Category : OS/2 Files
Archive   : GNUGREP.ZIP
Filename : KWSET.C

/* kwset.c - search for any of a set of keywords.
Copyright 1989 Free Software Foundation
Written August 1989 by Mike Haertel.

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 1, 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., 675 Mass Ave, Cambridge, MA 02139, USA.

The author may be reached (Email) at the address [email protected],
or (US mail) as Mike Haertel c/o Free Software Foundation. */

#include "std.h"

/* 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 "kwset.h"
#include "obstack.h"

#define NCHAR (UCHAR_MAX + 1)
#define obstack_chunk_alloc malloc
#define obstack_chunk_free free

/* 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. */
int delta[NCHAR]; /* Delta table for rapid search. */
struct trie *next[NCHAR]; /* Table of children of the root. */
const char *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
DEFUN(kwsalloc, (trans), const char *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->trans = trans;

return (kwset_t) kwset;
}

/* Add the given string to the contents of the keyword set. Return NULL
for success, an error message otherwise. */
const char *
DEFUN(kwsincr, (kws, text, len),
kwset_t kws AND const char *text AND size_t len)
{
struct kwset *kwset;
register struct trie *trie;
register unsigned char label;
register struct tree *link;
register int depth;
struct tree *links[12];
enum { L, R } dirs[12];
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[(unsigned char) *--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)
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;
}
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;
}
break;
}

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
DEFUN(enqueue, (tree, last), struct tree *tree AND 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
DEFUN(treefails, (tree, fail, recourse),
register struct tree *tree
AND struct trie *fail AND struct trie *recourse)
{
register 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
DEFUN(treedelta, (tree, depth, delta),
register struct tree *tree AND register int depth AND int 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
DEFUN(hasevery, (a, b), register struct tree *a AND register struct tree *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
DEFUN(treenext, (tree, next), struct tree *tree AND 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 *
DEFUN(kwsprep, (kws), kwset_t kws)
{
register struct kwset *kwset;
register int i;
register struct trie *curr, *fail;
register const char *trans;
int delta[NCHAR];
struct trie *last, *next[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. */
for (i = 0; i < NCHAR; ++i)
delta[i] = kwset->mind;

/* 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);

/* Fix things up for any translation table. */
if (trans = kwset->trans)
for (i = 0; i < NCHAR; ++i)
{
kwset->delta[i] = delta[(unsigned char) trans[i]];
kwset->next[i] = next[(unsigned char) trans[i]];
}
else
for (i = 0; i < NCHAR; ++i)
{
kwset->delta[i] = delta[i];
kwset->next[i] = next[i];
}

return NULL;
}

/* Search through the given text for a match of any member of the
given keyword set. Return a pointer to the first character of
the matching substring, or NULL if no match is found. If FOUNDLEN
is non-NULL store in the referenced location the length of the
matching substring. Similarly, if FOUNDIDX is non-NULL, store
in the referenced location the index number of the particular
keyword matched. */
char *
DEFUN(kwsexec, (kws, text, len, kwsmatch),
kwset_t kws AND char *text AND size_t len AND struct kwsmatch *kwsmatch)
{
struct kwset *kwset;
struct trie **next, *trie, *accept;
char *beg, *lim, *mch, *lmch;
register unsigned char c;
register int *delta, d;
register char *end, *qlim;
register struct tree *tree;
register const char *trans;

/* Initialize register copies and look for easy ways out. */
kwset = (struct kwset *) kws;
if (len < kwset->mind)
return NULL;
next = kwset->next;
delta = kwset->delta;
trans = kwset->trans;
lim = text + len;
end = text;
if (d = kwset->mind)
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[(unsigned char) *end];
end += delta[(unsigned char) *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[(unsigned char) *--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 NULL;

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 = NULL;
d = 1;
while (lim - end >= d)
{
if (d = delta[c = (end += d)[-1]])
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[(unsigned char) *--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;
}

if (kwsmatch)
{
kwsmatch->index = accept->accepting / 2;
kwsmatch->beg[0] = mch;
kwsmatch->size[0] = accept->depth;
}
return mch;
}

/* Free the components of the given keyword set. */
void
DEFUN(kwsfree, (kws), kwset_t kws)
{
struct kwset *kwset;

kwset = (struct kwset *) kws;
obstack_free(&kwset->obstack, (PTR) NULL);
free((PTR) kws);
}