dfa.c

生成C++的词法/语法分析的Flex语法分析器

/* dfa - DFA construction routines */

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Vern Paxson.
 * 
 * The United States Government has rights in this work pursuant
 * to contract no. DE-AC03-76SF00098 between the United States
 * Department of Energy and the University of California.
 *
 * Redistribution and use in source and binary forms are permitted provided
 * that: (1) source distributions retain this entire copyright notice and
 * comment, and (2) distributions including binaries display the following
 * acknowledgement:  ``This product includes software developed by the
 * University of California, Berkeley and its contributors'' in the
 * documentation or other materials provided with the distribution and in
 * all advertising materials mentioning features or use of this software.
 * Neither the name of the University nor the names of its contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#ifndef lint
static char rcsid[] =
    "@(#) $Header: /usr/fsys/odin/a/vern/flex/RCS/dfa.c,v 2.7 90/06/27 23:48:15 vern Exp $ (LBL)";
#endif

#include "flexdef.h"


/* declare functions that have forward references */

void dump_associated_rules PROTO((FILE*, int));
void dump_transitions PROTO((FILE*, int[]));
void sympartition PROTO((int[], int, int[], int[]));
int symfollowset PROTO((int[], int, int, int[]));


/* check_for_backtracking - check a DFA state for backtracking
 *
 * synopsis
 *     int ds, state[numecs];
 *     check_for_backtracking( ds, state );
 *
 * ds is the number of the state to check and state[] is its out-transitions,
 * indexed by equivalence class, and state_rules[] is the set of rules
 * associated with this state
 */

void check_for_backtracking( ds, state )
int ds;
int state[];

    {
    if ( (reject && ! dfaacc[ds].dfaacc_set) || ! dfaacc[ds].dfaacc_state )
	{ /* state is non-accepting */
	++num_backtracking;

	if ( backtrack_report )
	    {
	    fprintf( backtrack_file, "State #%d is non-accepting -\n", ds );

	    /* identify the state */
	    dump_associated_rules( backtrack_file, ds );

	    /* now identify it further using the out- and jam-transitions */
	    dump_transitions( backtrack_file, state );

	    putc( '\n', backtrack_file );
	    }
	}
    }


/* check_trailing_context - check to see if NFA state set constitutes
 *                          "dangerous" trailing context
 *
 * synopsis
 *    int nfa_states[num_states+1], num_states;
 *    int accset[nacc+1], nacc;
 *    check_trailing_context( nfa_states, num_states, accset, nacc );
 *
 * NOTES
 *    Trailing context is "dangerous" if both the head and the trailing
 *  part are of variable size \and/ there's a DFA state which contains
 *  both an accepting state for the head part of the rule and NFA states
 *  which occur after the beginning of the trailing context.
 *  When such a rule is matched, it's impossible to tell if having been
 *  in the DFA state indicates the beginning of the trailing context
 *  or further-along scanning of the pattern.  In these cases, a warning
 *  message is issued.
 *
 *    nfa_states[1 .. num_states] is the list of NFA states in the DFA.
 *    accset[1 .. nacc] is the list of accepting numbers for the DFA state.
 */

void check_trailing_context( nfa_states, num_states, accset, nacc )
int *nfa_states, num_states;
int *accset;
register int nacc;

    {
    register int i, j;

    for ( i = 1; i <= num_states; ++i )
	{
	int ns = nfa_states[i];
	register int type = state_type[ns];
	register int ar = assoc_rule[ns];

	if ( type == STATE_NORMAL || rule_type[ar] != RULE_VARIABLE )
	    { /* do nothing */
	    }

	else if ( type == STATE_TRAILING_CONTEXT )
	    {
	    /* potential trouble.  Scan set of accepting numbers for
	     * the one marking the end of the "head".  We assume that
	     * this looping will be fairly cheap since it's rare that
	     * an accepting number set is large.
	     */
	    for ( j = 1; j <= nacc; ++j )
		if ( accset[j] & YY_TRAILING_HEAD_MASK )
		    {
		    fprintf( stderr,
		     "%s: Dangerous trailing context in rule at line %d\n",
			     program_name, rule_linenum[ar] );
		    return;
		    }
	    }
	}
    }


