linux - Contrib clone of linux

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Diffstat (limited to 'net/x25/x25_facilities.c')

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/* * lib/ts_bm.c Boyer-Moore text search implementation * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. * * Authors: Pablo Neira Ayuso <pablo@eurodev.net> * * ========================================================================== * * Implements Boyer-Moore string matching algorithm: * * [1] A Fast String Searching Algorithm, R.S. Boyer and Moore. * Communications of the Association for Computing Machinery, * 20(10), 1977, pp. 762-772. * http://www.cs.utexas.edu/users/moore/publications/fstrpos.pdf * * [2] Handbook of Exact String Matching Algorithms, Thierry Lecroq, 2004 * http://www-igm.univ-mlv.fr/~lecroq/string/string.pdf * * Note: Since Boyer-Moore (BM) performs searches for matchings from right * to left, it's still possible that a matching could be spread over * multiple blocks, in that case this algorithm won't find any coincidence. * * If you're willing to ensure that such thing won't ever happen, use the * Knuth-Pratt-Morris (KMP) implementation instead. In conclusion, choose * the proper string search algorithm depending on your setting. * * Say you're using the textsearch infrastructure for filtering, NIDS or * any similar security focused purpose, then go KMP. Otherwise, if you * really care about performance, say you're classifying packets to apply * Quality of Service (QoS) policies, and you don't mind about possible * matchings spread over multiple fragments, then go BM. */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/types.h> #include <linux/string.h> #include <linux/ctype.h> #include <linux/textsearch.h> /* Alphabet size, use ASCII */ #define ASIZE 256 #if 0 #define DEBUGP printk #else #define DEBUGP(args, format...) #endif struct ts_bm { u8 * pattern; unsigned int patlen; unsigned int bad_shift[ASIZE]; unsigned int good_shift[0]; }; static unsigned int bm_find(struct ts_config *conf, struct ts_state *state) { struct ts_bm *bm = ts_config_priv(conf); unsigned int i, text_len, consumed = state->offset; const u8 *text; int shift = bm->patlen - 1, bs; const u8 icase = conf->flags & TS_IGNORECASE; for (;;) { text_len = conf->get_next_block(consumed, &text, conf, state); if (unlikely(text_len == 0)) break; while (shift < text_len) { DEBUGP("Searching in position %d (%c)\n", shift, text[shift]); for (i = 0; i < bm->patlen; i++) if ((icase ? toupper(text[shift-i]) : text[shift-i]) != bm->pattern[bm->patlen-1-i]) goto next; /* London calling... */ DEBUGP("found!\n"); return consumed += (shift-(bm->patlen-1)); next: bs = bm->bad_shift[text[shift-i]]; /* Now jumping to... */ shift = max_t(int, shift-i+bs, shift+bm->good_shift[i]); } consumed += text_len; } return UINT_MAX; } static int subpattern(u8 *pattern, int i, int j, int g) { int x = i+g-1, y = j+g-1, ret = 0; while(pattern[x--] == pattern[y--]) { if (y < 0) { ret = 1; break; } if (--g == 0) { ret = pattern[i-1] != pattern[j-1]; break; } } return ret; } static void compute_prefix_tbl(struct ts_bm *bm, int flags) { int i, j, g; for (i = 0; i < ASIZE; i++) bm->bad_shift[i] = bm->patlen; for (i = 0; i < bm->patlen - 1; i++) { bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i; if (flags & TS_IGNORECASE) bm->bad_shift[tolower(bm->pattern[i])] = bm->patlen - 1 - i; } /* Compute the good shift array, used to match reocurrences * of a subpattern */ bm->good_shift[0] = 1; for (i = 1; i < bm->patlen; i++) bm->good_shift[i] = bm->patlen; for (i = bm->patlen-1, g = 1; i > 0; g++, i--) { for (j = i-1; j >= 1-g ; j--) if (subpattern(bm->pattern, i, j, g)) { bm->good_shift[g] = bm->patlen-j-g; break; } } } static struct ts_config *bm_init(const void *pattern, unsigned int len, gfp_t gfp_mask, int flags) { struct ts_config *conf; struct ts_bm *bm; int i; unsigned int prefix_tbl_len = len * sizeof(unsigned int); size_t priv_size = sizeof(*bm) + len + prefix_tbl_len; conf = alloc_ts_config(priv_size, gfp_mask); if (IS_ERR(conf)) return conf; conf->flags = flags; bm = ts_config_priv(conf); bm->patlen = len; bm->pattern = (u8 *) bm->good_shift + prefix_tbl_len; if (flags & TS_IGNORECASE) for (i = 0; i < len; i++) bm->pattern[i] = toupper(((u8 *)pattern)[i]); else memcpy(bm->pattern, pattern, len); compute_prefix_tbl(bm, flags); return conf; } static void *bm_get_pattern(struct ts_config *conf) { struct ts_bm *bm = ts_config_priv(conf); return bm->pattern; } static unsigned int bm_get_pattern_len(struct ts_config *conf) { struct ts_bm *bm = ts_config_priv(conf); return bm->patlen; } static struct ts_ops bm_ops = { .name = "bm", .find = bm_find, .init = bm_init, .get_pattern = bm_get_pattern, .get_pattern_len = bm_get_pattern_len, .owner = THIS_MODULE, .list = LIST_HEAD_INIT(bm_ops.list) }; static int __init init_bm(void) { return textsearch_register(&bm_ops); } static void __exit exit_bm(void) { textsearch_unregister(&bm_ops); } MODULE_LICENSE("GPL"); module_init(init_bm); module_exit(exit_bm);


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