |
| 230 | Result::Match(t) => Result::Match(f(t)), |
| 231 | Result::NoMatch(x) => Result::NoMatch(x), |
| 232 | Result::Quit => Result::Quit, |
| 233 | } |
| 234 | } |
| 235 | |
| 236 | /// Sets the non-match position. |
| 237 | /// |
| 238 | /// If this isn't a non-match, then this is a no-op. |
| 239 | fn set_non_match(self, at: usize) -> Result<T> { |
| 240 | match self { |
| 241 | Result::NoMatch(_) => Result::NoMatch(at), |
| 242 | r => r, |
| 243 | } |
| 244 | } |
| 245 | } |
| 246 | |
| 247 | /// `State` is a DFA state. It contains an ordered set of NFA states (not |
| 248 | /// necessarily complete) and a smattering of flags. |
| 249 | /// |
| 250 | /// The flags are packed into the first byte of data. |
| 251 | /// |
| 252 | /// States don't carry their transitions. Instead, transitions are stored in |
| 253 | /// a single row-major table. |
| 254 | /// |
| 255 | /// Delta encoding is used to store the instruction pointers. |
| 256 | /// The first instruction pointer is stored directly starting |
| 257 | /// at data[1], and each following pointer is stored as an offset |
| 258 | /// to the previous one. If a delta is in the range -127..127, |
| 259 | /// it is packed into a single byte; Otherwise the byte 128 (-128 as an i8) |
| 260 | /// is coded as a flag, followed by 4 bytes encoding the delta. |
| 261 | #[derive(Clone, Eq, Hash, PartialEq)] |
| 262 | struct State { |
| 263 | data: Arc<[u8]>, |
| 264 | } |
| 265 | |
| 266 | /// `InstPtr` is a 32 bit pointer into a sequence of opcodes (i.e., it indexes |
| 267 | /// an NFA state). |
| 268 | /// |
| 269 | /// Throughout this library, this is usually set to `usize`, but we force a |
| 270 | /// `u32` here for the DFA to save on space. |
| 271 | type InstPtr = u32; |
| 272 | |
| 273 | /// Adds ip to data using delta encoding with respect to prev. |
| 274 | /// |
| 275 | /// After completion, `data` will contain `ip` and `prev` will be set to `ip`. |
| 276 | fn push_inst_ptr(data: &mut Vec<u8>, prev: &mut InstPtr, ip: InstPtr) { |
| 277 | let delta = (ip as i32) - (*prev as i32); |
| 278 | write_vari32(data, delta); |
| 279 | *prev = ip; |
| 280 | } |
| 281 | |
| 282 | struct InstPtrs<'a> { |
| 283 | base: usize, |
| 284 | data: &'a [u8], |
| 285 | } |
| 286 | |
| 287 | impl<'a> Iterator for InstPtrs<'a> { |
| 288 | type Item = usize; |
| 289 | |
| 290 | fn next(&mut self) -> Option<usize> { |
| 291 | if self.data.is_empty() { |
| 292 | return None; |
| 293 | } |
| 294 | let (delta, nread) = read_vari32(self.data); |
| 295 | let base = self.base as i32 + delta; |
| 296 | debug_assert!(base >= 0); |
| 297 | debug_assert!(nread > 0); |
| 298 | self.data = &self.data[nread..]; |
| 299 | self.base = base as usize; |
| 300 | Some(self.base) |
| 301 | } |
| 302 | } |
| 303 | |
| 304 | impl State { |
| 305 | fn flags(&self) -> StateFlags { |
| 306 | StateFlags(self.data[0]) |
| 307 | } |
| 308 | |
| 309 | fn inst_ptrs(&self) -> InstPtrs { |
| 310 | InstPtrs { base: 0, data: &self.data[1..] } |
| 311 | } |
| 312 | } |
| 313 | |
| 314 | /// `StatePtr` is a 32 bit pointer to the start of a row in the transition |
| 315 | /// table. |
| 316 | /// |
| 317 | /// It has many special values. There are two types of special values: |
| 318 | /// sentinels and flags. |
| 319 | /// |
| 320 | /// Sentinels corresponds to special states that carry some kind of |
| 321 | /// significance. There are three such states: unknown, dead and quit states. |
| 322 | /// |
| 323 | /// Unknown states are states that haven't been computed yet. They indicate |
| 324 | /// that a transition should be filled in that points to either an existing |
| 325 | /// cached state or a new state altogether. In general, an unknown state means |
| 326 | /// "follow the NFA's epsilon transitions." |
| 327 | /// |
| 328 | /// Dead states are states that can never lead to a match, no matter what |
| 329 | /// subsequent input is observed. This means that the DFA should quit |
| 330 | /// immediately and return the longest match it has found thus far. |
| 331 | /// |
| 332 | /// Quit states are states that imply the DFA is not capable of matching the |
| 333 | /// regex correctly. Currently, this is only used when a Unicode word boundary |
| 334 | /// exists in the regex *and* a non-ASCII byte is observed. |
| 335 | /// |
| 336 | /// The other type of state pointer is a state pointer with special flag bits. |
| 337 | /// There are two flags: a start flag and a match flag. The lower bits of both |
| 338 | /// kinds always contain a "valid" `StatePtr` (indicated by the `STATE_MAX` |
| 339 | /// mask). |
| 340 | /// |
| 341 | /// The start flag means that the state is a start state, and therefore may be |
| 342 | /// subject to special prefix scanning optimizations. |
| 343 | /// |
| 344 | /// The match flag means that the state is a match state, and therefore the |
| 345 | /// current position in the input (while searching) should be recorded. |
| 346 | /// |
| 347 | /// The above exists mostly in the service of making the inner loop fast. |
| 348 | /// In particular, the inner *inner* loop looks something like this: |
| 349 | /// |
| 350 | /// ```ignore |
| 351 | /// while state <= STATE_MAX and i < len(text): |
| 352 | /// state = state.next[i] |
| 353 | /// ``` |
| 354 | /// |
| 355 | /// This is nice because it lets us execute a lazy DFA as if it were an |
| 356 | /// entirely offline DFA (i.e., with very few instructions). The loop will |
| 357 | /// quit only when we need to examine a case that needs special attention. |
| 358 | type StatePtr = u32; |
| 359 | |
| 360 | /// An unknown state means that the state has not been computed yet, and that |
| 361 | /// the only way to progress is to compute it. |
| 362 | const STATE_UNKNOWN: StatePtr = 1 << 31; |
| 363 | |
| 364 | /// A dead state means that the state has been computed and it is known that |
| 365 | /// once it is entered, no future match can ever occur. |
| 366 | const STATE_DEAD: StatePtr = STATE_UNKNOWN + 1; |
| 367 | |
| 368 | /// A quit state means that the DFA came across some input that it doesn't |
| 369 | /// know how to process correctly. The DFA should quit and another matching |
| 370 | /// engine should be run in its place. |
| 371 | const STATE_QUIT: StatePtr = STATE_DEAD + 1; |
| 372 | |
| 373 | /// A start state is a state that the DFA can start in. |
| 374 | /// |
| 375 | /// Note that start states have their lower bits set to a state pointer. |
| 376 | const STATE_START: StatePtr = 1 << 30; |
| 377 | |
| 378 | /// A match state means that the regex has successfully matched. |
| 379 | /// |
| 380 | /// Note that match states have their lower bits set to a state pointer. |
| 381 | const STATE_MATCH: StatePtr = 1 << 29; |
| 382 | |
| 383 | /// The maximum state pointer. This is useful to mask out the "valid" state |
| 384 | /// pointer from a state with the "start" or "match" bits set. |
| 385 | /// |
| 386 | /// It doesn't make sense to use this with unknown, dead or quit state |
| 387 | /// pointers, since those pointers are sentinels and never have their lower |
| 388 | /// bits set to anything meaningful. |
| 389 | const STATE_MAX: StatePtr = STATE_MATCH - 1; |
| 390 | |
| 391 | /// Byte is a u8 in spirit, but a u16 in practice so that we can represent the |
| 392 | /// special EOF sentinel value. |
| 393 | #[derive(Copy, Clone, Debug)] |
| 394 | struct Byte(u16); |
| 395 | |
| 396 | /// A set of flags for zero-width assertions. |
| 397 | #[derive(Clone, Copy, Eq, Debug, Default, Hash, PartialEq)] |
| 398 | struct EmptyFlags { |
| 399 | start: bool, |
| 400 | end: bool, |
| 401 | start_line: bool, |
| 402 | end_line: bool, |
| 403 | word_boundary: bool, |
| 404 | not_word_boundary: bool, |
| 405 | } |
| 406 | |
| 407 | /// A set of flags describing various configurations of a DFA state. This is |
| 408 | /// represented by a `u8` so that it is compact. |
| 409 | #[derive(Clone, Copy, Eq, Default, Hash, PartialEq)] |
| 410 | struct StateFlags(u8); |
| 411 | |
| 412 | impl Cache { |
| 413 | /// Create new empty cache for the DFA engine. |
| 414 | pub fn new(prog: &Program) -> Self { |
| 415 | // We add 1 to account for the special EOF byte. |
| 416 | let num_byte_classes = (prog.byte_classes[255] as usize + 1) + 1; |
| 417 | let starts = vec![STATE_UNKNOWN; 256]; |
| 418 | let mut cache = Cache { |
| 419 | inner: CacheInner { |
| 420 | compiled: StateMap::new(num_byte_classes), |
| 421 | trans: Transitions::new(num_byte_classes), |
| 422 | start_states: starts, |
| 423 | stack: vec![], |
| 424 | flush_count: 0, |
| 425 | size: 0, |
| 426 | insts_scratch_space: vec![], |
| 427 | }, |
| 428 | qcur: SparseSet::new(prog.insts.len()), |
