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1c6da964 WJ |
1 | /* kwset.c - search for any of a set of keywords. |
2 | Copyright 1989 Free Software Foundation | |
3 | Written August 1989 by Mike Haertel. | |
4 | ||
5 | This program is free software; you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 1, or (at your option) | |
8 | any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
16 | along with this program; if not, write to the Free Software | |
17 | Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
18 | ||
19 | The author may be reached (Email) at the address mike@ai.mit.edu, | |
20 | or (US mail) as Mike Haertel c/o Free Software Foundation. */ | |
21 | ||
22 | #include "std.h" | |
23 | ||
24 | /* The algorithm implemented by these routines bears a startling resemblence | |
25 | to one discovered by Beate Commentz-Walter, although it is not identical. | |
26 | See "A String Matching Algorithm Fast on the Average," Technical Report, | |
27 | IBM-Germany, Scientific Center Heidelberg, Tiergartenstrasse 15, D-6900 | |
28 | Heidelberg, Germany. See also Aho, A.V., and M. Corasick, "Efficient | |
29 | String Matching: An Aid to Bibliographic Search," CACM June 1975, | |
30 | Vol. 18, No. 6, which describes the failure function used below. */ | |
31 | ||
32 | #include "kwset.h" | |
33 | #include "obstack.h" | |
34 | ||
35 | #define NCHAR (UCHAR_MAX + 1) | |
36 | #define obstack_chunk_alloc malloc | |
37 | #define obstack_chunk_free free | |
38 | ||
39 | /* Balanced tree of edges and labels leaving a given trie node. */ | |
40 | struct tree | |
41 | { | |
42 | struct tree *llink; /* Left link; MUST be first field. */ | |
43 | struct tree *rlink; /* Right link (to larger labels). */ | |
44 | struct trie *trie; /* Trie node pointed to by this edge. */ | |
45 | unsigned char label; /* Label on this edge. */ | |
46 | char balance; /* Difference in depths of subtrees. */ | |
47 | }; | |
48 | ||
49 | /* Node of a trie representing a set of reversed keywords. */ | |
50 | struct trie | |
51 | { | |
52 | unsigned int accepting; /* Word index of accepted word, or zero. */ | |
53 | struct tree *links; /* Tree of edges leaving this node. */ | |
54 | struct trie *parent; /* Parent of this node. */ | |
55 | struct trie *next; /* List of all trie nodes in level order. */ | |
56 | struct trie *fail; /* Aho-Corasick failure function. */ | |
57 | int depth; /* Depth of this node from the root. */ | |
58 | int shift; /* Shift function for search failures. */ | |
59 | int maxshift; /* Max shift of self and descendents. */ | |
60 | }; | |
61 | ||
62 | /* Structure returned opaquely to the caller, containing everything. */ | |
63 | struct kwset | |
64 | { | |
65 | struct obstack obstack; /* Obstack for node allocation. */ | |
66 | int words; /* Number of words in the trie. */ | |
67 | struct trie *trie; /* The trie itself. */ | |
68 | int mind; /* Minimum depth of an accepting node. */ | |
69 | int maxd; /* Maximum depth of any node. */ | |
70 | int delta[NCHAR]; /* Delta table for rapid search. */ | |
71 | struct trie *next[NCHAR]; /* Table of children of the root. */ | |
72 | const char *trans; /* Character translation table. */ | |
73 | }; | |
74 | ||
75 | /* Allocate and initialize a keyword set object, returning an opaque | |
76 | pointer to it. Return NULL if memory is not available. */ | |
77 | kwset_t | |
78 | DEFUN(kwsalloc, (trans), const char *trans) | |
79 | { | |
