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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 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);
}
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