| 429 | qnext: SparseSet::new(prog.insts.len()), |
| 430 | }; |
| 431 | cache.inner.reset_size(); |
| 432 | cache |
| 433 | } |
| 434 | } |
| 435 | |
| 436 | impl CacheInner { |
| 437 | /// Resets the cache size to account for fixed costs, such as the program |
| 438 | /// and stack sizes. |
| 439 | fn reset_size(&mut self) { |
| 440 | self.size = (self.start_states.len() * mem::size_of::<StatePtr>()) |
| 441 | + (self.stack.len() * mem::size_of::<InstPtr>()); |
| 442 | } |
| 443 | } |
| 444 | |
| 445 | impl<'a> Fsm<'a> { |
| 446 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 447 | pub fn forward( |
| 448 | prog: &'a Program, |
| 449 | cache: &ProgramCache, |
| 450 | quit_after_match: bool, |
| 451 | text: &[u8], |
| 452 | at: usize, |
| 453 | ) -> Result<usize> { |
| 454 | let mut cache = cache.borrow_mut(); |
| 455 | let cache = &mut cache.dfa; |
| 456 | let mut dfa = Fsm { |
| 457 | prog: prog, |
| 458 | start: 0, // filled in below |
| 459 | at: at, |
| 460 | quit_after_match: quit_after_match, |
| 461 | last_match_si: STATE_UNKNOWN, |
| 462 | last_cache_flush: at, |
| 463 | cache: &mut cache.inner, |
| 464 | }; |
| 465 | let (empty_flags, state_flags) = dfa.start_flags(text, at); |
| 466 | dfa.start = |
| 467 | match dfa.start_state(&mut cache.qcur, empty_flags, state_flags) { |
| 468 | None => return Result::Quit, |
| 469 | Some(STATE_DEAD) => return Result::NoMatch(at), |
| 470 | Some(si) => si, |
| 471 | }; |
| 472 | debug_assert!(dfa.start != STATE_UNKNOWN); |
| 473 | dfa.exec_at(&mut cache.qcur, &mut cache.qnext, text) |
| 474 | } |
| 475 | |
| 476 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 477 | pub fn reverse( |
| 478 | prog: &'a Program, |
| 479 | cache: &ProgramCache, |
| 480 | quit_after_match: bool, |
| 481 | text: &[u8], |
| 482 | at: usize, |
| 483 | ) -> Result<usize> { |
| 484 | let mut cache = cache.borrow_mut(); |
| 485 | let cache = &mut cache.dfa_reverse; |
| 486 | let mut dfa = Fsm { |
| 487 | prog: prog, |
| 488 | start: 0, // filled in below |
| 489 | at: at, |
| 490 | quit_after_match: quit_after_match, |
| 491 | last_match_si: STATE_UNKNOWN, |
| 492 | last_cache_flush: at, |
| 493 | cache: &mut cache.inner, |
| 494 | }; |
| 495 | let (empty_flags, state_flags) = dfa.start_flags_reverse(text, at); |
| 496 | dfa.start = |
| 497 | match dfa.start_state(&mut cache.qcur, empty_flags, state_flags) { |
| 498 | None => return Result::Quit, |
| 499 | Some(STATE_DEAD) => return Result::NoMatch(at), |
| 500 | Some(si) => si, |
| 501 | }; |
| 502 | debug_assert!(dfa.start != STATE_UNKNOWN); |
| 503 | dfa.exec_at_reverse(&mut cache.qcur, &mut cache.qnext, text) |
| 504 | } |
| 505 | |
| 506 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 507 | pub fn forward_many( |
| 508 | prog: &'a Program, |
| 509 | cache: &ProgramCache, |
| 510 | matches: &mut [bool], |
| 511 | text: &[u8], |
| 512 | at: usize, |
| 513 | ) -> Result<usize> { |
| 514 | debug_assert!(matches.len() == prog.matches.len()); |
| 515 | let mut cache = cache.borrow_mut(); |
| 516 | let cache = &mut cache.dfa; |
| 517 | let mut dfa = Fsm { |
| 518 | prog: prog, |
| 519 | start: 0, // filled in below |
| 520 | at: at, |
| 521 | quit_after_match: false, |
| 522 | last_match_si: STATE_UNKNOWN, |
| 523 | last_cache_flush: at, |
| 524 | cache: &mut cache.inner, |
| 525 | }; |
| 526 | let (empty_flags, state_flags) = dfa.start_flags(text, at); |
| 527 | dfa.start = |
| 528 | match dfa.start_state(&mut cache.qcur, empty_flags, state_flags) { |
| 529 | None => return Result::Quit, |
| 530 | Some(STATE_DEAD) => return Result::NoMatch(at), |
| 531 | Some(si) => si, |
| 532 | }; |
| 533 | debug_assert!(dfa.start != STATE_UNKNOWN); |
| 534 | let result = dfa.exec_at(&mut cache.qcur, &mut cache.qnext, text); |
| 535 | if result.is_match() { |
| 536 | if matches.len() == 1 { |
| 537 | matches[0] = true; |
| 538 | } else { |
| 539 | debug_assert!(dfa.last_match_si != STATE_UNKNOWN); |
| 540 | debug_assert!(dfa.last_match_si != STATE_DEAD); |
| 541 | for ip in dfa.state(dfa.last_match_si).inst_ptrs() { |
| 542 | if let Inst::Match(slot) = dfa.prog[ip] { |
| 543 | matches[slot] = true; |
| 544 | } |
| 545 | } |
| 546 | } |
| 547 | } |
| 548 | result |
| 549 | } |
| 550 | |
| 551 | /// Executes the DFA on a forward NFA. |
| 552 | /// |
| 553 | /// {qcur,qnext} are scratch ordered sets which may be non-empty. |
| 554 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 555 | fn exec_at( |
| 556 | &mut self, |
| 557 | qcur: &mut SparseSet, |
| 558 | qnext: &mut SparseSet, |
| 559 | text: &[u8], |
| 560 | ) -> Result<usize> { |
| 561 | // For the most part, the DFA is basically: |
| 562 | // |
| 563 | // last_match = null |
| 564 | // while current_byte != EOF: |
| 565 | // si = current_state.next[current_byte] |
| 566 | // if si is match |
| 567 | // last_match = si |
| 568 | // return last_match |
| 569 | // |
| 570 | // However, we need to deal with a few things: |
| 571 | // |
| 572 | // 1. This is an *online* DFA, so the current state's next list |
| 573 | // may not point to anywhere yet, so we must go out and compute |
| 574 | // them. (They are then cached into the current state's next list |
| 575 | // to avoid re-computation.) |
| 576 | // 2. If we come across a state that is known to be dead (i.e., never |
| 577 | // leads to a match), then we can quit early. |
| 578 | // 3. If the caller just wants to know if a match occurs, then we |
| 579 | // can quit as soon as we know we have a match. (Full leftmost |
| 580 | // first semantics require continuing on.) |
| 581 | // 4. If we're in the start state, then we can use a pre-computed set |
| 582 | // of prefix literals to skip quickly along the input. |
| 583 | // 5. After the input is exhausted, we run the DFA on one symbol |
| 584 | // that stands for EOF. This is useful for handling empty width |
| 585 | // assertions. |
| 586 | // 6. We can't actually do state.next[byte]. Instead, we have to do |
| 587 | // state.next[byte_classes[byte]], which permits us to keep the |
| 588 | // 'next' list very small. |
| 589 | // |
| 590 | // Since there's a bunch of extra stuff we need to consider, we do some |
| 591 | // pretty hairy tricks to get the inner loop to run as fast as |
| 592 | // possible. |
| 593 | debug_assert!(!self.prog.is_reverse); |
| 594 | |
| 595 | // The last match is the currently known ending match position. It is |
| 596 | // reported as an index to the most recent byte that resulted in a |
| 597 | // transition to a match state and is always stored in capture slot `1` |
| 598 | // when searching forwards. Its maximum value is `text.len()`. |
| 599 | let mut result = Result::NoMatch(self.at); |
| 600 | let (mut prev_si, mut next_si) = (self.start, self.start); |
| 601 | let mut at = self.at; |
| 602 | while at < text.len() { |
| 603 | // This is the real inner loop. We take advantage of special bits |
| 604 | // set in the state pointer to determine whether a state is in the |
| 605 | // "common" case or not. Specifically, the common case is a |
| 606 | // non-match non-start non-dead state that has already been |
| 607 | // computed. So long as we remain in the common case, this inner |
| 608 | // loop will chew through the input. |
| 609 | // |
| 610 | // We also unroll the loop 4 times to amortize the cost of checking |
| 611 | // whether we've consumed the entire input. We are also careful |
| 612 | // to make sure that `prev_si` always represents the previous state |
| 613 | // and `next_si` always represents the next state after the loop |
| 614 | // exits, even if it isn't always true inside the loop. |
| 615 | while next_si <= STATE_MAX && at < text.len() { |
| 616 | // Argument for safety is in the definition of next_si. |
| 617 | prev_si = unsafe { self.next_si(next_si, text, at) }; |
| 618 | at += 1; |
| 619 | if prev_si > STATE_MAX || at + 2 >= text.len() { |
| 620 | mem::swap(&mut prev_si, &mut next_si); |
| 621 | break; |
| 622 | } |
| 623 | next_si = unsafe { self.next_si(prev_si, text, at) }; |
| 624 | at += 1; |
| 625 | if next_si > STATE_MAX { |
| 626 | break; |
| 627 | } |
| 628 | prev_si = unsafe { self.next_si(next_si, text, at) }; |
| 629 | at += 1; |
| 630 | if prev_si > STATE_MAX { |
| 631 | mem::swap(&mut prev_si, &mut next_si); |
| 632 | break; |
| 633 | } |
| 634 | next_si = unsafe { self.next_si(prev_si, text, at) }; |
| 635 | at += 1; |
| 636 | } |
| 637 | if next_si & STATE_MATCH > 0 { |
| 638 | // A match state is outside of the common case because it needs |
| 639 | // special case analysis. In particular, we need to record the |
| 640 | // last position as having matched and possibly quit the DFA if |
| 641 | // we don't need to keep matching. |
