gnu/usr.bin/grep/dfa.h

/* dfa.h - declarations for GNU deterministic regexp compiler
   Copyright (C) 1988 Free Software Foundation, Inc.

   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, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Written June, 1988 by Mike Haertel */

/* FIXME:
   2.  We should not export so much of the DFA internals.
   In addition to clobbering modularity, we eat up valuable
   name space. */

/* Number of bits in an unsigned char. */
#define CHARBITS 8

/* First integer value that is greater than any character code. */
#define NOTCHAR (1 << CHARBITS)

/* INTBITS need not be exact, just a lower bound. */
#define INTBITS (CHARBITS * sizeof (int))

/* Number of ints required to hold a bit for every character. */
#define CHARCLASS_INTS ((NOTCHAR + INTBITS - 1) / INTBITS)

/* Sets of unsigned characters are stored as bit vectors in arrays of ints. */
typedef int charclass[CHARCLASS_INTS];

/* The regexp is parsed into an array of tokens in postfix form.  Some tokens
   are operators and others are terminal symbols.  Most (but not all) of these
   codes are returned by the lexical analyzer. */

typedef enum
{
  END = -1,                     /* END is a terminal symbol that matches the
                                   end of input; any value of END or less in
                                   the parse tree is such a symbol.  Accepting
                                   states of the DFA are those that would have
                                   a transition on END. */

  /* Ordinary character values are terminal symbols that match themselves. */

  EMPTY = NOTCHAR,              /* EMPTY is a terminal symbol that matches
                                   the empty string. */

  BACKREF,                      /* BACKREF is generated by \<digit>; it
                                   it not completely handled.  If the scanner
                                   detects a transition on backref, it returns
                                   a kind of "semi-success" indicating that
                                   the match will have to be verified with
                                   a backtracking matcher. */

  BEGLINE,                      /* BEGLINE is a terminal symbol that matches
                                   the empty string if it is at the beginning
                                   of a line. */

  ENDLINE,                      /* ENDLINE is a terminal symbol that matches
                                   the empty string if it is at the end of
                                   a line. */

  BEGWORD,                      /* BEGWORD is a terminal symbol that matches
                                   the empty string if it is at the beginning
                                   of a word. */

  ENDWORD,                      /* ENDWORD is a terminal symbol that matches
                                   the empty string if it is at the end of
                                   a word. */

  LIMWORD,                      /* LIMWORD is a terminal symbol that matches
                                   the empty string if it is at the beginning
                                   or the end of a word. */

  NOTLIMWORD,                   /* NOTLIMWORD is a terminal symbol that
                                   matches the empty string if it is not at
                                   the beginning or end of a word. */

  QMARK,                        /* QMARK is an operator of one argument that
                                   matches zero or one occurences of its
                                   argument. */

  STAR,                         /* STAR is an operator of one argument that
                                   matches the Kleene closure (zero or more
                                   occurrences) of its argument. */

  PLUS,                         /* PLUS is an operator of one argument that
                                   matches the positive closure (one or more
                                   occurrences) of its argument. */

  REPMN,                        /* REPMN is a lexical token corresponding
                                   to the {m,n} construct.  REPMN never
                                   appears in the compiled token vector. */

  CAT,                          /* CAT is an operator of two arguments that
                                   matches the concatenation of its
                                   arguments.  CAT is never returned by the
                                   lexical analyzer. */

  OR,                           /* OR is an operator of two arguments that
                                   matches either of its arguments. */

  ORTOP,                        /* OR at the toplevel in the parse tree.
                                   This is used for a boyer-moore heuristic. */

  LPAREN,                       /* LPAREN never appears in the parse tree,
                                   it is only a lexeme. */

  RPAREN,                       /* RPAREN never appears in the parse tree. */

  CSET                          /* CSET and (and any value greater) is a
                                   terminal symbol that matches any of a
                                   class of characters. */
} token;

/* Sets are stored in an array in the compiled dfa; the index of the
   array corresponding to a given set token is given by SET_INDEX(t). */
#define SET_INDEX(t) ((t) - CSET)

/* Sometimes characters can only be matched depending on the surrounding
   context.  Such context decisions depend on what the previous character
   was, and the value of the current (lookahead) character.  Context
   dependent constraints are encoded as 8 bit integers.  Each bit that
   is set indicates that the constraint succeeds in the corresponding
   context.

   bit 7 - previous and current are newlines
   bit 6 - previous was newline, current isn't
   bit 5 - previous wasn't newline, current is
   bit 4 - neither previous nor current is a newline
   bit 3 - previous and current are word-constituents
   bit 2 - previous was word-constituent, current isn't
   bit 1 - previous wasn't word-constituent, current is
   bit 0 - neither previous nor current is word-constituent

   Word-constituent characters are those that satisfy isalnum().

