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94b46f34 XL |
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; | |
0731742a | 43 | use std::sync::Arc; |
94b46f34 XL |
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.) | |
0731742a | 82 | #[derive(Debug)] |
94b46f34 XL |
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.) | |
0731742a | 101 | #[derive(Debug)] |
94b46f34 XL |
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. | |
0731742a | 111 | compiled: StateMap, |
94b46f34 XL |
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, | |
94b46f34 XL |
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, | |
0731742a XL |
146 | /// Scratch space used when building instruction pointer lists for new |
147 | /// states. This helps amortize allocation. | |
148 | insts_scratch_space: Vec<u8>, | |
94b46f34 XL |
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. | |
f9f354fc | 227 | #[cfg(feature = "perf-literal")] |
94b46f34 XL |
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)] | |
0731742a XL |
262 | struct State { |
263 | data: Arc<[u8]>, | |
94b46f34 XL |
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 | ||
f9f354fc | 287 | impl<'a> Iterator for InstPtrs<'a> { |
94b46f34 XL |
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 { | |
f9f354fc | 310 | InstPtrs { base: 0, data: &self.data[1..] } |
94b46f34 XL |
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. | |
f9f354fc | 362 | const STATE_UNKNOWN: StatePtr = 1 << 31; |
94b46f34 XL |
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. | |
f9f354fc | 376 | const STATE_START: StatePtr = 1 << 30; |
94b46f34 XL |
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. | |
f9f354fc | 381 | const STATE_MATCH: StatePtr = 1 << 29; |
94b46f34 XL |
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 { | |
0731742a | 420 | compiled: StateMap::new(num_byte_classes), |
94b46f34 | 421 | trans: Transitions::new(num_byte_classes), |
94b46f34 XL |
422 | start_states: starts, |
423 | stack: vec![], | |
424 | flush_count: 0, | |
425 | size: 0, | |
0731742a | 426 | insts_scratch_space: vec![], |
94b46f34 XL |
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) { | |
f9f354fc | 440 | self.size = (self.start_states.len() * mem::size_of::<StatePtr>()) |
94b46f34 XL |
441 | + (self.stack.len() * mem::size_of::<InstPtr>()); |
442 | } | |
443 | } | |
444 | ||
445 | impl<'a> Fsm<'a> { | |
f9f354fc | 446 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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); | |
f9f354fc XL |
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 | }; | |
94b46f34 XL |
472 | debug_assert!(dfa.start != STATE_UNKNOWN); |
473 | dfa.exec_at(&mut cache.qcur, &mut cache.qnext, text) | |
474 | } | |
475 | ||
f9f354fc | 476 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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); | |
f9f354fc XL |
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 | }; | |
94b46f34 XL |
502 | debug_assert!(dfa.start != STATE_UNKNOWN); |
503 | dfa.exec_at_reverse(&mut cache.qcur, &mut cache.qnext, text) | |
504 | } | |
505 | ||
f9f354fc | 506 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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); | |
f9f354fc XL |
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 | }; | |
94b46f34 XL |
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. | |
f9f354fc | 554 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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); | |
f9f354fc XL |
656 | let just_matches = |
657 | state.inst_ptrs().all(|ip| self.prog[ip].is_match()); | |
94b46f34 XL |
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 | |
f9f354fc XL |
669 | && at + 2 < text.len() |
670 | { | |
94b46f34 XL |
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 | |
5869c6ff | 682 | // want to do quick prefix scanning. If the program doesn't |
94b46f34 XL |
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 | ||
5869c6ff | 728 | // Run the DFA once more on the special EOF sentinel value. |
94b46f34 XL |
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. | |
