ack/util/LLgen/src/compute.c

/* Copyright (c) 1991 by the Vrije Universiteit, Amsterdam, the Netherlands.
 * For full copyright and restrictions on use see the file COPYING in the top
 * level of the LLgen tree.
 */

/*
 *  L L G E N
 *
 *  An Extended LL(1) Parser Generator
 *
 *  Author : Ceriel J.H. Jacobs
 */

/*
 * compute.c
 * Defines routines to compute FIRST, FOLLOW etc.
 * Also checks the continuation grammar from the specified grammar.
 */

# include <stdlib.h>
# include <stdio.h>
# include "types.h"
# include "extern.h"
# include "sets.h"
# include "assert.h"
# include "io.h"

# ifndef NORCSID
static string rcsid = "$Id$";
# endif

p_set get_set();
typedef struct lngth
{
	/* Structure used to compute the shortest possible
	 * length of a terminal production of a rule.
	 * In case of a tie, the second field is used.
	 */
	int cnt;
	int val;
} t_length, *p_length;

/* Defined in this file : */

void do_compute(void);
STATIC void createsets(void);
STATIC void walk(p_set u, register p_gram p);
STATIC void co_trans(int (*fc)());
STATIC int nempty(register p_nont p);
int empty(register p_gram p);
STATIC int nfirst(register p_nont p);
#ifdef NON_CORRECTING
STATIC int nc_nfirst(register p_nont p);
#endif
STATIC int first(p_set setp, register p_gram p, int flag);
#ifdef NON_CORRECTING
STATIC int nc_first(p_set setp,register p_gram p,int flag);
#endif
STATIC int nfollow(register p_nont p);
STATIC int follow(p_set setp, register p_gram p);
#ifdef NON_CORRECTING
STATIC int nc_nfollow(register p_nont p);
#endif
STATIC void co_dirsymb(p_set setp, register p_gram p);
STATIC void co_others(p_gram p);
STATIC int ncomplength(p_nont p);
STATIC void do_lengthcomp(void);
STATIC void complength(register p_gram p, p_length le);
STATIC void add(register p_length a, int c, int v);
STATIC int compare(p_length a, p_length b);
STATIC void setdefaults(register p_gram p);
STATIC void do_contains(register p_nont n);
STATIC void contains(register p_gram p, register p_set set);
STATIC int nsafes(register p_nont p);
STATIC int do_safes(register p_gram p, int safe, register int *ch);
int t_safety(int rep, int count, int persistent, int safety);
int t_after(int rep, int count, int outsafety);

/*
 * Does all the work, by calling other routines (divide and conquer)
 */
void do_compute(void)
{
	register p_nont p;
	register p_start st;

	createsets();
	co_trans(nempty); /* Which nonterminals produce empty? */
	co_trans(nfirst); /* Computes first sets */
	/*
	 * Compute FOLLOW sets.
	 * First put EOFILE in the follow set of the start nonterminals.
	 */
	for (st = start; st; st = st->ff_next)
	{
		p = &nonterms[st->ff_nont];
		PUTIN(p->n_follow, 0);
	}
	co_trans(nfollow);
	/*
	 * Compute the sets which determine which alternative to choose
	 * in case of a choice
	 */
	for (p = nonterms; p < maxnt; p++)
	{
		co_dirsymb(p->n_follow, p->n_rule);
	}
	/*
	 * Compute the minimum length of productions of nonterminals,
	 * and then determine the default choices
	 */
	do_lengthcomp();
	/*
	 * Compute the contains sets
	 */
	for (p = nonterms; p < maxnt; p++)
		do_contains(p);
	for (p = nonterms; p < maxnt; p++)
		contains(p->n_rule, (p_set) 0);
	/*
	 * Compute the safety of each nonterminal and term.
	 * The safety gives an answer to the question whether a scan is done,
	 * and how it should be handled.
	 */
	for (p = nonterms; p < maxnt; p++)
	{
		/*
		 * Don't know anything yet
		 */
		setntsafe(p, NOSAFETY);
		setntout(p, NOSAFETY);
	}
	for (st = start; st; st = st->ff_next)
	{
		/*
		 * But start symbols are called with lookahead done
		 */
		p = &nonterms[st->ff_nont];
		setntsafe(p, SCANDONE);
	}
	co_trans(nsafes);

