/
bitstate.cc
381 lines (332 loc) · 11.2 KB
/
bitstate.cc
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
// Copyright 2008 The RE2 Authors. All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Tested by search_test.cc, exhaustive_test.cc, tester.cc
// Prog::SearchBitState is a regular expression search with submatch
// tracking for small regular expressions and texts. Similarly to
// testing/backtrack.cc, it allocates a bitmap with (count of
// lists) * (length of text) bits to make sure it never explores the
// same (instruction list, character position) multiple times. This
// limits the search to run in time linear in the length of the text.
//
// Unlike testing/backtrack.cc, SearchBitState is not recursive
// on the text.
//
// SearchBitState is a fast replacement for the NFA code on small
// regexps and texts when SearchOnePass cannot be used.
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <limits>
#include <utility>
#include "util/logging.h"
#include "re2/pod_array.h"
#include "re2/prog.h"
#include "re2/regexp.h"
namespace re2 {
struct Job {
int id;
int rle; // run length encoding
const char* p;
};
class BitState {
public:
explicit BitState(Prog* prog);
// The usual Search prototype.
// Can only call Search once per BitState.
bool Search(absl::string_view text, absl::string_view context, bool anchored,
bool longest, absl::string_view* submatch, int nsubmatch);
private:
inline bool ShouldVisit(int id, const char* p);
void Push(int id, const char* p);
void GrowStack();
bool TrySearch(int id, const char* p);
// Search parameters
Prog* prog_; // program being run
absl::string_view text_; // text being searched
absl::string_view context_; // greater context of text being searched
bool anchored_; // whether search is anchored at text.begin()
bool longest_; // whether search wants leftmost-longest match
bool endmatch_; // whether match must end at text.end()
absl::string_view* submatch_; // submatches to fill in
int nsubmatch_; // # of submatches to fill in
// Search state
static constexpr int kVisitedBits = 64;
PODArray<uint64_t> visited_; // bitmap: (list ID, char*) pairs visited
PODArray<const char*> cap_; // capture registers
PODArray<Job> job_; // stack of text positions to explore
int njob_; // stack size
BitState(const BitState&) = delete;
BitState& operator=(const BitState&) = delete;
};
BitState::BitState(Prog* prog)
: prog_(prog),
anchored_(false),
longest_(false),
endmatch_(false),
submatch_(NULL),
nsubmatch_(0),
njob_(0) {
}
// Given id, which *must* be a list head, we can look up its list ID.
// Then the question is: Should the search visit the (list ID, p) pair?
// If so, remember that it was visited so that the next time,
// we don't repeat the visit.
bool BitState::ShouldVisit(int id, const char* p) {
int n = prog_->list_heads()[id] * static_cast<int>(text_.size()+1) +
static_cast<int>(p-text_.data());
if (visited_[n/kVisitedBits] & (uint64_t{1} << (n & (kVisitedBits-1))))
return false;
visited_[n/kVisitedBits] |= uint64_t{1} << (n & (kVisitedBits-1));
return true;
}
// Grow the stack.
void BitState::GrowStack() {
PODArray<Job> tmp(2*job_.size());
memmove(tmp.data(), job_.data(), njob_*sizeof job_[0]);
job_ = std::move(tmp);
}
// Push (id, p) onto the stack, growing it if necessary.
void BitState::Push(int id, const char* p) {
if (njob_ >= job_.size()) {
GrowStack();
if (njob_ >= job_.size()) {
LOG(DFATAL) << "GrowStack() failed: "
<< "njob_ = " << njob_ << ", "
<< "job_.size() = " << job_.size();
return;
}
}
// If id < 0, it's undoing a Capture,
// so we mustn't interfere with that.
if (id >= 0 && njob_ > 0) {
Job* top = &job_[njob_-1];
if (id == top->id &&
p == top->p + top->rle + 1 &&
top->rle < std::numeric_limits<int>::max()) {
++top->rle;
return;
}
}
Job* top = &job_[njob_++];
top->id = id;
top->rle = 0;
top->p = p;
}
// Try a search from instruction id0 in state p0.
// Return whether it succeeded.
bool BitState::TrySearch(int id0, const char* p0) {
bool matched = false;
const char* end = text_.data() + text_.size();
njob_ = 0;
// Push() no longer checks ShouldVisit(),
// so we must perform the check ourselves.
if (ShouldVisit(id0, p0))
Push(id0, p0);
while (njob_ > 0) {
// Pop job off stack.
--njob_;
int id = job_[njob_].id;
int& rle = job_[njob_].rle;
const char* p = job_[njob_].p;
if (id < 0) {
// Undo the Capture.
cap_[prog_->inst(-id)->cap()] = p;
continue;
}
if (rle > 0) {
p += rle;
// Revivify job on stack.
--rle;
++njob_;
}
Loop:
// Visit id, p.
Prog::Inst* ip = prog_->inst(id);
switch (ip->opcode()) {
default:
LOG(DFATAL) << "Unexpected opcode: " << ip->opcode();
return false;
case kInstFail:
break;
case kInstAltMatch:
if (ip->greedy(prog_)) {
// out1 is the Match instruction.
id = ip->out1();
p = end;
goto Loop;
}
if (longest_) {
// ip must be non-greedy...
