1 // Copyright 2011 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
6 // * Redistributions of source code must retain the above copyright
7 // notice, this list of conditions and the following disclaimer.
8 // * Redistributions in binary form must reproduce the above
9 // copyright notice, this list of conditions and the following
10 // disclaimer in the documentation and/or other materials provided
11 // with the distribution.
12 // * Neither the name of Google Inc. nor the names of its
13 // contributors may be used to endorse or promote products derived
14 // from this software without specific prior written permission.
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 #ifndef V8_STRING_SEARCH_H_
29 #define V8_STRING_SEARCH_H_
35 //---------------------------------------------------------------------
36 // String Search object.
37 //---------------------------------------------------------------------
39 // Class holding constants and methods that apply to all string search variants,
40 // independently of subject and pattern char size.
41 class StringSearchBase {
43 // Cap on the maximal shift in the Boyer-Moore implementation. By setting a
44 // limit, we can fix the size of tables. For a needle longer than this limit,
45 // search will not be optimal, since we only build tables for a suffix
46 // of the string, but it is a safe approximation.
47 static const int kBMMaxShift = Isolate::kBMMaxShift;
49 // Reduce alphabet to this size.
50 // One of the tables used by Boyer-Moore and Boyer-Moore-Horspool has size
51 // proportional to the input alphabet. We reduce the alphabet size by
52 // equating input characters modulo a smaller alphabet size. This gives
53 // a potentially less efficient searching, but is a safe approximation.
54 // For needles using only characters in the same Unicode 256-code point page,
55 // there is no search speed degradation.
56 static const int kAsciiAlphabetSize = 128;
57 static const int kUC16AlphabetSize = Isolate::kUC16AlphabetSize;
59 // Bad-char shift table stored in the state. It's length is the alphabet size.
60 // For patterns below this length, the skip length of Boyer-Moore is too short
61 // to compensate for the algorithmic overhead compared to simple brute force.
62 static const int kBMMinPatternLength = 7;
64 static inline bool IsAsciiString(Vector<const char>) {
68 static inline bool IsAsciiString(Vector<const uc16> string) {
69 return String::IsAscii(string.start(), string.length());
76 template <typename PatternChar, typename SubjectChar>
77 class StringSearch : private StringSearchBase {
79 StringSearch(Isolate* isolate, Vector<const PatternChar> pattern)
82 start_(Max(0, pattern.length() - kBMMaxShift)) {
83 if (sizeof(PatternChar) > sizeof(SubjectChar)) {
84 if (!IsAsciiString(pattern_)) {
85 strategy_ = &FailSearch;
89 int pattern_length = pattern_.length();
90 if (pattern_length < kBMMinPatternLength) {
91 if (pattern_length == 1) {
92 strategy_ = &SingleCharSearch;
95 strategy_ = &LinearSearch;
98 strategy_ = &InitialSearch;
101 int Search(Vector<const SubjectChar> subject, int index) {
102 return strategy_(this, subject, index);
105 static inline int AlphabetSize() {
106 if (sizeof(PatternChar) == 1) {
108 return kAsciiAlphabetSize;
110 ASSERT(sizeof(PatternChar) == 2);
112 return kUC16AlphabetSize;
117 typedef int (*SearchFunction)( // NOLINT - it's not a cast!
118 StringSearch<PatternChar, SubjectChar>*,
119 Vector<const SubjectChar>,
122 static int FailSearch(StringSearch<PatternChar, SubjectChar>*,
123 Vector<const SubjectChar>,
128 static int SingleCharSearch(StringSearch<PatternChar, SubjectChar>* search,
129 Vector<const SubjectChar> subject,
132 static int LinearSearch(StringSearch<PatternChar, SubjectChar>* search,
133 Vector<const SubjectChar> subject,
136 static int InitialSearch(StringSearch<PatternChar, SubjectChar>* search,
137 Vector<const SubjectChar> subject,
140 static int BoyerMooreHorspoolSearch(
141 StringSearch<PatternChar, SubjectChar>* search,
142 Vector<const SubjectChar> subject,
145 static int BoyerMooreSearch(StringSearch<PatternChar, SubjectChar>* search,
146 Vector<const SubjectChar> subject,
149 void PopulateBoyerMooreHorspoolTable();
151 void PopulateBoyerMooreTable();
153 static inline int CharOccurrence(int* bad_char_occurrence,
154 SubjectChar char_code) {
155 if (sizeof(SubjectChar) == 1) {
156 return bad_char_occurrence[static_cast<int>(char_code)];
158 if (sizeof(PatternChar) == 1) {
159 if (static_cast<unsigned int>(char_code) > String::kMaxAsciiCharCodeU) {
162 return bad_char_occurrence[static_cast<unsigned int>(char_code)];
164 // Both pattern and subject are UC16. Reduce character to equivalence class.
