1 files changed, 145 insertions, 0 deletions

diff --git a/lib/ts_kmp.c b/lib/ts_kmp.c
new file mode 100644
index 000000000000..73266b975585
--- /dev/null
+++ b/lib/ts_kmp.c
@@ -0,0 +1,145 @@
+/*
+ * lib/ts_kmp.c         Knuth-Morris-Pratt text search implementation
+ *
+ *              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
+ *              2 of the License, or (at your option) any later version.
+ *
+ * Authors:     Thomas Graf <tgraf@suug.ch>
+ *
+ * ==========================================================================
+ * 
+ *   Implements a linear-time string-matching algorithm due to Knuth,
+ *   Morris, and Pratt [1]. Their algorithm avoids the explicit
+ *   computation of the transition function DELTA altogether. Its
+ *   matching time is O(n), for n being length(text), using just an
+ *   auxiliary function PI[1..m], for m being length(pattern),
+ *   precomputed from the pattern in time O(m). The array PI allows
+ *   the transition function DELTA to be computed efficiently
+ *   "on the fly" as needed. Roughly speaking, for any state
+ *   "q" = 0,1,...,m and any character "a" in SIGMA, the value
+ *   PI["q"] contains the information that is independent of "a" and
+ *   is needed to compute DELTA("q", "a") [2]. Since the array PI
+ *   has only m entries, whereas DELTA has O(m|SIGMA|) entries, we
+ *   save a factor of |SIGMA| in the preprocessing time by computing
+ *   PI rather than DELTA.
+ *
+ *   [1] Cormen, Leiserson, Rivest, Stein
+ *       Introdcution to Algorithms, 2nd Edition, MIT Press
+ *   [2] See finite automation theory
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/textsearch.h>
+
+struct ts_kmp
+{
+        u8 *            pattern;
+        unsigned int    pattern_len;
+        unsigned int    prefix_tbl[0];
+};
+
+static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state)
+{
+        struct ts_kmp *kmp = ts_config_priv(conf);
+        unsigned int i, q = 0, text_len, consumed = state->offset;
+        const u8 *text;
+
+        for (;;) {
+                text_len = conf->get_next_block(consumed, &text, conf, state);
+
+                if (unlikely(text_len == 0))
+                        break;
+
+                for (i = 0; i < text_len; i++) {
+                        while (q > 0 && kmp->pattern[q] != text[i])
+                                q = kmp->prefix_tbl[q - 1];
+                        if (kmp->pattern[q] == text[i])
+                                q++;
+                        if (unlikely(q == kmp->pattern_len)) {
+                                state->offset = consumed + i + 1;
+                                return state->offset - kmp->pattern_len;
+                        }
+                }
+
+                consumed += text_len;
+        }
+
+        return UINT_MAX;
+}
+
+static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len,
+                                      unsigned int *prefix_tbl)
+{
+        unsigned int k, q;
+
+        for (k = 0, q = 1; q < len; q++) {
+                while (k > 0 && pattern[k] != pattern[q])
+                        k = prefix_tbl[k-1];
+                if (pattern[k] == pattern[q])
+                        k++;
+                prefix_tbl[q] = k;
+        }
+}
+
+static struct ts_config *kmp_init(const void *pattern, unsigned int len,
+                                  int gfp_mask)
+{
+        struct ts_config *conf;
+        struct ts_kmp *kmp;
+        unsigned int prefix_tbl_len = len * sizeof(unsigned int);
+        size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
+
+        conf = alloc_ts_config(priv_size, gfp_mask);
+        if (IS_ERR(conf))
+                return conf;
+
+        kmp = ts_config_priv(conf);
+        kmp->pattern_len = len;
+        compute_prefix_tbl(pattern, len, kmp->prefix_tbl);
+        kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len;
+        memcpy(kmp->pattern, pattern, len);
+
+        return conf;
+}
+
+static void *kmp_get_pattern(struct ts_config *conf)
+{
+        struct ts_kmp *kmp = ts_config_priv(conf);
+        return kmp->pattern;
+}
+
+static unsigned int kmp_get_pattern_len(struct ts_config *conf)
+{
+        struct ts_kmp *kmp = ts_config_priv(conf);
+        return kmp->pattern_len;
+}
+
+static struct ts_ops kmp_ops = {
+        .name             = "kmp",
+        .find             = kmp_find,
+        .init             = kmp_init,
+        .get_pattern      = kmp_get_pattern,
+        .get_pattern_len  = kmp_get_pattern_len,
+        .owner            = THIS_MODULE,
+        .list             = LIST_HEAD_INIT(kmp_ops.list)
+};
+
+static int __init init_kmp(void)
+{
+        return textsearch_register(&kmp_ops);
+}
+
+static void __exit exit_kmp(void)
+{
+        textsearch_unregister(&kmp_ops);
+}
+
+MODULE_LICENSE("GPL");
+
+module_init(init_kmp);
+module_exit(exit_kmp);