ack/util/LLgen/lib/nc_rec

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
	compile with -DNOFIRST to disable firstset optimization
		-DFOLLOW_OPT to enable followset optimization
		NOTE: Followset optimization is not
			supported when using -s option of LLgen
		-DDEBUG to print debug information
*/

extern int	LLsymb;
extern int	LLstartsymb;

void		LLmessage(int);


struct stacks {

	/* Acces to the stacks is through a 'dynamic array' of pointers
	 * to the heads. We implemented it this way to save on the number
	 * of Malloc() calls. nr_heads is the number of heads; heads_buf_size
	 * is the current size of heads_buf.
	 */

	int nr_heads;
	struct stack_elt **heads_buf;
	int heads_buf_size;

	/* r_rec contains nonterminals already tried to build a new
	 * stack with, to prevent right-recursive rules making the
	 * process loop forever
	 */

	char r_rec[(LLNNONTERMINALS + 7)/8];

	/* join_array contains pointers to already substituted stack
	 * elements, so that if the same nonterminal turns up again
	 * we can make a link
	 */

	struct stack_elt *join_array[LLNNONTERMINALS];

	/* cleanup_buf contains pointerts to elements that can possibly
	 * be deleted. Again this is implemented as a `growing array'.
	 * Although it's not so clean to do it this way, it DOES save
	 * a lot of time, mainly because much less pointer manipulation
	 * is required, and because it's not necessary to deallocate
	 * the buffer after each turn. Just set nr_cleanups to 0...
	 */

	int nr_cleanups;
	int cleanup_buf_size;
	struct stack_elt **cleanup_buf;

	/* visited_buf contains pointers to elements whose flags
	 * need to be cleared
	 */

	int nr_visited;
	int visited_buf_size;
	struct stack_elt **visited_buf;


	/* start_seen indicates if the last prediction phase
	 * has matched the start symbol
	 */

	int start_seen;

	/* exp_terminals will contain the terminals that are `on top'
	 * of the prediction graph after a prediction phase
	 */

	char exp_terminals[LLSETSIZE];

	/* check_run_ok indicates whether a stack element can be deleted
	 * or not
	*/

	int check_run_ok;
};


#ifdef DEBUG
static int allocates = 0;
static int deallocates = 0;
static int max_in_use = 0;
static int edge_allocates = 0;
static int edge_deallocates = 0;
static int edge_max_in_use = 0;
#endif

static int grammar_index = 0;

/* The grammar should only be build the first time we enter the
 * recovery routine. grammar_read == 0 indicates this has not
 * been done yet
 */

static int grammar_read = 0;

/* 'terminals' is an array indexed by the number of a terminal and links
 * all rules containing this terminal in the RHS
 */

static struct terminal *terminals;

/* 'nonterminals' is an array indexed by the number of a nonterminal
 * and contains all rules with this nonterminal in the LHS and links all
 * rules containing this nonterminal in the RHS
 */

static struct nonterminal *nonterminals;


/* These functions must be called instead of the original functions in
 * 'malloc.h'. They offer a checking allocation mechanism.
*/
static char *Malloc(unsigned);
static char *Realloc(char*, unsigned);



/* These functions build the grammar */
static void init_grammar(void);
static void build_grammar(void);
static struct lhs *build_rule(void);
static struct symbol *build_rhs(struct lhs*);
static struct symbol *make_link(struct symbol*);



/* These functions operate on the stacks */
static int optimize(struct stacks*, struct symbol*, int);
static void read_token(void);
static void start_stack(struct stacks*, int, int);
static void continuation(struct stacks*, int, int);
static struct stack_elt *push_rule(struct stack_elt*, struct symbol*);
static void new_head(struct stacks*, struct stack_elt*);
static void to_delete(struct stacks*, struct stack_elt*);
static void substitute(struct stacks*, struct stack_elt*, int);
static int join(struct stacks*, struct stack_elt*, int);
static int path(struct stack_elt*, struct stack_elt*);
static int part_of_loop(struct stack_elt*);
static void generate_heads(struct stacks*, struct stack_elt*, int);
static void delete(struct stacks*, struct stack_elt*);
static void hyp_run(struct stack_elt*);
static void check_run(struct stacks*, struct stack_elt*);
static struct stack_elt *split(struct stack_elt*);
#ifdef DEBUG
static void test(struct stacks*);
static void dump_stack(struct stack_elt*, int);
#endif
static void clear_flags(struct stack_elt*, char);
static void clear_gen_flags(struct stacks*);
static void match_heads(struct stacks*, int);
static void cleanup(struct stacks*);
static void initialize(struct stacks*);
static void calculate(struct stacks*, int);
static void kill_stack(struct stacks *stack);
void LLnc_recover(void);



static char *Malloc(unsigned size)
{
	char *p;

	if ((p = malloc(size)) == (char *)0) {
		fprintf(stderr, "fatal error: out of memory\n");
		exit(1);
	}
	return p;
}


static char *Realloc(char *ptr, unsigned size)
{
	char *p;

	if ((p = realloc(ptr, size)) == (char *)0) {
		fprintf(stderr, "fatal error: out of memory\n");
		exit(1);
	}
	return p;
}


static void init_grammar(void)
{
/* Allocate and initialize an array for terminals and nonterminals */

	int i;

	terminals = (struct terminal *)
		Malloc((unsigned) LLFIRST_NT * sizeof(struct terminal));
	for (i = 0; i < LLFIRST_NT; i++) {
		(terminals + i)->link = (struct symbol *)0;
	}