| 642 | next_si &= !STATE_MATCH; |
| 643 | result = Result::Match(at - 1); |
| 644 | if self.quit_after_match { |
| 645 | return result; |
| 646 | } |
| 647 | self.last_match_si = next_si; |
| 648 | prev_si = next_si; |
| 649 | |
| 650 | // This permits short-circuiting when matching a regex set. |
| 651 | // In particular, if this DFA state contains only match states, |
| 652 | // then it's impossible to extend the set of matches since |
| 653 | // match states are final. Therefore, we can quit. |
| 654 | if self.prog.matches.len() > 1 { |
| 655 | let state = self.state(next_si); |
| 656 | let just_matches = |
| 657 | state.inst_ptrs().all(|ip| self.prog[ip].is_match()); |
| 658 | if just_matches { |
| 659 | return result; |
| 660 | } |
| 661 | } |
| 662 | |
| 663 | // Another inner loop! If the DFA stays in this particular |
| 664 | // match state, then we can rip through all of the input |
| 665 | // very quickly, and only recording the match location once |
| 666 | // we've left this particular state. |
| 667 | let cur = at; |
| 668 | while (next_si & !STATE_MATCH) == prev_si |
| 669 | && at + 2 < text.len() |
| 670 | { |
| 671 | // Argument for safety is in the definition of next_si. |
| 672 | next_si = unsafe { |
| 673 | self.next_si(next_si & !STATE_MATCH, text, at) |
| 674 | }; |
| 675 | at += 1; |
| 676 | } |
| 677 | if at > cur { |
| 678 | result = Result::Match(at - 2); |
| 679 | } |
| 680 | } else if next_si & STATE_START > 0 { |
| 681 | // A start state isn't in the common case because we may |
Chih-Hung Hsieh | 849e445 | 2020-10-26 13:16:47 -0700 | [diff] [blame^] | 682 | // want to do quick prefix scanning. If the program doesn't |
Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 683 | // have a detected prefix, then start states are actually |
| 684 | // considered common and this case is never reached. |
| 685 | debug_assert!(self.has_prefix()); |
| 686 | next_si &= !STATE_START; |
| 687 | prev_si = next_si; |
| 688 | at = match self.prefix_at(text, at) { |
| 689 | None => return Result::NoMatch(text.len()), |
| 690 | Some(i) => i, |
| 691 | }; |
| 692 | } else if next_si >= STATE_UNKNOWN { |
| 693 | if next_si == STATE_QUIT { |
| 694 | return Result::Quit; |
| 695 | } |
| 696 | // Finally, this corresponds to the case where the transition |
| 697 | // entered a state that can never lead to a match or a state |
| 698 | // that hasn't been computed yet. The latter being the "slow" |
| 699 | // path. |
| 700 | let byte = Byte::byte(text[at - 1]); |
| 701 | // We no longer care about the special bits in the state |
| 702 | // pointer. |
| 703 | prev_si &= STATE_MAX; |
| 704 | // Record where we are. This is used to track progress for |
| 705 | // determining whether we should quit if we've flushed the |
| 706 | // cache too much. |
| 707 | self.at = at; |
| 708 | next_si = match self.next_state(qcur, qnext, prev_si, byte) { |
| 709 | None => return Result::Quit, |
| 710 | Some(STATE_DEAD) => return result.set_non_match(at), |
| 711 | Some(si) => si, |
| 712 | }; |
| 713 | debug_assert!(next_si != STATE_UNKNOWN); |
| 714 | if next_si & STATE_MATCH > 0 { |
| 715 | next_si &= !STATE_MATCH; |
| 716 | result = Result::Match(at - 1); |
| 717 | if self.quit_after_match { |
| 718 | return result; |
| 719 | } |
| 720 | self.last_match_si = next_si; |
| 721 | } |
| 722 | prev_si = next_si; |
| 723 | } else { |
| 724 | prev_si = next_si; |
| 725 | } |
| 726 | } |
| 727 | |
Chih-Hung Hsieh | 849e445 | 2020-10-26 13:16:47 -0700 | [diff] [blame^] | 728 | // Run the DFA once more on the special EOF sentinel value. |
Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 729 | // We don't care about the special bits in the state pointer any more, |
| 730 | // so get rid of them. |
| 731 | prev_si &= STATE_MAX; |
| 732 | prev_si = match self.next_state(qcur, qnext, prev_si, Byte::eof()) { |
| 733 | None => return Result::Quit, |
| 734 | Some(STATE_DEAD) => return result.set_non_match(text.len()), |
| 735 | Some(si) => si & !STATE_START, |
| 736 | }; |
| 737 | debug_assert!(prev_si != STATE_UNKNOWN); |
| 738 | if prev_si & STATE_MATCH > 0 { |
| 739 | prev_si &= !STATE_MATCH; |
| 740 | self.last_match_si = prev_si; |
| 741 | result = Result::Match(text.len()); |
| 742 | } |
| 743 | result |
| 744 | } |
| 745 | |
| 746 | /// Executes the DFA on a reverse NFA. |
| 747 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 748 | fn exec_at_reverse( |
| 749 | &mut self, |
| 750 | qcur: &mut SparseSet, |
| 751 | qnext: &mut SparseSet, |
| 752 | text: &[u8], |
| 753 | ) -> Result<usize> { |
| 754 | // The comments in `exec_at` above mostly apply here too. The main |
| 755 | // difference is that we move backwards over the input and we look for |
| 756 | // the longest possible match instead of the leftmost-first match. |
| 757 | // |
| 758 | // N.B. The code duplication here is regrettable. Efforts to improve |
| 759 | // it without sacrificing performance are welcome. ---AG |
| 760 | debug_assert!(self.prog.is_reverse); |
| 761 | let mut result = Result::NoMatch(self.at); |
| 762 | let (mut prev_si, mut next_si) = (self.start, self.start); |
| 763 | let mut at = self.at; |
| 764 | while at > 0 { |
| 765 | while next_si <= STATE_MAX && at > 0 { |
| 766 | // Argument for safety is in the definition of next_si. |
| 767 | at -= 1; |
| 768 | prev_si = unsafe { self.next_si(next_si, text, at) }; |
| 769 | if prev_si > STATE_MAX || at <= 4 { |
| 770 | mem::swap(&mut prev_si, &mut next_si); |
| 771 | break; |
| 772 | } |
| 773 | at -= 1; |
| 774 | next_si = unsafe { self.next_si(prev_si, text, at) }; |
| 775 | if next_si > STATE_MAX { |
| 776 | break; |
| 777 | } |
| 778 | at -= 1; |
| 779 | prev_si = unsafe { self.next_si(next_si, text, at) }; |
| 780 | if prev_si > STATE_MAX { |
| 781 | mem::swap(&mut prev_si, &mut next_si); |
| 782 | break; |
| 783 | } |
| 784 | at -= 1; |
| 785 | next_si = unsafe { self.next_si(prev_si, text, at) }; |
| 786 | } |
| 787 | if next_si & STATE_MATCH > 0 { |
| 788 | next_si &= !STATE_MATCH; |
| 789 | result = Result::Match(at + 1); |
| 790 | if self.quit_after_match { |
| 791 | return result; |
| 792 | } |
| 793 | self.last_match_si = next_si; |
| 794 | prev_si = next_si; |
| 795 | let cur = at; |
| 796 | while (next_si & !STATE_MATCH) == prev_si && at >= 2 { |
| 797 | // Argument for safety is in the definition of next_si. |
| 798 | at -= 1; |
| 799 | next_si = unsafe { |
| 800 | self.next_si(next_si & !STATE_MATCH, text, at) |
| 801 | }; |
| 802 | } |
| 803 | if at < cur { |
| 804 | result = Result::Match(at + 2); |
| 805 | } |
| 806 | } else if next_si >= STATE_UNKNOWN { |
| 807 | if next_si == STATE_QUIT { |
| 808 | return Result::Quit; |
| 809 | } |
| 810 | let byte = Byte::byte(text[at]); |
| 811 | prev_si &= STATE_MAX; |
| 812 | self.at = at; |
| 813 | next_si = match self.next_state(qcur, qnext, prev_si, byte) { |
| 814 | None => return Result::Quit, |
| 815 | Some(STATE_DEAD) => return result.set_non_match(at), |
| 816 | Some(si) => si, |
| 817 | }; |
| 818 | debug_assert!(next_si != STATE_UNKNOWN); |
| 819 | if next_si & STATE_MATCH > 0 { |
| 820 | next_si &= !STATE_MATCH; |
| 821 | result = Result::Match(at + 1); |
| 822 | if self.quit_after_match { |
| 823 | return result; |
| 824 | } |
| 825 | self.last_match_si = next_si; |
| 826 | } |
| 827 | prev_si = next_si; |
| 828 | } else { |
| 829 | prev_si = next_si; |
| 830 | } |
| 831 | } |
| 832 | |
Chih-Hung Hsieh | 849e445 | 2020-10-26 13:16:47 -0700 | [diff] [blame^] | 833 | // Run the DFA once more on the special EOF sentinel value. |
Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 834 | prev_si = match self.next_state(qcur, qnext, prev_si, Byte::eof()) { |
| 835 | None => return Result::Quit, |
| 836 | Some(STATE_DEAD) => return result.set_non_match(0), |
| 837 | Some(si) => si, |
| 838 | }; |
| 839 | debug_assert!(prev_si != STATE_UNKNOWN); |
| 840 | if prev_si & STATE_MATCH > 0 { |
| 841 | prev_si &= !STATE_MATCH; |
| 842 | self.last_match_si = prev_si; |
| 843 | result = Result::Match(0); |
| 844 | } |
| 845 | result |
| 846 | } |
| 847 | |
| 848 | /// next_si transitions to the next state, where the transition input |
| 849 | /// corresponds to text[i]. |
| 850 | /// |
| 851 | /// This elides bounds checks, and is therefore unsafe. |
| 852 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 853 | unsafe fn next_si(&self, si: StatePtr, text: &[u8], i: usize) -> StatePtr { |
| 854 | // What is the argument for safety here? |
| 855 | // We have three unchecked accesses that could possibly violate safety: |
| 856 | // |
| 857 | // 1. The given byte of input (`text[i]`). |
| 858 | // 2. The class of the byte of input (`classes[text[i]]`). |