   The macro SUCCEEDS_IN_CONTEXT determines whether a a given constraint
   succeeds in a particular context.  Prevn is true if the previous character
   was a newline, currn is true if the lookahead character is a newline.
   Prevl and currl similarly depend upon whether the previous and current
   characters are word-constituent letters. */
#define MATCHES_NEWLINE_CONTEXT(constraint, prevn, currn) \
  ((constraint) & 1 << (((prevn) ? 2 : 0) + ((currn) ? 1 : 0) + 4))
#define MATCHES_LETTER_CONTEXT(constraint, prevl, currl) \
  ((constraint) & 1 << (((prevl) ? 2 : 0) + ((currl) ? 1 : 0)))
#define SUCCEEDS_IN_CONTEXT(constraint, prevn, currn, prevl, currl) \
  (MATCHES_NEWLINE_CONTEXT(constraint, prevn, currn)                 \
   && MATCHES_LETTER_CONTEXT(constraint, prevl, currl))

/* The following macros give information about what a constraint depends on. */
#define PREV_NEWLINE_DEPENDENT(constraint) \
  (((constraint) & 0xc0) >> 2 != ((constraint) & 0x30))
#define PREV_LETTER_DEPENDENT(constraint) \
  (((constraint) & 0x0c) >> 2 != ((constraint) & 0x03))

/* Tokens that match the empty string subject to some constraint actually
   work by applying that constraint to determine what may follow them,
   taking into account what has gone before.  The following values are
   the constraints corresponding to the special tokens previously defined. */
#define NO_CONSTRAINT 0xff
#define BEGLINE_CONSTRAINT 0xcf
#define ENDLINE_CONSTRAINT 0xaf
#define BEGWORD_CONSTRAINT 0xf2
#define ENDWORD_CONSTRAINT 0xf4
#define LIMWORD_CONSTRAINT 0xf6
#define NOTLIMWORD_CONSTRAINT 0xf9

/* States of the recognizer correspond to sets of positions in the parse
   tree, together with the constraints under which they may be matched.
   So a position is encoded as an index into the parse tree together with
   a constraint. */
typedef struct
{
  unsigned index;               /* Index into the parse array. */
  unsigned constraint;          /* Constraint for matching this position. */
} position;

/* Sets of positions are stored as arrays. */
typedef struct
{
  position *elems;              /* Elements of this position set. */
  int nelem;                    /* Number of elements in this set. */
} position_set;

/* A state of the dfa consists of a set of positions, some flags,
   and the token value of the lowest-numbered position of the state that
   contains an END token. */
typedef struct
{
  int hash;                     /* Hash of the positions of this state. */
  position_set elems;           /* Positions this state could match. */
  char newline;                 /* True if previous state matched newline. */
  char letter;                  /* True if previous state matched a letter. */
  char backref;                 /* True if this state matches a \<digit>. */
  unsigned char constraint;     /* Constraint for this state to accept. */
  int first_end;                /* Token value of the first END in elems. */
} dfa_state;

/* Element of a list of strings, at least one of which is known to
   appear in any R.E. matching the DFA. */
struct dfamust
{
  int exact;
  char *must;
  struct dfamust *next;
};

/* A compiled regular expression. */
struct dfa
{
  /* Stuff built by the scanner. */
  charclass *charclasses;       /* Array of character sets for CSET tokens. */
  int cindex;                   /* Index for adding new charclasses. */
  int calloc;                   /* Number of charclasses currently allocated. */

  /* Stuff built by the parser. */
  token *tokens;                /* Postfix parse array. */
  int tindex;                   /* Index for adding new tokens. */
  int talloc;                   /* Number of tokens currently allocated. */
  int depth;                    /* Depth required of an evaluation stack
                                   used for depth-first traversal of the
                                   parse tree. */
  int nleaves;                  /* Number of leaves on the parse tree. */
  int nregexps;                 /* Count of parallel regexps being built
                                   with dfaparse(). */

  /* Stuff owned by the state builder. */
  dfa_state *states;            /* States of the dfa. */
  int sindex;                   /* Index for adding new states. */
  int salloc;                   /* Number of states currently allocated. */