#ifdef NON_CORRECTING
	if (subpars_sim)
	{
		int s;

		/* compute the union of the first sets of all start symbols
		 Used to compute the nc-first-sets when -s option is given */
		start_firsts = get_set();
		for (st = start; st; st = st->ff_next)
		{
			s = setunion(start_firsts, (&nonterms[st->ff_nont])->n_first);
		}
	}

	if (non_corr)
	{
		/* compute the non_corr first sets for all nonterminals and terms */

		co_trans(nc_nfirst);
		for (st = start; st; st = st->ff_next)
		{
			p = &nonterms[st->ff_nont];
			PUTIN(p->n_nc_follow,0);
		}
		co_trans(nc_nfollow);
	}
#endif

# ifndef NDEBUG
	if (debug)
	{
		fputs("Safeties:\n", stderr);
		for (p = nonterms; p < maxnt; p++)
		{
			fprintf(stderr, "%s\t%d\t%d\n", p->n_name, getntsafe(p),
					getntout(p));
		}
	}
# endif
}

/*
 * Allocate space for the sets. Also determine which files use
 * which nonterminals, and determine which nonterminals can be
 * made static.
 */STATIC void createsets(void)
{
	register p_nont p;
	register p_file f;
	register p_start st;
	register int i;
	int n = NINTS(NBYTES(nnonterms));
	p_mem alloc();

	for (f = files; f < maxfiles; f++)
	{
		register p_set s;
		f->f_used = s = (p_set) alloc(n * sizeof(*(f->f_used)));
		for (i = n; i; i--)
			*s++ = 0;
		for (i = f->f_nonterminals; i != -1; i = p->n_next)
		{
			p = &nonterms[i];
			p->n_flags |= GENSTATIC;
			p->n_first = get_set();
#ifdef NON_CORRECTING
			p->n_nc_first = get_set();
			p->n_nc_follow = get_set();
#endif
			p->n_follow = get_set();
			walk(f->f_used, p->n_rule);
		}
	}
	for (f = files; f < maxfiles; f++)
	{
		for (i = f->f_nonterminals; i != -1; i = p->n_next)
		{
			register p_file f2;

			p = &nonterms[i];
			for (f2 = files; f2 < maxfiles; f2++)
			{
				if (f2 != f && IN(f2->f_used, i))
				{
					p->n_flags &= ~GENSTATIC;
				}
			}
		}
	}
	for (st = start; st; st = st->ff_next)
	{
		nonterms[st->ff_nont].n_flags &= ~GENSTATIC;
	}
}

/*
 * Walk through the grammar rule p, allocating sets
 */
STATIC void walk(p_set u, register p_gram p)
{
	for (;;)
	{
		switch (g_gettype(p))
		{
		case TERM:
		{
			register p_term q;

			q = g_getterm(p);
			q->t_first = get_set();
#ifdef NON_CORRECTING
			q->t_nc_first = get_set();
			q->t_nc_follow = get_set();
#endif
			q->t_follow = get_set();
			walk(u, q->t_rule);
			break;
		}
		case ALTERNATION:
		{
			register p_link l;

			l = g_getlink(p);
			l->l_symbs = get_set();
#ifdef NON_CORRECTING
			l->l_nc_symbs = get_set();
#endif
			l->l_others = get_set();
			walk(u, l->l_rule);
			break;
		}
		case NONTERM:
		{
			register int i = g_getcont(p);

