Root/lib/ts_kmp.c

Source at commit b386be689295730688885552666ea40b2e639b14 created 8 years 11 months ago.
By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters."
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
39struct ts_kmp
40{
41    u8 * pattern;
42    unsigned int pattern_len;
43    unsigned int prefix_tbl[0];
44};
45
46static 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
78static 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
95static 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
122static void *kmp_get_pattern(struct ts_config *conf)
123{
124    struct ts_kmp *kmp = ts_config_priv(conf);
125    return kmp->pattern;
126}
127
128static 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
134static 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
144static int __init init_kmp(void)
145{
146    return textsearch_register(&kmp_ops);
147}
148
149static void __exit exit_kmp(void)
150{
151    textsearch_unregister(&kmp_ops);
152}
153
154MODULE_LICENSE("GPL");
155
156module_init(init_kmp);
157module_exit(exit_kmp);
158

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