80 | struct kwset *kwset; | |
81 | ||
82 | kwset = (struct kwset *) malloc(sizeof (struct kwset)); | |
83 | if (!kwset) | |
84 | return NULL; | |
85 | ||
86 | obstack_init(&kwset->obstack); | |
87 | kwset->words = 0; | |
88 | kwset->trie | |
89 | = (struct trie *) obstack_alloc(&kwset->obstack, sizeof (struct trie)); | |
90 | if (!kwset->trie) | |
91 | { | |
92 | kwsfree((kwset_t) kwset); | |
93 | return NULL; | |
94 | } | |
95 | kwset->trie->accepting = 0; | |
96 | kwset->trie->links = NULL; | |
97 | kwset->trie->parent = NULL; | |
98 | kwset->trie->next = NULL; | |
99 | kwset->trie->fail = NULL; | |
100 | kwset->trie->depth = 0; | |
101 | kwset->trie->shift = 0; | |
102 | kwset->mind = INT_MAX; | |
103 | kwset->maxd = -1; | |
104 | kwset->trans = trans; | |
105 | ||
106 | return (kwset_t) kwset; | |
107 | } | |
108 | ||
109 | /* Add the given string to the contents of the keyword set. Return NULL | |
110 | for success, an error message otherwise. */ | |
111 | const char * | |
112 | DEFUN(kwsincr, (kws, text, len), | |
113 | kwset_t kws AND const char *text AND size_t len) | |
114 | { | |
115 | struct kwset *kwset; | |
116 | register struct trie *trie; | |
117 | register unsigned char label; | |
118 | register struct tree *link; | |
119 | register int depth; | |
120 | struct tree *links[12]; | |
121 | enum { L, R } dirs[12]; | |
122 | struct tree *t, *r, *l, *rl, *lr; | |
123 | ||
124 | kwset = (struct kwset *) kws; | |
125 | trie = kwset->trie; | |
126 | text += len; | |
127 | ||
128 | /* Descend the trie (built of reversed keywords) character-by-character, | |
129 | installing new nodes when necessary. */ | |
130 | while (len--) | |
131 | { | |
132 | label = kwset->trans ? kwset->trans[(unsigned char) *--text] : *--text; | |
133 | ||
134 | /* Descend the tree of outgoing links for this trie node, | |
135 | looking for the current character and keeping track | |
136 | of the path followed. */ | |
137 | link = trie->links; | |
138 | links[0] = (struct tree *) &trie->links; | |
139 | dirs[0] = L; | |
140 | depth = 1; | |
141 | ||
142 | while (link && label != link->label) | |
143 | { | |
144 | links[depth] = link; | |
145 | if (label < link->label) | |
146 | dirs[depth++] = L, link = link->llink; | |
147 | else | |
148 | dirs[depth++] = R, link = link->rlink; | |
149 | } | |
150 | ||
151 | /* The current character doesn't have an outgoing link at | |
152 | this trie node, so build a new trie node and install | |
153 | a link in the current trie node's tree. */ | |
154 | if (!link) | |
155 | { | |
156 | link = (struct tree *) obstack_alloc(&kwset->obstack, | |
157 | sizeof (struct tree)); | |
158 | if (!link) | |
159 | return "memory exhausted"; | |
160 | link->llink = NULL; | |
161 | link->rlink = NULL; | |
162 | link->trie = (struct trie *) obstack_alloc(&kwset->obstack, | |
163 | sizeof (struct trie)); | |
164 | if (!link->trie) | |
165 | return "memory exhausted"; | |
166 | link->trie->accepting = 0; | |
167 | link->trie->links = NULL; | |
168 | link->trie->parent = trie; | |
169 | link->trie->next = NULL; | |
170 | link->trie->fail = NULL; | |
171 | link->trie->depth = trie->depth + 1; | |
172 | link->trie->shift = 0; | |
173 | link->label = label; | |
174 | link->balance = 0; | |
175 | ||
176 | /* Install the new tree node in its parent. */ | |
177 | if (dirs[--depth] == L) | |
178 | links[depth]->llink = link; | |
179 | else | |
180 | links[depth]->rlink = link; | |
181 | ||
