[LIB]: Knuth-Morris-Pratt textsearch algorithm

	  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

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

/*

 * 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);