			PUTIN(u, i);
			break;
		}
		case EORULE:
			return;
		}
		p++;
	}
}

STATIC void co_trans(int (*fc)())
{
	register p_nont p;
	register int change;

	do
	{
		change = 0;
		for (p = nonterms; p < maxnt; p++)
		{
			if ((*fc)(p))
				change = 1;
		}
	} while (change);
}

STATIC int nempty(register p_nont p)
{
	if (!(p->n_flags & EMPTY) && empty(p->n_rule))
	{
		p->n_flags |= EMPTY;
		return 1;
	}
	return 0;
}

/*
 * Does the rule pointed to by p produce empty ?
 */
int empty(register p_gram p)
{

	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return 1;
		case TERM:
		{
			register p_term q;

			q = g_getterm(p);
			if (r_getkind(q) == STAR || r_getkind(q) == OPT || empty(q->t_rule))
				break;
			return 0;
		}
		case ALTERNATION:
			if (empty(g_getlink(p)->l_rule))
			{
				return 1;
			}
			if (g_gettype(p+1) == EORULE)
				return 0;
			break;
		case NONTERM:
			if (nonterms[g_getcont(p)].n_flags & EMPTY)
			{
				break;
			}
			/* Fall through */
		case LITERAL:
		case TERMINAL:
			return 0;
		}
		p++;
	}
}

STATIC int nfirst(register p_nont p)
{
	return first(p->n_first, p->n_rule, 0);
}

#ifdef NON_CORRECTING
STATIC int nc_nfirst(register p_nont p)
{
	return nc_first(p->n_nc_first, p->n_rule, 0);
}
#endif

/*
 * Compute the FIRST set of rule p.
 * If flag = 0, also the first sets for terms and alternations in
 * the rule p are computed.
 * The FIRST set is put in setp.
 * return 1 if the set refered to by "setp" changed
 */
STATIC int first(p_set setp, register p_gram p, int flag)
{
	register int s; /* Will gather return value */
	int noenter;/* when set, unables entering of elements into
	 * setp. This is necessary to walk through the
	 * rest of rule p.
	 */

	s = 0;
	noenter = 0;
	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return s;
		case TERM:
		{
			register p_term q;

			q = g_getterm(p);
			if (flag == 0)
			{
				if (first(q->t_first, q->t_rule, 0))/*nothing*/
					;
			}
			if (!noenter)
				s |= setunion(setp, q->t_first);
			p++;
			if (r_getkind(q) == STAR || r_getkind(q) == OPT || empty(q->t_rule))
				continue;
			break;
		}
		case ALTERNATION:
		{
			register p_link l;

			l = g_getlink(p);
			if (flag == 0)
			{
				if (first(l->l_symbs, l->l_rule, 0))/*nothing*/
					;
			}
			if (noenter == 0)
			{
				s |= setunion(setp, l->l_symbs);
			}
			if (g_gettype(p+1) == EORULE)
				return s;
		}
			/* Fall Through */
		case ACTION:
			p++;
			continue;
		case LITERAL:
		case TERMINAL:
			if ((noenter == 0) && !IN(setp,g_getcont(p)))
			{
				s = 1;
				PUTIN(setp, g_getcont(p));
			}
			p++;
			break;
		case NONTERM:
		{
			register p_nont n;

			n = &nonterms[g_getcont(p)];
			if (noenter == 0)
			{
				s |= setunion(setp, n->n_first);
				if (ntneeded)
					NTPUTIN(setp, g_getcont(p));
			}
			p++;
			if (n->n_flags & EMPTY)
				continue;
			break;
		}
		}
		if (flag == 0)
		{
			noenter = 1;
			continue;
		}
		return s;
	}
}

