parse.c

操作系统源代码

/**
 * Copyright (c) 1985 Sun Microsystems, Inc.
 * Copyright (c) 1980 The Regents of the University of California.
 * Copyright (c) 1976 Board of Trustees of the University of Illinois.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley, the University of Illinois,
 * Urbana, and Sun Microsystems, Inc.  The name of either University
 * or Sun Microsystems may not be used to endorse or promote products
 * derived from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#define PUBLIC	extern
#include "./globs.h"
#include "./codes.h"
#include "proto.h"




void parse(tk)
   int             tk;			/* the code for the construct
					   scanned */
{
   int             i;

#ifdef debug
   printf("%2d - %s\n", tk, token);
#endif

   while (ps.p_stack[ps.tos] == ifhead && tk != elselit)
   {
      /* true if we have an if without an else */
      ps.p_stack[ps.tos] = stmt;	/* apply the if(..) stmt ::=
					   stmt reduction */
      reduce();				/* see if this allows any
					   reduction */
   }


   switch (tk)
   {					/* go on and figure out what to
					   do with the input */

   case decl:				/* scanned a declaration word */
      ps.search_brace = btype_2;
      /* indicate that following brace should be on same line */
      if (ps.p_stack[ps.tos] != decl)
      {					/* only put one declaration
					   onto stack */
	 break_comma = true;		/* while in declaration,
					   newline should be forced
					   after comma */
	 ps.p_stack[++ps.tos] = decl;
	 ps.il[ps.tos] = ps.i_l_follow;

	 if (ps.ljust_decl)
	 {				/* only do if we want left
					   justified declarations */
	    ps.ind_level = 0;
	    for (i = ps.tos - 1; i > 0; --i)
	       if (ps.p_stack[i] == decl)
		  ++ps.ind_level;	/* indentation is number of
					   declaration levels deep we
					   are */
	    ps.i_l_follow = ps.ind_level;
	 }
      }
      break;

   case ifstmt:			/* scanned if (...) */
      if (ps.p_stack[ps.tos] == elsehead && ps.else_if)	/* "else if ..." */
	 ps.i_l_follow = ps.il[ps.tos];
   case dolit:				/* 'do' */
   case forstmt:			/* for (...) */
      ps.p_stack[++ps.tos] = tk;
      ps.il[ps.tos] = ps.ind_level = ps.i_l_follow;
      ++ps.i_l_follow;			/* subsequent statements should
					   be indented 1 */
      ps.search_brace = btype_2;
      break;

   case lbrace:			/* scanned { */
      break_comma = false;		/* don't break comma in an
					   initial list */
      if (ps.p_stack[ps.tos] == stmt || ps.p_stack[ps.tos] == decl
	  || ps.p_stack[ps.tos] == stmtl)
	 ++ps.i_l_follow;		/* it is a random, isolated
					   stmt group or a declaration */
      else
      {
	 if (s_code == e_code)
	 {
	    /* only do this if there is nothing on the line */
	    --ps.ind_level;
	    /* it is a group as part of a while, for, etc. */
	    if (ps.p_stack[ps.tos] == swstmt && ps.case_indent >= 1)
	       --ps.ind_level;
	    /* for a switch, brace should be two levels out from the
	       code */
	 }
      }

      ps.p_stack[++ps.tos] = lbrace;
      ps.il[ps.tos] = ps.ind_level;
      ps.p_stack[++ps.tos] = stmt;
      /* allow null stmt between braces */
      ps.il[ps.tos] = ps.i_l_follow;
      break;

   case whilestmt:			/* scanned while (...) */
      if (ps.p_stack[ps.tos] == dohead)
      {
	 /* it is matched with do stmt */
	 ps.ind_level = ps.i_l_follow = ps.il[ps.tos];
	 ps.p_stack[++ps.tos] = whilestmt;
	 ps.il[ps.tos] = ps.ind_level = ps.i_l_follow;
      } else
      {					/* it is a while loop */
	 ps.p_stack[++ps.tos] = whilestmt;
	 ps.il[ps.tos] = ps.i_l_follow;
	 ++ps.i_l_follow;
	 ps.search_brace = btype_2;
      }

      break;

   case elselit:			/* scanned an else */

      if (ps.p_stack[ps.tos] != ifhead)
	 diag(1, "Unmatched 'else'");
      else
      {
	 ps.ind_level = ps.il[ps.tos];	/* indentation for else should
					   be same as for if */
	 ps.i_l_follow = ps.ind_level + 1;	/* everything following
						   should be in 1 level */
	 ps.p_stack[ps.tos] = elsehead;
	 /* remember if with else */
	 ps.search_brace = btype_2 | ps.else_if;
      }
      break;

