1 /* kwset.c - search for any of a set of keywords.
2 Copyright 1989, 1998, 2000 Free Software Foundation, Inc.
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2, or (at your option)
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software
16 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
21 /* Written August 1989 by Mike Haertel.
22 The author may be reached (Email) at the address mike@ai.mit.edu,
23 or (US mail) as Mike Haertel c/o Free Software Foundation. */
25 /* The algorithm implemented by these routines bears a startling resemblence
26 to one discovered by Beate Commentz-Walter, although it is not identical.
27 See "A String Matching Algorithm Fast on the Average," Technical Report,
28 IBM-Germany, Scientific Center Heidelberg, Tiergartenstrasse 15, D-6900
29 Heidelberg, Germany. See also Aho, A.V., and M. Corasick, "Efficient
30 String Matching: An Aid to Bibliographic Search," CACM June 1975,
31 Vol. 18, No. 6, which describes the failure function used below. */
36 #include <sys/types.h>
42 extern char *xmalloc();
44 # define malloc xmalloc
47 #define NCHAR (UCHAR_MAX + 1)
48 #define obstack_chunk_alloc malloc
49 #define obstack_chunk_free free
51 /* Balanced tree of edges and labels leaving a given trie node. */
54 struct tree *llink; /* Left link; MUST be first field. */
55 struct tree *rlink; /* Right link (to larger labels). */
56 struct trie *trie; /* Trie node pointed to by this edge. */
57 unsigned char label; /* Label on this edge. */
58 char balance; /* Difference in depths of subtrees. */
61 /* Node of a trie representing a set of reversed keywords. */
64 unsigned int accepting; /* Word index of accepted word, or zero. */
65 struct tree *links; /* Tree of edges leaving this node. */
66 struct trie *parent; /* Parent of this node. */
67 struct trie *next; /* List of all trie nodes in level order. */
68 struct trie *fail; /* Aho-Corasick failure function. */
69 int depth; /* Depth of this node from the root. */
70 int shift; /* Shift function for search failures. */
71 int maxshift; /* Max shift of self and descendents. */
74 /* Structure returned opaquely to the caller, containing everything. */
77 struct obstack obstack; /* Obstack for node allocation. */
78 int words; /* Number of words in the trie. */
79 struct trie *trie; /* The trie itself. */
80 int mind; /* Minimum depth of an accepting node. */
81 int maxd; /* Maximum depth of any node. */
82 unsigned char delta[NCHAR]; /* Delta table for rapid search. */
83 struct trie *next[NCHAR]; /* Table of children of the root. */
84 char *target; /* Target string if there's only one. */
85 int mind2; /* Used in Boyer-Moore search for one string. */
86 char const *trans; /* Character translation table. */
89 /* Allocate and initialize a keyword set object, returning an opaque
90 pointer to it. Return NULL if memory is not available. */
92 kwsalloc (char const *trans)
96 kwset = (struct kwset *) malloc(sizeof (struct kwset));
100 obstack_init(&kwset->obstack);
103 = (struct trie *) obstack_alloc(&kwset->obstack, sizeof (struct trie));
106 kwsfree((kwset_t) kwset);
109 kwset->trie->accepting = 0;
110 kwset->trie->links = 0;
111 kwset->trie->parent = 0;
112 kwset->trie->next = 0;
113 kwset->trie->fail = 0;
114 kwset->trie->depth = 0;
115 kwset->trie->shift = 0;
116 kwset->mind = INT_MAX;
119 kwset->trans = trans;
121 return (kwset_t) kwset;
124 /* Add the given string to the contents of the keyword set. Return NULL
125 for success, an error message otherwise. */
127 kwsincr (kwset_t kws, char const *text, size_t len)
130 register struct trie *trie;
131 register unsigned char label;
132 register struct tree *link;
134 struct tree *links[12];
135 enum { L, R } dirs[12];
136 struct tree *t, *r, *l, *rl, *lr;
138 kwset = (struct kwset *) kws;
142 /* Descend the trie (built of reversed keywords) character-by-character,
143 installing new nodes when necessary. */
146 label = kwset->trans ? kwset->trans[(unsigned char) *--text] : *--text;
148 /* Descend the tree of outgoing links for this trie node,
149 looking for the current character and keeping track