#ifdef NON_CORRECTING
/*
 * Compute the non_corr FIRST set of rule p.
 * If flag = 0, also the non_corr first sets for terms and
 * alternations in the rule p are computed.
 * The non_corr FIRST set is put in setp.
 * return 1 if the set refered to by "setp" changed
 * If the -s flag was given, the union of the first-sets of all
 * start symbols is used whenever an action occurs. Else, only the
 * first-sets of startsynbols in the  %substart are used
 */
STATIC int nc_first(p_set setp,register p_gram p,int flag)
{

	register int s; /* Will gather return value */
	int noenter;/* when set, unables entering of elements into
	 * setp. This is necessary to walk through the
	 * rest of rule p.
	 */

	s = 0;
	noenter = 0;
	for (;;)
	{
		switch (g_gettype(p))
		{
			case EORULE :
			return s;
			case TERM :
			{
				register p_term q;

				q = g_getterm(p);
				if (flag == 0)
					(void)nc_first(q->t_nc_first,q->t_rule,0);
				if (!noenter) s |= setunion(setp,q->t_nc_first);
				p++;
				if (r_getkind(q) == STAR ||
						r_getkind(q) == OPT ||
						empty(q->t_rule)) continue;
				break;}
			case ALTERNATION :
			{
				register p_link l;

				l = g_getlink(p);
				if (flag == 0)
					(void)nc_first(l->l_nc_symbs,l->l_rule,0);
				if (noenter == 0)
				{
					s |= setunion(setp,l->l_nc_symbs);
				}
				if (g_gettype(p+1) == EORULE) return s;
			}
			p++;
			continue;
			case ACTION :
			{
				register p_start subp;

				if (!noenter)
				{
					if (subpars_sim)
						s |= setunion(setp, start_firsts);
					else
					{
						for (subp = g_getsubparse(p); subp;
							subp = subp->ff_next)
							s |= setunion(setp, (&nonterms[subp->ff_nont])->n_nc_first);
					}
				}
				p++;
				continue;
			}
			case LITERAL :
			case TERMINAL :
			if (g_getcont(p) == g_getcont(illegal_gram))
			{
				/* Ignore for this set. */
				p++;
				continue;
			}
			if ((noenter == 0) && !IN(setp,g_getcont(p)))
			{
				s = 1;
				PUTIN(setp,g_getcont(p));
			}
			p++;
			break;
			case NONTERM :
			{
				register p_nont n;

				n = &nonterms[g_getcont(p)];
				if (noenter == 0)
				{
					s |= setunion(setp,n->n_nc_first);
					if (ntneeded) NTPUTIN(setp,g_getcont(p));
				}
				p++;
				if (n->n_flags & EMPTY) continue;
				break;}
		}
		if (flag == 0)
		{
			noenter = 1;
			continue;
		}
		return s;
	}
}
#endif

STATIC int nfollow(register p_nont p)
{
	return follow(p->n_follow, p->n_rule);
}

/*
 * setp is the follow set for the rule p.
 * Compute the follow sets in the rule p from this set.
 * Return 1 if a follow set of a nonterminal changed.
 */
STATIC int follow(p_set setp, register p_gram p)
{
	register int s; /* Will gather return value */

	s = 0;
	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return s;
		case TERM:
		{
			register p_term q;

			q = g_getterm(p);
			if (empty(p + 1))
			{
				/*
				 * If what follows the term can be empty,
				 * everything that can follow the whole
				 * rule can also follow the term
				 */
				s |= setunion(q->t_follow, setp);
			}
			/*
			 * Everything that can start the rest of the rule
			 * can follow the term
			 */
			s |= first(q->t_follow, p + 1, 1);
			if (r_getkind(q) == STAR || r_getkind(q) == PLUS || r_getnum(q))
			{
				/*
				 * If the term involves a repetition
				 * of possibly more than one,
				 * everything that can start the term
				 * can also follow it.
				 */
				s |= follow(q->t_first, q->t_rule);
			}
			/*
			 * Now propagate the set computed sofar
			 */
			s |= follow(q->t_follow, q->t_rule);
			break;
		}
		case ALTERNATION:
			/*
			 * Just propagate setp
			 */
			s |= follow(setp, g_getlink(p)->l_rule);
			break;
		case NONTERM:
		{
			register p_nont n;

