1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
use std::mem;

use aho_corasick::{self, packed, AhoCorasick, AhoCorasickBuilder};
use memchr::{memchr, memchr2, memchr3, memmem};
use regex_syntax::hir::literal::{Literal, Literals};

/// A prefix extracted from a compiled regular expression.
///
/// A regex prefix is a set of literal strings that *must* be matched at the
/// beginning of a regex in order for the entire regex to match. Similarly
/// for a regex suffix.
#[derive(Clone, Debug)]
pub struct LiteralSearcher {
    complete: bool,
    lcp: Memmem,
    lcs: Memmem,
    matcher: Matcher,
}

#[derive(Clone, Debug)]
enum Matcher {
    /// No literals. (Never advances through the input.)
    Empty,
    /// A set of four or more single byte literals.
    Bytes(SingleByteSet),
    /// A single substring, using vector accelerated routines when available.
    Memmem(Memmem),
    /// An Aho-Corasick automaton.
    AC { ac: AhoCorasick<u32>, lits: Vec<Literal> },
    /// A packed multiple substring searcher, using SIMD.
    ///
    /// Note that Aho-Corasick will actually use this packed searcher
    /// internally automatically, however, there is some overhead associated
    /// with going through the Aho-Corasick machinery. So using the packed
    /// searcher directly results in some gains.
    Packed { s: packed::Searcher, lits: Vec<Literal> },
}

impl LiteralSearcher {
    /// Returns a matcher that never matches and never advances the input.
    pub fn empty() -> Self {
        Self::new(Literals::empty(), Matcher::Empty)
    }

    /// Returns a matcher for literal prefixes from the given set.
    pub fn prefixes(lits: Literals) -> Self {
        let matcher = Matcher::prefixes(&lits);
        Self::new(lits, matcher)
    }

    /// Returns a matcher for literal suffixes from the given set.
    pub fn suffixes(lits: Literals) -> Self {
        let matcher = Matcher::suffixes(&lits);
        Self::new(lits, matcher)
    }

    fn new(lits: Literals, matcher: Matcher) -> Self {
        let complete = lits.all_complete();
        LiteralSearcher {
            complete,
            lcp: Memmem::new(lits.longest_common_prefix()),
            lcs: Memmem::new(lits.longest_common_suffix()),
            matcher,
        }
    }

    /// Returns true if all matches comprise the entire regular expression.
    ///
    /// This does not necessarily mean that a literal match implies a match
    /// of the regular expression. For example, the regular expression `^a`
    /// is comprised of a single complete literal `a`, but the regular
    /// expression demands that it only match at the beginning of a string.
    pub fn complete(&self) -> bool {
        self.complete && !self.is_empty()
    }

    /// Find the position of a literal in `haystack` if it exists.
    #[cfg_attr(feature = "perf-inline", inline(always))]
    pub fn find(&self, haystack: &[u8]) -> Option<(usize, usize)> {
        use self::Matcher::*;
        match self.matcher {
            Empty => Some((0, 0)),
            Bytes(ref sset) => sset.find(haystack).map(|i| (i, i + 1)),
            Memmem(ref s) => s.find(haystack).map(|i| (i, i + s.len())),
            AC { ref ac, .. } => {
                ac.find(haystack).map(|m| (m.start(), m.end()))
            }
            Packed { ref s, .. } => {
                s.find(haystack).map(|m| (m.start(), m.end()))
            }
        }
    }

    /// Like find, except matches must start at index `0`.
    pub fn find_start(&self, haystack: &[u8]) -> Option<(usize, usize)> {
        for lit in self.iter() {
            if lit.len() > haystack.len() {
                continue;
            }
            if lit == &haystack[0..lit.len()] {
                return Some((0, lit.len()));
            }
        }
        None
    }

    /// Like find, except matches must end at index `haystack.len()`.
    pub fn find_end(&self, haystack: &[u8]) -> Option<(usize, usize)> {
        for lit in self.iter() {
            if lit.len() > haystack.len() {
                continue;
            }
            if lit == &haystack[haystack.len() - lit.len()..] {
                return Some((haystack.len() - lit.len(), haystack.len()));
            }
        }
        None
    }

