# include "y1.h"     
# include <stdlib.h> 

/*
 * 12-Apr-83 (RBD) Add symbolic exit status
 */
void cempty( )
{
  /* mark nonterminals which derive the empty string */
  /* also, look for nonterminals which don't derive any token strings */

  # define EMPTY    1
  # define WHOKNOWS 0
  # define OK       1

  register i,
         * p;

  /* first, use the array pempty to detect productions that can never be reduced */
  /* set pempty to WHONOWS */
  aryfil( pempty, nnonter + 1, WHOKNOWS );

  /* now, look at productions, marking nonterminals which derive something */

  more  : PLOOP( 0, i )
    {
      if ( pempty[ *prdptr[ i ] - NTBASE ] )
        continue ;
      for ( p = prdptr[ i ] + 1; *p >= 0; ++p )
        {
          if ( *p >= NTBASE && pempty[ *p - NTBASE ] == WHOKNOWS )
            break ;
        }
      if ( *p < 0 )
        {
          /* production can be derived */
          pempty[ *prdptr[ i ] - NTBASE ] = OK;
          goto more;
        }
    }

  /* now, look at the nonterminals, to see if they are all OK */

  NTLOOP( i )
    {
      /* the added production rises or falls as the start symbol ... */
      if ( i == 0 )
        continue ;
      if ( pempty[ i ] != OK )
        {
          fatfl = 0;
          error( "nonterminal %s never derives any token string",
                 nontrst[ i ].name );
        }
    }

  if ( nerrors )
    {
      summary( );
      exit( EX_ERR );
    }

    /* now, compute the pempty array, to see which nonterminals derive the empty string */

    /* set pempty to WHOKNOWS */

  aryfil( pempty, nnonter + 1, WHOKNOWS );
  /* loop as long as we keep finding empty nonterminals */

  again : PLOOP( 1, i )
    {
      if ( pempty[ *prdptr[ i ] - NTBASE ] == WHOKNOWS )
        {
          /* not known to be empty */
          for ( p = prdptr[ i ] + 1;
                *p >= NTBASE &&
                pempty[ *p - NTBASE ] == EMPTY;
                ++p )
            ;
          if ( *p < 0 )
            {
              /* we have a nontrivially empty nonterminal */
              pempty[ *prdptr[ i ] - NTBASE ] = EMPTY;
              goto again; /* got one ... try for another */
            }
        }
    }

}