			n = &nonterms[g_getcont(p)];
			s |= first(n->n_follow, p + 1, 1);
			if (empty(p + 1))
			{
				/*
				 * If the rest of p can produce empty,
				 * everything that follows p can follow
				 * the nonterminal
				 */
				s |= setunion(n->n_follow, setp);
			}
			break;
		}
		}
		p++;
	}
	return 0;
}

#ifdef NON_CORRECTING

STATIC int nc_nfollow(register p_nont p)
{
	return follow(p->n_nc_follow, p->n_rule);
}

STATIC int nc_follow(p_set setp, register p_gram p)
{
	/*
	 * setp is the follow set for the rule p.
	 * Compute the follow sets in the rule p from this set.
	 * Return 1 if a follow set of a nonterminal changed.
	 */
	register int s; /* Will gather return value */

	s = 0;
	for (;;)
	{
		switch (g_gettype(p))
		{
			case EORULE :
			return s;
			case TERM :
			{
				register p_term q;

				q = g_getterm(p);
				if (empty(p+1))
				{
					/*
					 * If what follows the term can be empty,
					 * everything that can follow the whole
					 * rule can also follow the term
					 */
					s |= setunion(q->t_nc_follow,setp);
				}
				/*
				 * Everything that can start the rest of the rule
				 * can follow the term
				 */
				s |= nc_first(q->t_nc_follow,p+1,1);
				if (r_getkind(q) == STAR ||
						r_getkind(q) == PLUS ||
						r_getnum(q) )
				{
					/*
					 * If the term involves a repetition
					 * of possibly more than one,
					 * everything that can start the term
					 * can also follow it.
					 */
					s |= nc_follow(q->t_nc_first,q->t_rule);
				}
				/*
				 * Now propagate the set computed sofar
				 */
				s |= nc_follow(q->t_nc_follow, q->t_rule);
				break;}
			case ALTERNATION :
			/*
			 * Just propagate setp
			 */
			s |= nc_follow(setp,g_getlink(p)->l_rule);
			break;
			case NONTERM :
			{
				register p_nont n;

				n = &nonterms[g_getcont(p)];
				s |= nc_first(n->n_nc_follow,p+1,1);
				if (empty(p+1))
				{
					/*
					 * If the rest of p can produce empty,
					 * everything that follows p can follow
					 * the nonterminal
					 */
					s |= setunion(n->n_nc_follow,setp);
				}
				break;}
		}
		p++;
	}
	return 0;
}

#endif

STATIC void co_dirsymb(p_set setp, register p_gram p)
{
	/*
	 * Walk the rule p, doing the work for alternations
	 */
	register p_gram s = 0;

	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return;
		case TERM:
		{
			register p_term q;

			q = g_getterm(p);
			co_dirsymb(q->t_follow, q->t_rule);
			break;
		}
		case ALTERNATION:
		{
			register p_link l;
			/*
			 * Save first alternative
			 */
			if (!s)
				s = p;
			l = g_getlink(p);
			co_dirsymb(setp, l->l_rule);
			if (empty(l->l_rule))
			{
				/*
				 * If the rule can produce empty, everything
				 * that follows it can also start it
				 */
				setunion(l->l_symbs, setp);
			}
			if (g_gettype(p+1) == EORULE)
			{
				/*
				 * Every alternation is implemented as a
				 * choice between two alternatives :
				 * this one or one of the following.
				 * The l_others set will contain the starters
				 * of the other alternatives
				 */
				co_others(s);
				return;
			}
		}
		}
		p++;
	}
}