	nonterminals = (struct nonterminal *)
		Malloc((unsigned)LLNNONTERMINALS * sizeof(struct nonterminal));
	for (i = 0; i < LLNNONTERMINALS; i++) {
		(nonterminals + i)->rule = (struct lhs *)0;
		(nonterminals + i)->link = (struct symbol *)0;
	}
}


static void build_grammar(void)
{
/* Build a rule for every nonterminal. The LHS must be saved first because
 * of the fact that the right side of an assignment statement (in C) will
 * be evaluated before the left side
 */
	int nt, j;

	init_grammar();
	for (j = 0; j < LLNNONTERMINALS; j++) {
		nt = LLgrammar[grammar_index];
		(nonterminals + nt - LLFIRST_NT)->rule = build_rule();
	}
}


static struct lhs *build_rule(void)
{
/* Build LHS and call a funcion to create RHS */

	struct lhs *l;
	int j;

	l = (struct lhs *)Malloc(sizeof(struct lhs));
	l->nr = LLgrammar[grammar_index++];

	/* Build first set */
	for (j = 0; j < LLSETSIZE; j++)	{
		l->first[j] = LLgrammar[grammar_index++];
	}

	/* Build follow set */
	for (j = 0; j < LLSETSIZE; j++)	{
		l->follow[j] = LLgrammar[grammar_index++];
	}

	l->empty = LLgrammar[grammar_index++];	/* Can NT produce empty? */

	l->rhs = build_rhs(l);

	return l;
}


static struct symbol *build_rhs(struct lhs *l)
{
/* Build RHS by creating structs for all symbols including ALT and
 * EORULE. Also call a function for linking same terminals and
 * nonterminals.
 */

	struct symbol *r;

	r = (struct symbol *)Malloc(sizeof(struct symbol));
	if (LLgrammar[grammar_index] == LLALT) {
		grammar_index++;
		r->x = LLALT;
		r->nr = -1;			/* Not applicable */
		r->link = (struct symbol *)0;	/* Not applicable */
		r->next = build_rhs(l);
		r->lhs = l;
	}
	else if (LLgrammar[grammar_index] == LLEORULE) {
		grammar_index++;
		r->x = LLEORULE;
		r->nr = -1;			/* Not applicable */
		r->link = (struct symbol *)0;	/* Not applicable */
		r->next = (struct symbol *)0;	/* Not applicable */
		r->lhs = l;
	}
	else if (LLgrammar[grammar_index] < LLFIRST_NT) {
		r->x = LLTERMINAL;
		r->nr = LLgrammar[grammar_index++];
		r->link = make_link(r);
		r->next = build_rhs(l);
		r->lhs = l;
	}
	else {
		r->x = LLNONTERMINAL;
		r->nr = LLgrammar[grammar_index++];
		r->link = make_link(r);
		r->next = build_rhs(l);
		r->lhs = l;
	}
	return r;
}


static struct symbol *make_link(struct symbol *r)
{
/* Link same terminals and nonterminals. Every new symbol is appended
 * in front of the corresponding list for efficiency.
 */

	struct symbol *tmp;

	if (r->nr < LLFIRST_NT) {
		/* Terminal array */
		tmp = (terminals + r->nr)->link;
		(terminals + r->nr)->link = r;
	}
	else {					/* Nonterminal array */
		tmp = (nonterminals + (r->nr - LLFIRST_NT))->link;
		(nonterminals + (r->nr - LLFIRST_NT))->link = r;
	}
	return tmp;
}


/*****************************************************************************/


static int optimize(struct stacks* stack, struct symbol *symb_ptr, int l_ahead)
/* Return 1 if rule symb_ptr can start with terminal l_ahead, else return 0.
 * The array with expected terminals will also be filled in.
 */
{
	struct lhs *l;
	int i;

#ifdef NOFIRST
	return(1);
#else

	if ((l_ahead <= 0) || (l_ahead == EOFILE)) return 1;

	switch(symb_ptr->x) {
	case LLTERMINAL:
		LLPUTIN(stack->exp_terminals, LLindex[symb_ptr->nr]);
		if (symb_ptr->nr != l_ahead) return 0;
		else return 1;/*???*/

 	case LLNONTERMINAL:
		l = (nonterminals + symb_ptr->nr - LLFIRST_NT)->rule;
		if (LLIN(l->first, LLindex[l_ahead])) return 1;
		else if (l->empty) {
		 	/* Try next symbol */
			return optimize(stack, symb_ptr->next, l_ahead);
		}
		else {
			for (i = 0; i < LLSETSIZE; i++) {
				stack->exp_terminals[i] |= (l->first)[i];
			}
			return 0;
		}

	default:

#ifndef FOLLOW_OPT
		return(1);
#else

		l = (nonterminals + symb_ptr->lhs->nr - LLFIRST_NT)->rule;

		if (LLIN(l->follow, LLindex[l_ahead])) return 1;
		else {
			for (i = 0; i < LLSETSIZE; i++) {
				stack->exp_terminals[i] |= (l->follow)[i];
			}
			return 0;
		}
#endif /*FOLLOW_OPT */
	}
#endif /* NOFIRST */
}


static void read_token(void)
/* Read token and put it in global variable LLsymb, skipping
 * invalid tokens
 */
{
	LLsymb = LL_LEXI();
	while (LLindex[LLsymb] < 0) {
		/* Skip garbage tokens */
		LLmessage(0);
		LLsymb = LL_LEXI();
	}
}


static void start_stack(struct stacks *stack, int base, int l_ahead)
/* Start stack on base symbol base with lookahead l_ahead */
{
	struct stack_elt *bottom, *top;
	struct symbol *symb_ptr;
	int i;