165 int equiv_class = char_code % kUC16AlphabetSize;
166 return bad_char_occurrence[equiv_class];
169 // The following tables are shared by all searches.
170 // TODO(lrn): Introduce a way for a pattern to keep its tables
171 // between searches (e.g., for an Atom RegExp).
173 // Store for the BoyerMoore(Horspool) bad char shift table.
174 // Return a table covering the last kBMMaxShift+1 positions of
176 int* bad_char_table() {
177 return isolate_->bad_char_shift_table();
180 // Store for the BoyerMoore good suffix shift table.
181 int* good_suffix_shift_table() {
182 // Return biased pointer that maps the range [start_..pattern_.length()
183 // to the kGoodSuffixShiftTable array.
184 return isolate_->good_suffix_shift_table() - start_;
187 // Table used temporarily while building the BoyerMoore good suffix
189 int* suffix_table() {
190 // Return biased pointer that maps the range [start_..pattern_.length()
191 // to the kSuffixTable array.
192 return isolate_->suffix_table() - start_;
196 // The pattern to search for.
197 Vector<const PatternChar> pattern_;
198 // Pointer to implementation of the search.
199 SearchFunction strategy_;
200 // Cache value of Max(0, pattern_length() - kBMMaxShift)
205 //---------------------------------------------------------------------
206 // Single Character Pattern Search Strategy
207 //---------------------------------------------------------------------
209 template <typename PatternChar, typename SubjectChar>
210 int StringSearch<PatternChar, SubjectChar>::SingleCharSearch(
211 StringSearch<PatternChar, SubjectChar>* search,
212 Vector<const SubjectChar> subject,
214 ASSERT_EQ(1, search->pattern_.length());
215 PatternChar pattern_first_char = search->pattern_[0];
217 if (sizeof(SubjectChar) == 1 && sizeof(PatternChar) == 1) {
218 const SubjectChar* pos = reinterpret_cast<const SubjectChar*>(
219 memchr(subject.start() + i,
221 subject.length() - i));
222 if (pos == NULL) return -1;
223 return static_cast<int>(pos - subject.start());
225 if (sizeof(PatternChar) > sizeof(SubjectChar)) {
226 if (static_cast<uc16>(pattern_first_char) > String::kMaxAsciiCharCodeU) {
230 SubjectChar search_char = static_cast<SubjectChar>(pattern_first_char);
231 int n = subject.length();
233 if (subject[i++] == search_char) return i - 1;
239 //---------------------------------------------------------------------
240 // Linear Search Strategy
241 //---------------------------------------------------------------------
244 template <typename PatternChar, typename SubjectChar>
245 inline bool CharCompare(const PatternChar* pattern,
246 const SubjectChar* subject,
251 if (pattern[pos] != subject[pos]) {
255 } while (pos < length);
260 // Simple linear search for short patterns. Never bails out.
261 template <typename PatternChar, typename SubjectChar>
262 int StringSearch<PatternChar, SubjectChar>::LinearSearch(
263 StringSearch<PatternChar, SubjectChar>* search,
264 Vector<const SubjectChar> subject,
266 Vector<const PatternChar> pattern = search->pattern_;
267 ASSERT(pattern.length() > 1);
268 int pattern_length = pattern.length();
269 PatternChar pattern_first_char = pattern[0];
271 int n = subject.length() - pattern_length;
273 if (sizeof(SubjectChar) == 1 && sizeof(PatternChar) == 1) {
274 const SubjectChar* pos = reinterpret_cast<const SubjectChar*>(
275 memchr(subject.start() + i,
278 if (pos == NULL) return -1;
279 i = static_cast<int>(pos - subject.start()) + 1;
281 if (subject[i++] != pattern_first_char) continue;
283 // Loop extracted to separate function to allow using return to do
285 if (CharCompare(pattern.start() + 1,
287 pattern_length - 1)) {
294 //---------------------------------------------------------------------
295 // Boyer-Moore string search
296 //---------------------------------------------------------------------
298 template <typename PatternChar, typename SubjectChar>
299 int StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
300 StringSearch<PatternChar, SubjectChar>* search,
301 Vector<const SubjectChar> subject,
303 Vector<const PatternChar> pattern = search->pattern_;
304 int subject_length = subject.length();
305 int pattern_length = pattern.length();
306 // Only preprocess at most kBMMaxShift last characters of pattern.