    /// Returns an iterator over all literals to be matched.
    pub fn iter(&self) -> LiteralIter<'_> {
        match self.matcher {
            Matcher::Empty => LiteralIter::Empty,
            Matcher::Bytes(ref sset) => LiteralIter::Bytes(&sset.dense),
            Matcher::Memmem(ref s) => LiteralIter::Single(&s.finder.needle()),
            Matcher::AC { ref lits, .. } => LiteralIter::AC(lits),
            Matcher::Packed { ref lits, .. } => LiteralIter::Packed(lits),
        }
    }

    /// Returns a matcher for the longest common prefix of this matcher.
    pub fn lcp(&self) -> &Memmem {
        &self.lcp
    }

    /// Returns a matcher for the longest common suffix of this matcher.
    pub fn lcs(&self) -> &Memmem {
        &self.lcs
    }

    /// Returns true iff this prefix is empty.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Returns the number of prefixes in this machine.
    pub fn len(&self) -> usize {
        use self::Matcher::*;
        match self.matcher {
            Empty => 0,
            Bytes(ref sset) => sset.dense.len(),
            Memmem(_) => 1,
            AC { ref ac, .. } => ac.pattern_count(),
            Packed { ref lits, .. } => lits.len(),
        }
    }

    /// Return the approximate heap usage of literals in bytes.
    pub fn approximate_size(&self) -> usize {
        use self::Matcher::*;
        match self.matcher {
            Empty => 0,
            Bytes(ref sset) => sset.approximate_size(),
            Memmem(ref single) => single.approximate_size(),
            AC { ref ac, .. } => ac.heap_bytes(),
            Packed { ref s, .. } => s.heap_bytes(),
        }
    }
}

impl Matcher {
    fn prefixes(lits: &Literals) -> Self {
        let sset = SingleByteSet::prefixes(lits);
        Matcher::new(lits, sset)
    }

    fn suffixes(lits: &Literals) -> Self {
        let sset = SingleByteSet::suffixes(lits);
        Matcher::new(lits, sset)
    }

    fn new(lits: &Literals, sset: SingleByteSet) -> Self {
        if lits.literals().is_empty() {
            return Matcher::Empty;
        }
        if sset.dense.len() >= 26 {
            // Avoid trying to match a large number of single bytes.
            // This is *very* sensitive to a frequency analysis comparison
            // between the bytes in sset and the composition of the haystack.
            // No matter the size of sset, if its members all are rare in the
            // haystack, then it'd be worth using it. How to tune this... IDK.
            // ---AG
            return Matcher::Empty;
        }
        if sset.complete {
            return Matcher::Bytes(sset);
        }
        if lits.literals().len() == 1 {
            return Matcher::Memmem(Memmem::new(&lits.literals()[0]));
        }

        let pats = lits.literals().to_owned();
        let is_aho_corasick_fast = sset.dense.len() <= 1 && sset.all_ascii;
        if lits.literals().len() <= 100 && !is_aho_corasick_fast {
            let mut builder = packed::Config::new()
                .match_kind(packed::MatchKind::LeftmostFirst)
                .builder();
            if let Some(s) = builder.extend(&pats).build() {
                return Matcher::Packed { s, lits: pats };
            }
        }
        let ac = AhoCorasickBuilder::new()
            .match_kind(aho_corasick::MatchKind::LeftmostFirst)
            .dfa(true)
            .build_with_size::<u32, _, _>(&pats)
            .unwrap();
        Matcher::AC { ac, lits: pats }
    }
}

#[derive(Debug)]
pub enum LiteralIter<'a> {
    Empty,
    Bytes(&'a [u8]),
    Single(&'a [u8]),
    AC(&'a [Literal]),
    Packed(&'a [Literal]),
}

impl<'a> Iterator for LiteralIter<'a> {
    type Item = &'a [u8];

    fn next(&mut self) -> Option<Self::Item> {
        match *self {
            LiteralIter::Empty => None,
            LiteralIter::Bytes(ref mut many) => {
                if many.is_empty() {
                    None
                } else {
                    let next = &many[0..1];
                    *many = &many[1..];
                    Some(next)
                }
            }
            LiteralIter::Single(ref mut one) => {
                if one.is_empty() {
                    None
                } else {
                    let next = &one[..];
                    *one = &[];
                    Some(next)
                }
            }
            LiteralIter::AC(ref mut lits) => {
                if lits.is_empty() {
                    None
                } else {
                    let next = &lits[0];
                    *lits = &lits[1..];
                    Some(&**next)
                }
            }
            LiteralIter::Packed(ref mut lits) => {
                if lits.is_empty() {
                    None
                } else {
                    let next = &lits[0];
                    *lits = &lits[1..];
                    Some(&**next)
                }
            }
        }
    }
}