	/* Find first applicable rule */
	symb_ptr = (terminals + base)->link;

	/* Now try all applicable rules */
	while (symb_ptr != (struct symbol *)0) {

		/* If the current rule cannot start with l_ahead,
		 * try the next one
		 */
		if (!optimize(stack, symb_ptr->next, l_ahead)) {
			symb_ptr = symb_ptr->link;
			continue;
		}

		if (	(symb_ptr->next->x == LLTERMINAL)
		||	(symb_ptr->next->x == LLNONTERMINAL)
		) {
			/* Allocate an end-of-stack */
#ifdef DEBUG
			allocates++;
			if (allocates - deallocates > max_in_use) {
				max_in_use = allocates - deallocates;
			}
#endif
			bottom = (struct stack_elt *)
					Malloc(sizeof(struct stack_elt));
			bottom->edges = (struct edge *)0;
			bottom->nr = LLEOSTACK;
			bottom->flags = 0;
			bottom->nr_nexts = 0;
			bottom->ref_count = 0;
			bottom->hyp_ref_count = -1;

			/* And use the rule to build a stack on it */
			top = push_rule(bottom, symb_ptr->next);

			/* Remember that we're now trying to match the LHS
			 * of the used rule
			 */
			bottom->matched = symb_ptr->lhs->nr;

			if (top->nr >= LLFIRST_NT) {
				substitute(stack, top, l_ahead);
			}
			else {
				new_head(stack, top);
			}

			/* Perhaps this only has produced an empty stack, in
			 * that case bottom can be deallocated.
		 	 */
			if (bottom->ref_count == 0) {
				to_delete(stack, bottom);
			}
		}
		else {
			/* base was the last element of the rule, so we
			 * figure we have matched the LHS of this rule.
			 */
			if (symb_ptr->lhs->nr == LLstartsymb) {
				stack->start_seen = 1;
			}

			continuation(stack, symb_ptr->lhs->nr, l_ahead);
		}
		symb_ptr = symb_ptr->link;
	}


	/* Reinitialize some arrays */
	for (i = 0; i < (LLNNONTERMINALS + 7)/8; i++) {
		stack->r_rec[i] = (char) 0;
	}

	for (i = 0; i < LLNNONTERMINALS; i++) {
		stack->join_array[i] = (struct stack_elt *)0;
	}

	/* Delete all HEAD flags */
	for (i = 0; i < stack->nr_heads; i++) {
		(*(stack->heads_buf + i))->flags &= ~LLHEAD;
	}

	/* Delete flags turned on by 'generate_heads()' */
		clear_gen_flags(stack);
	/* Try to delete elements on cleanup_buf */
	cleanup(stack);
}


static void continuation(struct stacks *stack, int nt, int l_ahead)
/* We have 'eaten' a whole stack, and think we recognized nt. Now
look for rules that we can proceed with, ie containing nt in the RHS.
Each rule found will be developed untill a terminal is at the top
of the stack.*/
{

	struct symbol *symb_ptr;
	struct stack_elt *bottom, *top;

	/* If we've already tried this nt, don't do it again.
	 * Otherwise we may loop forever on right-recursive rules
	 */
	if (LLIN(stack->r_rec, nt - LLFIRST_NT)) return;

	/* Mark that we have looked for a continuation for nt */
	LLPUTIN(stack->r_rec, nt - LLFIRST_NT);

	/* Find first applicable rule */
	symb_ptr = (nonterminals + nt - LLFIRST_NT)->link;

	/* Try all applicable rules */
	while (symb_ptr != (struct symbol *)0) {

		/* If the current rule cannot start with l_ahead,
		 * try the next one
		 */
		if (!optimize(stack, symb_ptr->next, l_ahead)) {
			symb_ptr = symb_ptr->link;
			continue;
		}

		if (	(symb_ptr->next->x == LLTERMINAL)
		||	(symb_ptr->next->x == LLNONTERMINAL)
		) {
#ifdef DEBUG
			allocates++;
			if (allocates - deallocates > max_in_use) {
					max_in_use = allocates - deallocates;
				}
#endif
			bottom = (struct stack_elt *)
					Malloc(sizeof(struct stack_elt));
			bottom->edges = (struct edge *)0;
			bottom->nr = LLEOSTACK;
			bottom->flags = 0;
			bottom->nr_nexts = 0;
			bottom->ref_count = 0;
			bottom->hyp_ref_count = -1;

			/* Use the rule to build a stack on bottom */
			top = push_rule(bottom, symb_ptr->next);

			/* Remember that we're now trying to match the LHS
			 * of the used rule
			 */
			bottom->matched = symb_ptr->lhs->nr;

			if (top->nr >= LLFIRST_NT) {
				substitute(stack, top, l_ahead);
			}
			else {
				new_head(stack, top);
			}

			/* Perhaps this only has produced an empty stack, in
			 * that case bottom can be deallocated.
		 	 */
			if (bottom->ref_count == 0) {
				delete(stack, bottom);
			}
		}
		else {
			/* Stack is still empty */
			if (symb_ptr->lhs->nr == LLstartsymb) {
				stack->start_seen = 1;
			}

			continuation(stack, symb_ptr->lhs->nr, l_ahead);
		}

		symb_ptr = symb_ptr->link;
	}
}


static struct stack_elt *push_rule(struct stack_elt *element,
					struct symbol *symb_ptr)
/* Append the rule symb_ptr to stack element 'element'. Return a
 * pointer to the new top of the stack
 */
{
	struct stack_elt *se, *top;

	if (	(symb_ptr->next->x == LLTERMINAL)
	||	(symb_ptr->next->x == LLNONTERMINAL)
	) {
		top = push_rule(element, symb_ptr->next);
	}
	else {
		top = element;
	}