182 | /* Back up the tree fixing the balance flags. */ | |
183 | while (depth && !links[depth]->balance) | |
184 | { | |
185 | if (dirs[depth] == L) | |
186 | --links[depth]->balance; | |
187 | else | |
188 | ++links[depth]->balance; | |
189 | --depth; | |
190 | } | |
191 | ||
192 | /* Rebalance the tree by pointer rotations if necessary. */ | |
193 | if (depth && (dirs[depth] == L && --links[depth]->balance | |
194 | || dirs[depth] == R && ++links[depth]->balance)) | |
195 | { | |
196 | switch (links[depth]->balance) | |
197 | { | |
198 | case (char) -2: | |
199 | switch (dirs[depth + 1]) | |
200 | { | |
201 | case L: | |
202 | r = links[depth], t = r->llink, rl = t->rlink; | |
203 | t->rlink = r, r->llink = rl; | |
204 | t->balance = r->balance = 0; | |
205 | break; | |
206 | case R: | |
207 | r = links[depth], l = r->llink, t = l->rlink; | |
208 | rl = t->rlink, lr = t->llink; | |
209 | t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl; | |
210 | l->balance = t->balance != 1 ? 0 : -1; | |
211 | r->balance = t->balance != (char) -1 ? 0 : 1; | |
212 | t->balance = 0; | |
213 | break; | |
214 | } | |
215 | break; | |
216 | case 2: | |
217 | switch (dirs[depth + 1]) | |
218 | { | |
219 | case R: | |
220 | l = links[depth], t = l->rlink, lr = t->llink; | |
221 | t->llink = l, l->rlink = lr; | |
222 | t->balance = l->balance = 0; | |
223 | break; | |
224 | case L: | |
225 | l = links[depth], r = l->rlink, t = r->llink; | |
226 | lr = t->llink, rl = t->rlink; | |
227 | t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl; | |
228 | l->balance = t->balance != 1 ? 0 : -1; | |
229 | r->balance = t->balance != (char) -1 ? 0 : 1; | |
230 | t->balance = 0; | |
231 | break; | |
232 | } | |
233 | break; | |
234 | } | |
235 | ||
236 | if (dirs[depth - 1] == L) | |
237 | links[depth - 1]->llink = t; | |
238 | else | |
239 | links[depth - 1]->rlink = t; | |
240 | } | |
241 | } | |
242 | ||
243 | trie = link->trie; | |
244 | } | |
245 | ||
246 | /* Mark the node we finally reached as accepting, encoding the | |
247 | index number of this word in the keyword set so far. */ | |
248 | if (!trie->accepting) | |
249 | trie->accepting = 1 + 2 * kwset->words; | |
250 | ++kwset->words; | |
251 | ||
252 | /* Keep track of the longest and shortest string of the keyword set. */ | |
253 | if (trie->depth < kwset->mind) | |
254 | kwset->mind = trie->depth; | |
255 | if (trie->depth > kwset->maxd) | |
256 | kwset->maxd = trie->depth; | |
257 | ||
258 | return NULL; | |
259 | } | |
260 | ||
261 | /* Enqueue the trie nodes referenced from the given tree in the | |
262 | given queue. */ | |
263 | static void | |
264 | DEFUN(enqueue, (tree, last), struct tree *tree AND struct trie **last) | |
265 | { | |
266 | if (!tree) | |
267 | return; | |
268 | enqueue(tree->llink, last); | |
269 | enqueue(tree->rlink, last); | |
270 | (*last) = (*last)->next = tree->trie; | |
271 | } | |
272 | ||
273 | /* Compute the Aho-Corasick failure function for the trie nodes referenced | |
274 | from the given tree, given the failure function for their parent as | |
275 | well as a last resort failure node. */ | |
276 | static void | |
277 | DEFUN(treefails, (tree, fail, recourse), | |
278 | register struct tree *tree | |
279 | AND struct trie *fail AND struct trie *recourse) | |
280 | { | |
281 | register struct tree *link; | |
282 | ||
283 | if (!tree) | |
284 | return; | |
285 | ||
286 | treefails(tree->llink, fail, recourse); | |
