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 // SPDX-License-Identifier: GPL-2.0-or-later /* * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation * * Authors: Thomas Graf * * ========================================================================== * * 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 automaton theory */ #include #include #include #include #include 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; const int icase = conf->flags & TS_IGNORECASE; 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] != (icase ? toupper(text[i]) : text[i])) q = kmp->prefix_tbl[q - 1]; if (kmp->pattern[q] == (icase ? toupper(text[i]) : 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, int flags) { unsigned int k, q; const u8 icase = flags & TS_IGNORECASE; for (k = 0, q = 1; q < len; q++) { while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k]) != (icase ? toupper(pattern[q]) : pattern[q])) k = prefix_tbl[k-1]; if ((icase ? toupper(pattern[k]) : pattern[k]) == (icase ? toupper(pattern[q]) : pattern[q])) k++; prefix_tbl[q] = k; } } static struct ts_config *kmp_init(const void *pattern, unsigned int len, gfp_t gfp_mask, int flags) { struct ts_config *conf; struct ts_kmp *kmp; int i; 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; conf->flags = flags; kmp = ts_config_priv(conf); kmp->pattern_len = len; compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags); kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len; if (flags & TS_IGNORECASE) for (i = 0; i < len; i++) kmp->pattern[i] = toupper(((u8 *)pattern)[i]); else 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);