f9f354fc | 747 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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 { | |
f9f354fc | 791 | return result; |
94b46f34 XL |
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 | ||
5869c6ff | 833 | // Run the DFA once more on the special EOF sentinel value. |
94b46f34 XL |
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 | /// | |
cdc7bbd5 | 851 | /// This elides bounds checks, and is therefore not safe. |
f9f354fc | 852 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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. | |
5869c6ff XL |
916 | // (The "start" flags are computed immediately following the |
917 | // current byte and are handled below.) | |
94b46f34 XL |
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 | |
f9f354fc XL |
969 | && !qnext.contains(ip as usize) |
970 | { | |
94b46f34 XL |
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( | |
f9f354fc XL |
979 | inst.goto as InstPtr, |
980 | qnext, | |
981 | empty_flags, | |
982 | ); | |
94b46f34 XL |
983 | } |
984 | } | |
985 | } | |
986 | } | |
987 | ||
f9f354fc XL |
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 | }; | |
94b46f34 XL |
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. | |
f9f354fc XL |
1007 | let mut next = |
1008 | match self.cached_state(qnext, state_flags, Some(&mut si)) { | |
1009 | None => return None, | |
1010 | Some(next) => next, | |
1011 | }; | |
94b46f34 XL |
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 | |
5869c6ff | 1051 | /// be set in this case. (Even if the following byte is a `\n`, it will |
94b46f34 XL |
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 | ) { | |
94b46f34 | 1059 | use prog::EmptyLook::*; |
f9f354fc | 1060 | use prog::Inst::*; |
94b46f34 XL |
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 | } | |
f9f354fc XL |
1098 | NotWordBoundaryAscii |
1099 | if flags.not_word_boundary => | |
1100 | { | |
94b46f34 XL |
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. | |
f9f354fc | 1164 | if let Some(si) = self.cache.compiled.get_ptr(&key) { |
94b46f34 XL |
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) | |
f9f354fc XL |
1170 | { |
1171 | // Ooops. DFA is giving up. | |
1172 | return None; | |
1173 | } | |
94b46f34 XL |
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 | ||
f9f354fc XL |
1204 | let mut insts = |
1205 | mem::replace(&mut self.cache.insts_scratch_space, vec![]); | |
0731742a | 1206 | insts.clear(); |
94b46f34 | 1207 | // Reserve 1 byte for flags. |
0731742a XL |
1208 | insts.push(0); |
1209 | ||
94b46f34 XL |
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. | |
f9f354fc XL |
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 | }; | |
0731742a XL |
1240 | self.cache.insts_scratch_space = insts; |
1241 | opt_state | |
94b46f34 XL |
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 { | |
0731742a | 1256 | if self.cache.compiled.is_empty() { |
94b46f34 XL |
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. | |
0731742a | 1286 | let nstates = self.cache.compiled.len(); |
94b46f34 XL |
1287 | if self.cache.flush_count >= 3 |
1288 | && self.at >= self.last_cache_flush | |
f9f354fc XL |
1289 | && (self.at - self.last_cache_flush) <= 10 * nstates |
1290 | { | |
94b46f34 XL |
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(); | |
94b46f34 XL |
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. | |
0731742a | 1325 | if let Some(si) = self.cache.compiled.get_ptr(&state) { |
94b46f34 XL |
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. | |
f9f354fc | 1367 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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 = { | |
f9f354fc XL |
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 | |
94b46f34 XL |
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 { | |
0731742a | 1465 | self.cache.compiled.get_state(si).unwrap() |
94b46f34 XL |
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. | |
f9f354fc | 1496 | self.cache.size += self.cache.trans.state_heap_size() |
0731742a | 1497 | + state.data.len() |
94b46f34 XL |
1498 | + (2 * mem::size_of::<State>()) |
1499 | + mem::size_of::<StatePtr>(); | |
94b46f34 XL |
1500 | self.cache.compiled.insert(state, si); |
