/* Return true if A has every label in B. */
static int
hasevery (register struct tree const *a, register 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;
}
/* Return true if A has every label in B. */
static int _GL_ATTRIBUTE_PURE
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 the shift for each trie node, as well as the delta
table and next cache for the given keyword set. */
char *
kwsprep (kwset_t kws)
{
register struct kwset *kwset;
register int i;
register struct trie *curr, *fail;
register char const *trans;
unsigned char 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. */
if (kwset->mind < 256)
for (i = 0; i < NCHAR; ++i)
delta[i] = kwset->mind;
else
for (i = 0; i < NCHAR; ++i)
delta[i] = 255;
/* Check if we can use the simple boyer-moore algorithm, instead
of the hairy commentz-walter algorithm. */
if (kwset->words == 1 && kwset->trans == 0)
{
/* Looking for just one string. Extract it from the trie. */
kwset->target = obstack_alloc(&kwset->obstack, kwset->mind);
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[(unsigned char) kwset->target[i]] = kwset->mind - (i + 1);
kwset->mind2 = kwset->mind;
/* Find the minimal delta2 shift that we might make after
a backwards match has failed. */
for (i = 0; i < kwset->mind - 1; ++i)
if (kwset->target[i] == kwset->target[kwset->mind - 1])
kwset->mind2 = kwset->mind - (i + 1);
}
else
{
/* 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] = 0;
treenext(kwset->trie->links, next);
if ((trans = kwset->trans) != 0)
for (i = 0; i < NCHAR; ++i)
kwset->next[i] = next[(unsigned char) trans[i]];
else
for (i = 0; i < NCHAR; ++i)
kwset->next[i] = next[i];
}
/* Fix things up for any translation table. */
if ((trans = kwset->trans) != 0)
for (i = 0; i < NCHAR; ++i)
kwset->delta[i] = delta[(unsigned char) trans[i]];
else
for (i = 0; i < NCHAR; ++i)
kwset->delta[i] = delta[i];
return 0;
}