/* dump_associated_rules - list the rules associated with a DFA state
 *
 * synopisis
 *     int ds;
 *     FILE *file;
 *     dump_associated_rules( file, ds );
 *
 * goes through the set of NFA states associated with the DFA and
 * extracts the first MAX_ASSOC_RULES unique rules, sorts them,
 * and writes a report to the given file
 */

void dump_associated_rules( file, ds )
FILE *file;
int ds;

    {
    register int i, j;
    register int num_associated_rules = 0;
    int rule_set[MAX_ASSOC_RULES + 1];
    int *dset = dss[ds];
    int size = dfasiz[ds];
    
    for ( i = 1; i <= size; ++i )
	{
	register rule_num = rule_linenum[assoc_rule[dset[i]]];

	for ( j = 1; j <= num_associated_rules; ++j )
	    if ( rule_num == rule_set[j] )
		break;

	if ( j > num_associated_rules )
	    { /* new rule */
	    if ( num_associated_rules < MAX_ASSOC_RULES )
		rule_set[++num_associated_rules] = rule_num;
	    }
	}

    bubble( rule_set, num_associated_rules );

    fprintf( file, " associated rule line numbers:" );

    for ( i = 1; i <= num_associated_rules; ++i )
	{
	if ( i % 8 == 1 )
	    putc( '\n', file );
	
	fprintf( file, "\t%d", rule_set[i] );
	}
    
    putc( '\n', file );
    }


/* dump_transitions - list the transitions associated with a DFA state
 *
 * synopisis
 *     int state[numecs];
 *     FILE *file;
 *     dump_transitions( file, state );
 *
 * goes through the set of out-transitions and lists them in human-readable
 * form (i.e., not as equivalence classes); also lists jam transitions
 * (i.e., all those which are not out-transitions, plus EOF).  The dump
 * is done to the given file.
 */

void dump_transitions( file, state )
FILE *file;
int state[];

    {
    register int i, ec;
    int out_char_set[CSIZE];

    for ( i = 0; i < csize; ++i )
	{
	ec = abs( ecgroup[i] );
	out_char_set[i] = state[ec];
	}
    
    fprintf( file, " out-transitions: " );

    list_character_set( file, out_char_set );

    /* now invert the members of the set to get the jam transitions */
    for ( i = 0; i < csize; ++i )
	out_char_set[i] = ! out_char_set[i];

    fprintf( file, "\n jam-transitions: EOF " );

    list_character_set( file, out_char_set );

    putc( '\n', file );
    }


/* epsclosure - construct the epsilon closure of a set of ndfa states
 *
 * synopsis
 *    int t[current_max_dfa_size], numstates, accset[num_rules + 1], nacc;
 *    int hashval;
 *    int *epsclosure();
 *    t = epsclosure( t, &numstates, accset, &nacc, &hashval );
 *
 * NOTES
 *    the epsilon closure is the set of all states reachable by an arbitrary
 *  number of epsilon transitions which themselves do not have epsilon
 *  transitions going out, unioned with the set of states which have non-null
 *  accepting numbers.  t is an array of size numstates of nfa state numbers.
 *  Upon return, t holds the epsilon closure and numstates is updated.  accset
 *  holds a list of the accepting numbers, and the size of accset is given
 *  by nacc.  t may be subjected to reallocation if it is not large enough
 *  to hold the epsilon closure.
 *
 *    hashval is the hash value for the dfa corresponding to the state set
 */

int *epsclosure( t, ns_addr, accset, nacc_addr, hv_addr )
int *t, *ns_addr, accset[], *nacc_addr, *hv_addr;

    {
    register int stkpos, ns, tsp;
    int numstates = *ns_addr, nacc, hashval, transsym, nfaccnum;
    int stkend, nstate;
    static int did_stk_init = false, *stk; 

#define MARK_STATE(state) \
	trans1[state] = trans1[state] - MARKER_DIFFERENCE;

#define IS_MARKED(state) (trans1[state] < 0)

#define UNMARK_STATE(state) \
	trans1[state] = trans1[state] + MARKER_DIFFERENCE;

