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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation4 *5 * Authors: Thomas Graf <tgraf@suug.ch>6 *7 * ==========================================================================8 * 9 * Implements a linear-time string-matching algorithm due to Knuth,10 * Morris, and Pratt [1]. Their algorithm avoids the explicit11 * computation of the transition function DELTA altogether. Its12 * matching time is O(n), for n being length(text), using just an13 * auxiliary function PI[1..m], for m being length(pattern),14 * precomputed from the pattern in time O(m). The array PI allows15 * the transition function DELTA to be computed efficiently16 * "on the fly" as needed. Roughly speaking, for any state17 * "q" = 0,1,...,m and any character "a" in SIGMA, the value18 * PI["q"] contains the information that is independent of "a" and19 * is needed to compute DELTA("q", "a") [2]. Since the array PI20 * has only m entries, whereas DELTA has O(m|SIGMA|) entries, we21 * save a factor of |SIGMA| in the preprocessing time by computing22 * PI rather than DELTA.23 *24 * [1] Cormen, Leiserson, Rivest, Stein25 * Introdcution to Algorithms, 2nd Edition, MIT Press26 * [2] See finite automaton theory27 */28 29#include <linux/module.h>30#include <linux/types.h>31#include <linux/string.h>32#include <linux/ctype.h>33#include <linux/textsearch.h>34 35struct ts_kmp36{37 u8 * pattern;38 unsigned int pattern_len;39 unsigned int prefix_tbl[];40};41 42static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state)43{44 struct ts_kmp *kmp = ts_config_priv(conf);45 unsigned int i, q = 0, text_len, consumed = state->offset;46 const u8 *text;47 const int icase = conf->flags & TS_IGNORECASE;48 49 for (;;) {50 text_len = conf->get_next_block(consumed, &text, conf, state);51 52 if (unlikely(text_len == 0))53 break;54 55 for (i = 0; i < text_len; i++) {56 while (q > 0 && kmp->pattern[q]57 != (icase ? toupper(text[i]) : text[i]))58 q = kmp->prefix_tbl[q - 1];59 if (kmp->pattern[q]60 == (icase ? toupper(text[i]) : text[i]))61 q++;62 if (unlikely(q == kmp->pattern_len)) {63 state->offset = consumed + i + 1;64 return state->offset - kmp->pattern_len;65 }66 }67 68 consumed += text_len;69 }70 71 return UINT_MAX;72}73 74static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len,75 unsigned int *prefix_tbl, int flags)76{77 unsigned int k, q;78 const u8 icase = flags & TS_IGNORECASE;79 80 for (k = 0, q = 1; q < len; q++) {81 while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k])82 != (icase ? toupper(pattern[q]) : pattern[q]))83 k = prefix_tbl[k-1];84 if ((icase ? toupper(pattern[k]) : pattern[k])85 == (icase ? toupper(pattern[q]) : pattern[q]))86 k++;87 prefix_tbl[q] = k;88 }89}90 91static struct ts_config *kmp_init(const void *pattern, unsigned int len,92 gfp_t gfp_mask, int flags)93{94 struct ts_config *conf;95 struct ts_kmp *kmp;96 int i;97 unsigned int prefix_tbl_len = len * sizeof(unsigned int);98 size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;99 100 conf = alloc_ts_config(priv_size, gfp_mask);101 if (IS_ERR(conf))102 return conf;103 104 conf->flags = flags;105 kmp = ts_config_priv(conf);106 kmp->pattern_len = len;107 compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags);108 kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len;109 if (flags & TS_IGNORECASE)110 for (i = 0; i < len; i++)111 kmp->pattern[i] = toupper(((u8 *)pattern)[i]);112 else113 memcpy(kmp->pattern, pattern, len);114 115 return conf;116}117 118static void *kmp_get_pattern(struct ts_config *conf)119{120 struct ts_kmp *kmp = ts_config_priv(conf);121 return kmp->pattern;122}123 124static unsigned int kmp_get_pattern_len(struct ts_config *conf)125{126 struct ts_kmp *kmp = ts_config_priv(conf);127 return kmp->pattern_len;128}129 130static struct ts_ops kmp_ops = {131 .name = "kmp",132 .find = kmp_find,133 .init = kmp_init,134 .get_pattern = kmp_get_pattern,135 .get_pattern_len = kmp_get_pattern_len,136 .owner = THIS_MODULE,137 .list = LIST_HEAD_INIT(kmp_ops.list)138};139 140static int __init init_kmp(void)141{142 return textsearch_register(&kmp_ops);143}144 145static void __exit exit_kmp(void)146{147 textsearch_unregister(&kmp_ops);148}149 150MODULE_DESCRIPTION("Knuth-Morris-Pratt text search implementation");151MODULE_LICENSE("GPL");152 153module_init(init_kmp);154module_exit(exit_kmp);155