1 // SPDX-License-Identifier: GPL-2.0-or-later
3  * lib/ts_bm.c		Boyer-Moore text search implementation
9  *   Implements Boyer-Moore string matching algorithm:
12  *       Communications of the Association for Computing Machinery, 
13  *       20(10), 1977, pp. 762-772.
16  *   [2] Handbook of Exact String Matching Algorithms, Thierry Lecroq, 2004
17  *       http://www-igm.univ-mlv.fr/~lecroq/string/string.pdf
19  *   Note: Since Boyer-Moore (BM) performs searches for matchings from right 
24  *   Knuth-Pratt-Morris (KMP) implementation instead. In conclusion, choose 
30  *   Quality of Service (QoS) policies, and you don't mind about possible
61 	unsigned int i, text_len, consumed = state->offset;  in bm_find()
64 	const u8 icase = conf->flags & TS_IGNORECASE;  in bm_find()
67 		int shift = bm->patlen - 1;  in bm_find()
69 		text_len = conf->get_next_block(consumed, &text, conf, state);  in bm_find()
77 			for (i = 0; i < bm->patlen; i++)   in bm_find()
78 				if ((icase ? toupper(text[shift-i])  in bm_find()
79 				    : text[shift-i])  in bm_find()
80 					!= bm->pattern[bm->patlen-1-i])  in bm_find()
85 			return consumed += (shift-(bm->patlen-1));  in bm_find()
87 next:			bs = bm->bad_shift[text[shift-i]];  in bm_find()
90 			shift = max_t(int, shift-i+bs, shift+bm->good_shift[i]);  in bm_find()
100 	int x = i+g-1, y = j+g-1, ret = 0;  in subpattern()
102 	while(pattern[x--] == pattern[y--]) {  in subpattern()
107 		if (--g == 0) {  in subpattern()
108 			ret = pattern[i-1] != pattern[j-1];  in subpattern()
121 		bm->bad_shift[i] = bm->patlen;  in compute_prefix_tbl()
122 	for (i = 0; i < bm->patlen - 1; i++) {  in compute_prefix_tbl()
123 		bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i;  in compute_prefix_tbl()
125 			bm->bad_shift[tolower(bm->pattern[i])]  in compute_prefix_tbl()
126 			    = bm->patlen - 1 - i;  in compute_prefix_tbl()
130 	 * of a subpattern */  in compute_prefix_tbl()
131 	bm->good_shift[0] = 1;  in compute_prefix_tbl()
132 	for (i = 1; i < bm->patlen; i++)  in compute_prefix_tbl()
133 		bm->good_shift[i] = bm->patlen;  in compute_prefix_tbl()
134         for (i = bm->patlen-1, g = 1; i > 0; g++, i--) {  in compute_prefix_tbl()
135 		for (j = i-1; j >= 1-g ; j--)  in compute_prefix_tbl()
136 			if (subpattern(bm->pattern, i, j, g)) {  in compute_prefix_tbl()
137 				bm->good_shift[g] = bm->patlen-j-g;  in compute_prefix_tbl()
156 	conf->flags = flags;  in bm_init()
158 	bm->patlen = len;  in bm_init()
159 	bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len;  in bm_init()
162 			bm->pattern[i] = toupper(((u8 *)pattern)[i]);  in bm_init()
164 		memcpy(bm->pattern, pattern, len);  in bm_init()
173 	return bm->pattern;  in bm_get_pattern()
179 	return bm->patlen;  in bm_get_pattern_len()