#ifdef DEBUG
	allocates++;
	if (allocates - deallocates > max_in_use) {
		max_in_use = allocates - deallocates;
	}
#endif

	se = (struct stack_elt *)Malloc(sizeof(struct stack_elt));
	se->flags = 0;
	se->nr = symb_ptr->nr;
	se->ref_count = 0;
	se->hyp_ref_count = -1;
	se->matched = -1;
	se->nr_nexts = 1;

#ifdef DEBUG
	edge_allocates++;
	if (edge_allocates - edge_deallocates > edge_max_in_use) {
		edge_max_in_use = edge_allocates - edge_deallocates;
	}
#endif

	se->edges = (struct edge *)Malloc(sizeof(struct edge));
	se->edges->ptr = top;
	se->edges->flags = 0;

	top->ref_count++;
	return se;
}


static void new_head(struct stacks *stack, struct stack_elt *ptr)
/* Make ptr a head of stack */
{

	/* Is this already a head?*/
	if (ptr->flags & LLHEAD) return;

	if (stack->heads_buf_size == 0) {
		stack->heads_buf_size = LLHEADS_BUF_INCR;
		stack->heads_buf = (struct stack_elt **)
			Malloc(LLHEADS_BUF_INCR * sizeof(struct stack_elt *));
	}
	else if (stack->nr_heads == stack->heads_buf_size) {
		/* buffer full? */
		stack->heads_buf_size += LLHEADS_BUF_INCR;
		stack->heads_buf = (struct stack_elt **)
			Realloc((char *)
				stack->heads_buf, (unsigned)
				stack->heads_buf_size *
					sizeof(struct stack_elt *)
			);
	}

	*(stack->heads_buf + stack->nr_heads) = ptr;	/* Add at the tail */
	stack->nr_heads++;		/* Increase number of heads */
	ptr->flags |= LLHEAD;		/* Mark it as a head */
	ptr->ref_count++;		/* Increase reference count */
	LLPUTIN(stack->exp_terminals, LLindex[ptr->nr]);
}


static void to_delete(struct stacks *stack, struct stack_elt *ptr)
/* Remember that ptr has to be deleted */
{

	int i;

#ifdef NOCLEAN
	return;
#endif



	for (i = 0; i < stack->nr_cleanups; i++) {
		/* Check if already in buffer */
		if (*(stack->cleanup_buf + i) == ptr) return;
	}

	if (stack->cleanup_buf_size == 0) {
		stack->cleanup_buf_size = LLCLEANUP_BUF_INCR;
		stack->cleanup_buf = (struct stack_elt **)
		Malloc(LLCLEANUP_BUF_INCR * sizeof(struct stack_elt *));
	}
	else if (stack->nr_cleanups == stack->cleanup_buf_size) {
		stack->cleanup_buf_size += LLCLEANUP_BUF_INCR;
		stack->cleanup_buf = (struct stack_elt **)
			Realloc((char *) stack->cleanup_buf,
				(unsigned) stack->cleanup_buf_size *
				sizeof(struct stack_elt *));
	}
	*(stack->cleanup_buf + stack->nr_cleanups) = ptr;
	stack->nr_cleanups++;
}


static void substitute(struct stacks *stack, struct stack_elt *top, int l_ahead)
/* This function substitutes the NT pointed to by 'top'. 'top' should be a top
 * of a stack
 */
{
	struct symbol *symb_ptr;
	struct stack_elt *new_top;

	/* Try to join top NT */
	if (join(stack, top, l_ahead)) return;

	/* Find RHS of the rule of nonterminal 'top->nr' */
	symb_ptr = (nonterminals + top->nr - LLFIRST_NT)->rule->rhs;

	/* Mark top as dummy */
	top->flags |= LLDUMMY;

	while (1) {
		/* If this an empty production, search down the stack for
		 * terminals
		 */
		if ((symb_ptr->x == LLALT) || (symb_ptr->x == LLEORULE)) {
			generate_heads(stack, top, l_ahead);
		}

		/* Skip other empty productions, they have no effect. */
		while (symb_ptr->x == LLALT) {
			symb_ptr = symb_ptr->next;
		}

		if (symb_ptr->x == LLEORULE) {
			/* If there are only empty productions, the NT on top
			 * can be deleted
			 */
			if (top->ref_count == 0) {
				to_delete(stack, top);
			}
			return;
		}

		/* If this rule can produce 'l_ahead' on the top of the stack
		 * substitute the nonterminal
		 */
		if (optimize(stack, symb_ptr, l_ahead)) {
			new_top = push_rule(top, symb_ptr);

			/* If the new element on top is a nonterminal
			 * substitute it, else make it a head
			 */
			if (new_top->nr >= LLFIRST_NT) {
				substitute(stack, new_top, l_ahead);
			}
			else {
				new_head(stack, new_top);
			}
		}

		/* Search to next alternative */
		while (	(symb_ptr->x == LLTERMINAL)
		||	(symb_ptr->x == LLNONTERMINAL)
		) {
			symb_ptr = symb_ptr->next;
		}

		if (symb_ptr->x == LLEORULE) {
			if (top->ref_count == 0) {
				to_delete(stack, top);
			}
			return;
		}
		else {
			symb_ptr = symb_ptr->next;
		}
	}

