Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/lib/ts_kmp.c

  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 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us