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136 lines
3.3 KiB
C
136 lines
3.3 KiB
C
/* Part of the bison parser generator,
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Copyright 1984, 1989, 2000, 2001 Free Software Foundation, Inc.
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This file is part of Bison, the GNU Compiler Compiler.
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Bison is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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Bison is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Bison; see the file COPYING. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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/* Set up NULLABLE, a vector saying which nonterminals can expand into
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the null string. NULLABLE[I - NTOKENS] is nonzero if symbol I can
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do so. */
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#include "system.h"
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#include "getargs.h"
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#include "reader.h"
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#include "types.h"
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#include "gram.h"
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#include "reduce.h"
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#include "nullable.h"
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char *nullable = NULL;
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static void
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nullable_print (FILE *out)
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{
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int i;
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fputs ("NULLABLE\n", out);
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for (i = ntokens; i < nsyms; i++)
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fprintf (out, "\t%s: %s\n", tags[i], nullable[i] ? "yes" : "no");
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fputs ("\n\n", out);
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}
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void
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set_nullable (void)
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{
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short *r;
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short *s1;
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short *s2;
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shorts *p;
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short *squeue;
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short *rcount;
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shorts **rsets;
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shorts *relts;
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if (trace_flag)
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fprintf (stderr, "Entering set_nullable\n");
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nullable = XCALLOC (char, nvars) - ntokens;
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squeue = XCALLOC (short, nvars);
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s1 = s2 = squeue;
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rcount = XCALLOC (short, nrules + 1);
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/* RITEM contains all the rules, including useless productions.
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Hence we must allocate room for useless nonterminals too. */
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rsets = XCALLOC (shorts *, nvars + nuseless_nonterminals) - ntokens;
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/* This is said to be more elements than we actually use.
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Supposedly nitems - nrules is enough.
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But why take the risk? */
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relts = XCALLOC (shorts, nitems + nvars + nuseless_nonterminals + 1);
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p = relts;
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for (r = ritem; *r; ++r)
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{
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/* Walk RITEM to find (i), if there are any tokens in the
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RHS, and (ii), to find RULENO. */
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int ruleno;
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int any_tokens = 0;
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short *r1;
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for (r1 = r; *r1 > 0; ++r1)
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if (ISTOKEN (*r1))
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any_tokens = 1;
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ruleno = -*r1;
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/* Examine the RHS of the rule. */
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if (!any_tokens)
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for (/* Nothing. */; *r > 0; ++r)
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{
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rcount[ruleno]++;
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p->next = rsets[*r];
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p->value = ruleno;
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rsets[*r] = p;
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p++;
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}
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/* Examine its LHS. */
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if (rule_table[ruleno].useful && !nullable[rule_table[ruleno].lhs])
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{
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nullable[rule_table[ruleno].lhs] = 1;
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*s2++ = rule_table[ruleno].lhs;
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}
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}
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while (s1 < s2)
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for (p = rsets[*s1++]; p; p = p->next)
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{
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int ruleno = p->value;
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if (--rcount[ruleno] == 0)
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if (rule_table[ruleno].useful && !nullable[rule_table[ruleno].lhs])
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{
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nullable[rule_table[ruleno].lhs] = 1;
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*s2++ = rule_table[ruleno].lhs;
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}
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}
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XFREE (squeue);
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XFREE (rcount);
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XFREE (rsets + ntokens);
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XFREE (relts);
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if (trace_flag)
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nullable_print (stderr);
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}
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void
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free_nullable (void)
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{
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XFREE (nullable + ntokens);
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}
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