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1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * lib/ts_kmp.c Knuth-Morris-Pratt text search implementation
5 * Authors: Thomas Graf <tgraf@suug.ch>
7 * ==========================================================================
9 * Implements a linear-time string-matching algorithm due to Knuth,
10 * Morris, and Pratt [1]. Their algorithm avoids the explicit
11 * computation of the transition function DELTA altogether. Its
12 * matching time is O(n), for n being length(text), using just an
13 * auxiliary function PI[1..m], for m being length(pattern),
14 * precomputed from the pattern in time O(m). The array PI allows
15 * the transition function DELTA to be computed efficiently
16 * "on the fly" as needed. Roughly speaking, for any state
17 * "q" = 0,1,...,m and any character "a" in SIGMA, the value
18 * PI["q"] contains the information that is independent of "a" and
19 * is needed to compute DELTA("q", "a") [2]. Since the array PI
20 * has only m entries, whereas DELTA has O(m|SIGMA|) entries, we
21 * save a factor of |SIGMA| in the preprocessing time by computing
22 * PI rather than DELTA.
24 * [1] Cormen, Leiserson, Rivest, Stein
25 * Introdcution to Algorithms, 2nd Edition, MIT Press
26 * [2] See finite automaton theory
29 #include <linux/module.h>
30 #include <linux/types.h>
31 #include <linux/string.h>
32 #include <linux/ctype.h>
33 #include <linux/textsearch.h>
38 unsigned int pattern_len
;
39 unsigned int prefix_tbl
[0];
42 static unsigned int kmp_find(struct ts_config
*conf
, struct ts_state
*state
)
44 struct ts_kmp
*kmp
= ts_config_priv(conf
);
45 unsigned int i
, q
= 0, text_len
, consumed
= state
->offset
;
47 const int icase
= conf
->flags
& TS_IGNORECASE
;
50 text_len
= conf
->get_next_block(consumed
, &text
, conf
, state
);
52 if (unlikely(text_len
== 0))
55 for (i
= 0; i
< text_len
; i
++) {
56 while (q
> 0 && kmp
->pattern
[q
]
57 != (icase
? toupper(text
[i
]) : text
[i
]))
58 q
= kmp
->prefix_tbl
[q
- 1];
60 == (icase
? toupper(text
[i
]) : text
[i
]))
62 if (unlikely(q
== kmp
->pattern_len
)) {
63 state
->offset
= consumed
+ i
+ 1;
64 return state
->offset
- kmp
->pattern_len
;
74 static inline void compute_prefix_tbl(const u8
*pattern
, unsigned int len
,
75 unsigned int *prefix_tbl
, int flags
)
78 const u8 icase
= flags
& TS_IGNORECASE
;
80 for (k
= 0, q
= 1; q
< len
; q
++) {
81 while (k
> 0 && (icase
? toupper(pattern
[k
]) : pattern
[k
])
82 != (icase
? toupper(pattern
[q
]) : pattern
[q
]))
84 if ((icase
? toupper(pattern
[k
]) : pattern
[k
])
85 == (icase
? toupper(pattern
[q
]) : pattern
[q
]))
91 static struct ts_config
*kmp_init(const void *pattern
, unsigned int len
,
92 gfp_t gfp_mask
, int flags
)
94 struct ts_config
*conf
;
97 unsigned int prefix_tbl_len
= len
* sizeof(unsigned int);
98 size_t priv_size
= sizeof(*kmp
) + len
+ prefix_tbl_len
;
100 conf
= alloc_ts_config(priv_size
, gfp_mask
);
105 kmp
= ts_config_priv(conf
);
106 kmp
->pattern_len
= len
;
107 compute_prefix_tbl(pattern
, len
, kmp
->prefix_tbl
, flags
);
108 kmp
->pattern
= (u8
*) kmp
->prefix_tbl
+ prefix_tbl_len
;
109 if (flags
& TS_IGNORECASE
)
110 for (i
= 0; i
< len
; i
++)
111 kmp
->pattern
[i
] = toupper(((u8
*)pattern
)[i
]);
113 memcpy(kmp
->pattern
, pattern
, len
);
118 static void *kmp_get_pattern(struct ts_config
*conf
)
120 struct ts_kmp
*kmp
= ts_config_priv(conf
);
124 static unsigned int kmp_get_pattern_len(struct ts_config
*conf
)
126 struct ts_kmp
*kmp
= ts_config_priv(conf
);
127 return kmp
->pattern_len
;
130 static struct ts_ops kmp_ops
= {
134 .get_pattern
= kmp_get_pattern
,
135 .get_pattern_len
= kmp_get_pattern_len
,
136 .owner
= THIS_MODULE
,
137 .list
= LIST_HEAD_INIT(kmp_ops
.list
)
140 static int __init
init_kmp(void)
142 return textsearch_register(&kmp_ops
);
145 static void __exit
exit_kmp(void)
147 textsearch_unregister(&kmp_ops
);
150 MODULE_LICENSE("GPL");
152 module_init(init_kmp
);
153 module_exit(exit_kmp
);