150 of the path followed. */
152 links[0] = (struct tree *) &trie->links;
156 while (link && label != link->label)
159 if (label < link->label)
160 dirs[depth++] = L, link = link->llink;
162 dirs[depth++] = R, link = link->rlink;
165 /* The current character doesn't have an outgoing link at
166 this trie node, so build a new trie node and install
167 a link in the current trie node's tree. */
170 link = (struct tree *) obstack_alloc(&kwset->obstack,
171 sizeof (struct tree));
173 return _("memory exhausted");
176 link->trie = (struct trie *) obstack_alloc(&kwset->obstack,
177 sizeof (struct trie));
179 return _("memory exhausted");
180 link->trie->accepting = 0;
181 link->trie->links = 0;
182 link->trie->parent = trie;
183 link->trie->next = 0;
184 link->trie->fail = 0;
185 link->trie->depth = trie->depth + 1;
186 link->trie->shift = 0;
190 /* Install the new tree node in its parent. */
191 if (dirs[--depth] == L)
192 links[depth]->llink = link;
194 links[depth]->rlink = link;
196 /* Back up the tree fixing the balance flags. */
197 while (depth && !links[depth]->balance)
199 if (dirs[depth] == L)
200 --links[depth]->balance;
202 ++links[depth]->balance;
206 /* Rebalance the tree by pointer rotations if necessary. */
207 if (depth && ((dirs[depth] == L && --links[depth]->balance)
208 || (dirs[depth] == R && ++links[depth]->balance)))
210 switch (links[depth]->balance)
213 switch (dirs[depth + 1])
216 r = links[depth], t = r->llink, rl = t->rlink;
217 t->rlink = r, r->llink = rl;
218 t->balance = r->balance = 0;
221 r = links[depth], l = r->llink, t = l->rlink;
222 rl = t->rlink, lr = t->llink;
223 t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
224 l->balance = t->balance != 1 ? 0 : -1;
225 r->balance = t->balance != (char) -1 ? 0 : 1;
233 switch (dirs[depth + 1])
236 l = links[depth], t = l->rlink, lr = t->llink;
237 t->llink = l, l->rlink = lr;
238 t->balance = l->balance = 0;
241 l = links[depth], r = l->rlink, t = r->llink;
242 lr = t->llink, rl = t->rlink;
243 t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
244 l->balance = t->balance != 1 ? 0 : -1;
245 r->balance = t->balance != (char) -1 ? 0 : 1;
256 if (dirs[depth - 1] == L)
257 links[depth - 1]->llink = t;
259 links[depth - 1]->rlink = t;
266 /* Mark the node we finally reached as accepting, encoding the
267 index number of this word in the keyword set so far. */
268 if (!trie->accepting)
269 trie->accepting = 1 + 2 * kwset->words;
272 /* Keep track of the longest and shortest string of the keyword set. */
273 if (trie->depth < kwset->mind)
274 kwset->mind = trie->depth;
275 if (trie->depth > kwset->maxd)
276 kwset->maxd = trie->depth;
281 /* Enqueue the trie nodes referenced from the given tree in the
284 enqueue (struct tree *tree, struct trie **last)
288 enqueue(tree->llink, last);
289 enqueue(tree->rlink, last);
290 (*last) = (*last)->next = tree->trie;
293 /* Compute the Aho-Corasick failure function for the trie nodes referenced
294 from the given tree, given the failure function for their parent as
295 well as a last resort failure node. */
297 treefails (register struct tree const *tree, struct trie const *fail,
298 struct trie *recourse)
300 register struct tree *link;
305 treefails(tree->llink, fail, recourse);
306 treefails(tree->rlink, fail, recourse);
308 /* Find, in the chain of fails going back to the root, the first
309 node that has a descendent on the current label. */
313 while (link && tree->label != link->label)
314 if (tree->label < link->label)
320 tree->trie->fail = link->trie;
326 tree->trie->fail = recourse;
329 /* Set delta entries for the links of the given tree such that
330 the preexisting delta value is larger than the current depth. */
332 treedelta (register struct tree const *tree,
333 register unsigned int depth,
334 unsigned char delta[])
338 treedelta(tree->llink, depth, delta);
339 treedelta(tree->rlink, depth, delta);
340 if (depth < delta[tree->label])
341 delta[tree->label] = depth;
344 /* Return true if A has every label in B. */
346 hasevery (register struct tree const *a, register struct tree const *b)
