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140 lines
2.8 KiB
C
140 lines
2.8 KiB
C
/* Part of the bison parser generator,
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Copyright (C) 1984, 1989 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 the null string.
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nullable[i - ntokens] is nonzero if symbol i can do so. */
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#include <stdio.h>
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#include "system.h"
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#include "types.h"
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#include "gram.h"
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#include "alloc.h"
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char *nullable;
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void free_nullable PARAMS((void));
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void set_nullable PARAMS((void));
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void
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set_nullable (void)
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{
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register short *r;
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register short *s1;
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register short *s2;
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register int ruleno;
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register int symbol;
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register 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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char any_tokens;
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short *r1;
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#ifdef TRACE
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fprintf(stderr, _("Entering set_nullable"));
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#endif
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nullable = NEW2(nvars, char) - ntokens;
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squeue = NEW2(nvars, short);
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s1 = s2 = squeue;
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rcount = NEW2(nrules + 1, short);
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rsets = NEW2(nvars, shorts *) - 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 = NEW2(nitems + nvars + 1, shorts);
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p = relts;
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r = ritem;
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while (*r)
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{
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if (*r < 0)
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{
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symbol = rlhs[-(*r++)];
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if (symbol >= 0 && !nullable[symbol])
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{
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nullable[symbol] = 1;
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*s2++ = symbol;
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}
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}
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else
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{
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r1 = r;
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any_tokens = 0;
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for (symbol = *r++; symbol > 0; symbol = *r++)
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{
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if (ISTOKEN(symbol))
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any_tokens = 1;
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}
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if (!any_tokens)
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{
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ruleno = -symbol;
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r = r1;
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for (symbol = *r++; symbol > 0; symbol = *r++)
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{
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rcount[ruleno]++;
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p->next = rsets[symbol];
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p->value = ruleno;
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rsets[symbol] = p;
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p++;
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}
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}
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}
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}
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while (s1 < s2)
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{
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p = rsets[*s1++];
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while (p)
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{
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ruleno = p->value;
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p = p->next;
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if (--rcount[ruleno] == 0)
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{
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symbol = rlhs[ruleno];
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if (symbol >= 0 && !nullable[symbol])
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{
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nullable[symbol] = 1;
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*s2++ = symbol;
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}
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}
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}
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}
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FREE(squeue);
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FREE(rcount);
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FREE(rsets + ntokens);
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FREE(relts);
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}
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void
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free_nullable (void)
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{
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FREE(nullable + ntokens);
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}
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