first.c

its about compiler for LL1 and LR

/*@A (C) 1992 Allen I. Holub                                                */

#include <stdio.h>
#include <tools/debug.h>
#include <tools/set.h>
#include <tools/hash.h>
#include <tools/compiler.h>
#include <tools/l.h>
#include "parser.h"

/* FIRST.C	 Compute FIRST sets for all productions in a symbol table.
 *-------------------------------------------------------------------------
 */


void	first_closure	P(( SYMBOL *lhs ));			/* local */

void	first		P(( void ));				/* public */

int	first_rhs	P(( SET *dest, SYMBOL **rhs, int len ));

PRIVATE int Did_something;

/*----------------------------------------------------------------------*/

PUBLIC	void first( )
{
    /* Construct FIRST sets for all nonterminal symbols in the symbol table.  */

    D( printf("Finding FIRST sets\n"); )

    do
    {
	Did_something = 0;
	ptab( Symtab, (ptab_t) first_closure, NULL, 0 );

    } while( Did_something );
}

/*----------------------------------------------------------------------*/

PRIVATE	void first_closure( lhs )
SYMBOL	*lhs;				/* Current left-hand side	*/
{
    /* Called for every element in the FIRST sets. Adds elements to the first
     * sets. The following rules are used:
     *
     * 1) given lhs->...Y... where Y is a terminal symbol preceded by any number
     *    (including 0) of nullable nonterminal symbols or actions, add Y to
     *    FIRST(x).
     *
     * 2) given lhs->...y... where y is a nonterminal symbol preceded by any
     *    number (including 0) of nullable nonterminal symbols or actions, add
     *    FIRST(y) to FIRST(lhs).
     */

    PRODUCTION  *prod;  	/* Pointer to one production side	 */
    SYMBOL	**y;  	 	/* Pointer to one element of production  */
    static SET  *set = NULL;	/* Scratch-space set.			 */
    int	        i;

    if( !ISNONTERM(lhs) )	/* Ignore entries for terminal symbols	*/
	    return;

    if( !set )			/* Do this once. The set isn't free()d	*/
	set = newset();

    ASSIGN( set, lhs->first );

    for( prod = lhs->productions; prod ; prod = prod->next )
    {
	if( prod->non_acts <= 0 )		/* No non-action symbols    */
	{					/* add epsilon to first set */
	    ADD( set, EPSILON );
	    continue;
	}

	for( y = prod->rhs, i = prod->rhs_len; --i >= 0; y++ )
	{
	    if( ISACT( *y ) )		  	  /* pretend acts don't exist */
		continue;

	    if( ISTERM( *y ) )
		ADD( set, (*y)->val );

	    else if( *y )			        /* it's a nonterminal */
		UNION( set, (*y)->first );

	    if( !NULLABLE( *y ))	  /* it's not a nullable nonterminal  */
		break;
	}
    }

    if( !IS_EQUIVALENT(set, lhs->first) )
    {
	ASSIGN( lhs->first, set );
	Did_something = 1;
    }
}

/*----------------------------------------------------------------------*/
PUBLIC	int	first_rhs( dest, rhs, len )
SET		*dest;			/* Target set		*/
SYMBOL		**rhs;			/* A right-hand side	*/
int		len;			/* # of objects in rhs	*/
{
    /* Fill the destination set with FIRST(rhs) where rhs is the right-hand side
     * of a production represented as an array of pointers to symbol-table
     * elements. Return 1 if the entire right-hand side is nullable, otherwise
     * return 0.
     */

    if( len <= 0 )
    {
	ADD( dest, EPSILON );
	return 1;
    }

    for(; --len >= 0 ; ++rhs )
    {
	if( ISACT( rhs[0] ) )
	    continue;

	if( ISTERM( rhs[0] )  )
	    ADD( dest, rhs[0]->val );
	else
	    UNION( dest, rhs[0]->first );

	if( !NULLABLE( rhs[0] ) )
	    break;
    }

    return( len < 0 );
}