ia64/linux-2.6.18-xen.hg

view lib/ts_kmp.c @ 782:9ab1c319531f

merge with linux-2.6.18-xen.hg
author Isaku Yamahata <yamahata@valinux.co.jp>
date Wed Jan 28 13:07:23 2009 +0900 (2009-01-28)
parents 831230e53067
children
line source
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 */
33 #include <linux/module.h>
34 #include <linux/types.h>
35 #include <linux/string.h>
36 #include <linux/textsearch.h>
38 struct ts_kmp
39 {
40 u8 * pattern;
41 unsigned int pattern_len;
42 unsigned int prefix_tbl[0];
43 };
45 static unsigned int kmp_find(struct ts_config *conf, struct ts_state *state)
46 {
47 struct ts_kmp *kmp = ts_config_priv(conf);
48 unsigned int i, q = 0, text_len, consumed = state->offset;
49 const u8 *text;
51 for (;;) {
52 text_len = conf->get_next_block(consumed, &text, conf, state);
54 if (unlikely(text_len == 0))
55 break;
57 for (i = 0; i < text_len; i++) {
58 while (q > 0 && kmp->pattern[q] != text[i])
59 q = kmp->prefix_tbl[q - 1];
60 if (kmp->pattern[q] == 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 }
68 consumed += text_len;
69 }
71 return UINT_MAX;
72 }
74 static inline void compute_prefix_tbl(const u8 *pattern, unsigned int len,
75 unsigned int *prefix_tbl)
76 {
77 unsigned int k, q;
79 for (k = 0, q = 1; q < len; q++) {
80 while (k > 0 && pattern[k] != pattern[q])
81 k = prefix_tbl[k-1];
82 if (pattern[k] == pattern[q])
83 k++;
84 prefix_tbl[q] = k;
85 }
86 }
88 static struct ts_config *kmp_init(const void *pattern, unsigned int len,
89 gfp_t gfp_mask)
90 {
91 struct ts_config *conf;
92 struct ts_kmp *kmp;
93 unsigned int prefix_tbl_len = len * sizeof(unsigned int);
94 size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
96 conf = alloc_ts_config(priv_size, gfp_mask);
97 if (IS_ERR(conf))
98 return conf;
100 kmp = ts_config_priv(conf);
101 kmp->pattern_len = len;
102 compute_prefix_tbl(pattern, len, kmp->prefix_tbl);
103 kmp->pattern = (u8 *) kmp->prefix_tbl + prefix_tbl_len;
104 memcpy(kmp->pattern, pattern, len);
106 return conf;
107 }
109 static void *kmp_get_pattern(struct ts_config *conf)
110 {
111 struct ts_kmp *kmp = ts_config_priv(conf);
112 return kmp->pattern;
113 }
115 static unsigned int kmp_get_pattern_len(struct ts_config *conf)
116 {
117 struct ts_kmp *kmp = ts_config_priv(conf);
118 return kmp->pattern_len;
119 }
121 static struct ts_ops kmp_ops = {
122 .name = "kmp",
123 .find = kmp_find,
124 .init = kmp_init,
125 .get_pattern = kmp_get_pattern,
126 .get_pattern_len = kmp_get_pattern_len,
127 .owner = THIS_MODULE,
128 .list = LIST_HEAD_INIT(kmp_ops.list)
129 };
131 static int __init init_kmp(void)
132 {
133 return textsearch_register(&kmp_ops);
134 }
136 static void __exit exit_kmp(void)
137 {
138 textsearch_unregister(&kmp_ops);
139 }
141 MODULE_LICENSE("GPL");
143 module_init(init_kmp);
144 module_exit(exit_kmp);