From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Graf Subject: [PATCH 2/5] [LIB] Knuth-Morris-Pratt string-matching algorithm Date: Sat, 28 May 2005 00:48:18 +0200 Message-ID: <20050527224818.GI15391@postel.suug.ch> References: <20050527224725.GG15391@postel.suug.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jamal Hadi Salim Return-path: To: netdev@oss.sgi.com Content-Disposition: inline In-Reply-To: <20050527224725.GG15391@postel.suug.ch> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Signed-off-by: Thomas Graf --- commit 5b70ca8eab4c7d7ef884582d9713cdbffa0f4cd4 tree 4d90ca82120da7b308b9a6bf11a1069473ca5d30 parent bf7ae763f13d767bd039703b3ab4f5954561df39 author Thomas Graf Fri, 27 May 2005 23:44:02 +0200 committer Thomas Graf Fri, 27 May 2005 23:44:02 +0200 lib/Kconfig | 13 +++++ lib/Makefile | 2 lib/ts_kmp.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 160 insertions(+) Index: lib/Kconfig =================================================================== --- ab065819ea6e966aa3db4f1c5935c421dd689d2e/lib/Kconfig (mode:100644) +++ 4d90ca82120da7b308b9a6bf11a1069473ca5d30/lib/Kconfig (mode:100644) @@ -57,5 +57,18 @@ config REED_SOLOMON_DEC16 boolean +menu "Textsearch facility" + +config TEXTSEARCH_KMP + 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 + endmenu Index: lib/Makefile =================================================================== --- ab065819ea6e966aa3db4f1c5935c421dd689d2e/lib/Makefile (mode:100644) +++ 4d90ca82120da7b308b9a6bf11a1069473ca5d30/lib/Makefile (mode:100644) @@ -33,6 +33,8 @@ obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/ obj-$(CONFIG_REED_SOLOMON) += reed_solomon/ +obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o + hostprogs-y := gen_crc32table clean-files := crc32table.h Index: lib/ts_kmp.c =================================================================== --- /dev/null (tree:ab065819ea6e966aa3db4f1c5935c421dd689d2e) +++ 4d90ca82120da7b308b9a6bf11a1069473ca5d30/lib/ts_kmp.c (mode:100644) @@ -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 + * + * Implements a linear-time string-matching algorithm due to Knuth, + * Morris, and Pratt [0]. 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") [1]. 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. + * + * [0] Cormen, Leiserson, Rivest, Stein + * Introdcution to Algorithms, 2nd Edition, MIT Press + * [1] See finite automation theory + */ + +#include +#include +#include +#include +#include + +struct ts_kmp +{ + int pattern_len; + unsigned char * pattern; + unsigned int prefix_tbl[0]; +}; + +static int kmp_find(struct ts_config *conf, struct ts_state *state) +{ + struct ts_kmp *kmp = ts_config_priv(conf); + int i, q = 0, consumed = state->offset; + unsigned char *text; + size_t text_len; + + for (;;) { + text_len = conf->get_text(consumed, &text, conf, state); + + if (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 (q == kmp->pattern_len) { + state->offset = consumed + i + 1; + return state->offset - kmp->pattern_len; + } + } + + consumed += text_len; + } + + return -1; + +} + +static inline void compute_prefix_tbl(const unsigned char *pattern, size_t 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 unsigned char *pattern, size_t len, + int gfp_mask) +{ + struct ts_config *conf; + struct ts_kmp *kmp; + size_t 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 = (unsigned char *) kmp->prefix_tbl + prefix_tbl_len; + memcpy(kmp->pattern, pattern, len); + + return conf; +} + +static unsigned char *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);