// out is the Match instruction.
id = ip->out();
p = end;
goto Loop;
}
goto Next;
case kInstByteRange: {
int c = -1;
if (p < end)
c = *p & 0xFF;
if (!ip->Matches(c))
goto Next;
if (ip->hint() != 0)
Push(id+ip->hint(), p); // try the next when we're done
id = ip->out();
p++;
goto CheckAndLoop;
}
case kInstCapture:
if (!ip->last())
Push(id+1, p); // try the next when we're done
if (0 <= ip->cap() && ip->cap() < cap_.size()) {
// Capture p to register, but save old value first.
Push(-id, cap_[ip->cap()]); // undo when we're done
cap_[ip->cap()] = p;
}
id = ip->out();
goto CheckAndLoop;
case kInstEmptyWidth:
if (ip->empty() & ~Prog::EmptyFlags(context_, p))
goto Next;
if (!ip->last())
Push(id+1, p); // try the next when we're done
id = ip->out();
goto CheckAndLoop;
case kInstNop:
if (!ip->last())
Push(id+1, p); // try the next when we're done
id = ip->out();
CheckAndLoop:
// Sanity check: id is the head of its list, which must
// be the case if id-1 is the last of *its* list. :)
DCHECK(id == 0 || prog_->inst(id-1)->last());
if (ShouldVisit(id, p))
goto Loop;
break;
case kInstMatch: {
if (endmatch_ && p != end)
goto Next;
// We found a match. If the caller doesn't care
// where the match is, no point going further.
if (nsubmatch_ == 0)
return true;
// Record best match so far.
// Only need to check end point, because this entire
// call is only considering one start position.
matched = true;
cap_[1] = p;
if (submatch_[0].data() == NULL ||
(longest_ && p > submatch_[0].data() + submatch_[0].size())) {
for (int i = 0; i < nsubmatch_; i++)
submatch_[i] = absl::string_view(
cap_[2 * i],
static_cast<size_t>(cap_[2 * i + 1] - cap_[2 * i]));
}
// If going for first match, we're done.
if (!longest_)
return true;
// If we used the entire text, no longer match is possible.
if (p == end)
return true;
// Otherwise, continue on in hope of a longer match.
// Note the absence of the ShouldVisit() check here
// due to execution remaining in the same list.
Next:
if (!ip->last()) {
id++;
goto Loop;
}
break;
}
}
}
return matched;
}
// Search text (within context) for prog_.
bool BitState::Search(absl::string_view text, absl::string_view context,
bool anchored, bool longest, absl::string_view* submatch,
int nsubmatch) {
// Search parameters.
text_ = text;
context_ = context;
if (context_.data() == NULL)
context_ = text;
if (prog_->anchor_start() && BeginPtr(context_) != BeginPtr(text))
return false;
if (prog_->anchor_end() && EndPtr(context_) != EndPtr(text))
return false;
anchored_ = anchored || prog_->anchor_start();
longest_ = longest || prog_->anchor_end();
endmatch_ = prog_->anchor_end();
submatch_ = submatch;
nsubmatch_ = nsubmatch;
for (int i = 0; i < nsubmatch_; i++)
submatch_[i] = absl::string_view();
// Allocate scratch space.
int nvisited = prog_->list_count() * static_cast<int>(text.size()+1);
nvisited = (nvisited + kVisitedBits-1) / kVisitedBits;
visited_ = PODArray<uint64_t>(nvisited);
memset(visited_.data(), 0, nvisited*sizeof visited_[0]);
int ncap = 2*nsubmatch;
if (ncap < 2)
ncap = 2;
cap_ = PODArray<const char*>(ncap);
memset(cap_.data(), 0, ncap*sizeof cap_[0]);
// When sizeof(Job) == 16, we start with a nice round 1KiB. :)
job_ = PODArray<Job>(64);
// Anchored search must start at text.begin().
if (anchored_) {
cap_[0] = text.data();
return TrySearch(prog_->start(), text.data());
}
// Unanchored search, starting from each possible text position.
// Notice that we have to try the empty string at the end of
// the text, so the loop condition is p <= text.end(), not p < text.end().
// This looks like it's quadratic in the size of the text,
// but we are not clearing visited_ between calls to TrySearch,
// so no work is duplicated and it ends up still being linear.
const char* etext = text.data() + text.size();
for (const char* p = text.data(); p <= etext; p++) {
// Try to use prefix accel (e.g. memchr) to skip ahead.
if (p < etext && prog_->can_prefix_accel()) {
p = reinterpret_cast<const char*>(prog_->PrefixAccel(p, etext - p));
if (p == NULL)
p = etext;
}
cap_[0] = p;
if (TrySearch(prog_->start(), p)) // Match must be leftmost; done.
return true;
// Avoid invoking undefined behavior (arithmetic on a null pointer)
// by simply not continuing the loop.
if (p == NULL)
break;
}
return false;
}
// Bit-state search.
bool Prog::SearchBitState(absl::string_view text, absl::string_view context,
Anchor anchor, MatchKind kind,
absl::string_view* match, int nmatch) {
// If full match, we ask for an anchored longest match
// and then check that match[0] == text.
// So make sure match[0] exists.
absl::string_view sp0;
if (kind == kFullMatch) {
anchor = kAnchored;
if (nmatch < 1) {
match = &sp0;
nmatch = 1;
}
}
// Run the search.
BitState b(this);
bool anchored = anchor == kAnchored;
bool longest = kind != kFirstMatch;
if (!b.Search(text, context, anchored, longest, match, nmatch))
return false;
if (kind == kFullMatch && EndPtr(match[0]) != EndPtr(text))
return false;
return true;
}
} // namespace re2