}


static int join(struct stacks *stack, struct stack_elt *top, int l_ahead)
/* This function tries to connect a NT on top of a stack with another stack,
 * which has already substituted this NT
 */
{
	struct stack_elt *se;
	int size;

	if (	(se = stack->join_array[top->nr - LLFIRST_NT]) ==
			(struct stack_elt *)0
	) {
		stack->join_array[top->nr - LLFIRST_NT] = top;
		return 0;		/* Join not possible */
	}
	else {
		se->nr_nexts++;		/* Increase number of descendants */

#ifdef DEBUG
		edge_allocates++;
		if (edge_allocates - edge_deallocates > edge_max_in_use) {
			edge_max_in_use = edge_allocates - edge_deallocates;
		}
#endif

		/* Allocate one more pointer to descendants */
		size = se->nr_nexts * sizeof(struct edge);
		se->edges = (struct edge *)Realloc((char *) se->edges,
							(unsigned) size);

		/* Link it */
		(se->edges + se->nr_nexts - 1)->ptr = top->edges->ptr;
		(se->edges + se->nr_nexts - 1)->flags = 0;

		/* The successor of 'top' gets an extra predecessor.
		 * 'top' has always only one successor because the stacks are
		 * constructed in 'depth first' order
		 */
		top->edges->ptr->ref_count++;


#ifndef NOLOOPS
		/* If we have made a new loop find all stack elements of this
		 * loop and mark them
		 */
		if (path(top->edges->ptr, se)) {
			(se->edges + se->nr_nexts - 1)->flags |= LLLOOP;
			(se->edges + se->nr_nexts - 1)->flags |= LLYES;
		}
		clear_flags(top->edges->ptr, (LLNO | LLYES));
#endif


		/* Check if joined NT produces empty */
		if ((nonterminals + se->nr - LLFIRST_NT)->rule->empty) {
			generate_heads(stack, top, l_ahead);
		}

		/* Deallocate top symbol */
		if (top->ref_count == 0) {
			to_delete(stack, top);
		}

		return 1;
	}
}


#ifndef NOLOOPS

static int path(struct stack_elt *se1, struct stack_elt *se2)
/* If there is a path from se1 to se2 it returns 1 and marks all the paths
 * betweeen these two points, otherwise it returns 0. The flags LLYES and
 * LLNO are used for optimization. */
{
	int i, result = 0;

	if (se1 == se2) return 1;

	for (i = 0; i < se1->nr_nexts; i++) {
		if (	(!((se1->edges + i)->flags & LLNO))
		&&	(!((se1->edges + i)->flags & LLLOOP_SEARCH))
		) {
			(se1->edges + i)->flags |= LLLOOP_SEARCH;

			if (path((se1->edges + i)->ptr, se2)) {
				(se1->edges + i)->flags |= LLLOOP;
				result = 1;
			}
			else {
				(se1->edges + i)->flags |= LLNO;
			}

			(se1->edges + i)->flags &= ~LLLOOP_SEARCH;
		}
		(se1->edges + i)->flags |= LLYES;
	}
	return result;
}


static int part_of_loop(struct stack_elt *se)
/* Checks if 'se' belongs to a loop */
{
	int i;

	for (i = 0; i < se->nr_nexts; i++) {
		if ((se->edges + i)->flags & LLLOOP) return 1;
	}
	return 0;
}

#endif /* NOLOOPS */


static void generate_heads(struct stacks *stack, struct stack_elt *se,
				int l_ahead)
/* This funcion finds all heads starting at 'se'. */
{
	int i;
	struct stack_elt *next_se;


	for (i = 0; i < se->nr_nexts; i++) {

		if (!((se->edges + i)->ptr->flags & LLGEN_SEARCH)) {

			(se->edges + i)->ptr->flags |= LLGEN_SEARCH;

			next_se = (se->edges + i)->ptr;

			/* Remember a flag has to be cleared later */

			if (stack->visited_buf_size == 0) {
				stack->visited_buf_size = LL_VIS_INCR;
				stack->visited_buf = (struct stack_elt **)
				Malloc(LL_VIS_INCR * sizeof(struct stack_elt *));
			}
			else if (stack->nr_visited == stack->visited_buf_size) {
				stack->visited_buf_size += LL_VIS_INCR;
				stack->visited_buf = (struct stack_elt **)
					Realloc((char *) stack->visited_buf,
					(unsigned) stack->visited_buf_size *
					sizeof(struct stack_elt *));
			}
			*(stack->visited_buf + stack->nr_visited) = next_se;
			stack->nr_visited++;

			if (next_se->flags & LLDUMMY) {
				generate_heads(stack, next_se, l_ahead);
			}
			else if (next_se->nr == LLEOSTACK) {
				/* We have matched a nt */
				if (next_se->matched == LLstartsymb) {
					stack->start_seen = 1;
				}

				continuation(stack, next_se->matched, l_ahead);
				if (next_se->ref_count == 0) {
					to_delete(stack, next_se);
				}
			}
			else if (next_se->nr < LLFIRST_NT) {
				/* terminal */
				new_head(stack, next_se);
			}
			else {
				if (next_se->ref_count > 0) {
					next_se = split(next_se);
				}
				substitute(stack, next_se, l_ahead);
			}
		}
	}
}


static void delete(struct stacks *stack, struct stack_elt *se)
/* This function runs down the stack(s) deleting every element which cannot be
 * reached anymore. */
{
	int i;