STATIC void co_others(p_gram p)
{
	/*
	 * compute the l_others-sets for the list of alternatives
	 * indicated by p
	 */
	register p_link l1, l2;

	l1 = g_getlink(p);
	p++;
	l2 = g_getlink(p);
	setunion(l1->l_others, l2->l_symbs);
	if (g_gettype(p+1) != EORULE)
	{
		/*
		 * First compute l2->l_others
		 */
		co_others(p);
		/*
		 * and then l1->l_others
		 */
		setunion(l1->l_others, l2->l_others);
	}
}

static p_length length;
# define INFINITY 32767

STATIC int ncomplength(p_nont p)
{
	register p_length pl = &length[p - nonterms];
	int x = pl->cnt;

	pl->cnt = -1;
	complength(p->n_rule, pl);
	return pl->cnt < INFINITY && x == INFINITY;
}

/*
 * Compute the minimum length of a terminal production for each
 * nonterminal.
 * This length consists of two fields: the number of terminals,
 * and a number that is composed of
 * - the number of this alternative
 * - a crude measure of the number of terms and nonterminals in the
 *   production of this shortest string.
 */
STATIC void do_lengthcomp(void)
{
	register p_length pl;
	register p_nont p;
	p_mem alloc();

	length = (p_length) alloc(nnonterms * sizeof(*length));
	for (pl = &length[nnonterms - 1]; pl >= length; pl--)
	{
		pl->val = pl->cnt = INFINITY;
	}

	co_trans(ncomplength);

	pl = length;
	for (p = nonterms; p < maxnt; p++, pl++)
	{
		if (pl->cnt == INFINITY)
		{
			p->n_flags |= RECURSIVE;
		}
		setdefaults(p->n_rule);
	}
	free((p_mem) length);
}

STATIC void complength(register p_gram p, p_length le)
{
	/*
	 * Walk grammar rule p, computing minimum lengths
	 */
	register p_link l;
	register p_term q;
	t_length i;
	t_length X;
	int cnt = 0;

	X.cnt = 0;
	X.val = 0;
	for (;;)
	{
		switch (g_gettype(p))
		{
		case LITERAL:
		case TERMINAL:
#ifdef NON_CORRECTING
			if (g_getcont(p) == g_getcont(illegal_gram))
			{
				add(&X, INFINITY, 0);
				break;
			}
#endif
			add(&X, 1, 0);
			break;
		case ALTERNATION:

			X.cnt = INFINITY;
			X.val = INFINITY;
			while (g_gettype(p) != EORULE)
			{
				cnt++;
				l = g_getlink(p);
				p++;
				complength(l->l_rule, &i);
				i.val += cnt;
				if (l->l_flag & DEF)
				{
					X = i;
					break;
				}
				if (compare(&i, &X) < 0)
				{
					X = i;
				}
			}
			/* Fall through */
		case EORULE:
			le->cnt = X.cnt;
			le->val = X.val;
			return;
		case TERM:
		{
			register int rep;

			q = g_getterm(p);
			rep = r_getkind(q);
			X.val += 1;
			if ((q->t_flags & PERSISTENT) || rep == FIXED || rep == PLUS)
			{
				complength(q->t_rule, &i);
				add(&X, i.cnt, i.val);
				if (rep == FIXED && r_getnum(q) > 0)
				{
					for (rep = r_getnum(q) - 1; rep > 0; rep--)
					{
						add(&X, i.cnt, i.val);
					}
				}
			}
			break;
		}
		case NONTERM:
		{
			int nn = g_getcont(p);
			register p_length pl = &length[nn];
			int x = pl->cnt;

			if (x == INFINITY)
			{
				pl->cnt = -1;
				complength(nonterms[nn].n_rule, pl);
				x = pl->cnt;
			}
			else if (x == -1)
				x = INFINITY;
			add(&X, x, pl->val);
			X.val += 1;
		}
		}
		p++;
	}
}