287 | treefails(tree->rlink, fail, recourse); | |
288 | ||
289 | /* Find, in the chain of fails going back to the root, the first | |
290 | node that has a descendent on the current label. */ | |
291 | while (fail) | |
292 | { | |
293 | link = fail->links; | |
294 | while (link && tree->label != link->label) | |
295 | if (tree->label < link->label) | |
296 | link = link->llink; | |
297 | else | |
298 | link = link->rlink; | |
299 | if (link) | |
300 | { | |
301 | tree->trie->fail = link->trie; | |
302 | return; | |
303 | } | |
304 | fail = fail->fail; | |
305 | } | |
306 | ||
307 | tree->trie->fail = recourse; | |
308 | } | |
309 | ||
310 | /* Set delta entries for the links of the given tree such that | |
311 | the preexisting delta value is larger than the current depth. */ | |
312 | static void | |
313 | DEFUN(treedelta, (tree, depth, delta), | |
314 | register struct tree *tree AND register int depth AND int delta[]) | |
315 | { | |
316 | if (!tree) | |
317 | return; | |
318 | treedelta(tree->llink, depth, delta); | |
319 | treedelta(tree->rlink, depth, delta); | |
320 | if (depth < delta[tree->label]) | |
321 | delta[tree->label] = depth; | |
322 | } | |
323 | ||
324 | /* Return true if A has every label in B. */ | |
325 | static int | |
326 | DEFUN(hasevery, (a, b), register struct tree *a AND register struct tree *b) | |
327 | { | |
328 | if (!b) | |
329 | return 1; | |
330 | if (!hasevery(a, b->llink)) | |
331 | return 0; | |
332 | if (!hasevery(a, b->rlink)) | |
333 | return 0; | |
334 | while (a && b->label != a->label) | |
335 | if (b->label < a->label) | |
336 | a = a->llink; | |
337 | else | |
338 | a = a->rlink; | |
339 | return !!a; | |
340 | } | |
341 | ||
342 | /* Compute a vector, indexed by character code, of the trie nodes | |
343 | referenced from the given tree. */ | |
344 | static void | |
345 | DEFUN(treenext, (tree, next), struct tree *tree AND struct trie *next[]) | |
346 | { | |
347 | if (!tree) | |
348 | return; | |
349 | treenext(tree->llink, next); | |
350 | treenext(tree->rlink, next); | |
351 | next[tree->label] = tree->trie; | |
352 | } | |
353 | ||
354 | /* Compute the shift for each trie node, as well as the delta | |
355 | table and next cache for the given keyword set. */ | |
356 | const char * | |
357 | DEFUN(kwsprep, (kws), kwset_t kws) | |
358 | { | |
359 | register struct kwset *kwset; | |
360 | register int i; | |
361 | register struct trie *curr, *fail; | |
362 | register const char *trans; | |
363 | int delta[NCHAR]; | |
364 | struct trie *last, *next[NCHAR]; | |
365 | ||
366 | kwset = (struct kwset *) kws; | |
367 | ||
368 | /* Initial values for the delta table; will be changed later. The | |
369 | delta entry for a given character is the smallest depth of any | |
370 | node at which an outgoing edge is labeled by that character. */ | |
371 | for (i = 0; i < NCHAR; ++i) | |
372 | delta[i] = kwset->mind; | |
373 | ||
374 | /* Traverse the nodes of the trie in level order, simultaneously | |
375 | computing the delta table, failure function, and shift function. */ | |
376 | for (curr = last = kwset->trie; curr; curr = curr->next) | |
377 | { | |
378 | /* Enqueue the immediate descendents in the level order queue. */ | |
379 | enqueue(curr->links, &last); | |
380 | ||
381 | curr->shift = kwset->mind; | |
382 | curr->maxshift = kwset->mind; | |
383 | ||
384 | /* Update the delta table for the descendents of this node. */ | |