#ifdef NOCLEAN
	return;
#endif

	if (se->ref_count == 0) {

		/* Decrease reference counts of all successors */
		for (i = 0; i < se->nr_nexts; i++) {
			if ((se->edges + i)->ptr->ref_count != 0) {
				(se->edges + i)->ptr->ref_count--;

				/* Try to delete next element */
				delete(stack, (se->edges + i)->ptr);
			}
		}

		/* If this element is saved in the join_array clear it */
		if (se->nr >= LLFIRST_NT) {
			if (stack->join_array[se->nr - LLFIRST_NT] == se) {
				stack->join_array[se->nr - LLFIRST_NT] =
					(struct stack_elt *)0;
			}
		}
#ifdef DEBUG
		deallocates++;
		edge_deallocates += se->nr_nexts;
#endif
		free((char *) se->edges);
		free((char *) se);
	}

#ifndef NOLOOPS
	/* If this element belongs to a loop try to delete it */
	else if (part_of_loop(se)) {

		/* Do a temporary delete */
		hyp_run(se);

		/* Check it */
		stack->check_run_ok = 1;
		check_run(stack, se);

		/* If it can be deleted delete it */
		if (stack->check_run_ok) {
			se->ref_count = 0;
			delete(stack, se);
		}

	}
#endif
}


#ifndef NOLOOPS

static void hyp_run(struct stack_elt *se)
/* This function sets the 'hyp_ref_counts' of all elements of the loop that
 * 'se' belongs to to the value that 'ref_count' will get when 'se' is
 * deleted
 */
{
	int i;
	struct stack_elt *next_se;

	for (i = 0; i < se->nr_nexts; i++) {
		next_se = (se->edges + i)->ptr;

		if (	(!((se->edges + i)->flags & LLHYP_SEARCH))
		&&	((se->edges + i)->flags & LLLOOP)
		) {
			(se->edges + i)->flags |= LLHYP_SEARCH;

			/* If this element is not yet visited initialize
			 * 'hyp_ref_count' else decrease it by one
			 */
			if (next_se->hyp_ref_count == -1) {
				next_se->hyp_ref_count = next_se->ref_count - 1;
			}
			else {
				next_se->hyp_ref_count--;
			}

			/* Continue searching */
			hyp_run(next_se);
		}
	}
}


static void check_run(struct stacks *stack, struct stack_elt *se)
/* This function checks all 'hyp_ref_counts' that 'hyp_run()' has set.
 * If one of them is not 0, 'check_run_ok' will be set to 0 indicating
 * that 'se' cannot be deleted. 'check_run()' also resets all 'hyp_ref_counts'
 */
{
	int i;

	if (se->hyp_ref_count > 0) {
		stack->check_run_ok = 0;
	}

	/* Reset 'hyp_ref_count' */
	se->hyp_ref_count = -1;
	for (i = 0; i < se->nr_nexts; i++) {
		if ((se->edges + i)->flags & LLHYP_SEARCH) {
			(se->edges + i)->flags &= ~LLHYP_SEARCH;
			check_run(stack, (se->edges + i)->ptr);
		}
	}
}

#endif /* NOLOOPS */


static struct stack_elt *split(struct stack_elt *se)
/* This function splits of a NT in de stack, and returns a pointer to it */
{
	struct stack_elt *new_stack;
	int i;

#ifdef DEBUG
	allocates++;
	if (allocates - deallocates > max_in_use) {
		max_in_use = allocates - deallocates;
	}
#endif

	new_stack = (struct stack_elt *)Malloc(sizeof(struct stack_elt));
	new_stack->flags = 0;		/* Used by 'clear_gen_flags()' */
	new_stack->nr = se->nr;
	new_stack->ref_count = 0;	/* Copy is new top */
	new_stack->hyp_ref_count = -1;
	new_stack->matched = -1;
	new_stack->nr_nexts = se->nr_nexts;

#ifdef DEBUG
	edge_allocates++;
	if (edge_allocates - edge_deallocates > edge_max_in_use) {
		edge_max_in_use = edge_allocates - edge_deallocates;
	}
#endif

	new_stack->edges = (struct edge *)
		Malloc((unsigned)se->nr_nexts * sizeof(struct edge));

	/* Copy gets the same successors as the original */
	memcpy((char *) new_stack->edges, (char *) se->edges,
					se->nr_nexts * sizeof(struct edge));

	/* Each successor gets a new predecessor */
	for (i = 0; i < new_stack->nr_nexts; i++) {
		(new_stack->edges + i)->ptr->ref_count++;
		(new_stack->edges + i)->flags = 0;
	}

	return new_stack;
}


#ifdef DEBUG
static void test(struct stacks *stack)
{
	struct stack_elt *se;
	int i;

	printf("STACKS:\n");
	for (i = 0; i < stack->nr_heads; i++) {
		printf("%2d: ", i + 1);
		if (*(stack->heads_buf + i) == (struct stack_elt *)0) {
			printf("NIL\n");
			continue;
		}
		se = *(stack->heads_buf + i);
		dump_stack(se, 1);
		clear_flags(se, PRINT_SEARCH);
	}
}


static void dump_stack(struct stack_elt *se, int level)
{
	int i, j;