STATIC void add(register p_length a, int c, int v)
{

	if (a->cnt == INFINITY || c == INFINITY)
	{
		a->cnt = INFINITY;
		return;
	}
	a->val += v;
	a->cnt += c;
}

STATIC int compare(p_length a, p_length b)
{
	if (a->cnt != b->cnt)
		return a->cnt - b->cnt;
	return a->val - b->val;
}

STATIC void setdefaults(register p_gram p)
{
	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return;
		case TERM:
			setdefaults(g_getterm(p)->t_rule);
			break;
		case ALTERNATION:
		{
			register p_link l, l1;
			int temp = 0, temp1, cnt = 0;
			t_length count, i;

			count.cnt = INFINITY;
			count.val = INFINITY;
			l1 = g_getlink(p);
			do
			{
				cnt++;
				l = g_getlink(p);
				p++;
				complength(l->l_rule, &i);
				i.val += cnt;
				if (l->l_flag & DEF)
					temp = 1;
				temp1 = compare(&i, &count);
				if (temp1 < 0 || (temp1 == 0 && l1->l_flag & AVOIDING))
				{
					l1 = l;
					count = i;
				}
				setdefaults(l->l_rule);
			} while (g_gettype(p) != EORULE);
			if (!temp)
			{
				/* No user specified default */
				l1->l_flag |= DEF;
			}
			return;
		}
		}
		p++;
	}
}

STATIC void do_contains(register p_nont n)
{
	/*
	 * Compute the total set of symbols that nonterminal n can
	 * produce
	 */

	if (n->n_contains == 0)
	{
		n->n_contains = get_set();
		contains(n->n_rule, n->n_contains);
		/*
		 * If the rule can produce empty, delete all symbols that
		 * can follow the rule as well as be in the rule.
		 * This is needed because the contains-set may only contain
		 * symbols that are guaranteed to be eaten by the rule!
		 * Otherwise, the generated parser may loop forever
		 */
		if (n->n_flags & EMPTY)
		{
			setminus(n->n_contains, n->n_follow);
		}
		/*
		 * But the symbols that can start the rule are always
		 * eaten
		 */
		setunion(n->n_contains, n->n_first);
	}
}

STATIC void contains(register p_gram p, register p_set set)
{
	/*
	 * Does the real computation of the contains-sets
	 */

	for (;;)
	{
		switch (g_gettype(p))
		{
		case EORULE:
			return;
		case TERM:
		{
			register p_term q;
			int rep;

			q = g_getterm(p);
			rep = r_getkind(q);
			if ((q->t_flags & PERSISTENT) || rep == PLUS || rep == FIXED)
			{
				/*
				 * In these cases, the term belongs to the
				 * continuation grammar.
				 * Otherwise, q->t_contains is just
				 * q->t_first
				 */
				if (!q->t_contains)
				{
					q->t_contains = get_set();
				}
				contains(q->t_rule, q->t_contains);
				if (rep != FIXED || empty(q->t_rule))
				{
					setminus(q->t_contains, q->t_follow);
				}
				setunion(q->t_contains, q->t_first);
			}
			else
			{
				contains(q->t_rule, (p_set) 0);
				q->t_contains = q->t_first;
			}
			if (set)
				setunion(set, q->t_contains);
			break;
		}
		case NONTERM:
		{
			register p_nont n;

			n = &nonterms[g_getcont(p)];
			do_contains(n);
			if (set)
			{
				setunion(set, n->n_contains);
				if (ntneeded)
					NTPUTIN(set, g_getcont(p));
			}
			break;
		}
		case ALTERNATION:
		{
			register p_link l;

			l = g_getlink(p);
			contains(l->l_rule, (l->l_flag & DEF) ? set : (p_set) 0);
			break;
		}
		case LITERAL:
		case TERMINAL:
		{
			register int hulp;

			if (set)
			{
				hulp = g_getcont(p);
				assert(hulp < ntokens);
				PUTIN(set, hulp);
			}
		}
		}
		p++;
	}
}