| 859 | // 3. The transition for the class (`trans[si + cls]`). |
| 860 | // |
| 861 | // (1) is only safe when calling next_si is guarded by |
| 862 | // `i < text.len()`. |
| 863 | // |
| 864 | // (2) is the easiest case to guarantee since `text[i]` is always a |
| 865 | // `u8` and `self.prog.byte_classes` always has length `u8::MAX`. |
| 866 | // (See `ByteClassSet.byte_classes` in `compile.rs`.) |
| 867 | // |
| 868 | // (3) is only safe if (1)+(2) are safe. Namely, the transitions |
| 869 | // of every state are defined to have length equal to the number of |
| 870 | // byte classes in the program. Therefore, a valid class leads to a |
| 871 | // valid transition. (All possible transitions are valid lookups, even |
| 872 | // if it points to a state that hasn't been computed yet.) (3) also |
| 873 | // relies on `si` being correct, but StatePtrs should only ever be |
| 874 | // retrieved from the transition table, which ensures they are correct. |
| 875 | debug_assert!(i < text.len()); |
| 876 | let b = *text.get_unchecked(i); |
| 877 | debug_assert!((b as usize) < self.prog.byte_classes.len()); |
| 878 | let cls = *self.prog.byte_classes.get_unchecked(b as usize); |
| 879 | self.cache.trans.next_unchecked(si, cls as usize) |
| 880 | } |
| 881 | |
| 882 | /// Computes the next state given the current state and the current input |
| 883 | /// byte (which may be EOF). |
| 884 | /// |
| 885 | /// If STATE_DEAD is returned, then there is no valid state transition. |
| 886 | /// This implies that no permutation of future input can lead to a match |
| 887 | /// state. |
| 888 | /// |
| 889 | /// STATE_UNKNOWN can never be returned. |
| 890 | fn exec_byte( |
| 891 | &mut self, |
| 892 | qcur: &mut SparseSet, |
| 893 | qnext: &mut SparseSet, |
| 894 | mut si: StatePtr, |
| 895 | b: Byte, |
| 896 | ) -> Option<StatePtr> { |
| 897 | use prog::Inst::*; |
| 898 | |
| 899 | // Initialize a queue with the current DFA state's NFA states. |
| 900 | qcur.clear(); |
| 901 | for ip in self.state(si).inst_ptrs() { |
| 902 | qcur.insert(ip); |
| 903 | } |
| 904 | |
| 905 | // Before inspecting the current byte, we may need to also inspect |
| 906 | // whether the position immediately preceding the current byte |
| 907 | // satisfies the empty assertions found in the current state. |
| 908 | // |
| 909 | // We only need to do this step if there are any empty assertions in |
| 910 | // the current state. |
| 911 | let is_word_last = self.state(si).flags().is_word(); |
| 912 | let is_word = b.is_ascii_word(); |
| 913 | if self.state(si).flags().has_empty() { |
| 914 | // Compute the flags immediately preceding the current byte. |
| 915 | // This means we only care about the "end" or "end line" flags. |
Chih-Hung Hsieh | 849e445 | 2020-10-26 13:16:47 -0700 | [diff] [blame^] | 916 | // (The "start" flags are computed immediately following the |
| 917 | // current byte and are handled below.) |
Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 918 | let mut flags = EmptyFlags::default(); |
| 919 | if b.is_eof() { |
| 920 | flags.end = true; |
| 921 | flags.end_line = true; |
| 922 | } else if b.as_byte().map_or(false, |b| b == b'\n') { |
| 923 | flags.end_line = true; |
| 924 | } |
| 925 | if is_word_last == is_word { |
| 926 | flags.not_word_boundary = true; |
| 927 | } else { |
| 928 | flags.word_boundary = true; |
| 929 | } |
| 930 | // Now follow epsilon transitions from every NFA state, but make |
| 931 | // sure we only follow transitions that satisfy our flags. |
| 932 | qnext.clear(); |
| 933 | for &ip in &*qcur { |
| 934 | self.follow_epsilons(usize_to_u32(ip), qnext, flags); |
| 935 | } |
| 936 | mem::swap(qcur, qnext); |
| 937 | } |
| 938 | |
| 939 | // Now we set flags for immediately after the current byte. Since start |
| 940 | // states are processed separately, and are the only states that can |
| 941 | // have the StartText flag set, we therefore only need to worry about |
| 942 | // the StartLine flag here. |
| 943 | // |
| 944 | // We do also keep track of whether this DFA state contains a NFA state |
| 945 | // that is a matching state. This is precisely how we delay the DFA |
| 946 | // matching by one byte in order to process the special EOF sentinel |
| 947 | // byte. Namely, if this DFA state containing a matching NFA state, |
| 948 | // then it is the *next* DFA state that is marked as a match. |
| 949 | let mut empty_flags = EmptyFlags::default(); |
| 950 | let mut state_flags = StateFlags::default(); |
| 951 | empty_flags.start_line = b.as_byte().map_or(false, |b| b == b'\n'); |
| 952 | if b.is_ascii_word() { |
| 953 | state_flags.set_word(); |
| 954 | } |
| 955 | // Now follow all epsilon transitions again, but only after consuming |
| 956 | // the current byte. |
| 957 | qnext.clear(); |
| 958 | for &ip in &*qcur { |
| 959 | match self.prog[ip as usize] { |
| 960 | // These states never happen in a byte-based program. |
| 961 | Char(_) | Ranges(_) => unreachable!(), |
| 962 | // These states are handled when following epsilon transitions. |
| 963 | Save(_) | Split(_) | EmptyLook(_) => {} |
| 964 | Match(_) => { |
| 965 | state_flags.set_match(); |
| 966 | if !self.continue_past_first_match() { |
| 967 | break; |
| 968 | } else if self.prog.matches.len() > 1 |
| 969 | && !qnext.contains(ip as usize) |
| 970 | { |
| 971 | // If we are continuing on to find other matches, |
| 972 | // then keep a record of the match states we've seen. |
| 973 | qnext.insert(ip); |
| 974 | } |
| 975 | } |
| 976 | Bytes(ref inst) => { |
| 977 | if b.as_byte().map_or(false, |b| inst.matches(b)) { |
| 978 | self.follow_epsilons( |
| 979 | inst.goto as InstPtr, |
| 980 | qnext, |
| 981 | empty_flags, |
| 982 | ); |
| 983 | } |
| 984 | } |
| 985 | } |
| 986 | } |
| 987 | |
| 988 | let cache = if b.is_eof() && self.prog.matches.len() > 1 { |
| 989 | // If we're processing the last byte of the input and we're |
| 990 | // matching a regex set, then make the next state contain the |
| 991 | // previous states transitions. We do this so that the main |
| 992 | // matching loop can extract all of the match instructions. |
| 993 | mem::swap(qcur, qnext); |
| 994 | // And don't cache this state because it's totally bunk. |
| 995 | false |
| 996 | } else { |
| 997 | true |
| 998 | }; |
| 999 | |
| 1000 | // We've now built up the set of NFA states that ought to comprise the |
| 1001 | // next DFA state, so try to find it in the cache, and if it doesn't |
| 1002 | // exist, cache it. |
| 1003 | // |
| 1004 | // N.B. We pass `&mut si` here because the cache may clear itself if |
| 1005 | // it has gotten too full. When that happens, the location of the |
| 1006 | // current state may change. |
| 1007 | let mut next = |
| 1008 | match self.cached_state(qnext, state_flags, Some(&mut si)) { |
| 1009 | None => return None, |
| 1010 | Some(next) => next, |
| 1011 | }; |
| 1012 | if (self.start & !STATE_START) == next { |
| 1013 | // Start states can never be match states since all matches are |
| 1014 | // delayed by one byte. |
| 1015 | debug_assert!(!self.state(next).flags().is_match()); |
| 1016 | next = self.start_ptr(next); |
| 1017 | } |
| 1018 | if next <= STATE_MAX && self.state(next).flags().is_match() { |
| 1019 | next |= STATE_MATCH; |
| 1020 | } |
| 1021 | debug_assert!(next != STATE_UNKNOWN); |
| 1022 | // And now store our state in the current state's next list. |
| 1023 | if cache { |
| 1024 | let cls = self.byte_class(b); |
| 1025 | self.cache.trans.set_next(si, cls, next); |
| 1026 | } |
| 1027 | Some(next) |
| 1028 | } |
| 1029 | |
| 1030 | /// Follows the epsilon transitions starting at (and including) `ip`. The |
| 1031 | /// resulting states are inserted into the ordered set `q`. |
| 1032 | /// |
| 1033 | /// Conditional epsilon transitions (i.e., empty width assertions) are only |
| 1034 | /// followed if they are satisfied by the given flags, which should |
| 1035 | /// represent the flags set at the current location in the input. |
| 1036 | /// |
| 1037 | /// If the current location corresponds to the empty string, then only the |
| 1038 | /// end line and/or end text flags may be set. If the current location |
| 1039 | /// corresponds to a real byte in the input, then only the start line |
| 1040 | /// and/or start text flags may be set. |
| 1041 | /// |
| 1042 | /// As an exception to the above, when finding the initial state, any of |
| 1043 | /// the above flags may be set: |
| 1044 | /// |
| 1045 | /// If matching starts at the beginning of the input, then start text and |
| 1046 | /// start line should be set. If the input is empty, then end text and end |
| 1047 | /// line should also be set. |
