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-rw-r--r--lib/Kconfig10
-rw-r--r--lib/Makefile1
-rw-r--r--lib/ts_kmp.c145
3 files changed, 156 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig
index 5bc2d523e6d1..16b8fa2175e4 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -70,4 +70,14 @@ config TEXTSEARCH
Say Y here if you want to provide a textsearch infrastructure
to other subsystems.
+config TEXTSEARCH_KMP
+ depends on TEXTSEARCH
+ tristate "Knuth-Morris-Pratt"
+ help
+ Say Y here if you want to be able to search text using the
+ Knuth-Morris-Pratt textsearch algorithm.
+
+ To compile this code as a module, choose M here: the
+ module will be called ts_kmp.
+
endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 3e917436ad60..6cdb10f312df 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
obj-$(CONFIG_REED_SOLOMON) += reed_solomon/
lib-$(CONFIG_TEXTSEARCH) += textsearch.o
+obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o
hostprogs-y := gen_crc32table
clean-files := crc32table.h
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);

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