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- /* 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 1, 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 "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;
- relts = NEW2(nitems + nvars + 1, shorts);
- p = relts;
- r = ritem;
- while (*r)
- {
- if (*r < 0)
- {
- symbol = rlhs[-(*r++)];
- if (!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 (!nullable[symbol])
- {
- nullable[symbol] = 1;
- *s2++ = symbol;
- }
- }
- }
- }
- FREE(squeue);
- FREE(rcount);
- FREE(rsets + ntokens);
- FREE(relts);
- }
- void
- free_nullable()
- {
- FREE(nullable + ntokens);
- }
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