| 1048 | /// |
| 1049 | /// If matching starts after the beginning of the input, then only start |
| 1050 | /// line should be set if the preceding byte is `\n`. End line should never |
Chih-Hung Hsieh | 849e445 | 2020-10-26 13:16:47 -0700 | [diff] [blame^] | 1051 | /// be set in this case. (Even if the following byte is a `\n`, it will |
Chih-Hung Hsieh | e42c505 | 2020-04-16 10:44:21 -0700 | [diff] [blame] | 1052 | /// be handled in a subsequent DFA state.) |
| 1053 | fn follow_epsilons( |
| 1054 | &mut self, |
| 1055 | ip: InstPtr, |
| 1056 | q: &mut SparseSet, |
| 1057 | flags: EmptyFlags, |
| 1058 | ) { |
| 1059 | use prog::EmptyLook::*; |
| 1060 | use prog::Inst::*; |
| 1061 | |
| 1062 | // We need to traverse the NFA to follow epsilon transitions, so avoid |
| 1063 | // recursion with an explicit stack. |
| 1064 | self.cache.stack.push(ip); |
| 1065 | while let Some(mut ip) = self.cache.stack.pop() { |
| 1066 | // Try to munch through as many states as possible without |
| 1067 | // pushes/pops to the stack. |
| 1068 | loop { |
| 1069 | // Don't visit states we've already added. |
| 1070 | if q.contains(ip as usize) { |
| 1071 | break; |
| 1072 | } |
| 1073 | q.insert(ip as usize); |
| 1074 | match self.prog[ip as usize] { |
| 1075 | Char(_) | Ranges(_) => unreachable!(), |
| 1076 | Match(_) | Bytes(_) => { |
| 1077 | break; |
| 1078 | } |
| 1079 | EmptyLook(ref inst) => { |
| 1080 | // Only follow empty assertion states if our flags |
| 1081 | // satisfy the assertion. |
| 1082 | match inst.look { |
| 1083 | StartLine if flags.start_line => { |
| 1084 | ip = inst.goto as InstPtr; |
| 1085 | } |
| 1086 | EndLine if flags.end_line => { |
| 1087 | ip = inst.goto as InstPtr; |
| 1088 | } |
| 1089 | StartText if flags.start => { |
| 1090 | ip = inst.goto as InstPtr; |
| 1091 | } |
| 1092 | EndText if flags.end => { |
| 1093 | ip = inst.goto as InstPtr; |
| 1094 | } |
| 1095 | WordBoundaryAscii if flags.word_boundary => { |
| 1096 | ip = inst.goto as InstPtr; |
| 1097 | } |
| 1098 | NotWordBoundaryAscii |
| 1099 | if flags.not_word_boundary => |
| 1100 | { |
| 1101 | ip = inst.goto as InstPtr; |
| 1102 | } |
| 1103 | WordBoundary if flags.word_boundary => { |
| 1104 | ip = inst.goto as InstPtr; |
| 1105 | } |
| 1106 | NotWordBoundary if flags.not_word_boundary => { |
| 1107 | ip = inst.goto as InstPtr; |
| 1108 | } |
| 1109 | StartLine | EndLine | StartText | EndText |
| 1110 | | WordBoundaryAscii | NotWordBoundaryAscii |
| 1111 | | WordBoundary | NotWordBoundary => { |
| 1112 | break; |
| 1113 | } |
| 1114 | } |
| 1115 | } |
| 1116 | Save(ref inst) => { |
| 1117 | ip = inst.goto as InstPtr; |
| 1118 | } |
| 1119 | Split(ref inst) => { |
| 1120 | self.cache.stack.push(inst.goto2 as InstPtr); |
| 1121 | ip = inst.goto1 as InstPtr; |
| 1122 | } |
| 1123 | } |
| 1124 | } |
| 1125 | } |
| 1126 | } |
| 1127 | |
| 1128 | /// Find a previously computed state matching the given set of instructions |
| 1129 | /// and is_match bool. |
| 1130 | /// |
| 1131 | /// The given set of instructions should represent a single state in the |
| 1132 | /// NFA along with all states reachable without consuming any input. |
| 1133 | /// |
| 1134 | /// The is_match bool should be true if and only if the preceding DFA state |
| 1135 | /// contains an NFA matching state. The cached state produced here will |
| 1136 | /// then signify a match. (This enables us to delay a match by one byte, |
| 1137 | /// in order to account for the EOF sentinel byte.) |
| 1138 | /// |
| 1139 | /// If the cache is full, then it is wiped before caching a new state. |
| 1140 | /// |
| 1141 | /// The current state should be specified if it exists, since it will need |
| 1142 | /// to be preserved if the cache clears itself. (Start states are |
| 1143 | /// always saved, so they should not be passed here.) It takes a mutable |
| 1144 | /// pointer to the index because if the cache is cleared, the state's |
| 1145 | /// location may change. |
| 1146 | fn cached_state( |
| 1147 | &mut self, |
| 1148 | q: &SparseSet, |
| 1149 | mut state_flags: StateFlags, |
| 1150 | current_state: Option<&mut StatePtr>, |
| 1151 | ) -> Option<StatePtr> { |
| 1152 | // If we couldn't come up with a non-empty key to represent this state, |
| 1153 | // then it is dead and can never lead to a match. |
| 1154 | // |
| 1155 | // Note that inst_flags represent the set of empty width assertions |
| 1156 | // in q. We use this as an optimization in exec_byte to determine when |
| 1157 | // we should follow epsilon transitions at the empty string preceding |
| 1158 | // the current byte. |
| 1159 | let key = match self.cached_state_key(q, &mut state_flags) { |
| 1160 | None => return Some(STATE_DEAD), |
| 1161 | Some(v) => v, |
| 1162 | }; |
| 1163 | // In the cache? Cool. Done. |
| 1164 | if let Some(si) = self.cache.compiled.get_ptr(&key) { |
| 1165 | return Some(si); |
| 1166 | } |
| 1167 | // If the cache has gotten too big, wipe it. |
| 1168 | if self.approximate_size() > self.prog.dfa_size_limit |
| 1169 | && !self.clear_cache_and_save(current_state) |
| 1170 | { |
| 1171 | // Ooops. DFA is giving up. |
| 1172 | return None; |
| 1173 | } |
| 1174 | // Allocate room for our state and add it. |
| 1175 | self.add_state(key) |
| 1176 | } |
| 1177 | |
| 1178 | /// Produces a key suitable for describing a state in the DFA cache. |
| 1179 | /// |
| 1180 | /// The key invariant here is that equivalent keys are produced for any two |
| 1181 | /// sets of ordered NFA states (and toggling of whether the previous NFA |
| 1182 | /// states contain a match state) that do not discriminate a match for any |
| 1183 | /// input. |
| 1184 | /// |
| 1185 | /// Specifically, q should be an ordered set of NFA states and is_match |
| 1186 | /// should be true if and only if the previous NFA states contained a match |
| 1187 | /// state. |
| 1188 | fn cached_state_key( |
| 1189 | &mut self, |
| 1190 | q: &SparseSet, |
| 1191 | state_flags: &mut StateFlags, |
| 1192 | ) -> Option<State> { |
| 1193 | use prog::Inst::*; |
| 1194 | |
| 1195 | // We need to build up enough information to recognize pre-built states |
| 1196 | // in the DFA. Generally speaking, this includes every instruction |
| 1197 | // except for those which are purely epsilon transitions, e.g., the |
| 1198 | // Save and Split instructions. |
| 1199 | // |
| 1200 | // Empty width assertions are also epsilon transitions, but since they |
| 1201 | // are conditional, we need to make them part of a state's key in the |
| 1202 | // cache. |
| 1203 | |
| 1204 | let mut insts = |
| 1205 | mem::replace(&mut self.cache.insts_scratch_space, vec![]); |
| 1206 | insts.clear(); |
| 1207 | // Reserve 1 byte for flags. |
| 1208 | insts.push(0); |
| 1209 | |
| 1210 | let mut prev = 0; |
| 1211 | for &ip in q { |
| 1212 | let ip = usize_to_u32(ip); |
| 1213 | match self.prog[ip as usize] { |
| 1214 | Char(_) | Ranges(_) => unreachable!(), |
| 1215 | Save(_) | Split(_) => {} |
| 1216 | Bytes(_) => push_inst_ptr(&mut insts, &mut prev, ip), |
| 1217 | EmptyLook(_) => { |
| 1218 | state_flags.set_empty(); |
| 1219 | push_inst_ptr(&mut insts, &mut prev, ip) |
| 1220 | } |
| 1221 | Match(_) => { |
| 1222 | push_inst_ptr(&mut insts, &mut prev, ip); |
| 1223 | if !self.continue_past_first_match() { |
| 1224 | break; |
| 1225 | } |
| 1226 | } |
| 1227 | } |
| 1228 | } |
| 1229 | // If we couldn't transition to any other instructions and we didn't |
| 1230 | // see a match when expanding NFA states previously, then this is a |
| 1231 | // dead state and no amount of additional input can transition out |
| 1232 | // of this state. |
| 1233 | let opt_state = if insts.len() == 1 && !state_flags.is_match() { |
| 1234 | None |
| 1235 | } else { |
| 1236 | let StateFlags(f) = *state_flags; |
| 1237 | insts[0] = f; |
| 1238 | Some(State { data: Arc::from(&*insts) }) |
| 1239 | }; |
| 1240 | self.cache.insts_scratch_space = insts; |
| 1241 | opt_state |
| 1242 | } |
| 1243 | |
| 1244 | /// Clears the cache, but saves and restores current_state if it is not |
| 1245 | /// none. |
| 1246 | /// |
| 1247 | /// The current state must be provided here in case its location in the |
| 1248 | /// cache changes. |
| 1249 | /// |
| 1250 | /// This returns false if the cache is not cleared and the DFA should |
| 1251 | /// give up. |
| 1252 | fn clear_cache_and_save( |
| 1253 | &mut self, |
| 1254 | current_state: Option<&mut StatePtr>, |
| 1255 | ) -> bool { |
| 1256 | if self.cache.compiled.is_empty() { |
| 1257 | // Nothing to clear... |
| 1258 | return true; |
| 1259 | } |
| 1260 | match current_state { |
| 1261 | None => self.clear_cache(), |
| 1262 | Some(si) => { |
| 1263 | let cur = self.state(*si).clone(); |