1501 | // Transition table and set of states and map should all be in sync. | |
f9f354fc XL |
1502 | debug_assert!( |
1503 | self.cache.compiled.len() == self.cache.trans.num_states() | |
1504 | ); | |
94b46f34 XL |
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. | |
f9f354fc | 1529 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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. | |
f9f354fc | 1538 | #[cfg_attr(feature = "perf-inline", inline(always))] |
94b46f34 XL |
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 | |
f9f354fc XL |
1558 | && !self.prog.prefixes.is_empty() |
1559 | && !self.prog.is_anchored_start | |
94b46f34 XL |
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 | ||
0731742a XL |
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 | ||
94b46f34 XL |
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 { | |
f9f354fc | 1651 | Transitions { table: vec![], num_byte_classes: num_byte_classes } |
94b46f34 XL |
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 | ||
cdc7bbd5 | 1691 | /// Like `next`, but uses unchecked access and is therefore not safe. |
94b46f34 XL |
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 { | |
f9f354fc XL |
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 | } | |
94b46f34 XL |
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 { | |
f9f354fc | 1742 | b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'_' => true, |
94b46f34 XL |
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") | |
f9f354fc XL |
1760 | .field("flags", &self.flags()) |
1761 | .field("insts", &ips) | |
1762 | .finish() | |
94b46f34 XL |
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") | |
f9f354fc XL |
1801 | .field("is_match", &self.is_match()) |
1802 | .field("is_word", &self.is_word()) | |
1803 | .field("has_empty", &self.has_empty()) | |
1804 | .finish() | |
94b46f34 XL |
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 | ||
94b46f34 | 1894 | use super::{ |
f9f354fc XL |
1895 | push_inst_ptr, read_vari32, read_varu32, write_vari32, write_varu32, |
1896 | State, StateFlags, | |
94b46f34 | 1897 | }; |
cdc7bbd5 | 1898 | use quickcheck::{quickcheck, Gen, QuickCheck}; |
f9f354fc | 1899 | use std::sync::Arc; |
94b46f34 XL |
1900 | |
1901 | #[test] | |
1902 | fn prop_state_encode_decode() { | |
cdc7bbd5 XL |
1903 | fn p(mut ips: Vec<u32>, flags: u8) -> bool { |
1904 | // It looks like our encoding scheme can't handle instruction | |
1905 | // pointers at or above 2**31. We should fix that, but it seems | |
1906 | // unlikely to occur in real code due to the amount of memory | |
1907 | // required for such a state machine. So for now, we just clamp | |
1908 | // our test data. | |
1909 | for ip in &mut ips { | |
1910 | if *ip >= 1 << 31 { | |
1911 | *ip = (1 << 31) - 1; | |
1912 | } | |
1913 | } | |
94b46f34 XL |
1914 | let mut data = vec![flags]; |
1915 | let mut prev = 0; | |
1916 | for &ip in ips.iter() { | |
1917 | push_inst_ptr(&mut data, &mut prev, ip); | |
1918 | } | |
0731742a | 1919 | let state = State { data: Arc::from(&data[..]) }; |
94b46f34 XL |
1920 | |
1921 | let expected: Vec<usize> = | |
1922 | ips.into_iter().map(|ip| ip as usize).collect(); | |
1923 | let got: Vec<usize> = state.inst_ptrs().collect(); | |
1924 | expected == got && state.flags() == StateFlags(flags) | |
1925 | } | |
1926 | QuickCheck::new() | |
cdc7bbd5 | 1927 | .gen(Gen::new(10_000)) |
94b46f34 XL |
1928 | .quickcheck(p as fn(Vec<u32>, u8) -> bool); |
1929 | } | |
1930 | ||
1931 | #[test] | |
1932 | fn prop_read_write_u32() { | |
1933 | fn p(n: u32) -> bool { | |
1934 | let mut buf = vec![]; | |
1935 | write_varu32(&mut buf, n); | |
1936 | let (got, nread) = read_varu32(&buf); | |
1937 | nread == buf.len() && got == n | |
1938 | } | |
1939 | quickcheck(p as fn(u32) -> bool); | |
1940 | } | |
1941 | ||
1942 | #[test] | |
1943 | fn prop_read_write_i32() { | |
1944 | fn p(n: i32) -> bool { | |
1945 | let mut buf = vec![]; | |
1946 | write_vari32(&mut buf, n); | |
1947 | let (got, nread) = read_vari32(&buf); | |
1948 | nread == buf.len() && got == n | |
1949 | } | |
1950 | quickcheck(p as fn(i32) -> bool); | |
1951 | } | |
1952 | } |