385 | treedelta(curr->links, curr->depth, delta); | |
386 | ||
387 | /* Compute the failure function for the decendents of this node. */ | |
388 | treefails(curr->links, curr->fail, kwset->trie); | |
389 | ||
390 | /* Update the shifts at each node in the current node's chain | |
391 | of fails back to the root. */ | |
392 | for (fail = curr->fail; fail; fail = fail->fail) | |
393 | { | |
394 | /* If the current node has some outgoing edge that the fail | |
395 | doesn't, then the shift at the fail should be no larger | |
396 | than the difference of their depths. */ | |
397 | if (!hasevery(fail->links, curr->links)) | |
398 | if (curr->depth - fail->depth < fail->shift) | |
399 | fail->shift = curr->depth - fail->depth; | |
400 | ||
401 | /* If the current node is accepting then the shift at the | |
402 | fail and its descendents should be no larger than the | |
403 | difference of their depths. */ | |
404 | if (curr->accepting && fail->maxshift > curr->depth - fail->depth) | |
405 | fail->maxshift = curr->depth - fail->depth; | |
406 | } | |
407 | } | |
408 | ||
409 | /* Traverse the trie in level order again, fixing up all nodes whose | |
410 | shift exceeds their inherited maxshift. */ | |
411 | for (curr = kwset->trie->next; curr; curr = curr->next) | |
412 | { | |
413 | if (curr->maxshift > curr->parent->maxshift) | |
414 | curr->maxshift = curr->parent->maxshift; | |
415 | if (curr->shift > curr->maxshift) | |
416 | curr->shift = curr->maxshift; | |
417 | } | |
418 | ||
419 | /* Create a vector, indexed by character code, of the outgoing links | |
420 | from the root node. */ | |
421 | for (i = 0; i < NCHAR; ++i) | |
422 | next[i] = NULL; | |
423 | treenext(kwset->trie->links, next); | |
424 | ||
425 | /* Fix things up for any translation table. */ | |
426 | if (trans = kwset->trans) | |
427 | for (i = 0; i < NCHAR; ++i) | |
428 | { | |
429 | kwset->delta[i] = delta[(unsigned char) trans[i]]; | |
430 | kwset->next[i] = next[(unsigned char) trans[i]]; | |
431 | } | |
432 | else | |
433 | for (i = 0; i < NCHAR; ++i) | |
434 | { | |
435 | kwset->delta[i] = delta[i]; | |
436 | kwset->next[i] = next[i]; | |
437 | } | |
438 | ||
439 | return NULL; | |
440 | } | |
441 | ||
442 | /* Search through the given text for a match of any member of the | |
443 | given keyword set. Return a pointer to the first character of | |
444 | the matching substring, or NULL if no match is found. If FOUNDLEN | |
445 | is non-NULL store in the referenced location the length of the | |
446 | matching substring. Similarly, if FOUNDIDX is non-NULL, store | |
447 | in the referenced location the index number of the particular | |
448 | keyword matched. */ | |
449 | char * | |
450 | DEFUN(kwsexec, (kws, text, len, kwsmatch), | |
451 | kwset_t kws AND char *text AND size_t len AND struct kwsmatch *kwsmatch) | |
452 | { | |
453 | struct kwset *kwset; | |
454 | struct trie **next, *trie, *accept; | |
455 | char *beg, *lim, *mch, *lmch; | |
456 | register unsigned char c; | |
457 | register int *delta, d; | |
458 | register char *end, *qlim; | |
459 | register struct tree *tree; | |
460 | register const char *trans; | |
461 | ||
462 | /* Initialize register copies and look for easy ways out. */ | |
463 | kwset = (struct kwset *) kws; | |
464 | if (len < kwset->mind) | |
465 | return NULL; | |
466 | next = kwset->next; | |
467 | delta = kwset->delta; | |
468 | trans = kwset->trans; | |
469 | lim = text + len; | |