| 1264 | if !self.clear_cache() { |
| 1265 | return false; |
| 1266 | } |
| 1267 | // The unwrap is OK because we just cleared the cache and |
| 1268 | // therefore know that the next state pointer won't exceed |
| 1269 | // STATE_MAX. |
| 1270 | *si = self.restore_state(cur).unwrap(); |
| 1271 | true |
| 1272 | } |
| 1273 | } |
| 1274 | } |
| 1275 | |
| 1276 | /// Wipes the state cache, but saves and restores the current start state. |
| 1277 | /// |
| 1278 | /// This returns false if the cache is not cleared and the DFA should |
| 1279 | /// give up. |
| 1280 | fn clear_cache(&mut self) -> bool { |
| 1281 | // Bail out of the DFA if we're moving too "slowly." |
| 1282 | // A heuristic from RE2: assume the DFA is too slow if it is processing |
| 1283 | // 10 or fewer bytes per state. |
| 1284 | // Additionally, we permit the cache to be flushed a few times before |
| 1285 | // caling it quits. |
| 1286 | let nstates = self.cache.compiled.len(); |
| 1287 | if self.cache.flush_count >= 3 |
| 1288 | && self.at >= self.last_cache_flush |
| 1289 | && (self.at - self.last_cache_flush) <= 10 * nstates |
| 1290 | { |
| 1291 | return false; |
| 1292 | } |
| 1293 | // Update statistics tracking cache flushes. |
| 1294 | self.last_cache_flush = self.at; |
| 1295 | self.cache.flush_count += 1; |
| 1296 | |
| 1297 | // OK, actually flush the cache. |
| 1298 | let start = self.state(self.start & !STATE_START).clone(); |
| 1299 | let last_match = if self.last_match_si <= STATE_MAX { |
| 1300 | Some(self.state(self.last_match_si).clone()) |
| 1301 | } else { |
| 1302 | None |
| 1303 | }; |
| 1304 | self.cache.reset_size(); |
| 1305 | self.cache.trans.clear(); |
| 1306 | self.cache.compiled.clear(); |
| 1307 | for s in &mut self.cache.start_states { |
| 1308 | *s = STATE_UNKNOWN; |
| 1309 | } |
| 1310 | // The unwraps are OK because we just cleared the cache and therefore |
| 1311 | // know that the next state pointer won't exceed STATE_MAX. |
| 1312 | let start_ptr = self.restore_state(start).unwrap(); |
| 1313 | self.start = self.start_ptr(start_ptr); |
| 1314 | if let Some(last_match) = last_match { |
| 1315 | self.last_match_si = self.restore_state(last_match).unwrap(); |
| 1316 | } |
| 1317 | true |
| 1318 | } |
| 1319 | |
| 1320 | /// Restores the given state back into the cache, and returns a pointer |
| 1321 | /// to it. |
| 1322 | fn restore_state(&mut self, state: State) -> Option<StatePtr> { |
| 1323 | // If we've already stored this state, just return a pointer to it. |
| 1324 | // None will be the wiser. |
| 1325 | if let Some(si) = self.cache.compiled.get_ptr(&state) { |
| 1326 | return Some(si); |
| 1327 | } |
| 1328 | self.add_state(state) |
| 1329 | } |
| 1330 | |
| 1331 | /// Returns the next state given the current state si and current byte |
| 1332 | /// b. {qcur,qnext} are used as scratch space for storing ordered NFA |
| 1333 | /// states. |
| 1334 | /// |
| 1335 | /// This tries to fetch the next state from the cache, but if that fails, |
| 1336 | /// it computes the next state, caches it and returns a pointer to it. |
| 1337 | /// |
| 1338 | /// The pointer can be to a real state, or it can be STATE_DEAD. |
| 1339 | /// STATE_UNKNOWN cannot be returned. |
| 1340 | /// |
| 1341 | /// None is returned if a new state could not be allocated (i.e., the DFA |
| 1342 | /// ran out of space and thinks it's running too slowly). |
| 1343 | fn next_state( |
| 1344 | &mut self, |
| 1345 | qcur: &mut SparseSet, |
| 1346 | qnext: &mut SparseSet, |
| 1347 | si: StatePtr, |
| 1348 | b: Byte, |
| 1349 | ) -> Option<StatePtr> { |
| 1350 | if si == STATE_DEAD { |
| 1351 | return Some(STATE_DEAD); |
| 1352 | } |
| 1353 | match self.cache.trans.next(si, self.byte_class(b)) { |
| 1354 | STATE_UNKNOWN => self.exec_byte(qcur, qnext, si, b), |
| 1355 | STATE_QUIT => None, |
| 1356 | STATE_DEAD => Some(STATE_DEAD), |
| 1357 | nsi => Some(nsi), |
| 1358 | } |
| 1359 | } |
| 1360 | |
| 1361 | /// Computes and returns the start state, where searching begins at |
| 1362 | /// position `at` in `text`. If the state has already been computed, |
| 1363 | /// then it is pulled from the cache. If the state hasn't been cached, |
| 1364 | /// then it is computed, cached and a pointer to it is returned. |
| 1365 | /// |
| 1366 | /// This may return STATE_DEAD but never STATE_UNKNOWN. |
| 1367 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 1368 | fn start_state( |
| 1369 | &mut self, |
| 1370 | q: &mut SparseSet, |
| 1371 | empty_flags: EmptyFlags, |
| 1372 | state_flags: StateFlags, |
| 1373 | ) -> Option<StatePtr> { |
| 1374 | // Compute an index into our cache of start states based on the set |
| 1375 | // of empty/state flags set at the current position in the input. We |
| 1376 | // don't use every flag since not all flags matter. For example, since |
| 1377 | // matches are delayed by one byte, start states can never be match |
| 1378 | // states. |
| 1379 | let flagi = { |
| 1380 | (((empty_flags.start as u8) << 0) |
| 1381 | | ((empty_flags.end as u8) << 1) |
| 1382 | | ((empty_flags.start_line as u8) << 2) |
| 1383 | | ((empty_flags.end_line as u8) << 3) |
| 1384 | | ((empty_flags.word_boundary as u8) << 4) |
| 1385 | | ((empty_flags.not_word_boundary as u8) << 5) |
| 1386 | | ((state_flags.is_word() as u8) << 6)) as usize |
| 1387 | }; |
| 1388 | match self.cache.start_states[flagi] { |
| 1389 | STATE_UNKNOWN => {} |
| 1390 | STATE_DEAD => return Some(STATE_DEAD), |
| 1391 | si => return Some(si), |
| 1392 | } |
| 1393 | q.clear(); |
| 1394 | let start = usize_to_u32(self.prog.start); |
| 1395 | self.follow_epsilons(start, q, empty_flags); |
| 1396 | // Start states can never be match states because we delay every match |
| 1397 | // by one byte. Given an empty string and an empty match, the match |
| 1398 | // won't actually occur until the DFA processes the special EOF |
| 1399 | // sentinel byte. |
| 1400 | let sp = match self.cached_state(q, state_flags, None) { |
| 1401 | None => return None, |
| 1402 | Some(sp) => self.start_ptr(sp), |
| 1403 | }; |
| 1404 | self.cache.start_states[flagi] = sp; |
| 1405 | Some(sp) |
| 1406 | } |
| 1407 | |
| 1408 | /// Computes the set of starting flags for the given position in text. |
| 1409 | /// |
| 1410 | /// This should only be used when executing the DFA forwards over the |
| 1411 | /// input. |
| 1412 | fn start_flags(&self, text: &[u8], at: usize) -> (EmptyFlags, StateFlags) { |
| 1413 | let mut empty_flags = EmptyFlags::default(); |
| 1414 | let mut state_flags = StateFlags::default(); |
| 1415 | empty_flags.start = at == 0; |
| 1416 | empty_flags.end = text.is_empty(); |
| 1417 | empty_flags.start_line = at == 0 || text[at - 1] == b'\n'; |
| 1418 | empty_flags.end_line = text.is_empty(); |
| 1419 | |
| 1420 | let is_word_last = at > 0 && Byte::byte(text[at - 1]).is_ascii_word(); |
| 1421 | let is_word = at < text.len() && Byte::byte(text[at]).is_ascii_word(); |
| 1422 | if is_word_last { |
| 1423 | state_flags.set_word(); |
| 1424 | } |
| 1425 | if is_word == is_word_last { |
| 1426 | empty_flags.not_word_boundary = true; |
| 1427 | } else { |
| 1428 | empty_flags.word_boundary = true; |
| 1429 | } |
| 1430 | (empty_flags, state_flags) |
| 1431 | } |
| 1432 | |
| 1433 | /// Computes the set of starting flags for the given position in text. |
| 1434 | /// |
| 1435 | /// This should only be used when executing the DFA in reverse over the |
| 1436 | /// input. |
| 1437 | fn start_flags_reverse( |
| 1438 | &self, |
| 1439 | text: &[u8], |
| 1440 | at: usize, |
| 1441 | ) -> (EmptyFlags, StateFlags) { |
| 1442 | let mut empty_flags = EmptyFlags::default(); |
| 1443 | let mut state_flags = StateFlags::default(); |
| 1444 | empty_flags.start = at == text.len(); |
| 1445 | empty_flags.end = text.is_empty(); |
| 1446 | empty_flags.start_line = at == text.len() || text[at] == b'\n'; |
| 1447 | empty_flags.end_line = text.is_empty(); |
| 1448 | |
| 1449 | let is_word_last = |
| 1450 | at < text.len() && Byte::byte(text[at]).is_ascii_word(); |
| 1451 | let is_word = at > 0 && Byte::byte(text[at - 1]).is_ascii_word(); |
| 1452 | if is_word_last { |
| 1453 | state_flags.set_word(); |
| 1454 | } |
| 1455 | if is_word == is_word_last { |
| 1456 | empty_flags.not_word_boundary = true; |
| 1457 | } else { |
| 1458 | empty_flags.word_boundary = true; |
| 1459 | } |
| 1460 | (empty_flags, state_flags) |
| 1461 | } |
| 1462 | |
| 1463 | /// Returns a reference to a State given a pointer to it. |
| 1464 | fn state(&self, si: StatePtr) -> &State { |
| 1465 | self.cache.compiled.get_state(si).unwrap() |
| 1466 | } |
| 1467 | |
| 1468 | /// Adds the given state to the DFA. |
| 1469 | /// |
