/*
   * lib/ts_fsm.c	   A naive finite state machine text search approach
   *
   *		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:	Thomas Graf <tgraf@suug.ch>
   *
   * ==========================================================================
   *
   *   A finite state machine consists of n states (struct ts_fsm_token)
   *   representing the pattern as a finite automation. The data is read

   *   sequentially on an octet basis. Every state token specifies the number

   *   of recurrences and the type of value accepted which can be either a
   *   specific character or ctype based set of characters. The available
   *   type of recurrences include 1, (0|1), [0 n], and [1 n].
   *

   *   The algorithm differs between strict/non-strict mode specifying
   *   whether the pattern has to start at the first octet. Strict mode

   *   is enabled by default and can be disabled by inserting
   *   TS_FSM_HEAD_IGNORE as the first token in the chain.
   *
   *   The runtime performance of the algorithm should be around O(n),
   *   however while in strict mode the average runtime can be better.
   */

  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/string.h>
  #include <linux/ctype.h>
  #include <linux/textsearch.h>
  #include <linux/textsearch_fsm.h>
  
  struct ts_fsm
  {
  	unsigned int		ntokens;
  	struct ts_fsm_token	tokens[0];
  };
  
  /* other values derived from ctype.h */
  #define _A		0x100 /* ascii */
  #define _W		0x200 /* wildcard */
  
  /* Map to _ctype flags and some magic numbers */

  static const u16 token_map[TS_FSM_TYPE_MAX+1] = {

  	[TS_FSM_SPECIFIC] = 0,
  	[TS_FSM_WILDCARD] = _W,
  	[TS_FSM_CNTRL]	  = _C,
  	[TS_FSM_LOWER]	  = _L,
  	[TS_FSM_UPPER]	  = _U,
  	[TS_FSM_PUNCT]	  = _P,
  	[TS_FSM_SPACE]	  = _S,
  	[TS_FSM_DIGIT]	  = _D,
  	[TS_FSM_XDIGIT]	  = _D | _X,
  	[TS_FSM_ALPHA]	  = _U | _L,
  	[TS_FSM_ALNUM]	  = _U | _L | _D,
  	[TS_FSM_PRINT]	  = _P | _U | _L | _D | _SP,
  	[TS_FSM_GRAPH]	  = _P | _U | _L | _D,
  	[TS_FSM_ASCII]	  = _A,
  };