#define CHECK_ACCEPT(state) \
	{ \
	nfaccnum = accptnum[state]; \
	if ( nfaccnum != NIL ) \
	    accset[++nacc] = nfaccnum; \
	}

#define DO_REALLOCATION \
	{ \
	current_max_dfa_size += MAX_DFA_SIZE_INCREMENT; \
	++num_reallocs; \
	t = reallocate_integer_array( t, current_max_dfa_size ); \
	stk = reallocate_integer_array( stk, current_max_dfa_size ); \
	} \

#define PUT_ON_STACK(state) \
	{ \
	if ( ++stkend >= current_max_dfa_size ) \
	    DO_REALLOCATION \
	stk[stkend] = state; \
	MARK_STATE(state) \
	}

#define ADD_STATE(state) \
	{ \
	if ( ++numstates >= current_max_dfa_size ) \
	    DO_REALLOCATION \
	t[numstates] = state; \
	hashval = hashval + state; \
	}

#define STACK_STATE(state) \
	{ \
	PUT_ON_STACK(state) \
	CHECK_ACCEPT(state) \
	if ( nfaccnum != NIL || transchar[state] != SYM_EPSILON ) \
	    ADD_STATE(state) \
	}

    if ( ! did_stk_init )
	{
	stk = allocate_integer_array( current_max_dfa_size );
	did_stk_init = true;
	}

    nacc = stkend = hashval = 0;

    for ( nstate = 1; nstate <= numstates; ++nstate )
	{
	ns = t[nstate];

	/* the state could be marked if we've already pushed it onto
	 * the stack
	 */
	if ( ! IS_MARKED(ns) )
	    PUT_ON_STACK(ns)

	CHECK_ACCEPT(ns)
	hashval = hashval + ns;
	}

    for ( stkpos = 1; stkpos <= stkend; ++stkpos )
	{
	ns = stk[stkpos];
	transsym = transchar[ns];

	if ( transsym == SYM_EPSILON )
	    {
	    tsp = trans1[ns] + MARKER_DIFFERENCE;

	    if ( tsp != NO_TRANSITION )
		{
		if ( ! IS_MARKED(tsp) )
		    STACK_STATE(tsp)

		tsp = trans2[ns];

		if ( tsp != NO_TRANSITION )
		    if ( ! IS_MARKED(tsp) )
			STACK_STATE(tsp)
		}
	    }
	}

    /* clear out "visit" markers */

    for ( stkpos = 1; stkpos <= stkend; ++stkpos )
	{
	if ( IS_MARKED(stk[stkpos]) )
	    {
	    UNMARK_STATE(stk[stkpos])
	    }
	else
	    flexfatal( "consistency check failed in epsclosure()" );
	}

    *ns_addr = numstates;
    *hv_addr = hashval;
    *nacc_addr = nacc;

    return ( t );
    }


/* increase_max_dfas - increase the maximum number of DFAs */

void increase_max_dfas()

    {
    current_max_dfas += MAX_DFAS_INCREMENT;

    ++num_reallocs;

    base = reallocate_integer_array( base, current_max_dfas );
    def = reallocate_integer_array( def, current_max_dfas );
    dfasiz = reallocate_integer_array( dfasiz, current_max_dfas );
    accsiz = reallocate_integer_array( accsiz, current_max_dfas );
    dhash = reallocate_integer_array( dhash, current_max_dfas );
    dss = reallocate_int_ptr_array( dss, current_max_dfas );
    dfaacc = reallocate_dfaacc_union( dfaacc, current_max_dfas );

    if ( nultrans )
	nultrans = reallocate_integer_array( nultrans, current_max_dfas );
    }


/* ntod - convert an ndfa to a dfa
 *
 * synopsis
 *    ntod();
 *
 *  creates the dfa corresponding to the ndfa we've constructed.  the
 *  dfa starts out in state #1.
 */

void ntod()

    {
    int *accset, ds, nacc, newds;
    int sym, hashval, numstates, dsize;
    int num_full_table_rows;	/* used only for -f */
    int *nset, *dset;
    int targptr, totaltrans, i, comstate, comfreq, targ;
    int *epsclosure(), snstods(), symlist[CSIZE + 1];
    int num_start_states;
    int todo_head, todo_next;

