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| 1 | /* |
| 2 | * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or |
| 5 | * modify it under the terms of the GNU General Public License |
| 6 | * as published by the Free Software Foundation; either version |
| 7 | * 2 of the License, or (at your option) any later version. |
| 8 | * |
| 9 | * Authors: Thomas Graf <tgraf@suug.ch> |
| 10 | * |
| 11 | * ========================================================================== |
| 12 | * |
| 13 | * Implements a linear-time string-matching algorithm due to Knuth, |
| 14 | * Morris, and Pratt [1]. Their algorithm avoids the explicit |
| 15 | * computation of the transition function DELTA altogether. Its |
| 16 | * matching time is O(n), for n being length(text), using just an |
| 17 | * auxiliary function PI[1..m], for m being length(pattern), |
| 18 | * precomputed from the pattern in time O(m). The array PI allows |
| 19 | * the transition function DELTA to be computed efficiently |
| 20 | * "on the fly" as needed. Roughly speaking, for any state |
| 21 | * "q" = 0,1,...,m and any character "a" in SIGMA, the value |
| 22 | * PI["q"] contains the information that is independent of "a" and |
| 23 | * is needed to compute DELTA("q", "a") [2]. Since the array PI |
| 24 | * has only m entries, whereas DELTA has O(m|SIGMA|) entries, we |
| 25 | * save a factor of |SIGMA| in the preprocessing time by computing |
| 26 | * PI rather than DELTA. |
| 27 | * |
| 28 | * [1] Cormen, Leiserson, Rivest, Stein |
| 29 | * Introdcution to Algorithms, 2nd Edition, MIT Press |
| 30 | * [2] See finite automation theory |
| 31 | */ |
| 32 | |
| 33 | #include <linux/module.h> |
| 34 | #include <linux/types.h> |
| 35 | #include <linux/string.h> |
| 36 | #include <linux/ctype.h> |
| 37 | #include <linux/textsearch.h> |
| 38 | |
| 39 | struct ts_kmp |
| 40 | { |
| 41 | u8 * pattern; |
| 42 | unsigned int pattern_len; |
| 43 | unsigned int prefix_tbl[0]; |
| 44 | }; |
| 45 | |
| 46 | static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state) |
| 47 | { |
| 48 | struct ts_kmp *kmp = ts_config_priv(conf); |
| 49 | unsigned int i, q = 0, text_len, consumed = state->offset; |
| 50 | const u8 *text; |
| 51 | const int icase = conf->flags & TS_IGNORECASE; |
| 52 | |
| 53 | for (;;) { |
| 54 | text_len = conf->get_next_block(consumed, &text, conf, state); |
| 55 | |
| 56 | if (unlikely(text_len == 0)) |
| 57 | break; |
| 58 | |
| 59 | for (i = 0; i < text_len; i++) { |
| 60 | while (q > 0 && kmp->pattern[q] |
| 61 | != (icase ? toupper(text[i]) : text[i])) |
| 62 | q = kmp->prefix_tbl[q - 1]; |
| 63 | if (kmp->pattern[q] |
| 64 | == (icase ? toupper(text[i]) : text[i])) |
| 65 | q++; |
| 66 | if (unlikely(q == kmp->pattern_len)) { |
| 67 | state->offset = consumed + i + 1; |
| 68 | return state->offset - kmp->pattern_len; |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | consumed += text_len; |
| 73 | } |
| 74 | |
| 75 | return UINT_MAX; |
| 76 | } |
| 77 | |
| 78 | static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len, |
| 79 | unsigned int *prefix_tbl, int flags) |
| 80 | { |
| 81 | unsigned int k, q; |
| 82 | const u8 icase = flags & TS_IGNORECASE; |
| 83 | |
| 84 | for (k = 0, q = 1; q < len; q++) { |
| 85 | while (k > 0 && (icase ? toupper(pattern[k]) : pattern[k]) |
| 86 | != (icase ? toupper(pattern[q]) : pattern[q])) |
| 87 | k = prefix_tbl[k-1]; |
| 88 | if ((icase ? toupper(pattern[k]) : pattern[k]) |
| 89 | == (icase ? toupper(pattern[q]) : pattern[q])) |
| 90 | k++; |
| 91 | prefix_tbl[q] = k; |
| 92 | } |
| 93 | } |
| 94 | |
| 95 | static struct ts_config *kmp_init(const void *pattern, unsigned int len, |
| 96 | gfp_t gfp_mask, int flags) |
| 97 | { |
| 98 | struct ts_config *conf; |
| 99 | struct ts_kmp *kmp; |
| 100 | int i; |
| 101 | unsigned int prefix_tbl_len = len * sizeof(unsigned int); |
| 102 | size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len; |
| 103 | |
| 104 | conf = alloc_ts_config(priv_size, gfp_mask); |
| 105 | if (IS_ERR(conf)) |
| 106 | return conf; |
| 107 | |
| 108 | conf->flags = flags; |
| 109 | kmp = ts_config_priv(conf); |
| 110 | kmp->pattern_len = len; |
| 111 | compute_prefix_tbl(pattern, len, kmp->prefix_tbl, flags); |
| 112 | kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len; |
| 113 | if (flags & TS_IGNORECASE) |
| 114 | for (i = 0; i < len; i++) |
| 115 | kmp->pattern[i] = toupper(((u8 *)pattern)[i]); |
| 116 | else |
| 117 | memcpy(kmp->pattern, pattern, len); |
| 118 | |
| 119 | return conf; |
| 120 | } |
| 121 | |
| 122 | static void *kmp_get_pattern(struct ts_config *conf) |
| 123 | { |
| 124 | struct ts_kmp *kmp = ts_config_priv(conf); |
| 125 | return kmp->pattern; |
| 126 | } |
| 127 | |
| 128 | static unsigned int kmp_get_pattern_len(struct ts_config *conf) |
| 129 | { |
| 130 | struct ts_kmp *kmp = ts_config_priv(conf); |
| 131 | return kmp->pattern_len; |
| 132 | } |
| 133 | |
| 134 | static struct ts_ops kmp_ops = { |
| 135 | .name = "kmp", |
| 136 | .find = kmp_find, |
| 137 | .init = kmp_init, |
| 138 | .get_pattern = kmp_get_pattern, |
| 139 | .get_pattern_len = kmp_get_pattern_len, |
| 140 | .owner = THIS_MODULE, |
| 141 | .list = LIST_HEAD_INIT(kmp_ops.list) |
| 142 | }; |
| 143 | |
| 144 | static int __init init_kmp(void) |
| 145 | { |
| 146 | return textsearch_register(&kmp_ops); |
| 147 | } |
| 148 | |
| 149 | static void __exit exit_kmp(void) |
| 150 | { |
| 151 | textsearch_unregister(&kmp_ops); |
| 152 | } |
| 153 | |
| 154 | MODULE_LICENSE("GPL"); |
| 155 | |
| 156 | module_init(init_kmp); |
| 157 | module_exit(exit_kmp); |
| 158 |
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