derives.c

bison源代码.bison 是替代yacc的语法分析程序生成器. yacc是 Yet Another Compiler Compiler的缩写. bison又是什么呐 是一个生成可以分析文本文件结构

/* Match rules with nonterminals for bison,
   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_derives finds, for each variable (nonterminal), which rules can derive it.
   It sets up the value of derives so that
   derives[i - ntokens] points to a vector of rule numbers,
   terminated with -1.  */

#include <stdio.h>
#include "system.h"
#include "new.h"
#include "types.h"
#include "gram.h"


short **derives;

void
set_derives()
{
  register int i;
  register int lhs;
  register shorts *p;
  register short *q;
  register shorts **dset;
  register shorts *delts;

  dset = NEW2(nvars, shorts *) - ntokens;
  delts = NEW2(nrules + 1, shorts);

  p = delts;
  for (i = nrules; i > 0; i--)
    {
      lhs = rlhs[i];
      if (lhs >= 0)
	{
	  p->next = dset[lhs];
	  p->value = i;
	  dset[lhs] = p;
	  p++;
	}
    }

  derives = NEW2(nvars, short *) - ntokens;
  q = NEW2(nvars + nrules, short);

  for (i = ntokens; i < nsyms; i++)
    {
      derives[i] = q;
      p = dset[i];
      while (p)
	{
	  *q++ = p->value;
	  p = p->next;
	}
      *q++ = -1;
    }

#ifdef	DEBUG
  print_derives();
#endif

  FREE(dset + ntokens);
  FREE(delts);
}

void
free_derives()
{
  FREE(derives[ntokens]);
  FREE(derives + ntokens);
}



#ifdef	DEBUG

print_derives()
{
  register int i;
  register short *sp;

  extern char **tags;

  printf("\n\n\nDERIVES\n\n");

  for (i = ntokens; i < nsyms; i++)
    {
      printf("%s derives", tags[i]);
      for (sp = derives[i]; *sp > 0; sp++)
	{
	  printf("  %d", *sp);
	}
      putchar('\n');
    }

  putchar('\n');
}

#endif