NT4/private/sdktools/vctools/nmake/parser.c

/***  PARSER.C -- parsing routines *********************************************
*
*	Copyright (c) 1988-1989, Microsoft Corporation.  All rights reserved.
*
* Purpose:
*  This module contains the NMAKE grammar parser. It parses input and uses the
*  getToken() routine to get the next token.
*
* Revision History:
*   05-Apr-1989 SB made all funcs NEAR; Reqd to make all function calls NEAR
*   17-Aug-1988 RB Clean up.
*
*******************************************************************************/

#include "nmake.h"
#include "nmmsg.h"
#include "proto.h"
#include "globals.h"
#include "grammar.h"
#pragma hdrstop
#include "table.h"

/*  ----------------------------------------------------------------------------
 *  macros that deal w/ the productions stack and the actions function table
 */

#define topStack()	(stack[top])
#define popStack()	(stack[top--])
#define pushStack(A)	(stack[++top] = A)
#define doAction(A)	(*(actions[A & LOW_NIBBLE]))()



/*  ----------------------------------------------------------------------------
 *  parse()	    table-driven parser for makefile grammar
 *
 *  arguments:	    init	global boolean value -- TRUE if tools.ini is the
 *				    file being parsed
 *
 *  actions:	    initializes the stack (by pushing the empty-stack symbol
 *			and the start symbol)
 *		    keeps track of current line (because the lexer may have
 *			read '\n' as a delimiter, and will thus be one line
 *			ahead of the parser)
 *		    while the stack is not empty
 *			if the top symbol on the stack is an action
 *			    do the action, popping the stack
 *			if the symbol on top of the stack now is a token
 *			    if it's not the token we're expecting
 *				syntax error, halt
 *			    else
 *				pop token off the stack
 *				if the top symbol on the stack is an action
 *				    do the action, popping the stack
 *				reset curent line to lexer's current line
 *				get another token (use the lookahead token
 *				    if it exists, and if it had caused the
 *				    lexer's line count to be incremented,
 *				    decrement our local count because we're
 *				    still parsing the preceding line)
 *			else the symbol on top of the stack is a production
 *			    find next production to do in production table
 *				(based on current input token and current
 *				production on stack)
 *			    if the table entry is an error condition
 *				print appropriate error message, halt
 *			    pop current production off stack
 *			    if the "next production" can be one of two
 *				things, decide which one to use by peeking
 *				at the next input token and looking in the
 *				"useAlternate" decision table (using the last
 *				production and next input token as indexes)
 *				if the appropriate table entry is YES,
 *				    use the next larger production from the one
 *				    we found in the production table
 *			    push each symbol in the production on the stack
 *		    loop
 *
 *  modifies:	    stack	production stack, static to this module
 *		    top 	index of current symbol at top of stack
 *
 *  Use extreme care in modifying this code or any of the tables associated
 *  with it.  The methods used to build the tables are described in detail
 *  in grammar.h and table.h.  This parser is based on the predictive parser
 *  described on pages 186-191 of Aho & Ullman "Principles of Compiler Design."
 *  I have modified it to use an extra symbol of lookahead to deal w/ an
 *  ambiguous grammar and have added code to perform appropriate actions as
 *  it parses the productions.
 */

void NEAR
parse()
{
    UCHAR stackTop,
	  token,
	  nextToken = 0;
    register unsigned n,
		      i;

    firstToken = TRUE;					    /* global var     */
    pushStack(ACCEPT);					    /* init stack     */
    pushStack(START);
    currentLine = line;
    token = getToken(MAXBUF,START);		    /* get first token*/
    while ((stackTop = topStack()) != ACCEPT) {
	if (ON(stackTop,ACTION_MASK))
	    doAction(popStack());
	else if (ON(stackTop,TOKEN_MASK)) {
	    if (stackTop != token)
		makeError(currentLine,SYNTAX+FATAL_ERR,buf);
	    else {
		popStack();
#ifdef DEBUG_ALL
	printf ("DEBUG: parse 1: %d\n", line);
#endif
		if (ON(topStack(),ACTION_MASK))
		    doAction(popStack());
#ifdef DEBUG_ALL
	printf ("DEBUG: parse 2: %d\n", line);
#endif
		currentLine = line;
		if (nextToken) {			    /* if we already  */
		    if (*buf == '\n') --currentLine;	    /*	have a token, */
		    token = nextToken;			    /*	use it . . .  */
		    nextToken = 0;
		}
		else token = getToken(MAXBUF,topStack());
	    }
	}
	else {
	    n = table[stackTop][token & LOW_NIBBLE];
#ifdef DEBUG_ALL
	printf ("DEBUG: parse 3: %x %d %x %x\n", n, stackTop, token & LOW_NIBBLE, token);
#endif
	    if (ON(n,ERROR_MASK)) {
#ifdef DEBUG_ALL
	printf ("DEBUG: parse 4: %d %s\n", line, buf);
#endif
		makeError(currentLine,n+FATAL_ERR,buf);
	    }
	    popStack();
	    if (ON(n,AMBIG_MASK)) {			    /* 2 possible prod*/
		n &= LOW_NIBBLE;			    /* only use 4 bits*/
		if (!nextToken) 			    /* peek to decide */
		    nextToken = getToken(MAXBUF,stackTop);
		n += (useAlternate[stackTop][nextToken & LOW_NIBBLE]);
	    }
	    for (i = productions[n][0]; i; --i) 	    /* put production */
		pushStack(productions[n][i]);		    /*	on stack      */
	}						    /* 1st elt in prod*/
    }							    /*	is its length */
    popStack();    /* pop the ACCEPT off the stack */
}