   case rbrace:			/* scanned a } */
      /* stack should have <lbrace> <stmt> or <lbrace> <stmtl> */
      if (ps.p_stack[ps.tos - 1] == lbrace)
      {
	 ps.ind_level = ps.i_l_follow = ps.il[--ps.tos];
	 ps.p_stack[ps.tos] = stmt;
      } else
	 diag(1, "Stmt nesting error.");
      break;

   case swstmt:			/* had switch (...) */
      ps.p_stack[++ps.tos] = swstmt;
      ps.cstk[ps.tos] = case_ind;
      /* save current case indent level */
      ps.il[ps.tos] = ps.i_l_follow;
      case_ind = ps.i_l_follow + ps.case_indent;	/* cases should be one
							   level down from
							   switch */
      ps.i_l_follow += ps.case_indent + 1;	/* statements should be
						   two levels in */
      ps.search_brace = btype_2;
      break;

   case semicolon:			/* this indicates a simple stmt */
      break_comma = false;		/* turn off flag to break after
					   commas in a declaration */
      ps.p_stack[++ps.tos] = stmt;
      ps.il[ps.tos] = ps.ind_level;
      break;

   default:				/* this is an error */
      diag(1, "Unknown code to parser");
      return;


   }					/* end of switch */

   reduce();				/* see if any reduction can be
					   done */

#ifdef debug
   for (i = 1; i <= ps.tos; ++i)
      printf("(%d %d)", ps.p_stack[i], ps.il[i]);
   printf("\n");
#endif

   return;
}

/*
 * Copyright (C) 1976 by the Board of Trustees of the University of Illinois
 *
 * All rights reserved
 *
 *
 * NAME: reduce
 *
 * FUNCTION: Implements the reduce part of the parsing algorithm
 *
 * ALGORITHM: The following reductions are done.  Reductions are repeated until
 * no more are possible.
 *
 * Old TOS		New TOS <stmt> <stmt>	<stmtl> <stmtl> <stmt>	<stmtl> do
 * <stmt>	"dostmt" if <stmt>	"ifstmt" switch <stmt>	<stmt> decl
 * <stmt>	<stmt> "ifelse" <stmt>	<stmt> for <stmt>	<stmt> while
 * <stmt>	<stmt> "dostmt" while	<stmt>
 *
 * On each reduction, ps.i_l_follow (the indentation for the following line) is
 * set to the indentation level associated with the old TOS.
 *
 * PARAMETERS: None
 *
 * RETURNS: Nothing
 *
 * GLOBALS: ps.cstk ps.i_l_follow = ps.il ps.p_stack = ps.tos =
 *
 * CALLS: None
 *
 * CALLED BY: parse
 *
 * HISTORY: initial coding 	November 1976	D A Willcox of CAC
 *
 */
/*----------------------------------------------*\
|   REDUCTION PHASE				    |
\*----------------------------------------------*/
void reduce()
{

   register int    i;

   for (;;)
   {					/* keep looping until there is
					   nothing left to reduce */

      switch (ps.p_stack[ps.tos])
      {

      case stmt:
	 switch (ps.p_stack[ps.tos - 1])
	 {

	 case stmt:
	 case stmtl:
	    /* stmtl stmt or stmt stmt */
	    ps.p_stack[--ps.tos] = stmtl;
	    break;

	 case dolit:			/* <do> <stmt> */
	    ps.p_stack[--ps.tos] = dohead;
	    ps.i_l_follow = ps.il[ps.tos];
	    break;

	 case ifstmt:
	    /* <if> <stmt> */
	    ps.p_stack[--ps.tos] = ifhead;
	    for (i = ps.tos - 1;
		 (
		  ps.p_stack[i] != stmt
		  &&
		  ps.p_stack[i] != stmtl
		  &&
		  ps.p_stack[i] != lbrace
		  );
		 --i);
	    ps.i_l_follow = ps.il[i];
	    /* for the time being, we will assume that there is no else
	       on this if, and set the indentation level accordingly.
	       If an else is scanned, it will be fixed up later */
	    break;

	 case swstmt:
	    /* <switch> <stmt> */
	    case_ind = ps.cstk[ps.tos - 1];

	 case decl:			/* finish of a declaration */
	 case elsehead:
	    /* <<if> <stmt> else> <stmt> */
	 case forstmt:
	    /* <for> <stmt> */
	 case whilestmt:
	    /* <while> <stmt> */
	    ps.p_stack[--ps.tos] = stmt;
	    ps.i_l_follow = ps.il[ps.tos];
	    break;

	 default:			/* <anything else> <stmt> */
	    return;

	 }				/* end of section for <stmt> on
					   top of stack */
	 break;

      case whilestmt:			/* while (...) on top */
	 if (ps.p_stack[ps.tos - 1] == dohead)
	 {
	    /* it is termination of a do while */
	    ps.p_stack[--ps.tos] = stmt;
	    break;
	 } else
	    return;

      default:				/* anything else on top */
	 return;

      }
   }
}