307 int start = search->start_;
309 int* bad_char_occurence = search->bad_char_table();
310 int* good_suffix_shift = search->good_suffix_shift_table();
312 PatternChar last_char = pattern[pattern_length - 1];
313 int index = start_index;
314 // Continue search from i.
315 while (index <= subject_length - pattern_length) {
316 int j = pattern_length - 1;
318 while (last_char != (c = subject[index + j])) {
320 j - CharOccurrence(bad_char_occurence, c);
322 if (index > subject_length - pattern_length) {
326 while (j >= 0 && pattern[j] == (c = subject[index + j])) j--;
329 } else if (j < start) {
330 // we have matched more than our tables allow us to be smart about.
331 // Fall back on BMH shift.
332 index += pattern_length - 1
333 - CharOccurrence(bad_char_occurence,
334 static_cast<SubjectChar>(last_char));
336 int gs_shift = good_suffix_shift[j + 1];
338 CharOccurrence(bad_char_occurence, c);
339 int shift = j - bc_occ;
340 if (gs_shift > shift) {
351 template <typename PatternChar, typename SubjectChar>
352 void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreTable() {
353 int pattern_length = pattern_.length();
354 const PatternChar* pattern = pattern_.start();
355 // Only look at the last kBMMaxShift characters of pattern (from start_
356 // to pattern_length).
358 int length = pattern_length - start;
360 // Biased tables so that we can use pattern indices as table indices,
361 // even if we only cover the part of the pattern from offset start.
362 int* shift_table = good_suffix_shift_table();
363 int* suffix_table = this->suffix_table();
366 for (int i = start; i < pattern_length; i++) {
367 shift_table[i] = length;
369 shift_table[pattern_length] = 1;
370 suffix_table[pattern_length] = pattern_length + 1;
372 if (pattern_length <= start) {
377 PatternChar last_char = pattern[pattern_length - 1];
378 int suffix = pattern_length + 1;
380 int i = pattern_length;
382 PatternChar c = pattern[i - 1];
383 while (suffix <= pattern_length && c != pattern[suffix - 1]) {
384 if (shift_table[suffix] == length) {
385 shift_table[suffix] = suffix - i;
387 suffix = suffix_table[suffix];
389 suffix_table[--i] = --suffix;
390 if (suffix == pattern_length) {
391 // No suffix to extend, so we check against last_char only.
392 while ((i > start) && (pattern[i - 1] != last_char)) {
393 if (shift_table[pattern_length] == length) {
394 shift_table[pattern_length] = pattern_length - i;
396 suffix_table[--i] = pattern_length;
399 suffix_table[--i] = --suffix;
404 // Build shift table using suffixes.
405 if (suffix < pattern_length) {
406 for (int i = start; i <= pattern_length; i++) {
407 if (shift_table[i] == length) {
408 shift_table[i] = suffix - start;
411 suffix = suffix_table[suffix];
417 //---------------------------------------------------------------------
418 // Boyer-Moore-Horspool string search.
419 //---------------------------------------------------------------------
421 template <typename PatternChar, typename SubjectChar>
422 int StringSearch<PatternChar, SubjectChar>::BoyerMooreHorspoolSearch(
423 StringSearch<PatternChar, SubjectChar>* search,
424 Vector<const SubjectChar> subject,
426 Vector<const PatternChar> pattern = search->pattern_;
427 int subject_length = subject.length();
428 int pattern_length = pattern.length();
429 int* char_occurrences = search->bad_char_table();
430 int badness = -pattern_length;
432 // How bad we are doing without a good-suffix table.