| 1470 | /// This allocates room for transitions out of this state in |
| 1471 | /// self.cache.trans. The transitions can be set with the returned |
| 1472 | /// StatePtr. |
| 1473 | /// |
| 1474 | /// If None is returned, then the state limit was reached and the DFA |
| 1475 | /// should quit. |
| 1476 | fn add_state(&mut self, state: State) -> Option<StatePtr> { |
| 1477 | // This will fail if the next state pointer exceeds STATE_PTR. In |
| 1478 | // practice, the cache limit will prevent us from ever getting here, |
| 1479 | // but maybe callers will set the cache size to something ridiculous... |
| 1480 | let si = match self.cache.trans.add() { |
| 1481 | None => return None, |
| 1482 | Some(si) => si, |
| 1483 | }; |
| 1484 | // If the program has a Unicode word boundary, then set any transitions |
| 1485 | // for non-ASCII bytes to STATE_QUIT. If the DFA stumbles over such a |
| 1486 | // transition, then it will quit and an alternative matching engine |
| 1487 | // will take over. |
| 1488 | if self.prog.has_unicode_word_boundary { |
| 1489 | for b in 128..256 { |
| 1490 | let cls = self.byte_class(Byte::byte(b as u8)); |
| 1491 | self.cache.trans.set_next(si, cls, STATE_QUIT); |
| 1492 | } |
| 1493 | } |
| 1494 | // Finally, put our actual state on to our heap of states and index it |
| 1495 | // so we can find it later. |
| 1496 | self.cache.size += self.cache.trans.state_heap_size() |
| 1497 | + state.data.len() |
| 1498 | + (2 * mem::size_of::<State>()) |
| 1499 | + mem::size_of::<StatePtr>(); |
| 1500 | self.cache.compiled.insert(state, si); |
| 1501 | // Transition table and set of states and map should all be in sync. |
| 1502 | debug_assert!( |
| 1503 | self.cache.compiled.len() == self.cache.trans.num_states() |
| 1504 | ); |
| 1505 | Some(si) |
| 1506 | } |
| 1507 | |
| 1508 | /// Quickly finds the next occurrence of any literal prefixes in the regex. |
| 1509 | /// If there are no literal prefixes, then the current position is |
| 1510 | /// returned. If there are literal prefixes and one could not be found, |
| 1511 | /// then None is returned. |
| 1512 | /// |
| 1513 | /// This should only be called when the DFA is in a start state. |
| 1514 | fn prefix_at(&self, text: &[u8], at: usize) -> Option<usize> { |
| 1515 | self.prog.prefixes.find(&text[at..]).map(|(s, _)| at + s) |
| 1516 | } |
| 1517 | |
| 1518 | /// Returns the number of byte classes required to discriminate transitions |
| 1519 | /// in each state. |
| 1520 | /// |
| 1521 | /// invariant: num_byte_classes() == len(State.next) |
| 1522 | fn num_byte_classes(&self) -> usize { |
| 1523 | // We add 1 to account for the special EOF byte. |
| 1524 | (self.prog.byte_classes[255] as usize + 1) + 1 |
| 1525 | } |
| 1526 | |
| 1527 | /// Given an input byte or the special EOF sentinel, return its |
| 1528 | /// corresponding byte class. |
| 1529 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 1530 | fn byte_class(&self, b: Byte) -> usize { |
| 1531 | match b.as_byte() { |
| 1532 | None => self.num_byte_classes() - 1, |
| 1533 | Some(b) => self.u8_class(b), |
| 1534 | } |
| 1535 | } |
| 1536 | |
| 1537 | /// Like byte_class, but explicitly for u8s. |
| 1538 | #[cfg_attr(feature = "perf-inline", inline(always))] |
| 1539 | fn u8_class(&self, b: u8) -> usize { |
| 1540 | self.prog.byte_classes[b as usize] as usize |
| 1541 | } |
| 1542 | |
| 1543 | /// Returns true if the DFA should continue searching past the first match. |
| 1544 | /// |
| 1545 | /// Leftmost first semantics in the DFA are preserved by not following NFA |
| 1546 | /// transitions after the first match is seen. |
| 1547 | /// |
| 1548 | /// On occasion, we want to avoid leftmost first semantics to find either |
| 1549 | /// the longest match (for reverse search) or all possible matches (for |
| 1550 | /// regex sets). |
| 1551 | fn continue_past_first_match(&self) -> bool { |
| 1552 | self.prog.is_reverse || self.prog.matches.len() > 1 |
| 1553 | } |
| 1554 | |
| 1555 | /// Returns true if there is a prefix we can quickly search for. |
| 1556 | fn has_prefix(&self) -> bool { |
| 1557 | !self.prog.is_reverse |
| 1558 | && !self.prog.prefixes.is_empty() |
| 1559 | && !self.prog.is_anchored_start |
| 1560 | } |
| 1561 | |
| 1562 | /// Sets the STATE_START bit in the given state pointer if and only if |
| 1563 | /// we have a prefix to scan for. |
| 1564 | /// |
| 1565 | /// If there's no prefix, then it's a waste to treat the start state |
| 1566 | /// specially. |
| 1567 | fn start_ptr(&self, si: StatePtr) -> StatePtr { |
| 1568 | if self.has_prefix() { |
| 1569 | si | STATE_START |
| 1570 | } else { |
| 1571 | si |
| 1572 | } |
| 1573 | } |
| 1574 | |
| 1575 | /// Approximate size returns the approximate heap space currently used by |
| 1576 | /// the DFA. It is used to determine whether the DFA's state cache needs to |
| 1577 | /// be wiped. Namely, it is possible that for certain regexes on certain |
| 1578 | /// inputs, a new state could be created for every byte of input. (This is |
| 1579 | /// bad for memory use, so we bound it with a cache.) |
| 1580 | fn approximate_size(&self) -> usize { |
| 1581 | self.cache.size + self.prog.approximate_size() |
| 1582 | } |
| 1583 | } |
| 1584 | |
| 1585 | /// An abstraction for representing a map of states. The map supports two |
| 1586 | /// different ways of state lookup. One is fast constant time access via a |
| 1587 | /// state pointer. The other is a hashmap lookup based on the DFA's |
| 1588 | /// constituent NFA states. |
| 1589 | /// |
| 1590 | /// A DFA state internally uses an Arc such that we only need to store the |
| 1591 | /// set of NFA states on the heap once, even though we support looking up |
| 1592 | /// states by two different means. A more natural way to express this might |
| 1593 | /// use raw pointers, but an Arc is safe and effectively achieves the same |
| 1594 | /// thing. |
| 1595 | #[derive(Debug)] |
| 1596 | struct StateMap { |
| 1597 | /// The keys are not actually static but rely on always pointing to a |
| 1598 | /// buffer in `states` which will never be moved except when clearing |
| 1599 | /// the map or on drop, in which case the keys of this map will be |
| 1600 | /// removed before |
| 1601 | map: HashMap<State, StatePtr>, |
| 1602 | /// Our set of states. Note that `StatePtr / num_byte_classes` indexes |
| 1603 | /// this Vec rather than just a `StatePtr`. |
| 1604 | states: Vec<State>, |
| 1605 | /// The number of byte classes in the DFA. Used to index `states`. |
| 1606 | num_byte_classes: usize, |
| 1607 | } |
| 1608 | |
| 1609 | impl StateMap { |
| 1610 | fn new(num_byte_classes: usize) -> StateMap { |
| 1611 | StateMap { |
| 1612 | map: HashMap::new(), |
| 1613 | states: vec![], |
| 1614 | num_byte_classes: num_byte_classes, |
| 1615 | } |
| 1616 | } |
| 1617 | |
| 1618 | fn len(&self) -> usize { |
| 1619 | self.states.len() |
| 1620 | } |
| 1621 | |
| 1622 | fn is_empty(&self) -> bool { |
| 1623 | self.states.is_empty() |
| 1624 | } |
| 1625 | |
| 1626 | fn get_ptr(&self, state: &State) -> Option<StatePtr> { |
| 1627 | self.map.get(state).cloned() |
| 1628 | } |
| 1629 | |
| 1630 | fn get_state(&self, si: StatePtr) -> Option<&State> { |
| 1631 | self.states.get(si as usize / self.num_byte_classes) |
| 1632 | } |
| 1633 | |
| 1634 | fn insert(&mut self, state: State, si: StatePtr) { |
| 1635 | self.map.insert(state.clone(), si); |
| 1636 | self.states.push(state); |
| 1637 | } |
| 1638 | |
| 1639 | fn clear(&mut self) { |
| 1640 | self.map.clear(); |
| 1641 | self.states.clear(); |
| 1642 | } |
| 1643 | } |
| 1644 | |
| 1645 | impl Transitions { |
| 1646 | /// Create a new transition table. |
| 1647 | /// |
| 1648 | /// The number of byte classes corresponds to the stride. Every state will |
| 1649 | /// have `num_byte_classes` slots for transitions. |
| 1650 | fn new(num_byte_classes: usize) -> Transitions { |
| 1651 | Transitions { table: vec![], num_byte_classes: num_byte_classes } |
| 1652 | } |
| 1653 | |
| 1654 | /// Returns the total number of states currently in this table. |
| 1655 | fn num_states(&self) -> usize { |
| 1656 | self.table.len() / self.num_byte_classes |
| 1657 | } |
| 1658 | |
| 1659 | /// Allocates room for one additional state and returns a pointer to it. |
| 1660 | /// |
| 1661 | /// If there's no more room, None is returned. |
| 1662 | fn add(&mut self) -> Option<StatePtr> { |
| 1663 | let si = self.table.len(); |
| 1664 | if si > STATE_MAX as usize { |
| 1665 | return None; |
| 1666 | } |
| 1667 | self.table.extend(repeat(STATE_UNKNOWN).take(self.num_byte_classes)); |
| 1668 | Some(usize_to_u32(si)) |
| 1669 | } |
| 1670 | |
| 1671 | /// Clears the table of all states. |
