/* kwset.c - search for any of a set of keywords. Copyright (C) 1989, 1998, 2000, 2005, 2007, 2009-2011 Free Software Foundation, Inc. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA. */ /* Written August 1989 by Mike Haertel. The author may be reached (Email) at the address mike@ai.mit.edu, or (US mail) as Mike Haertel c/o Free Software Foundation. */ /* The algorithm implemented by these routines bears a startling resemblence to one discovered by Beate Commentz-Walter, although it is not identical. See "A String Matching Algorithm Fast on the Average," Technical Report, IBM-Germany, Scientific Center Heidelberg, Tiergartenstrasse 15, D-6900 Heidelberg, Germany. See also Aho, A.V., and M. Corasick, "Efficient String Matching: An Aid to Bibliographic Search," CACM June 1975, Vol. 18, No. 6, which describes the failure function used below. */ #include #include #include "system.h" #include "kwset.h" #include "obstack.h" #define link kwset_link #ifdef GREP # include "xalloc.h" # undef malloc # define malloc xmalloc #endif #define NCHAR (UCHAR_MAX + 1) #define obstack_chunk_alloc malloc #define obstack_chunk_free free #define U(c) ((unsigned char) (c)) /* Balanced tree of edges and labels leaving a given trie node. */ struct tree { struct tree *llink; /* Left link; MUST be first field. */ struct tree *rlink; /* Right link (to larger labels). */ struct trie *trie; /* Trie node pointed to by this edge. */ unsigned char label; /* Label on this edge. */ char balance; /* Difference in depths of subtrees. */ }; /* Node of a trie representing a set of reversed keywords. */ struct trie { unsigned int accepting; /* Word index of accepted word, or zero. */ struct tree *links; /* Tree of edges leaving this node. */ struct trie *parent; /* Parent of this node. */ struct trie *next; /* List of all trie nodes in level order. */ struct trie *fail; /* Aho-Corasick failure function. */ int depth; /* Depth of this node from the root. */ int shift; /* Shift function for search failures. */ int maxshift; /* Max shift of self and descendents. */ }; /* Structure returned opaquely to the caller, containing everything. */ struct kwset { struct obstack obstack; /* Obstack for node allocation. */ int words; /* Number of words in the trie. */ struct trie *trie; /* The trie itself. */ int mind; /* Minimum depth of an accepting node. */ int maxd; /* Maximum depth of any node. */ unsigned char delta[NCHAR]; /* Delta table for rapid search. */ struct trie *next[NCHAR]; /* Table of children of the root. */ char *target; /* Target string if there's only one. */ int mind2; /* Used in Boyer-Moore search for one string. */ char const *trans; /* Character translation table. */ }; /* Allocate and initialize a keyword set object, returning an opaque pointer to it. Return NULL if memory is not available. */ kwset_t kwsalloc (char const *trans) { struct kwset *kwset; kwset = (struct kwset *) malloc(sizeof (struct kwset)); if (!kwset) return NULL; obstack_init(&kwset->obstack); kwset->words = 0; kwset->trie = (struct trie *) obstack_alloc(&kwset->obstack, sizeof (struct trie)); if (!kwset->trie) { kwsfree((kwset_t) kwset); return NULL; } kwset->trie->accepting = 0; kwset->trie->links = NULL; kwset->trie->parent = NULL; kwset->trie->next = NULL; kwset->trie->fail = NULL; kwset->trie->depth = 0; kwset->trie->shift = 0; kwset->mind = INT_MAX; kwset->maxd = -1; kwset->target = NULL; kwset->trans = trans; return (kwset_t) kwset; } /* This upper bound is valid for CHAR_BIT >= 4 and exact for CHAR_BIT in { 4..11, 13, 15, 17, 19 }. */ #define DEPTH_SIZE (CHAR_BIT + CHAR_BIT/2) /* Add the given string to the contents of the keyword set. Return NULL for success, an error message otherwise. */ const char * kwsincr (kwset_t kws, char const *text, size_t len) { struct kwset *kwset; struct trie *trie; unsigned char label; struct tree *link; int depth; struct tree *links[DEPTH_SIZE]; enum { L, R } dirs[DEPTH_SIZE]; struct tree *t, *r, *l, *rl, *lr; kwset = (struct kwset *) kws; trie = kwset->trie; text += len; /* Descend the trie (built of reversed keywords) character-by-character, installing new nodes when necessary. */ while (len--) { label = kwset->trans ? kwset->trans[U(*--text)] : *--text; /* Descend the tree of outgoing links for this trie node, looking for the current character and keeping track of the path followed. */ link = trie->links; links[0] = (struct tree *) &trie->links; dirs[0] = L; depth = 1; while (link && label != link->label) { links[depth] = link; if (label < link->label) dirs[depth++] = L, link = link->llink; else dirs[depth++] = R, link = link->rlink; } /* The current character doesn't have an outgoing link at this trie node, so build a new trie node and install a link in the current trie node's tree. */ if (!link) { link = (struct tree *) obstack_alloc(&kwset->obstack, sizeof (struct tree)); if (!link) return _("memory exhausted"); link->llink = NULL; link->rlink = NULL; link->trie = (struct trie *) obstack_alloc(&kwset->obstack, sizeof (struct trie)); if (!link->trie) { obstack_free(&kwset->obstack, link); return _("memory exhausted"); } link->trie->accepting = 0; link->trie->links = NULL; link->trie->parent = trie; link->trie->next = NULL; link->trie->fail = NULL; link->trie->depth = trie->depth + 1; link->trie->shift = 0; link->label = label; link->balance = 0; /* Install the new tree node in its parent. */ if (dirs[--depth] == L) links[depth]->llink = link; else links[depth]->rlink = link; /* Back up the tree fixing the balance flags. */ while (depth && !links[depth]->balance) { if (dirs[depth] == L) --links[depth]->balance; else ++links[depth]->balance; --depth; } /* Rebalance the tree by pointer rotations if necessary. */ if (depth && ((dirs[depth] == L && --links[depth]->balance) || (dirs[depth] == R && ++links[depth]->balance))) { switch (links[depth]->balance) { case (char) -2: switch (dirs[depth + 1]) { case L: r = links[depth], t = r->llink, rl = t->rlink; t->rlink = r, r->llink = rl; t->balance = r->balance = 0; break; case R: r = links[depth], l = r->llink, t = l->rlink; rl = t->rlink, lr = t->llink; t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl; l->balance = t->balance != 1 ? 0 : -1; r->balance = t->balance != (char) -1 ? 0 : 1; t->balance = 0; break; default: abort (); } break; case 2: switch (dirs[depth + 1]) { case R: l = links[depth], t = l->rlink, lr = t->llink; t->llink = l, l->rlink = lr; t->balance = l->balance = 0; break; case L: l = links[depth], r = l->rlink, t = r->llink; lr = t->llink, rl = t->rlink; t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl; l->balance = t->balance != 1 ? 0 : -1; r->balance = t->balance != (char) -1 ? 0 : 1; t->balance = 0; break; default: abort (); } break; default: abort (); } if (dirs[depth - 1] == L) links[depth - 1]->llink = t; else links[depth - 1]->rlink = t; } } trie = link->trie; } /* Mark the node we finally reached as accepting, encoding the index number of this word in the keyword set so far. */ if (!trie->accepting) trie->accepting = 1 + 2 * kwset->words; ++kwset->words; /* Keep track of the longest and shortest string of the keyword set. */ if (trie->depth < kwset->mind) kwset->mind = trie->depth; if (trie->depth > kwset->maxd) kwset->maxd = trie->depth; return NULL; } /* Enqueue the trie nodes referenced from the given tree in the given queue. */ static void enqueue (struct tree *tree, struct trie **last) { if (!tree) return; enqueue(tree->llink, last); enqueue(tree->rlink, last); (*last) = (*last)->next = tree->trie; } /* Compute the Aho-Corasick failure function for the trie nodes referenced from the given tree, given the failure function for their parent as well as a last resort failure node. */ static void treefails (struct tree const *tree, struct trie const *fail, struct trie *recourse) { struct tree *link; if (!tree) return; treefails(tree->llink, fail, recourse); treefails(tree->rlink, fail, recourse); /* Find, in the chain of fails going back to the root, the first node that has a descendent on the current label. */ while (fail) { link = fail->links; while (link && tree->label != link->label) if (tree->label < link->label) link = link->llink; else link = link->rlink; if (link) { tree->trie->fail = link->trie; return; } fail = fail->fail; } tree->trie->fail = recourse; } /* Set delta entries for the links of the given tree such that the preexisting delta value is larger than the current depth. */ static void treedelta (struct tree const *tree, unsigned int depth, unsigned char delta[]) { if (!tree) return; treedelta(tree->llink, depth, delta); treedelta(tree->rlink, depth, delta); if (depth < delta[tree->label]) delta[tree->label] = depth; } /* Return true if A has every label in B. */ static int hasevery (struct tree const *a, struct tree const *b) { if (!b) return 1; if (!hasevery(a, b->llink)) return 0; if (!hasevery(a, b->rlink)) return 0; while (a && b->label != a->label) if (b->label < a->label) a = a->llink; else a = a->rlink; return !!a; } /* Compute a vector, indexed by character code, of the trie nodes referenced from the given tree. */ static void treenext (struct tree const *tree, struct trie *next[]) { if (!tree) return; treenext(tree->llink, next); treenext(tree->rlink, next); next[tree->label] = tree->trie; } /* Compute the shift for each trie node, as well as the delta table and next cache for the given keyword set. */ const char * kwsprep (kwset_t kws) { struct kwset *kwset; int i; struct trie *curr; char const *trans; unsigned char delta[NCHAR]; kwset = (struct kwset *) kws; /* Initial values for the delta table; will be changed later. The delta entry for a given character is the smallest depth of any node at which an outgoing edge is labeled by that character. */ memset(delta, kwset->mind < UCHAR_MAX ? kwset->mind : UCHAR_MAX, NCHAR); /* Check if we can use the simple boyer-moore algorithm, instead of the hairy commentz-walter algorithm. */ if (kwset->words == 1 && kwset->trans == NULL) { char c; /* Looking for just one string. Extract it from the trie. */ kwset->target = obstack_alloc(&kwset->obstack, kwset->mind); if (!kwset->target) return _("memory exhausted"); for (i = kwset->mind - 1, curr = kwset->trie; i >= 0; --i) { kwset->target[i] = curr->links->label; curr = curr->links->trie; } /* Build the Boyer Moore delta. Boy that's easy compared to CW. */ for (i = 0; i < kwset->mind; ++i) delta[U(kwset->target[i])] = kwset->mind - (i + 1); /* Find the minimal delta2 shift that we might make after a backwards match has failed. */ c = kwset->target[kwset->mind - 1]; for (i = kwset->mind - 2; i >= 0; --i) if (kwset->target[i] == c) break; kwset->mind2 = kwset->mind - (i + 1); } else { struct trie *fail; struct trie *last, *next[NCHAR]; /* Traverse the nodes of the trie in level order, simultaneously computing the delta table, failure function, and shift function. */ for (curr = last = kwset->trie; curr; curr = curr->next) { /* Enqueue the immediate descendents in the level order queue. */ enqueue(curr->links, &last); curr->shift = kwset->mind; curr->maxshift = kwset->mind; /* Update the delta table for the descendents of this node. */ treedelta(curr->links, curr->depth, delta); /* Compute the failure function for the decendents of this node. */ treefails(curr->links, curr->fail, kwset->trie); /* Update the shifts at each node in the current node's chain of fails back to the root. */ for (fail = curr->fail; fail; fail = fail->fail) { /* If the current node has some outgoing edge that the fail doesn't, then the shift at the fail should be no larger than the difference of their depths. */ if (!hasevery(fail->links, curr->links)) if (curr->depth - fail->depth < fail->shift) fail->shift = curr->depth - fail->depth; /* If the current node is accepting then the shift at the fail and its descendents should be no larger than the difference of their depths. */ if (curr->accepting && fail->maxshift > curr->depth - fail->depth) fail->maxshift = curr->depth - fail->depth; } } /* Traverse the trie in level order again, fixing up all nodes whose shift exceeds their inherited maxshift. */ for (curr = kwset->trie->next; curr; curr = curr->next) { if (curr->maxshift > curr->parent->maxshift) curr->maxshift = curr->parent->maxshift; if (curr->shift > curr->maxshift) curr->shift = curr->maxshift; } /* Create a vector, indexed by character code, of the outgoing links from the root node. */ for (i = 0; i < NCHAR; ++i) next[i] = NULL; treenext(kwset->trie->links, next); if ((trans = kwset->trans) != NULL) for (i = 0; i < NCHAR; ++i) kwset->next[i] = next[U(trans[i])]; else memcpy(kwset->next, next, NCHAR * sizeof(struct trie *)); } /* Fix things up for any translation table. */ if ((trans = kwset->trans) != NULL) for (i = 0; i < NCHAR; ++i) kwset->delta[i] = delta[U(trans[i])]; else memcpy(kwset->delta, delta, NCHAR); return NULL; } /* Fast boyer-moore search. */ static size_t bmexec (kwset_t kws, char const *text, size_t size) { struct kwset const *kwset; unsigned char const *d1; char const *ep, *sp, *tp; int d, gc, i, len, md2; kwset = (struct kwset const *) kws; len = kwset->mind; if (len == 0) return 0; if (len > size) return -1; if (len == 1) { tp = memchr (text, kwset->target[0], size); return tp ? tp - text : -1; } d1 = kwset->delta; sp = kwset->target + len; gc = U(sp[-2]); md2 = kwset->mind2; tp = text + len; /* Significance of 12: 1 (initial offset) + 10 (skip loop) + 1 (md2). */ if (size > 12 * len) /* 11 is not a bug, the initial offset happens only once. */ for (ep = text + size - 11 * len;;) { while (tp <= ep) { d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; if (d == 0) goto found; d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; if (d == 0) goto found; d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; if (d == 0) goto found; d = d1[U(tp[-1])], tp += d; d = d1[U(tp[-1])], tp += d; } break; found: if (U(tp[-2]) == gc) { for (i = 3; i <= len && U(tp[-i]) == U(sp[-i]); ++i) ; if (i > len) return tp - len - text; } tp += md2; } /* Now we have only a few characters left to search. We carefully avoid ever producing an out-of-bounds pointer. */ ep = text + size; d = d1[U(tp[-1])]; while (d <= ep - tp) { d = d1[U((tp += d)[-1])]; if (d != 0) continue; if (U(tp[-2]) == gc) { for (i = 3; i <= len && U(tp[-i]) == U(sp[-i]); ++i) ; if (i > len) return tp - len - text; } d = md2; } return -1; } /* Hairy multiple string search. */ static size_t _GL_ARG_NONNULL ((4)) cwexec (kwset_t kws, char const *text, size_t len, struct kwsmatch *kwsmatch) { struct kwset const *kwset; struct trie * const *next; struct trie const *trie; struct trie const *accept; char const *beg, *lim, *mch, *lmch; unsigned char c; unsigned char const *delta; int d; char const *end, *qlim; struct tree const *tree; char const *trans; #ifdef lint accept = NULL; #endif /* Initialize register copies and look for easy ways out. */ kwset = (struct kwset *) kws; if (len < kwset->mind) return -1; next = kwset->next; delta = kwset->delta; trans = kwset->trans; lim = text + len; end = text; if ((d = kwset->mind) != 0) mch = NULL; else { mch = text, accept = kwset->trie; goto match; } if (len >= 4 * kwset->mind) qlim = lim - 4 * kwset->mind; else qlim = NULL; while (lim - end >= d) { if (qlim && end <= qlim) { end += d - 1; while ((d = delta[c = *end]) && end < qlim) { end += d; end += delta[U(*end)]; end += delta[U(*end)]; } ++end; } else d = delta[c = (end += d)[-1]]; if (d) continue; beg = end - 1; trie = next[c]; if (trie->accepting) { mch = beg; accept = trie; } d = trie->shift; while (beg > text) { c = trans ? trans[U(*--beg)] : *--beg; tree = trie->links; while (tree && c != tree->label) if (c < tree->label) tree = tree->llink; else tree = tree->rlink; if (tree) { trie = tree->trie; if (trie->accepting) { mch = beg; accept = trie; } } else break; d = trie->shift; } if (mch) goto match; } return -1; match: /* Given a known match, find the longest possible match anchored at or before its starting point. This is nearly a verbatim copy of the preceding main search loops. */ if (lim - mch > kwset->maxd) lim = mch + kwset->maxd; lmch = 0; d = 1; while (lim - end >= d) { if ((d = delta[c = (end += d)[-1]]) != 0) continue; beg = end - 1; if (!(trie = next[c])) { d = 1; continue; } if (trie->accepting && beg <= mch) { lmch = beg; accept = trie; } d = trie->shift; while (beg > text) { c = trans ? trans[U(*--beg)] : *--beg; tree = trie->links; while (tree && c != tree->label) if (c < tree->label) tree = tree->llink; else tree = tree->rlink; if (tree) { trie = tree->trie; if (trie->accepting && beg <= mch) { lmch = beg; accept = trie; } } else break; d = trie->shift; } if (lmch) { mch = lmch; goto match; } if (!d) d = 1; } kwsmatch->index = accept->accepting / 2; kwsmatch->offset[0] = mch - text; kwsmatch->size[0] = accept->depth; return mch - text; } /* Search TEXT for a match of any member of the keyword set, KWS. Return the offset (into TEXT) of the first byte of the matching substring, or (size_t) -1 if no match is found. Upon a match, store details in *KWSMATCH: index of matched keyword, start offset (same as the return value), and length. */ size_t kwsexec (kwset_t kws, char const *text, size_t size, struct kwsmatch *kwsmatch) { struct kwset const *kwset = (struct kwset *) kws; if (kwset->words == 1 && kwset->trans == NULL) { size_t ret = bmexec (kws, text, size); if (ret != (size_t) -1) { kwsmatch->index = 0; kwsmatch->offset[0] = ret; kwsmatch->size[0] = kwset->mind; } return ret; } else return cwexec(kws, text, size, kwsmatch); } /* Free the components of the given keyword set. */ void kwsfree (kwset_t kws) { struct kwset *kwset; kwset = (struct kwset *) kws; obstack_free(&kwset->obstack, NULL); free(kws); }