2 * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation
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.
9 * Authors: Thomas Graf <tgraf@suug.ch>
11 * ==========================================================================
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.
28 * [1] Cormen, Leiserson, Rivest, Stein
29 * Introdcution to Algorithms, 2nd Edition, MIT Press
30 * [2] See finite automation theory
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>
42 unsigned int pattern_len
;
43 unsigned int prefix_tbl
[0];
46 static unsigned int kmp_find(struct ts_config
*conf
, struct ts_state
*state
)
48 struct ts_kmp
*kmp
= ts_config_priv(conf
);
49 unsigned int i
, q
= 0, text_len
, consumed
= state
->offset
;
51 const int icase
= conf
->flags
& TS_IGNORECASE
;
54 text_len
= conf
->get_next_block(consumed
, &text
, conf
, state
);
56 if (unlikely(text_len
== 0))
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];
64 == (icase
? toupper(text
[i
]) : text
[i
]))
66 if (unlikely(q
== kmp
->pattern_len
)) {
67 state
->offset
= consumed
+ i
+ 1;
68 return state
->offset
- kmp
->pattern_len
;
78 static inline void compute_prefix_tbl(const u8
*pattern
, unsigned int len
,
79 unsigned int *prefix_tbl
, int flags
)
82 const u8 icase
= flags
& TS_IGNORECASE
;
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
]))
88 if ((icase
? toupper(pattern
[k
]) : pattern
[k
])
89 == (icase
? toupper(pattern
[q
]) : pattern
[q
]))
95 static struct ts_config
*kmp_init(const void *pattern
, unsigned int len
,
96 gfp_t gfp_mask
, int flags
)
98 struct ts_config
*conf
;
101 unsigned int prefix_tbl_len
= len
* sizeof(unsigned int);
102 size_t priv_size
= sizeof(*kmp
) + len
+ prefix_tbl_len
;
104 conf
= alloc_ts_config(priv_size
, gfp_mask
);
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
]);
117 memcpy(kmp
->pattern
, pattern
, len
);
122 static void *kmp_get_pattern(struct ts_config
*conf
)
124 struct ts_kmp
*kmp
= ts_config_priv(conf
);
128 static unsigned int kmp_get_pattern_len(struct ts_config
*conf
)
130 struct ts_kmp
*kmp
= ts_config_priv(conf
);
131 return kmp
->pattern_len
;
134 static struct ts_ops kmp_ops
= {
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
)
144 static int __init
init_kmp(void)
146 return textsearch_register(&kmp_ops
);
149 static void __exit
exit_kmp(void)
151 textsearch_unregister(&kmp_ops
);
154 MODULE_LICENSE("GPL");
156 module_init(init_kmp
);
157 module_exit(exit_kmp
);
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