  static const u16 token_lookup_tbl[256] = {

  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*   0-  3 */
  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*   4-  7 */
  _W|_A|_C,      _W|_A|_C|_S,  _W|_A|_C|_S,  _W|_A|_C|_S,		/*   8- 11 */
  _W|_A|_C|_S,   _W|_A|_C|_S,  _W|_A|_C,     _W|_A|_C,		/*  12- 15 */
  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  16- 19 */
  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  20- 23 */
  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  24- 27 */
  _W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  28- 31 */
  _W|_A|_S|_SP,  _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  32- 35 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  36- 39 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  40- 43 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  44- 47 */
  _W|_A|_D,      _W|_A|_D,     _W|_A|_D,     _W|_A|_D,		/*  48- 51 */
  _W|_A|_D,      _W|_A|_D,     _W|_A|_D,     _W|_A|_D,		/*  52- 55 */
  _W|_A|_D,      _W|_A|_D,     _W|_A|_P,     _W|_A|_P,		/*  56- 59 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  60- 63 */
  _W|_A|_P,      _W|_A|_U|_X,  _W|_A|_U|_X,  _W|_A|_U|_X,		/*  64- 67 */
  _W|_A|_U|_X,   _W|_A|_U|_X,  _W|_A|_U|_X,  _W|_A|_U,		/*  68- 71 */
  _W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  72- 75 */
  _W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  76- 79 */
  _W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  80- 83 */
  _W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  84- 87 */
  _W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_P,		/*  88- 91 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  92- 95 */
  _W|_A|_P,      _W|_A|_L|_X,  _W|_A|_L|_X,  _W|_A|_L|_X,		/*  96- 99 */
  _W|_A|_L|_X,   _W|_A|_L|_X,  _W|_A|_L|_X,  _W|_A|_L,		/* 100-103 */
  _W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 104-107 */
  _W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 108-111 */
  _W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 112-115 */
  _W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 116-119 */
  _W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_P,		/* 120-123 */
  _W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_C,		/* 124-127 */
  _W,            _W,           _W,           _W,			/* 128-131 */
  _W,            _W,           _W,           _W,			/* 132-135 */
  _W,            _W,           _W,           _W,			/* 136-139 */
  _W,            _W,           _W,           _W,			/* 140-143 */
  _W,            _W,           _W,           _W,			/* 144-147 */
  _W,            _W,           _W,           _W,			/* 148-151 */
  _W,            _W,           _W,           _W,			/* 152-155 */
  _W,            _W,           _W,           _W,			/* 156-159 */
  _W|_S|_SP,     _W|_P,        _W|_P,        _W|_P,		/* 160-163 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 164-167 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 168-171 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 172-175 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 176-179 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 180-183 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 184-187 */
  _W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 188-191 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 192-195 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 196-199 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 200-203 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 204-207 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 208-211 */
  _W|_U,         _W|_U,        _W|_U,        _W|_P,		/* 212-215 */
  _W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 216-219 */
  _W|_U,         _W|_U,        _W|_U,        _W|_L,		/* 220-223 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 224-227 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 228-231 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 232-235 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 236-239 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 240-243 */
  _W|_L,         _W|_L,        _W|_L,        _W|_P,		/* 244-247 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 248-251 */
  _W|_L,         _W|_L,        _W|_L,        _W|_L};		/* 252-255 */
  
  static inline int match_token(struct ts_fsm_token *t, u8 d)
  {
  	if (t->type)
  		return (token_lookup_tbl[d] & t->type) != 0;
  	else
  		return t->value == d;
  }
  
  static unsigned int fsm_find(struct ts_config *conf, struct ts_state *state)
  {
  	struct ts_fsm *fsm = ts_config_priv(conf);
  	struct ts_fsm_token *cur = NULL, *next;
  	unsigned int match_start, block_idx = 0, tok_idx;
  	unsigned block_len = 0, strict, consumed = state->offset;
  	const u8 *data;
  
  #define GET_NEXT_BLOCK()		\
  ({	consumed += block_idx;		\
  	block_idx = 0;			\
  	block_len = conf->get_next_block(consumed, &data, conf, state); })
  
  #define TOKEN_MISMATCH()		\
  	do {				\
  		if (strict)		\
  			goto no_match;	\
  		block_idx++;		\
  		goto startover;		\
  	} while(0)
  
  #define end_of_data() unlikely(block_idx >= block_len && !GET_NEXT_BLOCK())
  
  	if (end_of_data())
  		goto no_match;
  
  	strict = fsm->tokens[0].recur != TS_FSM_HEAD_IGNORE;
  
  startover:
  	match_start = consumed + block_idx;
  
  	for (tok_idx = 0; tok_idx < fsm->ntokens; tok_idx++) {
  		cur = &fsm->tokens[tok_idx];
  
  		if (likely(tok_idx < (fsm->ntokens - 1)))
  			next = &fsm->tokens[tok_idx + 1];
  		else
  			next = NULL;
  
  		switch (cur->recur) {
  		case TS_FSM_SINGLE:
  			if (end_of_data())
  				goto no_match;
  
  			if (!match_token(cur, data[block_idx]))
  				TOKEN_MISMATCH();
  			break;
  
  		case TS_FSM_PERHAPS:
  			if (end_of_data() ||
  			    !match_token(cur, data[block_idx]))
  				continue;
  			break;
  
  		case TS_FSM_MULTI:
  			if (end_of_data())
  				goto no_match;
  
  			if (!match_token(cur, data[block_idx]))
  				TOKEN_MISMATCH();
  
  			block_idx++;
  			/* fall through */
  
  		case TS_FSM_ANY:
  			if (next == NULL)
  				goto found_match;
  
  			if (end_of_data())
  				continue;
  
  			while (!match_token(next, data[block_idx])) {
  				if (!match_token(cur, data[block_idx]))
  					TOKEN_MISMATCH();
  				block_idx++;
  				if (end_of_data())
  					goto no_match;
  			}
  			continue;
  