350 if (!hasevery(a, b->llink))
352 if (!hasevery(a, b->rlink))
354 while (a && b->label != a->label)
355 if (b->label < a->label)
362 /* Compute a vector, indexed by character code, of the trie nodes
363 referenced from the given tree. */
365 treenext (struct tree const *tree, struct trie *next[])
369 treenext(tree->llink, next);
370 treenext(tree->rlink, next);
371 next[tree->label] = tree->trie;
374 /* Compute the shift for each trie node, as well as the delta
375 table and next cache for the given keyword set. */
377 kwsprep (kwset_t kws)
379 register struct kwset *kwset;
381 register struct trie *curr, *fail;
382 register char const *trans;
383 unsigned char delta[NCHAR];
384 struct trie *last, *next[NCHAR];
386 kwset = (struct kwset *) kws;
388 /* Initial values for the delta table; will be changed later. The
389 delta entry for a given character is the smallest depth of any
390 node at which an outgoing edge is labeled by that character. */
391 if (kwset->mind < 256)
392 for (i = 0; i < NCHAR; ++i)
393 delta[i] = kwset->mind;
395 for (i = 0; i < NCHAR; ++i)
398 /* Check if we can use the simple boyer-moore algorithm, instead
399 of the hairy commentz-walter algorithm. */
400 if (kwset->words == 1 && kwset->trans == 0)
402 /* Looking for just one string. Extract it from the trie. */
403 kwset->target = obstack_alloc(&kwset->obstack, kwset->mind);
404 for (i = kwset->mind - 1, curr = kwset->trie; i >= 0; --i)
406 kwset->target[i] = curr->links->label;
407 curr = curr->links->trie;
409 /* Build the Boyer Moore delta. Boy that's easy compared to CW. */
410 for (i = 0; i < kwset->mind; ++i)
411 delta[(unsigned char) kwset->target[i]] = kwset->mind - (i + 1);
412 kwset->mind2 = kwset->mind;
413 /* Find the minimal delta2 shift that we might make after
414 a backwards match has failed. */
415 for (i = 0; i < kwset->mind - 1; ++i)
416 if (kwset->target[i] == kwset->target[kwset->mind - 1])
417 kwset->mind2 = kwset->mind - (i + 1);
421 /* Traverse the nodes of the trie in level order, simultaneously
422 computing the delta table, failure function, and shift function. */
423 for (curr = last = kwset->trie; curr; curr = curr->next)
425 /* Enqueue the immediate descendents in the level order queue. */
426 enqueue(curr->links, &last);
428 curr->shift = kwset->mind;
429 curr->maxshift = kwset->mind;
431 /* Update the delta table for the descendents of this node. */
432 treedelta(curr->links, curr->depth, delta);
434 /* Compute the failure function for the decendents of this node. */
435 treefails(curr->links, curr->fail, kwset->trie);
437 /* Update the shifts at each node in the current node's chain
438 of fails back to the root. */
439 for (fail = curr->fail; fail; fail = fail->fail)
441 /* If the current node has some outgoing edge that the fail
442 doesn't, then the shift at the fail should be no larger
443 than the difference of their depths. */
444 if (!hasevery(fail->links, curr->links))
445 if (curr->depth - fail->depth < fail->shift)
446 fail->shift = curr->depth - fail->depth;
448 /* If the current node is accepting then the shift at the
449 fail and its descendents should be no larger than the
450 difference of their depths. */
451 if (curr->accepting && fail->maxshift > curr->depth - fail->depth)
452 fail->maxshift = curr->depth - fail->depth;
456 /* Traverse the trie in level order again, fixing up all nodes whose
457 shift exceeds their inherited maxshift. */
458 for (curr = kwset->trie->next; curr; curr = curr->next)
460 if (curr->maxshift > curr->parent->maxshift)
461 curr->maxshift = curr->parent->maxshift;
462 if (curr->shift > curr->maxshift)
463 curr->shift = curr->maxshift;
466 /* Create a vector, indexed by character code, of the outgoing links
467 from the root node. */
468 for (i = 0; i < NCHAR; ++i)
470 treenext(kwset->trie->links, next);
472 if ((trans = kwset->trans) != 0)
473 for (i = 0; i < NCHAR; ++i)
474 kwset->next[i] = next[(unsigned char) trans[i]];
476 for (i = 0; i < NCHAR; ++i)
477 kwset->next[i] = next[i];
480 /* Fix things up for any translation table. */
481 if ((trans = kwset->trans) != 0)