#[derive(Clone, Debug)]
struct SingleByteSet {
    sparse: Vec<bool>,
    dense: Vec<u8>,
    complete: bool,
    all_ascii: bool,
}

impl SingleByteSet {
    fn new() -> SingleByteSet {
        SingleByteSet {
            sparse: vec![false; 256],
            dense: vec![],
            complete: true,
            all_ascii: true,
        }
    }

    fn prefixes(lits: &Literals) -> SingleByteSet {
        let mut sset = SingleByteSet::new();
        for lit in lits.literals() {
            sset.complete = sset.complete && lit.len() == 1;
            if let Some(&b) = lit.get(0) {
                if !sset.sparse[b as usize] {
                    if b > 0x7F {
                        sset.all_ascii = false;
                    }
                    sset.dense.push(b);
                    sset.sparse[b as usize] = true;
                }
            }
        }
        sset
    }

    fn suffixes(lits: &Literals) -> SingleByteSet {
        let mut sset = SingleByteSet::new();
        for lit in lits.literals() {
            sset.complete = sset.complete && lit.len() == 1;
            if let Some(&b) = lit.get(lit.len().checked_sub(1).unwrap()) {
                if !sset.sparse[b as usize] {
                    if b > 0x7F {
                        sset.all_ascii = false;
                    }
                    sset.dense.push(b);
                    sset.sparse[b as usize] = true;
                }
            }
        }
        sset
    }

    /// Faster find that special cases certain sizes to use memchr.
    #[cfg_attr(feature = "perf-inline", inline(always))]
    fn find(&self, text: &[u8]) -> Option<usize> {
        match self.dense.len() {
            0 => None,
            1 => memchr(self.dense[0], text),
            2 => memchr2(self.dense[0], self.dense[1], text),
            3 => memchr3(self.dense[0], self.dense[1], self.dense[2], text),
            _ => self._find(text),
        }
    }

    /// Generic find that works on any sized set.
    fn _find(&self, haystack: &[u8]) -> Option<usize> {
        for (i, &b) in haystack.iter().enumerate() {
            if self.sparse[b as usize] {
                return Some(i);
            }
        }
        None
    }

    fn approximate_size(&self) -> usize {
        (self.dense.len() * mem::size_of::<u8>())
            + (self.sparse.len() * mem::size_of::<bool>())
    }
}

/// A simple wrapper around the memchr crate's memmem implementation.
///
/// The API this exposes mirrors the API of previous substring searchers that
/// this supplanted.
#[derive(Clone, Debug)]
pub struct Memmem {
    finder: memmem::Finder<'static>,
    char_len: usize,
}

impl Memmem {
    fn new(pat: &[u8]) -> Memmem {
        Memmem {
            finder: memmem::Finder::new(pat).into_owned(),
            char_len: char_len_lossy(pat),
        }
    }

    #[cfg_attr(feature = "perf-inline", inline(always))]
    pub fn find(&self, haystack: &[u8]) -> Option<usize> {
        self.finder.find(haystack)
    }

    #[cfg_attr(feature = "perf-inline", inline(always))]
    pub fn is_suffix(&self, text: &[u8]) -> bool {
        if text.len() < self.len() {
            return false;
        }
        &text[text.len() - self.len()..] == self.finder.needle()
    }

    pub fn len(&self) -> usize {
        self.finder.needle().len()
    }

    pub fn char_len(&self) -> usize {
        self.char_len
    }

    fn approximate_size(&self) -> usize {
        self.finder.needle().len() * mem::size_of::<u8>()
    }
}

fn char_len_lossy(bytes: &[u8]) -> usize {
    String::from_utf8_lossy(bytes).chars().count()
}