	while (se->nr != LLEOSTACK) {
		if ((se->flags & LLDUMMY) && (se->nr_nexts > 1)) {
			printf("[%d] <%d,%d,%d>\n",
				se->nr, se->ref_count,
				se->hyp_ref_count,
				se->flags
			);
			for (j = 0; j < se->nr_nexts; j++) {
				for (i = 1; i <= level; i++) {
					printf("    ");
				}
				printf("%d: ", j + 1);
				if (!((se->edges + j)->flags & PRINT_SEARCH)) {
					printf(" (%d) ", (se->edges + j)->flags);
					(se->edges + j)->flags |= PRINT_SEARCH;
					dump_stack((se->edges+j)->ptr,level+1);
					/*clear_flags((se->edges+j)->ptr,PRINT_SEARCH);*/
				}
				else {
					printf("LOOP\n");
				}
			}
			return;
		}
		else {
			if (se->flags & LLDUMMY) {
				printf("[%d] <%d,%d,%d> ",
					se->nr,se->ref_count,
					se->hyp_ref_count,
					se->flags
				);
			}
			else {
				printf("%d <%d,%d,%d> ",
					se->nr, se->ref_count,
					se->hyp_ref_count,
					se->flags
				);
			}
			if (!(se->edges->flags & PRINT_SEARCH)) {
				printf(" (%d) ", se->edges->flags);
				se->edges->flags |= PRINT_SEARCH;
				se = se->edges->ptr;
			}
			else {
				printf("LOOP\n");
				return;
			}
		}
	}
	printf("\n");
}
#endif


static void clear_flags(struct stack_elt *se, char flag)
/* Clears edge flag 'flag' */
{
	int i;

	for (i = 0; i < se->nr_nexts; i++) {
		if ((se->edges + i)->flags & flag) {
			(se->edges + i)->flags &= ~flag; /* clear flag */
			clear_flags((se->edges + i)->ptr, flag);
		}
	}
}

static void clear_gen_flags(struct stacks *stack)
{
	int i;

	for (i = 0; i < stack->nr_visited; i++) {
		(*(stack->visited_buf + i))->flags &= ~(LLGEN_SEARCH);
	}

	stack->nr_visited = 0;
}


static void match_heads(struct stacks *stack, int symb)
/* Match heads_buf against symb, leaving only matching heads,
 * whilst deallocating the non-matching stacks
 */
{
	int i;

	int old_nr_heads;
	struct stack_elt **old_heads_buf;


	/* Copy the 'old' heads */
	old_nr_heads = stack->nr_heads;
	old_heads_buf = stack->heads_buf;


	/* Set heads in stack to 0 */
	stack->nr_heads = 0;
	stack->heads_buf_size = 0;
	stack->heads_buf = (struct stack_elt **) 0;


	for (i = 0; i < old_nr_heads; i++) {
		if ((*(old_heads_buf + i))->nr != symb) {
			/* Does not match? */
			(*(old_heads_buf + i))->ref_count--;
			(*(old_heads_buf + i))->flags &= ~LLHEAD;
			delete(stack, *(old_heads_buf + i));
		}
		else {	/* Matches */
			if (stack->heads_buf_size == 0) {
				stack->heads_buf_size = LLHEADS_BUF_INCR;
				stack->heads_buf = (struct stack_elt **)
					Malloc((unsigned)stack->heads_buf_size *
						sizeof(struct stack_elt *));
			}
			else if (stack->nr_heads == stack->heads_buf_size) {
				stack->heads_buf_size += LLHEADS_BUF_INCR;
				stack->heads_buf = (struct stack_elt **)
					Realloc((char *) stack->heads_buf,
						(unsigned) stack->heads_buf_size *
						sizeof(struct stack_elt *));
			}
			*(stack->heads_buf + stack->nr_heads) =
				*(old_heads_buf + i);
			stack->nr_heads++;
		}
	}
	free((char *) old_heads_buf);
}


static void cleanup(struct stacks *stack)
/* Deletes all elements in 'cleanup_buf()' */
{
	int i;

	for (i = 0; i < stack->nr_cleanups; i++) {
		delete(stack, *(stack->cleanup_buf + i));
	}

	stack->nr_cleanups = 0;

}


static void initialize(struct stacks *stack)
/* Initializes some variables and arrays */
{
	int j;

	stack->nr_heads = 0;
	stack->heads_buf_size = 0;
	stack->heads_buf = (struct stack_elt **)0;

	stack->nr_cleanups = 0;
	stack->cleanup_buf_size = 0;
	stack->cleanup_buf = (struct stack_elt **)0;

	stack->nr_visited = 0;
	stack->visited_buf_size = 0;
	stack->visited_buf = (struct stack_elt **)0;

	for (j = 0; j < (LLNNONTERMINALS + 7)/8; j++) {
		stack->r_rec[j] = (char) 0;
	}

	for (j = 0; j < LLNNONTERMINALS; j++) {
		stack->join_array[j] = (struct stack_elt *)0;
	}

	for (j = 0; j < LLSETSIZE; j++) {
		stack->exp_terminals[j] = 0;
	}

	stack->start_seen = 0;
}


static void calculate(struct stacks *stack, int l_ahead)
/* This function finds all new heads and deletes the old heads */
{
	int i;
	int old_nr_heads;
	struct stack_elt **old_heads_buf;

	/* Make a copy of the heads */
	old_nr_heads = stack->nr_heads;
	old_heads_buf = stack->heads_buf;

	stack->nr_heads = 0;
	stack->heads_buf = (struct stack_elt **) 0;
	stack->heads_buf_size = 0;

	for (i = 0; i < old_nr_heads; i++) {
		/* Find all new heads */
		generate_heads(stack, *(old_heads_buf + i), l_ahead);
		clear_gen_flags(stack);