470 | end = text; | |
471 | if (d = kwset->mind) | |
472 | mch = NULL; | |
473 | else | |
474 | { | |
475 | mch = text, accept = kwset->trie; | |
476 | goto match; | |
477 | } | |
478 | ||
479 | if (len >= 4 * kwset->mind) | |
480 | qlim = lim - 4 * kwset->mind; | |
481 | else | |
482 | qlim = NULL; | |
483 | ||
484 | while (lim - end >= d) | |
485 | { | |
486 | if (qlim && end <= qlim) | |
487 | { | |
488 | end += d - 1; | |
489 | while ((d = delta[c = *end]) && end < qlim) | |
490 | { | |
491 | end += d; | |
492 | end += delta[(unsigned char) *end]; | |
493 | end += delta[(unsigned char) *end]; | |
494 | } | |
495 | ++end; | |
496 | } | |
497 | else | |
498 | d = delta[c = (end += d)[-1]]; | |
499 | if (d) | |
500 | continue; | |
501 | beg = end - 1; | |
502 | trie = next[c]; | |
503 | if (trie->accepting) | |
504 | { | |
505 | mch = beg; | |
506 | accept = trie; | |
507 | } | |
508 | d = trie->shift; | |
509 | while (beg > text) | |
510 | { | |
511 | c = trans ? trans[(unsigned char) *--beg] : *--beg; | |
512 | tree = trie->links; | |
513 | while (tree && c != tree->label) | |
514 | if (c < tree->label) | |
515 | tree = tree->llink; | |
516 | else | |
517 | tree = tree->rlink; | |
518 | if (tree) | |
519 | { | |
520 | trie = tree->trie; | |
521 | if (trie->accepting) | |
522 | { | |
523 | mch = beg; | |
524 | accept = trie; | |
525 | } | |
526 | } | |
527 | else | |
528 | break; | |
529 | d = trie->shift; | |
530 | } | |
531 | if (mch) | |
532 | goto match; | |
533 | } | |
534 | return NULL; | |
535 | ||
536 | match: | |
537 | /* Given a known match, find the longest possible match anchored | |
538 | at or before its starting point. This is nearly a verbatim | |
539 | copy of the preceding main search loops. */ | |
540 | if (lim - mch > kwset->maxd) | |
541 | lim = mch + kwset->maxd; | |
542 | lmch = NULL; | |
543 | d = 1; | |
544 | while (lim - end >= d) | |
545 | { | |
546 | if (d = delta[c = (end += d)[-1]]) | |
547 | continue; | |
548 | beg = end - 1; | |
549 | if (!(trie = next[c])) | |
550 | { | |
551 | d = 1; | |
552 | continue; | |
553 | } | |
554 | if (trie->accepting && beg <= mch) | |
555 | { | |
556 | lmch = beg; | |
557 | accept = trie; | |
558 | } | |
559 | d = trie->shift; | |
560 | while (beg > text) | |
561 | { | |
562 | c = trans ? trans[(unsigned char) *--beg] : *--beg; | |
563 | tree = trie->links; | |
564 | while (tree && c != tree->label) | |
565 | if (c < tree->label) | |
566 | tree = tree->llink; | |
567 | else | |
568 | tree = tree->rlink; | |
569 | if (tree) | |
570 | { | |
571 | trie = tree->trie; | |
572 | if (trie->accepting && beg <= mch) | |
573 | { | |
574 | lmch = beg; | |
575 | accept = trie; | |
576 | } | |
577 | } | |
578 | else | |
579 | break; | |
580 | d = trie->shift; | |
581 | } | |
582 | if (lmch) | |
583 | { | |
584 | mch = lmch; | |
585 | goto match; | |
586 | } | |
587 | if (!d) | |
588 | d = 1; | |
589 | } | |
590 | ||
591 | if (kwsmatch) | |
592 | { | |
593 | kwsmatch->index = accept->accepting / 2; | |
594 | kwsmatch->beg[0] = mch; | |
595 | kwsmatch->size[0] = accept->depth; | |
596 | } | |
597 | return mch; | |
598 | } | |
599 | ||
600 | /* Free the components of the given keyword set. */ | |
601 | void | |
602 | DEFUN(kwsfree, (kws), kwset_t kws) | |
603 | { | |
604 | struct kwset *kwset; | |
605 | ||
606 | kwset = (struct kwset *) kws; | |
607 | obstack_free(&kwset->obstack, (PTR) NULL); | |
608 | free((PTR) kws); | |
609 | } |