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authorPaul Eggert <eggert@cs.ucla.edu>2017-01-18 20:25:01 (GMT)
committerPaul Eggert <eggert@cs.ucla.edu>2017-01-18 23:53:03 (GMT)
commit57d32889c95e04a0f0237ec09538b22aa39fe908 (patch)
tree06962d9f8a49a1b72c5c9a629828aed887b32b06
parent8486cc9546c61eeb0decf65eca788e550254a93e (diff)
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grep: remove Commentz-Walter code
This code was not being used, and complicated maintenance. We can bring it back from the repository if it turns out to be useful later. * src/kwset.c (struct kwset.reverse): Remove. All uses of FOO->reverse replaced by (FOO->kwsexec == bmexec). (kwsalloc): Remove 'reverse' arg, as callers outside this module do not care about algorithm choice. All callers changed. (kwsprep): When deciding whether to use Boyer-Moore, do not worry about being called twice on the same kwset, as that is not allowed. (cwexec): Remove; it was never called. All uses removed.
-rw-r--r--src/kwset.c240
-rw-r--r--src/kwset.h2
-rw-r--r--src/searchutils.c2
3 files changed, 35 insertions, 209 deletions
diff --git a/src/kwset.c b/src/kwset.c
index 0c0993d..ace720b 100644
--- a/src/kwset.c
+++ b/src/kwset.c
@@ -19,13 +19,7 @@
/* Written August 1989 by Mike Haertel. */
-/* The algorithm called "Commentz-Walter" below bears a startling resemblance
- to that of Beate Commentz-Walter, although it is not identical.
- See: Commentz-Walter B. A string matching algorithm fast on the average.
- Lecture Notes in Computer Science 71 (1979), 118-32
- <http://dx.doi.org/10.1007/3-540-09510-1_10>.
-
- For the Aho-Corasick algorithm, see:
+/* For the Aho-Corasick algorithm, see:
Aho AV, Corasick MJ. Efficient string matching: an aid to
bibliographic search. CACM 18, 6 (1975), 333-40
<http://dx.doi.org/10.1145/360825.360855>, which describes the
@@ -76,7 +70,7 @@ struct tree
struct trie
{
/* If an accepting node, this is either 2*W + 1 where W is the word
- index, or is SIZE_MAX if Commentz-Walter is in use and FAIL
+ index, or is SIZE_MAX if Aho-Corasick is in use and FAIL
specifies where to look for more info. If not an accepting node,
this is zero. */
size_t accepting;
@@ -123,10 +117,6 @@ struct kwset
all match when case-folding. */
int gc1help;
- /* If true, prefer Aho-Corasick to Commentz-Walter when searching
- for multiple words. */
- bool reverse;
-
/* kwsexec implementation. */
ptrdiff_t (*kwsexec) (kwset_t, char const *, ptrdiff_t,
struct kwsmatch *, bool);
@@ -141,17 +131,14 @@ tr (char const *trans, char c)
static ptrdiff_t acexec (kwset_t, char const *, ptrdiff_t,
struct kwsmatch *, bool);
-static ptrdiff_t cwexec (kwset_t, char const *, ptrdiff_t,
- struct kwsmatch *, bool);
static ptrdiff_t bmexec (kwset_t, char const *, ptrdiff_t,
struct kwsmatch *, bool);
/* Return a newly allocated keyword set. A nonnull TRANS specifies a
table of character translations to be applied to all pattern and
- search text. If REVERSE, prefer the Aho-Corasick algorithm to the
- Commentz-Walter algorithm. */
+ search text. */
kwset_t
-kwsalloc (char const *trans, bool reverse)
+kwsalloc (char const *trans)
{
struct kwset *kwset = xmalloc (sizeof *kwset);
@@ -169,8 +156,7 @@ kwsalloc (char const *trans, bool reverse)
kwset->maxd = -1;
kwset->target = NULL;
kwset->trans = trans;
- kwset->reverse = reverse;
- kwset->kwsexec = reverse ? cwexec : acexec;
+ kwset->kwsexec = acexec;
return kwset;
}
@@ -186,15 +172,16 @@ kwsincr (kwset_t kwset, char const *text, ptrdiff_t len)
assume (0 <= len);
struct trie *trie = kwset->trie;
char const *trans = kwset->trans;
+ bool reverse = kwset->kwsexec == bmexec;
- if (kwset->reverse)
+ if (reverse)
text += len;
/* Descend the trie (built of keywords) character-by-character,
installing new nodes when necessary. */
while (len--)
{
- unsigned char uc = kwset->reverse ? *--text : *text++;
+ unsigned char uc = reverse ? *--text : *text++;
unsigned char label = trans ? trans[uc] : uc;
/* Descend the tree of outgoing links for this trie node,
@@ -438,31 +425,31 @@ kwsprep (kwset_t kwset)
unsigned char *delta = trans ? deltabuf : kwset->delta;
struct trie *curr, *last;
- if (kwset->words == 1)
- {
- if (!kwset->reverse)
- {
- kwset_t new_kwset;
+ /* Use Boyer-Moore if just one pattern, Aho-Corasick otherwise. */