433 PatternChar last_char = pattern[pattern_length - 1];
434 int last_char_shift = pattern_length - 1 -
435 CharOccurrence(char_occurrences, static_cast<SubjectChar>(last_char));
437 int index = start_index; // No matches found prior to this index.
438 while (index <= subject_length - pattern_length) {
439 int j = pattern_length - 1;
441 while (last_char != (subject_char = subject[index + j])) {
442 int bc_occ = CharOccurrence(char_occurrences, subject_char);
443 int shift = j - bc_occ;
445 badness += 1 - shift; // at most zero, so badness cannot increase.
446 if (index > subject_length - pattern_length) {
451 while (j >= 0 && pattern[j] == (subject[index + j])) j--;
455 index += last_char_shift;
456 // Badness increases by the number of characters we have
457 // checked, and decreases by the number of characters we
458 // can skip by shifting. It's a measure of how we are doing
459 // compared to reading each character exactly once.
460 badness += (pattern_length - j) - last_char_shift;
462 search->PopulateBoyerMooreTable();
463 search->strategy_ = &BoyerMooreSearch;
464 return BoyerMooreSearch(search, subject, index);
472 template <typename PatternChar, typename SubjectChar>
473 void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreHorspoolTable() {
474 int pattern_length = pattern_.length();
476 int* bad_char_occurrence = bad_char_table();
478 // Only preprocess at most kBMMaxShift last characters of pattern.
480 // Run forwards to populate bad_char_table, so that *last* instance
481 // of character equivalence class is the one registered.
482 // Notice: Doesn't include the last character.
483 int table_size = AlphabetSize();
484 if (start == 0) { // All patterns less than kBMMaxShift in length.
485 memset(bad_char_occurrence,
487 table_size * sizeof(*bad_char_occurrence));
489 for (int i = 0; i < table_size; i++) {
490 bad_char_occurrence[i] = start - 1;
493 for (int i = start; i < pattern_length - 1; i++) {
494 PatternChar c = pattern_[i];
495 int bucket = (sizeof(PatternChar) == 1) ? c : c % AlphabetSize();
496 bad_char_occurrence[bucket] = i;
500 //---------------------------------------------------------------------
501 // Linear string search with bailout to BMH.
502 //---------------------------------------------------------------------
504 // Simple linear search for short patterns, which bails out if the string
505 // isn't found very early in the subject. Upgrades to BoyerMooreHorspool.
506 template <typename PatternChar, typename SubjectChar>
507 int StringSearch<PatternChar, SubjectChar>::InitialSearch(
508 StringSearch<PatternChar, SubjectChar>* search,
509 Vector<const SubjectChar> subject,
511 Vector<const PatternChar> pattern = search->pattern_;
512 int pattern_length = pattern.length();
513 // Badness is a count of how much work we have done. When we have
514 // done enough work we decide it's probably worth switching to a better
516 int badness = -10 - (pattern_length << 2);
518 // We know our pattern is at least 2 characters, we cache the first so
519 // the common case of the first character not matching is faster.
520 PatternChar pattern_first_char = pattern[0];
521 for (int i = index, n = subject.length() - pattern_length; i <= n; i++) {
524 if (sizeof(SubjectChar) == 1 && sizeof(PatternChar) == 1) {
525 const SubjectChar* pos = reinterpret_cast<const SubjectChar*>(
526 memchr(subject.start() + i,
532 i = static_cast<int>(pos - subject.start());
534 if (subject[i] != pattern_first_char) continue;
538 if (pattern[j] != subject[i + j]) {
542 } while (j < pattern_length);
543 if (j == pattern_length) {
548 search->PopulateBoyerMooreHorspoolTable();
549 search->strategy_ = &BoyerMooreHorspoolSearch;
550 return BoyerMooreHorspoolSearch(search, subject, i);
557 // Perform a a single stand-alone search.
558 // If searching multiple times for the same pattern, a search
559 // object should be constructed once and the Search function then called
561 template <typename SubjectChar, typename PatternChar>
562 int SearchString(Isolate* isolate,
563 Vector<const SubjectChar> subject,
564 Vector<const PatternChar> pattern,
566 StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
567 return search.Search(subject, start_index);
570 }} // namespace v8::internal
572 #endif // V8_STRING_SEARCH_H_