bwb_int.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

/***************************************************************f

        bwb_int.c       Line Interpretation Routines
                        for Bywater BASIC Interpreter

                        Copyright (c) 1993, Ted A. Campbell
                        Bywater Software

                        email: [e-mail]

        Copyright and Permissions Information:

        All U.S. and international rights are claimed by the author,
        Ted A. Campbell.

	This software is released under the terms of the GNU General
	Public License (GPL), which is distributed with this software
	in the file "COPYING".  The GPL specifies the terms under
	which users may copy and use the software in this distribution.

	A separate license is available for commercial distribution,
	for information on which you should contact the author.

***************************************************************/

/*---------------------------------------------------------------*/
/* NOTE: Modifications marked "JBV" were made by Jon B. Volkoff, */
/* 11/1995 ([e-mail]).                                  */
/*                                                               */
/* Those additionally marked with "DD" were at the suggestion of */
/* Dale DePriest ([e-mail]).                            */
/*---------------------------------------------------------------*/

#include <stdio.h>
#include <ctype.h>

#include "bwbasic.h"
#include "bwb_mes.h"

/***************************************************************

        FUNCTION:       adv_element()

        DESCRIPTION:    This function reads characters in <buffer>
                        beginning at <pos> and advances past a
                        line element, incrementing <pos> appropri-
                        ately and returning the line element in
                        <element>.

***************************************************************/

#if ANSI_C
int
adv_element( char *buffer, int *pos, char *element )
#else
int
adv_element( buffer, pos, element )
   char *buffer;
   int *pos;
   char *element;
#endif
   {
   int loop;                                    /* control loop */
   int e_pos;                                   /* position in element buffer */
   int str_const;                               /* boolean: building a string constant */

   /* advance beyond any initial whitespace */

   adv_ws( buffer, pos );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in adv_element(): receieved <%s>.", &( buffer[ *pos ] ));
   bwb_debug( bwb_ebuf );
#endif

   /* now loop while building an element and looking for an
      element terminator */

   loop = TRUE;
   e_pos = 0;
   element[ e_pos ] = '\0';
   str_const = FALSE;

   while ( loop == TRUE )
      {
      switch( buffer[ *pos ] )
         {
         case ',':                      /* element terminators */
         case ';':
#if MULTISEG_LINES
         case ':':
#endif
         case '=':
         case ' ':
         case '\t':
         /* case '\0': */ /* Removed by JBV (found by DD) */
         case '\n':
         case '\r':
            if ( str_const == TRUE )
               {
               element[ e_pos ] = buffer[ *pos ];
               ++e_pos;
               ++( *pos );
               element[ e_pos ] = '\0';
               }
            else
               {
               return TRUE;
               }
            break;

         case '\0':                     /* Added by JBV (found by DD) */
            if ( str_const == TRUE )    /* termination of string constant */
               {
               element[ e_pos ] = '\"';
               element[ ++e_pos ] = '\0';
               }
            return TRUE;
            break;

         case '\"':                     /* string constant */
            element[ e_pos ] = buffer[ *pos ];
            ++e_pos;
            ++( *pos );
            element[ e_pos ] = '\0';
            if ( str_const == TRUE )    /* termination of string constant */
               {
               return TRUE;
               }
            else                        /* beginning of string constant */
               {
               str_const = TRUE;
               }
            break;

         default:
            element[ e_pos ] = buffer[ *pos ];
            ++e_pos;
            ++( *pos );
            element[ e_pos ] = '\0';
            break;
         }
      }

   /* This should not happen */

   return FALSE;

   }

/***************************************************************

        FUNCTION:       adv_ws()

        DESCRIPTION:    This function reads characters in <buffer>
                        beginning at <pos> and advances past any
                        whitespace, incrementing <pos> appropri-
                        ately.

***************************************************************/

#if ANSI_C
int
adv_ws( char *buffer, int *pos )
#else
int
adv_ws( buffer, pos )
   char *buffer;
   int *pos;
#endif
   {
   int loop;

   loop = TRUE;
   while ( loop == TRUE )
      {
      switch( buffer[ *pos ] )
         {
         case ' ':
         case '\t':
            ++( *pos );
            break;
         default:
            return TRUE;
         }
      }

   /* This should not happen */

   return FALSE;

   }

/***************************************************************

	FUNCTION:       adv_eos()

	DESCRIPTION:    This function reads characters in <buffer>
			beginning at <pos> and advances to the
			end of a segment delimited by ':',
			incrementing <pos> appropriately.

***************************************************************/

#if MULTISEG_LINES
#if ANSI_C
int
adv_eos( char *buffer, int *pos )
#else
int
adv_eos( buffer, pos )
   char *buffer;
   int *pos;
#endif
   {
   int loop;

   loop = TRUE;
   while ( loop == TRUE )
      {

      if ( is_eol( buffer, pos ) == TRUE )
	 {
	 return FALSE;
	 }

      switch( buffer[ *pos ] )
	 {
	 case ':':              /* end of segment marker */
	    ++( *pos );
	    return TRUE;

	 case '\"':             /* begin quoted string */

	    ++( *pos );

	    while ( buffer[ *pos ] != '\"' )
	       {
	       if ( is_eol( buffer, pos ) == TRUE )
		  {
		  return FALSE;
		  }
	       else
		  {
		  ++( *pos );
		  }
	       }

	    break;

	 default:
	    ++( *pos );
	 }
      }

   /* This should not happen */

   return FALSE;

   }

#endif                          /* MULTISEG_LINES */

/***************************************************************

        FUNCTION:       bwb_strtoupper()

        DESCRIPTION:    This function converts the string in
                        <buffer> to upper-case characters.

