1 files changed, 136 insertions, 0 deletions
diff --git a/tools/bison++/nullable.cc b/tools/bison++/nullable.cc
new file mode 100644
index 000000000..b85dec610
--- /dev/null
+++ b/tools/bison++/nullable.cc
@@ -0,0 +1,136 @@
+/* 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);
+}