482 for (i = 0; i < NCHAR; ++i)
483 kwset->delta[i] = delta[(unsigned char) trans[i]];
485 for (i = 0; i < NCHAR; ++i)
486 kwset->delta[i] = delta[i];
491 #define U(C) ((unsigned char) (C))
493 /* Fast boyer-moore search. */
495 bmexec (kwset_t kws, char const *text, size_t size)
497 struct kwset const *kwset;
498 register unsigned char const *d1;
499 register char const *ep, *sp, *tp;
500 register int d, gc, i, len, md2;
502 kwset = (struct kwset const *) kws;
511 tp = memchr (text, kwset->target[0], size);
512 return tp ? tp - text : -1;
516 sp = kwset->target + len;
521 /* Significance of 12: 1 (initial offset) + 10 (skip loop) + 1 (md2). */
523 /* 11 is not a bug, the initial offset happens only once. */
524 for (ep = text + size - 11 * len;;)
528 d = d1[U(tp[-1])], tp += d;
529 d = d1[U(tp[-1])], tp += d;
532 d = d1[U(tp[-1])], tp += d;
533 d = d1[U(tp[-1])], tp += d;
534 d = d1[U(tp[-1])], tp += d;
537 d = d1[U(tp[-1])], tp += d;
538 d = d1[U(tp[-1])], tp += d;
539 d = d1[U(tp[-1])], tp += d;
542 d = d1[U(tp[-1])], tp += d;
543 d = d1[U(tp[-1])], tp += d;
549 for (i = 3; i <= len && U(tp[-i]) == U(sp[-i]); ++i)
552 return tp - len - text;
557 /* Now we have only a few characters left to search. We
558 carefully avoid ever producing an out-of-bounds pointer. */
563 d = d1[U((tp += d)[-1])];
568 for (i = 3; i <= len && U(tp[-i]) == U(sp[-i]); ++i)
571 return tp - len - text;
579 /* Hairy multiple string search. */
581 cwexec (kwset_t kws, char const *text, size_t len, struct kwsmatch *kwsmatch)
583 struct kwset const *kwset;
584 struct trie * const *next;
585 struct trie const *trie;
586 struct trie const *accept;
587 char const *beg, *lim, *mch, *lmch;
588 register unsigned char c;
589 register unsigned char const *delta;
591 register char const *end, *qlim;
592 register struct tree const *tree;
593 register char const *trans;
599 /* Initialize register copies and look for easy ways out. */
600 kwset = (struct kwset *) kws;
601 if (len < kwset->mind)
604 delta = kwset->delta;
605 trans = kwset->trans;
608 if ((d = kwset->mind) != 0)
612 mch = text, accept = kwset->trie;
616 if (len >= 4 * kwset->mind)
617 qlim = lim - 4 * kwset->mind;
621 while (lim - end >= d)
623 if (qlim && end <= qlim)
626 while ((d = delta[c = *end]) && end < qlim)
629 end += delta[(unsigned char) *end];
630 end += delta[(unsigned char) *end];
635 d = delta[c = (end += d)[-1]];
648 c = trans ? trans[(unsigned char) *--beg] : *--beg;
650 while (tree && c != tree->label)
674 /* Given a known match, find the longest possible match anchored
675 at or before its starting point. This is nearly a verbatim
676 copy of the preceding main search loops. */
677 if (lim - mch > kwset->maxd)
678 lim = mch + kwset->maxd;
681 while (lim - end >= d)
683 if ((d = delta[c = (end += d)[-1]]) != 0)
686 if (!(trie = next[c]))
691 if (trie->accepting && beg <= mch)
699 c = trans ? trans[(unsigned char) *--beg] : *--beg;
701 while (tree && c != tree->label)
709 if (trie->accepting && beg <= mch)
730 kwsmatch->index = accept->accepting / 2;
731 kwsmatch->offset[0] = mch - text;
732 kwsmatch->size[0] = accept->depth;
737 /* Search through the given text for a match of any member of the
738 given keyword set. Return a pointer to the first character of
739 the matching substring, or NULL if no match is found. If FOUNDLEN
740 is non-NULL store in the referenced location the length of the
741 matching substring. Similarly, if FOUNDIDX is non-NULL, store
742 in the referenced location the index number of the particular
745 kwsexec (kwset_t kws, char const *text, size_t size,
746 struct kwsmatch *kwsmatch)
748 struct kwset const *kwset = (struct kwset *) kws;
749 if (kwset->words == 1 && kwset->trans == 0)
751 size_t ret = bmexec (kws, text, size);
752 if (kwsmatch != 0 && ret != (size_t) -1)
755 kwsmatch->offset[0] = ret;
756 kwsmatch->size[0] = kwset->mind;
761 return cwexec(kws, text, size, kwsmatch);
764 /* Free the components of the given keyword set. */
766 kwsfree (kwset_t kws)
770 kwset = (struct kwset *) kws;
771 obstack_free(&kwset->obstack, 0);