src/nullable.c

/* Part of the bison parser generator,
   Copyright (C) 1984, 1989 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, 675 Mass Ave, Cambridge, MA 02139, 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 <stdio.h>
#include "system.h"
#include "types.h"
#include "gram.h"
#include "new.h"


char *nullable;


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

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

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

  nullable = NEW2(nvars, char) - ntokens;

  squeue = NEW2(nvars, short);
  s1 = s2 = squeue;

  rcount = NEW2(nrules + 1, short);
  rsets = NEW2(nvars, shorts *) - ntokens;
  /* This is said to be more elements than we actually use.
     Supposedly nitems - nrules is enough.
     But why take the risk?  */
  relts = NEW2(nitems + nvars + 1, shorts);
  p = relts;

  r = ritem;
  while (*r)
    {
      if (*r < 0)
	{
	  symbol = rlhs[-(*r++)];
	  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 = rlhs[ruleno];
	      if (symbol >= 0 && !nullable[symbol])
		{
		  nullable[symbol] = 1;
		  *s2++ = symbol;
		}
	    }
	}
    }

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


void
free_nullable()
{
  FREE(nullable + ntokens);
}
Commit	Line	Data
	1	/* Part of the bison parser generator,
	2	Copyright (C) 1984, 1989 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, 675 Mass Ave, Cambridge, MA 02139, USA. */
	19
	20
	21	/* set up nullable, a vector saying which nonterminals can expand into the null string.
	22	nullable[i - ntokens] is nonzero if symbol i can do so. */
	23
	24	#include <stdio.h>
	25	#include "system.h"
	26	#include "types.h"
	27	#include "gram.h"
	28	#include "new.h"
	29
	30
	31	char *nullable;
	32
	33
	34	void
	35	set_nullable()
	36	{
	37	register short *r;
	38	register short *s1;
	39	register short *s2;
	40	register int ruleno;
	41	register int symbol;
	42	register shorts *p;
	43
	44	short *squeue;
	45	short *rcount;
	46	shorts **rsets;
	47	shorts *relts;
	48	char any_tokens;
	49	short *r1;
	50
	51	#ifdef TRACE
	52	fprintf(stderr, "Entering set_nullable");
	53	#endif
	54
	55	nullable = NEW2(nvars, char) - ntokens;
	56
	57	squeue = NEW2(nvars, short);
	58	s1 = s2 = squeue;
	59
	60	rcount = NEW2(nrules + 1, short);
	61	rsets = NEW2(nvars, shorts *) - ntokens;
	62	/* This is said to be more elements than we actually use.
	63	Supposedly nitems - nrules is enough.
	64	But why take the risk? */
	65	relts = NEW2(nitems + nvars + 1, shorts);
	66	p = relts;
	67
	68	r = ritem;
	69	while (*r)
	70	{
	71	if (*r < 0)
	72	{
	73	symbol = rlhs[-(*r++)];
	74	if (symbol >= 0 && !nullable[symbol])
	75	{
	76	nullable[symbol] = 1;
	77	*s2++ = symbol;
	78	}
	79	}
	80	else
	81	{
	82	r1 = r;
	83	any_tokens = 0;
	84	for (symbol = r++; symbol > 0; symbol = r++)
	85	{
	86	if (ISTOKEN(symbol))
	87	any_tokens = 1;
	88	}
	89
	90	if (!any_tokens)
	91	{
	92	ruleno = -symbol;
	93	r = r1;
	94	for (symbol = r++; symbol > 0; symbol = r++)
	95	{
	96	rcount[ruleno]++;
	97	p->next = rsets[symbol];
	98	p->value = ruleno;
	99	rsets[symbol] = p;
	100	p++;
	101	}
	102	}
	103	}
	104	}
	105
	106	while (s1 < s2)
	107	{
	108	p = rsets[*s1++];
	109	while (p)
	110	{
	111	ruleno = p->value;
	112	p = p->next;
	113	if (--rcount[ruleno] == 0)
	114	{
	115	symbol = rlhs[ruleno];
	116	if (symbol >= 0 && !nullable[symbol])
	117	{
	118	nullable[symbol] = 1;
	119	*s2++ = symbol;
	120	}
	121	}
	122	}
	123	}
	124
	125	FREE(squeue);
	126	FREE(rcount);
	127	FREE(rsets + ntokens);
	128	FREE(relts);
	129	}
	130
	131
	132	void
	133	free_nullable()
	134	{
	135	FREE(nullable + ntokens);
	136	}