parser.c

Version 6 Unix 核心源代码 Version 6 Unix 核心源代码

# define _maxdepth 150

/*	parser for yacc output	*/
extern int yyval; /* defined in the table file */
extern int yylval; /* defined in the table file */
extern int *yypv; /* defined in the table file */


int yydebug 0; /* 1 for debugging */
int yyv[_maxdepth]; /* where the values are stored */
int yystate 0; /* current parser state */
int yychar -1; /* current input token number */
int yynerrs 0;  /* number of errors */
int yyerrflag 0;  /* error recovery flag */


yyparse() {

   extern int yygo[], yypgo[], yyr1[], yyr2[], yyact[], yypact[];
   auto int *ps, s[_maxdepth];
   auto int ac, n, *p;

   yystate = 0;
   yychar = -1;
   yynerrs = 0;
   yyerrflag = 0;
   ps= &s[0]-1;
   yypv= &yyv[0]-1;

 stack:    /* put a state and value onto the stack */

   if( yydebug  ) printf( "state %d, value %d, char %d\n",yystate,yyval,yychar );
   *++ps = yystate;
   *++yypv = yyval;

 newstate:      /* set ap to point to the parsing actions for the new state */

   p = &yyact[ yypact[yystate+1] ]; 

 actn:       /* get the next action, and perform it */

   n = ( ac = *p++ ) & 07777;  /* n is the "address" of the action */

   switch( ac>>12 ) { /* switch on operation */

   case 1:		/* skip on test */
      if( yydebug && (yychar<0) ){
        yychar = yylex();
        printf( "character %d read\n", yychar );
        }
      if( n != ( (yychar<0) ? ( yychar=yylex() ) : yychar ) ) ++p;
      goto actn;  /* get next action */

   case 2:		/* shift */

      yystate=n;
      yyval=yylval;
      yychar= -1;
      if( yyerrflag ) --yyerrflag;
      goto stack;   /* stack new state */

   case 3:		/* reduce */

      if( yydebug ) printf("reduce %d\n",n);
      ps =- yyr2[n];
      yypv =- yyr2[n];
      yyval=yypv[1];
      yyactr(n);
         /* consult goto table to find next state */
      for( p= &yygo[yypgo[yyr1[n]]]; *p != *ps && *p >= 0 ; p =+ 2 ) ;
      yystate = p[1];
      goto stack;  /* stack new state and value */

   case 4:		/* accept */
      return(0);

   case 0:   /* error ... attempt to resume parsing */

      switch( yyerrflag ){

      case 0:   /* brand new error */

         ++yynerrs;
         yyerror( "syntax error" );

      case 1:
      case 2: /* incompletely recovered error ... try again */

         yyerrflag = 3;

         /* find a state where "error" is a legal shift action */

         while ( ps >= s ) {
            for( p= &yyact[ yypact[*ps+1] ] ; (*p>>12) == 1 ; p =+ 2 ) /* search ps actions */
                if( *p == 4352 ) goto found;

            /* the current ps has no shift onn "error", pop stack */

            if( yydebug ) printf( "error recovery pops state %d, uncovers %d\n", *ps, ps[-1] );
            --ps;
            --yypv;
            }

         /* there is no state on the stack with an error shift ... abort */

    abort:
         return(1);

      found:   /* we have a state with a shift on "error", resume parsing */

         yystate = p[1] & 07777;
         goto stack;

      case 3:  /* no shift yet; clobber input char */

         if( yydebug ) printf( "error recovery discards char %d\n", yychar );

         if( yychar == 0 ) goto abort; /* don't discard EOF, quit */
         yychar = -1;
         goto newstate;   /* try again in the same state */

         }

      }
   }