STATIC int nsafes(register p_nont p)
{
	int ch;
	register int i;

	ch = 0;
	i = getntsafe(p);
	if (i != NOSAFETY)
	{
		i = do_safes(p->n_rule, i, &ch);
		if (i < SCANDONE)
			i = SCANDONE;
		/* After a nonterminal, we only know whether a scan was done
		 or not
		 */
		if (getntout(p) != i)
		{
			ch = 1;
			setntout(p, i);
		}
	}
	return ch;
}

STATIC int do_safes(register p_gram p, int safe, register int *ch)
{
	/*
	 * Walk the grammar rule, doing the computation described in the
	 * comment of the procedure above this one.
	 */
	int retval;

	for (;;)
	{
		switch (g_gettype(p))
		{
		case ACTION:
			p++;
			continue;
		case LITERAL:
		case TERMINAL:
			safe = NOSCANDONE;
			break;
		case TERM:
		{
			register p_term q;
			int i, rep;

			q = g_getterm(p);
			i = r_getnum(q);
			rep = r_getkind(q);
			retval = do_safes(q->t_rule,
					t_safety(rep, i, q->t_flags & PERSISTENT, safe), ch);
			settout(q, retval);
			safe = t_after(rep, i, retval);
			break;
		}
		case ALTERNATION:
		{
			register p_link l;
			register int i;

			retval = -1;
			while (g_gettype(p) == ALTERNATION)
			{
				l = g_getlink(p);
				p++;
				if (safe > SAFE && (l->l_flag & DEF))
				{
					i = do_safes(l->l_rule, SAFESCANDONE, ch);
				}
				else
					i = do_safes(l->l_rule, SAFE, ch);
				if (retval == -1)
					retval = i;
				else if (i != retval)
				{
					if (i == NOSCANDONE || retval == NOSCANDONE)
					{
						retval = SCANDONE;
					}
					else if (i > retval)
						retval = i;
				}
			}
			return retval;
		}
		case NONTERM:
		{
			register p_nont n;
			register int nsafe, osafe;

			n = &nonterms[g_getcont(p)];
			nsafe = getntsafe(n);
			osafe = safe;
			safe = getntout(n);
			if (safe == NOSAFETY)
				safe = SCANDONE;
			if (osafe == nsafe)
				break;
			if (nsafe == NOSAFETY)
			{
				*ch = 1;
				setntsafe(n, osafe);
				break;
			}
			if (osafe == NOSCANDONE || nsafe == NOSCANDONE)
			{
				if (nsafe != SCANDONE)
				{
					*ch = 1;
					setntsafe(n, SCANDONE);
				}
				break;
			}
			if (osafe > nsafe)
			{
				setntsafe(n, osafe);
				*ch = 1;
			}
			break;
		}
		case EORULE:
			return safe;
		}
		p++;
	}
}

int t_safety(int rep, int count, int persistent, int safety)
{

	if (safety == NOSCANDONE)
		safety = SCANDONE;
	switch (rep)
	{
	default:
		assert(0);
	case OPT:
		if (!persistent || safety < SAFESCANDONE)
			return SAFE;
		return SAFESCANDONE;
	case STAR:
		if (persistent)
			return SAFESCANDONE;
		return SAFE;
	case PLUS:
		if (persistent)
		{
			if (safety > SAFESCANDONE)
				return safety;
			return SAFESCANDONE;
		}
		return safety;
	case FIXED:
		if (!count)
			return safety;
		return SCANDONE;
	}
	/* NOTREACHED */
}

int t_after(int rep, int count, int outsafety)
{
	if (count == 0 && (rep == STAR || rep == PLUS))
	{
		return SAFESCANDONE;
	}
	if (rep != FIXED)
	{
		if (outsafety <= SAFESCANDONE)
			return SAFESCANDONE;
		return SCANDONE;
	}
	return outsafety;
}