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153 lines
4.1 KiB
153 lines
4.1 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* lib/ts_kmp.c Knuth-Morris-Pratt text search implementation |
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* |
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* Authors: Thomas Graf <[email protected]> |
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* |
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* ========================================================================== |
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* |
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* Implements a linear-time string-matching algorithm due to Knuth, |
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* Morris, and Pratt [1]. Their algorithm avoids the explicit |
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* computation of the transition function DELTA altogether. Its |
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* matching time is O(n), for n being length(text), using just an |
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* auxiliary function PI[1..m], for m being length(pattern), |
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* precomputed from the pattern in time O(m). The array PI allows |
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* the transition function DELTA to be computed efficiently |
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* "on the fly" as needed. Roughly speaking, for any state |
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* "q" = 0,1,...,m and any character "a" in SIGMA, the value |
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* PI["q"] contains the information that is independent of "a" and |
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* is needed to compute DELTA("q", "a") [2]. Since the array PI |
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* has only m entries, whereas DELTA has O(m|SIGMA|) entries, we |
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* save a factor of |SIGMA| in the preprocessing time by computing |
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* PI rather than DELTA. |
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* |
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* [1] Cormen, Leiserson, Rivest, Stein |
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* Introdcution to Algorithms, 2nd Edition, MIT Press |
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* [2] See finite automaton theory |
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*/ |
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#include <linux/module.h> |
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#include <linux/types.h> |
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#include <linux/string.h> |
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#include <linux/ctype.h> |
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#include <linux/textsearch.h> |
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struct ts_kmp |
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{ |
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u8 * pattern; |
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unsigned int pattern_len; |
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unsigned int prefix_tbl[]; |
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}; |
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static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state) |
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{ |
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struct ts_kmp *kmp = ts_config_priv(conf); |
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unsigned int i, q = 0, text_len, consumed = state->offset; |
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const u8 *text; |
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const int icase = conf->flags & TS_IGNORECASE; |
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for (;;) { |
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text_len = conf->get_next_block(consumed, &text, conf, state); |
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if (unlikely(text_len == 0)) |
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break; |
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for (i = 0; i < text_len; i++) { |
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while (q > 0 && kmp->pattern[q] |
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!= (icase ? toupper(text[i]) : text[i])) |
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q = kmp->prefix_tbl[q - 1]; |
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if (kmp->pattern[q] |
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== (icase ? toupper(text[i]) : text[i])) |
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q++; |
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if (unlikely(q == kmp->pattern_len)) { |
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state->offset = consumed + i + 1; |
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return state->offset - kmp->pattern_len; |
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} |
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} |
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consumed += text_len; |
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} |
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return UINT_MAX; |
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} |
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static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len, |
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unsigned int *prefix_tbl, int flags) |
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{ |
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unsigned int k, q; |
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const u8 icase = flags & TS_IGNORECASE; |
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for (k = 0, q = 1; q < len; q++) { |
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while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k]) |
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!= (icase ? toupper(pattern[q]) : pattern[q])) |
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k = prefix_tbl[k-1]; |
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if ((icase ? toupper(pattern[k]) : pattern[k]) |
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== (icase ? toupper(pattern[q]) : pattern[q])) |
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k++; |
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prefix_tbl[q] = k; |
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} |
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} |
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static struct ts_config *kmp_init(const void *pattern, unsigned int len, |
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gfp_t gfp_mask, int flags) |
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{ |
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struct ts_config *conf; |
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struct ts_kmp *kmp; |
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int i; |
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unsigned int prefix_tbl_len = len * sizeof(unsigned int); |
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size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len; |
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conf = alloc_ts_config(priv_size, gfp_mask); |
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if (IS_ERR(conf)) |
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return conf; |
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conf->flags = flags; |
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kmp = ts_config_priv(conf); |
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kmp->pattern_len = len; |
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compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags); |
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kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len; |
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if (flags & TS_IGNORECASE) |
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for (i = 0; i < len; i++) |
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kmp->pattern[i] = toupper(((u8 *)pattern)[i]); |
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else |
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memcpy(kmp->pattern, pattern, len); |
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return conf; |
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} |
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static void *kmp_get_pattern(struct ts_config *conf) |
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{ |
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struct ts_kmp *kmp = ts_config_priv(conf); |
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return kmp->pattern; |
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} |
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static unsigned int kmp_get_pattern_len(struct ts_config *conf) |
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{ |
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struct ts_kmp *kmp = ts_config_priv(conf); |
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return kmp->pattern_len; |
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} |
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static struct ts_ops kmp_ops = { |
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.name = "kmp", |
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.find = kmp_find, |
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.init = kmp_init, |
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.get_pattern = kmp_get_pattern, |
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.get_pattern_len = kmp_get_pattern_len, |
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.owner = THIS_MODULE, |
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.list = LIST_HEAD_INIT(kmp_ops.list) |
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}; |
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static int __init init_kmp(void) |
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{ |
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return textsearch_register(&kmp_ops); |
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} |
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static void __exit exit_kmp(void) |
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{ |
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textsearch_unregister(&kmp_ops); |
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} |
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MODULE_LICENSE("GPL"); |
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module_init(init_kmp); |
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module_exit(exit_kmp);
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