+ bool reverse = kwset->words == 1;
- /* Enqueue the immediate descendants in the level order queue. */
- for (curr = last = kwset->trie; curr; curr = curr->next)
- enqueue (curr->links, &last);
+ if (reverse)
+ {
+ kwset_t new_kwset;
- /* Looking for just one string. Extract it from the trie. */
- kwset->target = obstack_alloc (&kwset->obstack, kwset->mind);
- for (i = 0, curr = kwset->trie; i < kwset->mind; ++i)
- {
- kwset->target[i] = curr->links->label;
- curr = curr->next;
- }
+ /* Enqueue the immediate descendants in the level order queue. */
+ for (curr = last = kwset->trie; curr; curr = curr->next)
+ enqueue (curr->links, &last);
- new_kwset = kwsalloc (kwset->trans, true);
- kwsincr (new_kwset, kwset->target, kwset->mind);
- obstack_free (&kwset->obstack, NULL);
- *kwset = *new_kwset;
- free (new_kwset);
+ /* Looking for just one string. Extract it from the trie. */
+ kwset->target = obstack_alloc (&kwset->obstack, kwset->mind);
+ for (i = 0, curr = kwset->trie; i < kwset->mind; ++i)
+ {
+ kwset->target[i] = curr->links->label;
+ curr = curr->next;
}
- kwset->kwsexec = bmexec;
+
+ new_kwset = kwsalloc (kwset->trans);
+ new_kwset->kwsexec = bmexec;
+ kwsincr (new_kwset, kwset->target, kwset->mind);
+ obstack_free (&kwset->obstack, NULL);
+ *kwset = *new_kwset;
+ free (new_kwset);
}
/* Initial values for the delta table; will be changed later. The
@@ -481,9 +468,9 @@ kwsprep (kwset_t kwset)
treedelta (curr->links, curr->depth, delta);
/* Compute the failure function for the descendants of this node. */
- treefails (curr->links, curr->fail, kwset->trie, kwset->reverse);
+ treefails (curr->links, curr->fail, kwset->trie, reverse);
- if (kwset->reverse)
+ if (reverse)
{
curr->shift = kwset->mind;
curr->maxshift = kwset->mind;
@@ -509,7 +496,7 @@ kwsprep (kwset_t kwset)
}
}
- if (kwset->reverse)
+ if (reverse)
{
/* Traverse the trie in level order again, fixing up all nodes whose
shift exceeds their inherited maxshift. */
@@ -532,9 +519,7 @@ kwsprep (kwset_t kwset)
for (i = 0; i < NCHAR; ++i)
kwset->next[i] = next[U(trans[i])];
- /* Decide whether to use the simple Boyer-Moore algorithm, instead
- of the hairy Commentz-Walter algorithm. */
- if (kwset->words == 1)
+ if (reverse)
{
/* Looking for just one string. Extract it from the trie. */
kwset->target = obstack_alloc (&kwset->obstack, kwset->mind);
@@ -794,165 +779,6 @@ bmexec (kwset_t kwset, char const *text, ptrdiff_t size,
return ret;
}
-/* Hairy multiple string search with the Commentz-Walter algorithm. */
-static ptrdiff_t
-cwexec (kwset_t kwset, char const *text, ptrdiff_t len,
- struct kwsmatch *kwsmatch, bool longest)
-{
- assume (0 <= len);
- 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;
- ptrdiff_t d;
- char const *end, *qlim;
- struct tree const *tree;
- char const *trans;
-
- /* Initialize register copies and look for easy ways out. */
- if (len < kwset->mind)
- return -1;
- if (!kwset->trans && kwset->maxd == 1 && kwset->words == 2)
- return memoff2_kwset (text, len, kwset, kwsmatch);
- 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)
- {
- unsigned char uc = *--beg;
- c = trans ? trans[uc] : uc;
- 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 (longest)
- {
- 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)
- {
- unsigned char uc = *--beg;
- c = trans ? trans[uc] : uc;
- 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;
-}
-
/* Hairy multiple string search with the Aho-Corasick algorithm.
(inlinable version) */
static inline ptrdiff_t
diff --git a/src/kwset.h b/src/kwset.h
index 5c78e54..b1defbb 100644
--- a/src/kwset.h
+++ b/src/kwset.h
@@ -34,7 +34,7 @@ struct kwsmatch
struct kwset;
typedef struct kwset *kwset_t;
-extern kwset_t kwsalloc (char const *, bool);
+extern kwset_t kwsalloc (char const *);
extern void kwsincr (kwset_t, char const *, ptrdiff_t);
extern ptrdiff_t kwswords (kwset_t) _GL_ATTRIBUTE_PURE;
extern void kwsprep (kwset_t);
diff --git a/src/searchutils.c b/src/searchutils.c
index e0a94e2..336d9f9 100644
--- a/src/searchutils.c
+++ b/src/searchutils.c
@@ -68,7 +68,7 @@ kwsinit (bool mb_trans)
}
}
- return kwsalloc (trans, false);
+ return kwsalloc (trans);
}
/* In the buffer *MB_START, return the number of bytes needed to go