| 1 | |
| 2 | * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation
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| 3 | *
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| 4 | * This program is free software; you can redistribute it and/or
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| 5 | * modify it under the terms of the GNU General Public License
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| 6 | * as published by the Free Software Foundation; either version
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| 7 | * 2 of the License, or (at your option) any later version.
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| 8 | *
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| 9 | * Authors: Thomas Graf <[email protected]>
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| 10 | *
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| 11 | * ==========================================================================
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| 12 | *
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| 13 | * Implements a linear-time string-matching algorithm due to Knuth,
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| 14 | * Morris, and Pratt [1]. Their algorithm avoids the explicit
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| 15 | * computation of the transition function DELTA altogether. Its
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| 16 | * matching time is O(n), for n being length(text), using just an
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| 17 | * auxiliary function PI[1..m], for m being length(pattern),
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| 18 | * precomputed from the pattern in time O(m). The array PI allows
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| 19 | * the transition function DELTA to be computed efficiently
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| 20 | * "on the fly" as needed. Roughly speaking, for any state
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| 21 | * "q" = 0,1,...,m and any character "a" in SIGMA, the value
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| 22 | * PI["q"] contains the information that is independent of "a" and
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| 23 | * is needed to compute DELTA("q", "a") [2]. Since the array PI
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| 24 | * has only m entries, whereas DELTA has O(m|SIGMA|) entries, we
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| 25 | * save a factor of |SIGMA| in the preprocessing time by computing
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| 26 | * PI rather than DELTA.
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| 27 | *
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| 28 | * [1] Cormen, Leiserson, Rivest, Stein
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| 29 | * Introdcution to Algorithms, 2nd Edition, MIT Press
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| 30 | * [2] See finite automation theory
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| 31 |
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| 32 |
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| 33 | #include <linux/module.h>
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| 34 | #include <linux/types.h>
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| 35 | #include <linux/string.h>
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| 36 | #include <linux/ctype.h>
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| 37 | #include <linux/textsearch.h>
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| 38 |
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| 39 | struct ts_kmp
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| 40 | {
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| 41 | u8 * pattern;
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| 42 | unsigned int pattern_len;
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| 43 | unsigned int prefix_tbl[0];
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| 44 | };
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| 45 |
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| 46 | static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state)
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| 47 | {
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| 48 | struct ts_kmp *kmp = ts_config_priv(conf);
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| 49 | unsigned int i, q = 0, text_len, consumed = state->offset;
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| 50 | const u8 *text;
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| 51 | const int icase = conf->flags & TS_IGNORECASE;
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| 52 |
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| 53 | for (;;) {
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| 54 | text_len = conf->get_next_block(consumed, &text, conf, state);
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| 55 |
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| 56 | if (unlikely(text_len == 0))
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| 57 | break;
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| 58 |
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| 59 | for (i = 0; i < text_len; i++) {
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| 60 | while (q > 0 && kmp->pattern[q]
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| 61 | != (icase ? toupper(text[i]) : text[i]))
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| 62 | q = kmp->prefix_tbl[q - 1];
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| 63 | if (kmp->pattern[q]
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| 64 | == (icase ? toupper(text[i]) : text[i]))
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| 65 | q++;
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| 66 | if (unlikely(q == kmp->pattern_len)) {
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| 67 | state->offset = consumed + i + 1;
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| 68 | return state->offset - kmp->pattern_len;
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| 69 | }
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| 70 | }
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| 71 |
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| 72 | consumed += text_len;
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| 73 | }
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| 74 |
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| 75 | return UINT_MAX;
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| 76 | }
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| 77 |
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| 78 | static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len,
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| 79 | unsigned int *prefix_tbl, int flags)
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| 80 | {
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| 81 | unsigned int k, q;
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| 82 | const u8 icase = flags & TS_IGNORECASE;
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| 83 |
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| 84 | for (k = 0, q = 1; q < len; q++) {
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| 85 | while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k])
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| 86 | != (icase ? toupper(pattern[q]) : pattern[q]))
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| 87 | k = prefix_tbl[k-1];
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| 88 | if ((icase ? toupper(pattern[k]) : pattern[k])
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| 89 | == (icase ? toupper(pattern[q]) : pattern[q]))
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| 90 | k++;
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| 91 | prefix_tbl[q] = k;
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| 92 | }
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| 93 | }
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| 94 |
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| 95 | static struct ts_config *kmp_init(const void *pattern, unsigned int len,
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| 96 | gfp_t gfp_mask, int flags)
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| 97 | {
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| 98 | struct ts_config *conf;
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| 99 | struct ts_kmp *kmp;
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| 100 | int i;
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| 101 | unsigned int prefix_tbl_len = len * sizeof(unsigned int);
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| 102 | size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
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| 103 |
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| 104 | conf = alloc_ts_config(priv_size, gfp_mask);
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| 105 | if (IS_ERR(conf))
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| 106 | return conf;
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| 107 |
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| 108 | conf->flags = flags;
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| 109 | kmp = ts_config_priv(conf);
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| 110 | kmp->pattern_len = len;
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| 111 | compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags);
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| 112 | kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len;
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| 113 | if (flags & TS_IGNORECASE)
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| 114 | for (i = 0; i < len; i++)
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| 115 | kmp->pattern[i] = toupper(((u8 *)pattern)[i]);
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| 116 | else
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| 117 | memcpy(kmp->pattern, pattern, len);
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| 118 |
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| 119 | return conf;
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| 120 | }
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| 121 |
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| 122 | static void *kmp_get_pattern(struct ts_config *conf)
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| 123 | {
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| 124 | struct ts_kmp *kmp = ts_config_priv(conf);
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| 125 | return kmp->pattern;
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| 126 | }
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| 127 |
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| 128 | static unsigned int kmp_get_pattern_len(struct ts_config *conf)
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| 129 | {
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| 130 | struct ts_kmp *kmp = ts_config_priv(conf);
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| 131 | return kmp->pattern_len;
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| 132 | }
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| 133 |
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| 134 | static struct ts_ops kmp_ops = {
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| 135 | .name = "kmp",
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| 136 | .find = kmp_find,
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| 137 | .init = kmp_init,
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| 138 | .get_pattern = kmp_get_pattern,
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| 139 | .get_pattern_len = kmp_get_pattern_len,
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| 140 | .owner = THIS_MODULE,
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| 141 | .list = LIST_HEAD_INIT(kmp_ops.list)
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| 142 | };
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| 143 |
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| 144 | static int __init init_kmp(void)
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| 145 | {
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| 146 | return textsearch_register(&kmp_ops);
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| 147 | }
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| 148 |
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| 149 | static void __exit exit_kmp(void)
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| 150 | {
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| 151 | textsearch_unregister(&kmp_ops);
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| 152 | }
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| 153 |
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| 154 | MODULE_LICENSE("GPL");
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| 155 |
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| 156 | module_init(init_kmp);
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| 157 | module_exit(exit_kmp);
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