| 1672 | fn clear(&mut self) { |
| 1673 | self.table.clear(); |
| 1674 | } |
| 1675 | |
| 1676 | /// Sets the transition from (si, cls) to next. |
| 1677 | fn set_next(&mut self, si: StatePtr, cls: usize, next: StatePtr) { |
| 1678 | self.table[si as usize + cls] = next; |
| 1679 | } |
| 1680 | |
| 1681 | /// Returns the transition corresponding to (si, cls). |
| 1682 | fn next(&self, si: StatePtr, cls: usize) -> StatePtr { |
| 1683 | self.table[si as usize + cls] |
| 1684 | } |
| 1685 | |
| 1686 | /// The heap size, in bytes, of a single state in the transition table. |
| 1687 | fn state_heap_size(&self) -> usize { |
| 1688 | self.num_byte_classes * mem::size_of::<StatePtr>() |
| 1689 | } |
| 1690 | |
| 1691 | /// Like `next`, but uses unchecked access and is therefore unsafe. |
| 1692 | unsafe fn next_unchecked(&self, si: StatePtr, cls: usize) -> StatePtr { |
| 1693 | debug_assert!((si as usize) < self.table.len()); |
| 1694 | debug_assert!(cls < self.num_byte_classes); |
| 1695 | *self.table.get_unchecked(si as usize + cls) |
| 1696 | } |
| 1697 | } |
| 1698 | |
| 1699 | impl StateFlags { |
| 1700 | fn is_match(&self) -> bool { |
| 1701 | self.0 & 0b0000000_1 > 0 |
| 1702 | } |
| 1703 | |
| 1704 | fn set_match(&mut self) { |
| 1705 | self.0 |= 0b0000000_1; |
| 1706 | } |
| 1707 | |
| 1708 | fn is_word(&self) -> bool { |
| 1709 | self.0 & 0b000000_1_0 > 0 |
| 1710 | } |
| 1711 | |
| 1712 | fn set_word(&mut self) { |
| 1713 | self.0 |= 0b000000_1_0; |
| 1714 | } |
| 1715 | |
| 1716 | fn has_empty(&self) -> bool { |
| 1717 | self.0 & 0b00000_1_00 > 0 |
| 1718 | } |
| 1719 | |
| 1720 | fn set_empty(&mut self) { |
| 1721 | self.0 |= 0b00000_1_00; |
| 1722 | } |
| 1723 | } |
| 1724 | |
| 1725 | impl Byte { |
| 1726 | fn byte(b: u8) -> Self { |
| 1727 | Byte(b as u16) |
| 1728 | } |
| 1729 | fn eof() -> Self { |
| 1730 | Byte(256) |
| 1731 | } |
| 1732 | fn is_eof(&self) -> bool { |
| 1733 | self.0 == 256 |
| 1734 | } |
| 1735 | |
| 1736 | fn is_ascii_word(&self) -> bool { |
| 1737 | let b = match self.as_byte() { |
| 1738 | None => return false, |
| 1739 | Some(b) => b, |
| 1740 | }; |
| 1741 | match b { |
| 1742 | b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'_' => true, |
| 1743 | _ => false, |
| 1744 | } |
| 1745 | } |
| 1746 | |
| 1747 | fn as_byte(&self) -> Option<u8> { |
| 1748 | if self.is_eof() { |
| 1749 | None |
| 1750 | } else { |
| 1751 | Some(self.0 as u8) |
| 1752 | } |
| 1753 | } |
| 1754 | } |
| 1755 | |
| 1756 | impl fmt::Debug for State { |
| 1757 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 1758 | let ips: Vec<usize> = self.inst_ptrs().collect(); |
| 1759 | f.debug_struct("State") |
| 1760 | .field("flags", &self.flags()) |
| 1761 | .field("insts", &ips) |
| 1762 | .finish() |
| 1763 | } |
| 1764 | } |
| 1765 | |
| 1766 | impl fmt::Debug for Transitions { |
| 1767 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 1768 | let mut fmtd = f.debug_map(); |
| 1769 | for si in 0..self.num_states() { |
| 1770 | let s = si * self.num_byte_classes; |
| 1771 | let e = s + self.num_byte_classes; |
| 1772 | fmtd.entry(&si.to_string(), &TransitionsRow(&self.table[s..e])); |
| 1773 | } |
| 1774 | fmtd.finish() |
| 1775 | } |
| 1776 | } |
| 1777 | |
| 1778 | struct TransitionsRow<'a>(&'a [StatePtr]); |
| 1779 | |
| 1780 | impl<'a> fmt::Debug for TransitionsRow<'a> { |
| 1781 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 1782 | let mut fmtd = f.debug_map(); |
| 1783 | for (b, si) in self.0.iter().enumerate() { |
| 1784 | match *si { |
| 1785 | STATE_UNKNOWN => {} |
| 1786 | STATE_DEAD => { |
| 1787 | fmtd.entry(&vb(b as usize), &"DEAD"); |
| 1788 | } |
| 1789 | si => { |
| 1790 | fmtd.entry(&vb(b as usize), &si.to_string()); |
| 1791 | } |
| 1792 | } |
| 1793 | } |
| 1794 | fmtd.finish() |
| 1795 | } |
| 1796 | } |
| 1797 | |
| 1798 | impl fmt::Debug for StateFlags { |
| 1799 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 1800 | f.debug_struct("StateFlags") |
| 1801 | .field("is_match", &self.is_match()) |
| 1802 | .field("is_word", &self.is_word()) |
| 1803 | .field("has_empty", &self.has_empty()) |
| 1804 | .finish() |
| 1805 | } |
| 1806 | } |
| 1807 | |
| 1808 | /// Helper function for formatting a byte as a nice-to-read escaped string. |
| 1809 | fn vb(b: usize) -> String { |
| 1810 | use std::ascii::escape_default; |
| 1811 | |
| 1812 | if b > ::std::u8::MAX as usize { |
| 1813 | "EOF".to_owned() |
| 1814 | } else { |
| 1815 | let escaped = escape_default(b as u8).collect::<Vec<u8>>(); |
| 1816 | String::from_utf8_lossy(&escaped).into_owned() |
| 1817 | } |
| 1818 | } |
| 1819 | |
| 1820 | fn usize_to_u32(n: usize) -> u32 { |
| 1821 | if (n as u64) > (::std::u32::MAX as u64) { |
| 1822 | panic!("BUG: {} is too big to fit into u32", n) |
| 1823 | } |
| 1824 | n as u32 |
| 1825 | } |
| 1826 | |
| 1827 | #[allow(dead_code)] // useful for debugging |
| 1828 | fn show_state_ptr(si: StatePtr) -> String { |
| 1829 | let mut s = format!("{:?}", si & STATE_MAX); |
| 1830 | if si == STATE_UNKNOWN { |
| 1831 | s = format!("{} (unknown)", s); |
| 1832 | } |
| 1833 | if si == STATE_DEAD { |
| 1834 | s = format!("{} (dead)", s); |
| 1835 | } |
| 1836 | if si == STATE_QUIT { |
| 1837 | s = format!("{} (quit)", s); |
| 1838 | } |
| 1839 | if si & STATE_START > 0 { |
| 1840 | s = format!("{} (start)", s); |
| 1841 | } |
| 1842 | if si & STATE_MATCH > 0 { |
| 1843 | s = format!("{} (match)", s); |
| 1844 | } |
| 1845 | s |
| 1846 | } |
| 1847 | |
| 1848 | /// https://developers.google.com/protocol-buffers/docs/encoding#varints |
| 1849 | fn write_vari32(data: &mut Vec<u8>, n: i32) { |
| 1850 | let mut un = (n as u32) << 1; |
| 1851 | if n < 0 { |
| 1852 | un = !un; |
| 1853 | } |
| 1854 | write_varu32(data, un) |
| 1855 | } |
| 1856 | |
| 1857 | /// https://developers.google.com/protocol-buffers/docs/encoding#varints |
| 1858 | fn read_vari32(data: &[u8]) -> (i32, usize) { |
| 1859 | let (un, i) = read_varu32(data); |
| 1860 | let mut n = (un >> 1) as i32; |
| 1861 | if un & 1 != 0 { |
| 1862 | n = !n; |
| 1863 | } |
| 1864 | (n, i) |
| 1865 | } |
| 1866 | |
| 1867 | /// https://developers.google.com/protocol-buffers/docs/encoding#varints |
| 1868 | fn write_varu32(data: &mut Vec<u8>, mut n: u32) { |
| 1869 | while n >= 0b1000_0000 { |
| 1870 | data.push((n as u8) | 0b1000_0000); |
| 1871 | n >>= 7; |
| 1872 | } |
| 1873 | data.push(n as u8); |
| 1874 | } |
| 1875 | |
| 1876 | /// https://developers.google.com/protocol-buffers/docs/encoding#varints |
| 1877 | fn read_varu32(data: &[u8]) -> (u32, usize) { |
| 1878 | let mut n: u32 = 0; |
| 1879 | let mut shift: u32 = 0; |
| 1880 | for (i, &b) in data.iter().enumerate() { |
| 1881 | if b < 0b1000_0000 { |
| 1882 | return (n | ((b as u32) << shift), i + 1); |
| 1883 | } |
| 1884 | n |= ((b as u32) & 0b0111_1111) << shift; |
| 1885 | shift += 7; |
| 1886 | } |
| 1887 | (0, 0) |
| 1888 | } |
| 1889 | |
| 1890 | #[cfg(test)] |
| 1891 | mod tests { |
| 1892 | extern crate rand; |
| 1893 | |
| 1894 | use super::{ |
| 1895 | push_inst_ptr, read_vari32, read_varu32, write_vari32, write_varu32, |
| 1896 | State, StateFlags, |
| 1897 | }; |
| 1898 | use quickcheck::{quickcheck, QuickCheck, StdGen}; |
| 1899 | use std::sync::Arc; |
| 1900 | |
| 1901 | #[test] |
| 1902 | fn prop_state_encode_decode() { |
| 1903 | fn p(ips: Vec<u32>, flags: u8) -> bool { |
| 1904 | let mut data = vec![flags]; |
| 1905 | let mut prev = 0; |
| 1906 | for &ip in ips.iter() { |
| 1907 | push_inst_ptr(&mut data, &mut prev, ip); |
| 1908 | } |
| 1909 | let state = State { data: Arc::from(&data[..]) }; |
| 1910 | |
| 1911 | let expected: Vec<usize> = |
| 1912 | ips.into_iter().map(|ip| ip as usize).collect(); |
| 1913 | let got: Vec<usize> = state.inst_ptrs().collect(); |
| 1914 | expected == got && state.flags() == StateFlags(flags) |
| 1915 | } |
| 1916 | QuickCheck::new() |
| 1917 | .gen(StdGen::new(self::rand::thread_rng(), 10_000)) |
| 1918 | .quickcheck(p as fn(Vec<u32>, u8) -> bool); |
| 1919 | } |
| 1920 | |
| 1921 | #[test] |
| 1922 | fn prop_read_write_u32() { |
| 1923 | fn p(n: u32) -> bool { |
| 1924 | let mut buf = vec![]; |
| 1925 | write_varu32(&mut buf, n); |
| 1926 | let (got, nread) = read_varu32(&buf); |
| 1927 | nread == buf.len() && got == n |
| 1928 | } |
| 1929 | quickcheck(p as fn(u32) -> bool); |
| 1930 | } |
| 1931 | |
| 1932 | #[test] |
| 1933 | fn prop_read_write_i32() { |
| 1934 | fn p(n: i32) -> bool { |
| 1935 | let mut buf = vec![]; |
| 1936 | write_vari32(&mut buf, n); |
| 1937 | let (got, nread) = read_vari32(&buf); |
| 1938 | nread == buf.len() && got == n |
| 1939 | } |
| 1940 | quickcheck(p as fn(i32) -> bool); |
| 1941 | } |
| 1942 | } |