		/* Old head can be deleted now */
		(*(old_heads_buf + i))->ref_count--;
		delete(stack, *(old_heads_buf + i));
	}


	cleanup(stack);
	free((char *) old_heads_buf);

	/* Reinitialize some things */
	for (i = 0; i < (LLNNONTERMINALS + 7)/8; i++) {
		stack->r_rec[i] = (char) 0;
	}

	for (i = 0; i < LLNNONTERMINALS; i++) {
		stack->join_array[i] = (struct stack_elt *)0;
	}

	/* Delete all HEAD flags */
	for (i = 0; i < stack->nr_heads; i++) {
		(*(stack->heads_buf + i))->flags &= ~LLHEAD;
	}
}

static void kill_stack(struct stacks *stack)
{
	int i;

	for (i = 0; i < stack->nr_heads; i++) {
		(*(stack->heads_buf + i))->ref_count--;
		delete(stack, *(stack->heads_buf + i));
	}
}



void LLnc_recover(void)
/* This function contains the main loop for non correcting syntax error
 * recovery
 */
{
	int j;
	int base_symb;
	struct stacks stack;
	int max_nr_heads;
	int max_nr_good_heads;

	initialize(&stack);
	max_nr_heads = 0;
	max_nr_good_heads = 0;

	/* Grammar has to be read only once */
	if (!grammar_read) {
		build_grammar();
		grammar_read = 1;
	}

	/* Read first token */
	read_token();
	base_symb = LLsymb;

	/* Check on end of file */
	if ((base_symb <= 0) || (base_symb == EOFILE)) {

		if ((nonterminals + LLstartsymb - LLFIRST_NT)->rule->empty != 1
		) {
			LLsymb = EOFILE;
			LLmessage(0);
		}

		kill_stack(&stack);
		return;
	}

	/* Read look ahead token */
	read_token();

	/* Now search applicable rules and starts the ball rolling */
	start_stack(&stack, base_symb, LLsymb);

	if (stack.nr_heads > max_nr_heads) {
		max_nr_heads = stack.nr_heads;
	}


	/* Only matching heads are needed */
	match_heads(&stack, LLsymb);

	if (stack.nr_heads > max_nr_good_heads) {
		max_nr_good_heads = stack.nr_heads;
	}


#ifdef DEBUG
	test(&stack);
#endif

	/* Loop untill end of inputfile */
	while ((LLsymb > 0) && (LLsymb != EOFILE)) {
		/* When entering the loop LLsymb always contains the
		 * symbol that was used as look_ahead to construct the stacks,
		 * or, if optimization is OFF, it contains the symbol with
		 * which the current heads have been matched 
		 */

		if (stack.nr_heads == 0) {
			/* No more heads left */
			LLmessage(0);

			/* Restart the whole thing */
			initialize(&stack);

			/* The look-ahead caused the empty stack, don't
			 * use it to start a new one !
			 */

			read_token();
			base_symb = LLsymb;

			/* Check on end of file */
			if ((base_symb <= 0) || (base_symb == EOFILE)) {
				if ((nonterminals + LLstartsymb - LLFIRST_NT)->rule->empty != 1) {
					LLsymb = EOFILE;
					LLmessage(0);
				}
				kill_stack(&stack);
				return;
			}

			read_token();

			start_stack(&stack, base_symb, LLsymb);

			if (stack.nr_heads > max_nr_heads) {
				max_nr_heads = stack.nr_heads;
			}


			match_heads(&stack, LLsymb);

			if (stack.nr_heads > max_nr_good_heads) {
				max_nr_good_heads = stack.nr_heads;
			}

			continue;
		}


		/* Normal case starts here */
		stack.start_seen = 0;

		for (j = 0; j < LLSETSIZE; j++) {
			stack.exp_terminals[j] = 0;
		}

		/* Read next symbol */
		read_token();

		/* Generate all new heads and delete old ones */
		calculate(&stack, LLsymb);

		/* Leave out not wanted heads */

		if (stack.nr_heads > max_nr_heads) {
			max_nr_heads = stack.nr_heads;
		}

		match_heads(&stack, LLsymb);

		if (stack.nr_heads > max_nr_good_heads) {
			max_nr_good_heads = stack.nr_heads;
		}



#ifdef DEBUG
		test(&stack);
#endif

	}

	/* End of file reached, check if we have seen a start symbol */
	if (stack.start_seen == 1) return;
	else {
		LLsymb = EOFILE;
		LLmessage(0);
	}

	kill_stack(&stack);

#ifdef DEBUG
	printf("Maximum number of heads: %d\n", max_nr_heads);
	printf("Maximum number of good heads: %d\n", max_nr_good_heads);
	printf("Number of node allocates: %d\n", allocates);
	printf("Number of node deallocates: %d\n", deallocates);
	printf("Maximum number of nodes in use: %8d\n", max_in_use);
	printf("Sizeof(struct stack_elt)              = %8d\n", sizeof(struct stack_elt));
	printf("                                        --------x\n");
	printf("                                        %8d\n", max_in_use * sizeof(
					struct stack_elt));
	printf("Number of edge allocates: %d\n", edge_allocates);
	printf("Number of edge deallocates: %d\n", edge_deallocates);
	printf("Maximum number of edges in use: %8d\n", edge_max_in_use);
	printf("Sizeof(struct edge)              = %8d\n", sizeof(struct edge));
	printf("                                   --------x\n");
	printf("                                   %8d\n", edge_max_in_use * sizeof(struct edge));

#endif
}