aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorPablo Neira Ayuso <pablo@netfilter.org>2006-02-02 20:15:41 -0500
committerDavid S. Miller <davem@davemloft.net>2006-02-02 20:15:41 -0500
commit3f330317ab4973178423aba750d6d0ca5ce0024a (patch)
tree177b1a3f213410bc526fda0cdb1b0568ea282d82
parentf00c401b9b5f0a90e2eb05705f5988fbda0b082b (diff)
[TEXTSEARCH]: Fix broken good shift array calculation in Boyer-Moore
The current logic does not calculate correctly the good shift array: Let x be the pattern that is being searched. Let y be the block of data. The good shift array aligns the segment: x[i+1 ... m-1] = y[i+j+1 ... j+m-1] with its rightmost occurrence in x that fulfils x[i] neq y[i+j]. In previous version, the good shift array for the pattern ANPANMAN is: [1, 8, 3, 8, 8, 8, 8, 8] and should be: [1, 8, 3, 6, 6, 6, 6, 6] Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--lib/ts_bm.c40
1 files changed, 25 insertions, 15 deletions
diff --git a/lib/ts_bm.c b/lib/ts_bm.c
index 8a8b3a16133e..c4c1ac5fbd1a 100644
--- a/lib/ts_bm.c
+++ b/lib/ts_bm.c
@@ -94,10 +94,28 @@ next: bs = bm->bad_shift[text[shift-i]];
94 return UINT_MAX; 94 return UINT_MAX;
95} 95}
96 96
97static int subpattern(u8 *pattern, int i, int j, int g)
98{
99 int x = i+g-1, y = j+g-1, ret = 0;
100
101 while(pattern[x--] == pattern[y--]) {
102 if (y < 0) {
103 ret = 1;
104 break;
105 }
106 if (--g == 0) {
107 ret = pattern[i-1] != pattern[j-1];
108 break;
109 }
110 }
111
112 return ret;
113}
114
97static void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern, 115static void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern,
98 unsigned int len) 116 unsigned int len)
99{ 117{
100 int i, j, ended, l[ASIZE]; 118 int i, j, g;
101 119
102 for (i = 0; i < ASIZE; i++) 120 for (i = 0; i < ASIZE; i++)
103 bm->bad_shift[i] = len; 121 bm->bad_shift[i] = len;
@@ -106,23 +124,15 @@ static void compute_prefix_tbl(struct ts_bm *bm, const u8 *pattern,
106 124
107 /* Compute the good shift array, used to match reocurrences 125 /* Compute the good shift array, used to match reocurrences
108 * of a subpattern */ 126 * of a subpattern */
109 for (i = 1; i < bm->patlen; i++) {
110 for (j = 0; j < bm->patlen && bm->pattern[bm->patlen - 1 - j]
111 == bm->pattern[bm->patlen - 1 - i - j]; j++);
112 l[i] = j;
113 }
114
115 bm->good_shift[0] = 1; 127 bm->good_shift[0] = 1;
116 for (i = 1; i < bm->patlen; i++) 128 for (i = 1; i < bm->patlen; i++)
117 bm->good_shift[i] = bm->patlen; 129 bm->good_shift[i] = bm->patlen;
118 for (i = bm->patlen - 1; i > 0; i--) 130 for (i = bm->patlen-1, g = 1; i > 0; g++, i--) {
119 bm->good_shift[l[i]] = i; 131 for (j = i-1; j >= 1-g ; j--)
120 ended = 0; 132 if (subpattern(bm->pattern, i, j, g)) {
121 for (i = 0; i < bm->patlen; i++) { 133 bm->good_shift[g] = bm->patlen-j-g;
122 if (l[i] == bm->patlen - 1 - i) 134 break;
123 ended = i; 135 }
124 if (ended)
125 bm->good_shift[i] = ended;
126 } 136 }
127} 137}
128 138