src/nullable.c

/* Part of the bison parser generator,
   Copyright 1984, 1989, 2000 Free Software Foundation, Inc.

   This file is part of Bison, the GNU Compiler Compiler.

   Bison 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.

   Bison 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 Bison; see the file COPYING.  If not, write to
   the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */


/* Set up NULLABLE, a vector saying which nonterminals can expand into
   the null string.  NULLABLE[I - NTOKENS] is nonzero if symbol I can
   do so.  */

#include "system.h"
#include "types.h"
#include "gram.h"
#include "nullable.h"

char *nullable = NULL;

void
set_nullable (void)
{
  short *r;
  short *s1;
  short *s2;
  int ruleno;
  int symbol;
  shorts *p;

  short *squeue;
  short *rcount;
  shorts **rsets;
  shorts *relts;
  char any_tokens;
  short *r1;

#ifdef	TRACE
  fprintf (stderr, _("Entering set_nullable"));
#endif

  nullable = XCALLOC (char, nvars) - ntokens;

  squeue = XCALLOC (short, nvars);
  s1 = s2 = squeue;

  rcount = XCALLOC (short, nrules + 1);
  rsets = XCALLOC (shorts *, nvars) - ntokens;
  /* This is said to be more elements than we actually use.
     Supposedly nitems - nrules is enough.
     But why take the risk?  */
  relts = XCALLOC (shorts, nitems + nvars + 1);
  p = relts;

  r = ritem;
  while (*r)
    {
      if (*r < 0)
	{
	  symbol = rule_table[-(*r++)].lhs;
	  if (symbol >= 0 && !nullable[symbol])
	    {
	      nullable[symbol] = 1;
	      *s2++ = symbol;
	    }
	}
      else
	{
	  r1 = r;
	  any_tokens = 0;
	  for (symbol = *r++; symbol > 0; symbol = *r++)
	    {
	      if (ISTOKEN (symbol))
		any_tokens = 1;
	    }

	  if (!any_tokens)
	    {
	      ruleno = -symbol;
	      r = r1;
	      for (symbol = *r++; symbol > 0; symbol = *r++)
		{
		  rcount[ruleno]++;
		  p->next = rsets[symbol];
		  p->value = ruleno;
		  rsets[symbol] = p;
		  p++;
		}
	    }
	}
    }

  while (s1 < s2)
    {
      p = rsets[*s1++];
      while (p)
	{
	  ruleno = p->value;
	  p = p->next;
	  if (--rcount[ruleno] == 0)
	    {
	      symbol = rule_table[ruleno].lhs;
	      if (symbol >= 0 && !nullable[symbol])
		{
		  nullable[symbol] = 1;
		  *s2++ = symbol;
		}
	    }
	}
    }

  XFREE (squeue);
  XFREE (rcount);
  XFREE (rsets + ntokens);
  XFREE (relts);
}


void
free_nullable (void)
{
  XFREE (nullable + ntokens);
}
Commit	Line	Data
	1	/* Part of the bison parser generator,
	2	Copyright 1984, 1989, 2000 Free Software Foundation, Inc.
	3
	4	This file is part of Bison, the GNU Compiler Compiler.
	5
	6	Bison is free software; you can redistribute it and/or modify
	7	it under the terms of the GNU General Public License as published by
	8	the Free Software Foundation; either version 2, or (at your option)
	9	any later version.
	10
	11	Bison is distributed in the hope that it will be useful,
	12	but WITHOUT ANY WARRANTY; without even the implied warranty of
	13	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	GNU General Public License for more details.
	15
	16	You should have received a copy of the GNU General Public License
	17	along with Bison; see the file COPYING. If not, write to
	18	the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	19	Boston, MA 02111-1307, USA. */
	20
	21
	22	/* Set up NULLABLE, a vector saying which nonterminals can expand into
	23	the null string. NULLABLE[I - NTOKENS] is nonzero if symbol I can
	24	do so. */
	25
	26	#include "system.h"
	27	#include "types.h"
	28	#include "gram.h"
	29	#include "nullable.h"
	30
	31	char *nullable = NULL;
	32
	33	void
	34	set_nullable (void)
	35	{
	36	short *r;
	37	short *s1;
	38	short *s2;
	39	int ruleno;
	40	int symbol;
	41	shorts *p;
	42
	43	short *squeue;
	44	short *rcount;
	45	shorts **rsets;
	46	shorts *relts;
	47	char any_tokens;
	48	short *r1;
	49
	50	#ifdef TRACE
	51	fprintf (stderr, _("Entering set_nullable"));
	52	#endif
	53
	54	nullable = XCALLOC (char, nvars) - ntokens;
	55
	56	squeue = XCALLOC (short, nvars);
	57	s1 = s2 = squeue;
	58
	59	rcount = XCALLOC (short, nrules + 1);
	60	rsets = XCALLOC (shorts *, nvars) - ntokens;
	61	/* This is said to be more elements than we actually use.
	62	Supposedly nitems - nrules is enough.
	63	But why take the risk? */
	64	relts = XCALLOC (shorts, nitems + nvars + 1);
	65	p = relts;
	66
	67	r = ritem;
	68	while (*r)
	69	{
	70	if (*r < 0)
	71	{
	72	symbol = rule_table[-(*r++)].lhs;
	73	if (symbol >= 0 && !nullable[symbol])
	74	{
	75	nullable[symbol] = 1;
	76	*s2++ = symbol;
	77	}
	78	}
	79	else
	80	{
	81	r1 = r;
	82	any_tokens = 0;
	83	for (symbol = r++; symbol > 0; symbol = r++)
	84	{
	85	if (ISTOKEN (symbol))
	86	any_tokens = 1;
	87	}
	88
	89	if (!any_tokens)
	90	{
	91	ruleno = -symbol;
	92	r = r1;
	93	for (symbol = r++; symbol > 0; symbol = r++)
	94	{
	95	rcount[ruleno]++;
	96	p->next = rsets[symbol];
	97	p->value = ruleno;
	98	rsets[symbol] = p;
	99	p++;
	100	}
	101	}
	102	}
	103	}
	104
	105	while (s1 < s2)
	106	{
	107	p = rsets[*s1++];
	108	while (p)
	109	{
	110	ruleno = p->value;
	111	p = p->next;
	112	if (--rcount[ruleno] == 0)
	113	{
	114	symbol = rule_table[ruleno].lhs;
	115	if (symbol >= 0 && !nullable[symbol])
	116	{
	117	nullable[symbol] = 1;
	118	*s2++ = symbol;
	119	}
	120	}
	121	}
	122	}
	123
	124	XFREE (squeue);
	125	XFREE (rcount);
	126	XFREE (rsets + ntokens);
	127	XFREE (relts);
	128	}
	129
	130
	131	void
	132	free_nullable (void)
	133	{
	134	XFREE (nullable + ntokens);
	135	}