    /* note that the following are indexed by *equivalence classes*
     * and not by characters.  Since equivalence classes are indexed
     * beginning with 1, even if the scanner accepts NUL's, this
     * means that (since every character is potentially in its own
     * equivalence class) these arrays must have room for indices
     * from 1 to CSIZE, so their size must be CSIZE + 1.
     */
    int duplist[CSIZE + 1], state[CSIZE + 1];
    int targfreq[CSIZE + 1], targstate[CSIZE + 1];

    /* this is so find_table_space(...) will know where to start looking in
     * chk/nxt for unused records for space to put in the state
     */
    if ( fullspd )
	firstfree = 0;

    accset = allocate_integer_array( num_rules + 1 );
    nset = allocate_integer_array( current_max_dfa_size );

    /* the "todo" queue is represented by the head, which is the DFA
     * state currently being processed, and the "next", which is the
     * next DFA state number available (not in use).  We depend on the
     * fact that snstods() returns DFA's \in increasing order/, and thus
     * need only know the bounds of the dfas to be processed.
     */
    todo_head = todo_next = 0;

    for ( i = 0; i <= csize; ++i )
	{
	duplist[i] = NIL;
	symlist[i] = false;
	}

    for ( i = 0; i <= num_rules; ++i )
	accset[i] = NIL;

    if ( trace )
	{
	dumpnfa( scset[1] );
	fputs( "\n\nDFA Dump:\n\n", stderr );
	}

    inittbl();

    /* check to see whether we should build a separate table for transitions
     * on NUL characters.  We don't do this for full-speed (-F) scanners,
     * since for them we don't have a simple state number lying around with
     * which to index the table.  We also don't bother doing it for scanners
     * unless (1) NUL is in its own equivalence class (indicated by a
     * positive value of ecgroup[NUL]), (2) NUL's equilvalence class is
     * the last equivalence class, and (3) the number of equivalence classes
     * is the same as the number of characters.  This latter case comes about
     * when useecs is false or when its true but every character still
     * manages to land in its own class (unlikely, but it's cheap to check
     * for).  If all these things are true then the character code needed
     * to represent NUL's equivalence class for indexing the tables is
     * going to take one more bit than the number of characters, and therefore
     * we won't be assured of being able to fit it into a YY_CHAR variable.
     * This rules out storing the transitions in a compressed table, since
     * the code for interpreting them uses a YY_CHAR variable (perhaps it
     * should just use an integer, though; this is worth pondering ... ###).
     *
     * Finally, for full tables, we want the number of entries in the
     * table to be a power of two so the array references go fast (it
     * will just take a shift to compute the major index).  If encoding
     * NUL's transitions in the table will spoil this, we give it its
     * own table (note that this will be the case if we're not using
     * equivalence classes).
     */

    /* note that the test for ecgroup[0] == numecs below accomplishes
     * both (1) and (2) above
     */
    if ( ! fullspd && ecgroup[0] == numecs )
	{ /* NUL is alone in its equivalence class, which is the last one */
	int use_NUL_table = (numecs == csize);

	if ( fulltbl && ! use_NUL_table )
	    { /* we still may want to use the table if numecs is a power of 2 */
	    int power_of_two;

	    for ( power_of_two = 1; power_of_two <= csize; power_of_two *= 2 )
		if ( numecs == power_of_two )
		    {
		    use_NUL_table = true;
		    break;
		    }
	    }

	if ( use_NUL_table )
	    nultrans = allocate_integer_array( current_max_dfas );
	    /* from now on, nultrans != nil indicates that we're
	     * saving null transitions for later, separate encoding
	     */
	}


    if ( fullspd )
	{
	for ( i = 0; i <= numecs; ++i )
	    state[i] = 0;
	place_state( state, 0, 0 );
	}

    else if ( fulltbl )
	{
	if ( nultrans )
	    /* we won't be including NUL's transitions in the table,
	     * so build it for entries from 0 .. numecs - 1
	     */
	    num_full_table_rows = numecs;

	else
	    /* take into account the fact that we'll be including
	     * the NUL entries in the transition table.  Build it
	     * from 0 .. numecs.