  /* Stuff built by the structure analyzer. */
  position_set *follows;        /* Array of follow sets, indexed by position
                                   index.  The follow of a position is the set
                                   of positions containing characters that
                                   could conceivably follow a character
                                   matching the given position in a string
                                   matching the regexp.  Allocated to the
                                   maximum possible position index. */
  int searchflag;               /* True if we are supposed to build a searching
                                   as opposed to an exact matcher.  A searching
                                   matcher finds the first and shortest string
                                   matching a regexp anywhere in the buffer,
                                   whereas an exact matcher finds the longest
                                   string matching, but anchored to the
                                   beginning of the buffer. */

  /* Stuff owned by the executor. */
  int tralloc;                  /* Number of transition tables that have
                                   slots so far. */
  int trcount;                  /* Number of transition tables that have
                                   actually been built. */
  int **trans;                  /* Transition tables for states that can
                                   never accept.  If the transitions for a
                                   state have not yet been computed, or the
                                   state could possibly accept, its entry in
                                   this table is NULL. */
  int **realtrans;              /* Trans always points to realtrans + 1; this
                                   is so trans[-1] can contain NULL. */
  int **fails;                  /* Transition tables after failing to accept
                                   on a state that potentially could do so. */
  int *success;                 /* Table of acceptance conditions used in
                                   dfaexec and computed in build_state. */
  int *newlines;                /* Transitions on newlines.  The entry for a
                                   newline in any transition table is always
                                   -1 so we can count lines without wasting
                                   too many cycles.  The transition for a
                                   newline is stored separately and handled
                                   as a special case.  Newline is also used
                                   as a sentinel at the end of the buffer. */
  struct dfamust *musts;        /* List of strings, at least one of which
                                   is known to appear in any r.e. matching
                                   the dfa. */
};

/* Some macros for user access to dfa internals. */

/* ACCEPTING returns true if s could possibly be an accepting state of r. */
#define ACCEPTING(s, r) ((r).states[s].constraint)

/* ACCEPTS_IN_CONTEXT returns true if the given state accepts in the
   specified context. */
#define ACCEPTS_IN_CONTEXT(prevn, currn, prevl, currl, state, dfa) \
  SUCCEEDS_IN_CONTEXT((dfa).states[state].constraint,              \
                       prevn, currn, prevl, currl)

/* FIRST_MATCHING_REGEXP returns the index number of the first of parallel
   regexps that a given state could accept.  Parallel regexps are numbered
   starting at 1. */
#define FIRST_MATCHING_REGEXP(state, dfa) (-(dfa).states[state].first_end)

/* Entry points. */

#if __STDC__

/* dfasyntax() takes two arguments; the first sets the syntax bits described
   earlier in this file, and the second sets the case-folding flag. */
extern void dfasyntax(int, int);

/* Compile the given string of the given length into the given struct dfa.
   Final argument is a flag specifying whether to build a searching or an
   exact matcher. */
extern void dfacomp(char *, size_t, struct dfa *, int);

/* Execute the given struct dfa on the buffer of characters.  The
   first char * points to the beginning, and the second points to the
   first character after the end of the buffer, which must be a writable
   place so a sentinel end-of-buffer marker can be stored there.  The
   second-to-last argument is a flag telling whether to allow newlines to
   be part of a string matching the regexp.  The next-to-last argument,
   if non-NULL, points to a place to increment every time we see a
   newline.  The final argument, if non-NULL, points to a flag that will
   be set if further examination by a backtracking matcher is needed in
   order to verify backreferencing; otherwise the flag will be cleared.
   Returns NULL if no match is found, or a pointer to the first
   character after the first & shortest matching string in the buffer. */
extern char *dfaexec(struct dfa *, char *, char *, int, int *, int *);

/* Free the storage held by the components of a struct dfa. */
extern void dfafree(struct dfa *);

/* Entry points for people who know what they're doing. */

/* Initialize the components of a struct dfa. */
extern void dfainit(struct dfa *);

/* Incrementally parse a string of given length into a struct dfa. */
extern void dfaparse(char *, size_t, struct dfa *);

/* Analyze a parsed regexp; second argument tells whether to build a searching
   or an exact matcher. */
extern void dfaanalyze(struct dfa *, int);

/* Compute, for each possible character, the transitions out of a given
   state, storing them in an array of integers. */
extern void dfastate(int, struct dfa *, int []);

/* Error handling. */

/* dfaerror() is called by the regexp routines whenever an error occurs.  It
   takes a single argument, a NUL-terminated string describing the error.
   The default dfaerror() prints the error message to stderr and exits.
   The user can provide a different dfafree() if so desired. */
extern void dfaerror(char *);

#else /* ! __STDC__ */
extern void dfasyntax(), dfacomp(), dfafree(), dfainit(), dfaparse();
extern void dfaanalyze(), dfastate(), dfaerror();
extern char *dfaexec();
#endif /* ! __STDC__ */