  		/*
  		 * Optimization: Prefer small local loop over jumping
  		 * back and forth until garbage at head is munched.
  		 */
  		case TS_FSM_HEAD_IGNORE:
  			if (end_of_data())
  				continue;
  
  			while (!match_token(next, data[block_idx])) {
  				/*
  				 * Special case, don't start over upon
  				 * a mismatch, give the user the
  				 * chance to specify the type of data
  				 * allowed to be ignored.
  				 */
  				if (!match_token(cur, data[block_idx]))
  					goto no_match;
  
  				block_idx++;
  				if (end_of_data())
  					goto no_match;
  			}
  
  			match_start = consumed + block_idx;
  			continue;
  		}
  
  		block_idx++;
  	}
  
  	if (end_of_data())
  		goto found_match;
  
  no_match:
  	return UINT_MAX;
  
  found_match:
  	state->offset = consumed + block_idx;
  	return match_start;
  }
  
  static struct ts_config *fsm_init(const void *pattern, unsigned int len,

  				    gfp_t gfp_mask, int flags)

  {
  	int i, err = -EINVAL;
  	struct ts_config *conf;
  	struct ts_fsm *fsm;
  	struct ts_fsm_token *tokens = (struct ts_fsm_token *) pattern;
  	unsigned int ntokens = len / sizeof(*tokens);
  	size_t priv_size = sizeof(*fsm) + len;
  
  	if (len  % sizeof(struct ts_fsm_token) || ntokens < 1)
  		goto errout;

  	if (flags & TS_IGNORECASE)
  		goto errout;

  	for (i = 0; i < ntokens; i++) {
  		struct ts_fsm_token *t = &tokens[i];
  
  		if (t->type > TS_FSM_TYPE_MAX || t->recur > TS_FSM_RECUR_MAX)
  			goto errout;
  
  		if (t->recur == TS_FSM_HEAD_IGNORE &&
  		    (i != 0 || i == (ntokens - 1)))
  			goto errout;
  	}
  
  	conf = alloc_ts_config(priv_size, gfp_mask);
  	if (IS_ERR(conf))
  		return conf;

  	conf->flags = flags;

  	fsm = ts_config_priv(conf);
  	fsm->ntokens = ntokens;
  	memcpy(fsm->tokens, pattern, len);
  
  	for (i = 0; i < fsm->ntokens; i++) {
  		struct ts_fsm_token *t = &fsm->tokens[i];
  		t->type = token_map[t->type];
  	}
  
  	return conf;
  
  errout:
  	return ERR_PTR(err);
  }
  
  static void *fsm_get_pattern(struct ts_config *conf)
  {
  	struct ts_fsm *fsm = ts_config_priv(conf);
  	return fsm->tokens;
  }
  
  static unsigned int fsm_get_pattern_len(struct ts_config *conf)
  {
  	struct ts_fsm *fsm = ts_config_priv(conf);
  	return fsm->ntokens * sizeof(struct ts_fsm_token);
  }
  
  static struct ts_ops fsm_ops = {
  	.name		  = "fsm",
  	.find		  = fsm_find,
  	.init		  = fsm_init,
  	.get_pattern	  = fsm_get_pattern,
  	.get_pattern_len  = fsm_get_pattern_len,
  	.owner		  = THIS_MODULE,
  	.list		  = LIST_HEAD_INIT(fsm_ops.list)
  };
  
  static int __init init_fsm(void)
  {
  	return textsearch_register(&fsm_ops);
  }
  
  static void __exit exit_fsm(void)
  {
  	textsearch_unregister(&fsm_ops);
  }
  
  MODULE_LICENSE("GPL");
  
  module_init(init_fsm);
  module_exit(exit_fsm);