***************************************************************/

#if ANSI_C
int
bwb_strtoupper( char *buffer )
#else
int
bwb_strtoupper( buffer )
   char *buffer;
#endif
   {
   char *p;

   p = buffer;
   while ( *p != '\0' )
      {
      if ( islower( *p ) != FALSE )
         {
         *p = (char) toupper( *p );
         }
      ++p;
      }

   return TRUE;

   }

/***************************************************************

        FUNCTION:       line_start()

        DESCRIPTION:    This function reads a line buffer in
                        <buffer> beginning at the position
                        <pos> and attempts to determine (a)
                        the position of the line number in the
                        buffer (returned in <lnpos>), (b) the
                        line number at this position (returned
                        in <lnum>), (c) the position of the
                        BASIC command in the buffer (returned
                        in <cmdpos>), (d) the position of this
                        BASIC command in the command table
                        (returned in <cmdnum>), and (e) the
                        position of the beginning of the rest
                        of the line (returned in <startpos>).
                        Although <startpos> must be returned
                        as a positive integer, the other
                        searches may fail, in which case FALSE
                        will be returned in their positions.
                        <pos> is not incremented.

***************************************************************/

#if ANSI_C
int
line_start( char *buffer, int *pos, int *lnpos, int *lnum, int *cmdpos,
   int *cmdnum, int *startpos )
#else
int
line_start( buffer, pos, lnpos, lnum, cmdpos, cmdnum, startpos )
   char *buffer;
   int *pos;
   int *lnpos;
   int *lnum;
   int *cmdpos;
   int *cmdnum;
   int *startpos;
#endif
   {
   static int position;
   static char *tbuf;
   static int init = FALSE;

   /* get memory for temporary buffer if necessary */

   if ( init == FALSE )
      {
      init = TRUE;

      /* Revised to CALLOC pass-thru call by JBV */
      if ( ( tbuf = CALLOC( MAXSTRINGSIZE + 1, sizeof( char ), "line_start")) == NULL )
         {
#if PROG_ERRORS
	 bwb_error( "in line_start(): failed to get memory for tbuf" );
#else
	 bwb_error( err_getmem );
#endif
	 }
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in line_start(): pos <%d> buffer <%s>", *pos,
      buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* set initial values */

   *startpos = position = *pos;
   *cmdpos = *lnpos = *pos;
   *cmdnum = *lnum = -1;

   /* check for null line */

   adv_ws( buffer, &position );
   if ( buffer[ position ] == '\0' )
      {
#if INTENSIVE_DEBUG
      bwb_debug( "in line_start(): found NULL line" );
#endif
      *cmdnum = getcmdnum( CMD_REM );
      return TRUE;
      }

   /* advance beyond the first element */

   *lnpos = position;
   scan_element( buffer, &position, tbuf );
   adv_ws( buffer, &position );

   /* test for a line number in the first element */

   if ( is_numconst( tbuf ) == TRUE )               /* a line number */
      {

      *lnum = atoi( tbuf );
      *startpos = position;                             /* temp */
      *cmdpos = position;

      scan_element( buffer, &position, tbuf );       /* advance past next element */

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in line_start(): new element is <%s>", tbuf );
      bwb_debug( bwb_ebuf );
#endif

#if STRUCT_CMDS
      if ( is_label( tbuf ) == TRUE )
         {
         *cmdnum = getcmdnum( CMD_LABEL );
         adv_ws( buffer, &position );
         *startpos = position;
         }

      else if ( is_cmd( tbuf, cmdnum ) == TRUE )
#else
      if ( is_cmd( tbuf, cmdnum ) == TRUE )
#endif
         {
         adv_ws( buffer, &position );
         *startpos = position;
         }

      else if ( is_let( &( buffer[ *cmdpos ] ), cmdnum ) == TRUE )
         {
         *cmdpos = -1;
         }

      else
         {
         *cmdpos = *cmdnum = -1;
         }
      }

   /* not a line number */

   else
      {
      *lnum = -1;
      *lnpos = -1;

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in line_start(): no line number, element <%s>.",
         tbuf );
      bwb_debug( bwb_ebuf );
#endif

#if STRUCT_CMDS
      if ( is_label( tbuf ) == TRUE )
         {

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in line_start(): label detected <%s>.",
	    tbuf );
	 bwb_debug( bwb_ebuf );
#endif

         *cmdnum = getcmdnum( CMD_LABEL );
         adv_ws( buffer, &position );
         *startpos = position;
         }

      else if ( is_cmd( tbuf, cmdnum ) == TRUE )
#else
      if ( is_cmd( tbuf, cmdnum ) == TRUE )
#endif
         {
         adv_ws( buffer, &position );
         *startpos = position;
         }

      else if ( is_let( &( buffer[ position ] ), cmdnum ) == TRUE )
         {
         adv_ws( buffer, &position );
         *cmdpos = -1;
         }

      else
         {
         *cmdpos = *cmdnum = -1;
         }
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in line_start(): lnpos <%d> lnum <%d>",
      *lnpos, *lnum );
   bwb_debug( bwb_ebuf );
   sprintf( bwb_ebuf, "in line_start(): cmdpos <%d> cmdnum <%d> startpos <%d>",
      *cmdpos, *cmdnum, *startpos );
   bwb_debug( bwb_ebuf );
#endif

   /* return */