src/nullable.c

/* Part of the bison parser generator,
   Copyright 1984, 1989, 2000, 2001 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 "getargs.h"
#include "reader.h"
#include "types.h"
#include "gram.h"
#include "nullable.h"

char *nullable = NULL;

static void
nullable_print (FILE *out)
{
  int i;
  fputs ("NULLABLE\n", out);
  for (i = ntokens; i < nsyms; i++)
    fprintf (out, "\t%s: %s\n", tags[i], nullable[i] ? "yes" : "no");
  fputs ("\n\n", out);
}

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

  short *squeue;
  short *rcount;
  shorts **rsets;
  shorts *relts;

  if (trace_flag)
    fprintf (stderr, "Entering set_nullable\n");

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

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

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

  if (trace_flag)
    nullable_print (stderr);
}


void
free_nullable (void)
{
  XFREE (nullable + ntokens);
}
Commit	Line	Data
	1	/* Part of the bison parser generator,
	2	Copyright 1984, 1989, 2000, 2001 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 "getargs.h"
	28	#include "reader.h"
	29	#include "types.h"
	30	#include "gram.h"
	31	#include "nullable.h"
	32
	33	char *nullable = NULL;
	34
	35	static void
	36	nullable_print (FILE *out)
	37	{
	38	int i;
	39	fputs ("NULLABLE\n", out);
	40	for (i = ntokens; i < nsyms; i++)
	41	fprintf (out, "\t%s: %s\n", tags[i], nullable[i] ? "yes" : "no");
	42	fputs ("\n\n", out);
	43	}
	44
	45	void
	46	set_nullable (void)
	47	{
	48	short *r;
	49	short *s1;
	50	short *s2;
	51	shorts *p;
	52
	53	short *squeue;
	54	short *rcount;
	55	shorts **rsets;
	56	shorts *relts;
	57
	58	if (trace_flag)
	59	fprintf (stderr, "Entering set_nullable\n");
	60
	61	nullable = XCALLOC (char, nvars) - ntokens;
	62
	63	squeue = XCALLOC (short, nvars);
	64	s1 = s2 = squeue;
	65
	66	rcount = XCALLOC (short, nrules + 1);
	67	rsets = XCALLOC (shorts *, nvars) - ntokens;
	68	/* This is said to be more elements than we actually use.
	69	Supposedly nitems - nrules is enough.
	70	But why take the risk? */
	71	relts = XCALLOC (shorts, nitems + nvars + 1);
	72	p = relts;
	73
	74	r = ritem;
	75	while (*r)
	76	{
	77	if (*r < 0)
	78	{
	79	int symbol = rule_table[-(*r++)].lhs;
	80	if (symbol >= 0 && !nullable[symbol])
	81	{
	82	nullable[symbol] = 1;
	83	*s2++ = symbol;
	84	}
	85	}
	86	else
	87	{
	88	int any_tokens = 0;
	89	int symbol;
	90	short *r1 = r;
	91	for (symbol = r++; symbol > 0; symbol = r++)
	92	if (ISTOKEN (symbol))
	93	any_tokens = 1;
	94
	95	if (!any_tokens)
	96	{
	97	int ruleno = -symbol;
	98	r = r1;
	99	for (symbol = r++; symbol > 0; symbol = r++)
	100	{
	101	rcount[ruleno]++;
	102	p->next = rsets[symbol];
	103	p->value = ruleno;
	104	rsets[symbol] = p;
	105	p++;
	106	}
	107	}
	108	}
	109	}
	110
	111	while (s1 < s2)
	112	{
	113	p = rsets[*s1++];
	114	while (p)
	115	{
	116	int ruleno = p->value;
	117	p = p->next;
	118	if (--rcount[ruleno] == 0)
	119	{
	120	int symbol = rule_table[ruleno].lhs;
	121	if (symbol >= 0 && !nullable[symbol])
	122	{
	123	nullable[symbol] = 1;
	124	*s2++ = symbol;
	125	}
	126	}
	127	}
	128	}
	129
	130	XFREE (squeue);
	131	XFREE (rcount);
	132	XFREE (rsets + ntokens);
	133	XFREE (relts);
	134
	135	if (trace_flag)
	136	nullable_print (stderr);
	137	}
	138
	139
	140	void
	141	free_nullable (void)
	142	{
	143	XFREE (nullable + ntokens);
	144	}