bwb_cnd.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

   var_setnval( v, exp_getnval( exp ) );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): initial value <%d> pos <%d>",
      exp_getnval( exp ), l->position );
   bwb_debug( bwb_ebuf );
#endif

   /* copy target value to small buffer and evaluate it */

   tbuf[ 0 ] = '\0';
   p = 0;
   l->position = to + 2;
   if ( step < 1 )
      {
      e = strlen( l->buffer );
      }
   else
      {
      e = step - 1;
      }

   loop = TRUE;
   n = l->position;
   while( loop == TRUE )
      {
      tbuf[ p ] = l->buffer[ n ];
      ++p;
      ++l->position;
      tbuf[ p ] = '\0';

      if ( n >= e )
          {
          loop = FALSE;
          }

      ++n;

      if ( l->buffer[ n ] == ':' )
         {
         loop = FALSE;
         }

      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): target value string <%s>",
      tbuf );
   bwb_debug( bwb_ebuf );
#endif

   p = 0;
   exp = bwb_exp( tbuf, FALSE, &p );
   for_target = (int) exp_getnval( exp );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): target value <%d> pos <%d>",
      exp_getnval( exp ), l->position );
   bwb_debug( bwb_ebuf );
#endif

   /* If there is a STEP statement, copy it to a buffer
      and evaluate it */

   if ( step > 1 )
      {
      tbuf[ 0 ] = '\0';
      p = 0;
      l->position = step + 4;

      for ( n = l->position; n < (int) strlen( l->buffer ); ++n )
         {
         tbuf[ p ] = l->buffer[ n ];
         ++p;
         ++l->position;
         tbuf[ p ] = '\0';
         }

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_for(): step value string <%s>",
         tbuf );
      bwb_debug( bwb_ebuf );
#endif

      p = 0;
      exp = bwb_exp( tbuf, FALSE, &p );
      for_step = (int) exp_getnval( exp );

      }
   else
      {
      for_step = 1;
      }


#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): step value <%d>",
      for_step );
   bwb_debug( bwb_ebuf );
#endif

   /* set position in current line and increment EXEC counter */

   /* bwb_setexec( l, l->position, EXEC_NORM ); */  /* WRONG */
   bwb_incexec();

   CURTASK excs[ CURTASK exsc ].local_variable  = v;
   CURTASK excs[ CURTASK exsc ].for_step   = for_step;
   CURTASK excs[ CURTASK exsc ].for_target = for_target;

   /* set exit line to be used by EXIT FOR */

#if STRUCT_CMDS
   CURTASK excs[ CURTASK exsc ].wend_line  = find_next( l );
#endif

   /* set top line and position to be used in multisegmented FOR-NEXT loop */

#if MULTISEG_LINES
   CURTASK excs[ CURTASK exsc ].for_line     = l;
   CURTASK excs[ CURTASK exsc ].for_position = l->position;
#endif

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): setting code to EXEC_FOR",
      l->position );
   bwb_debug( bwb_ebuf );
#endif

   bwb_setexec( l, l->position, EXEC_FOR );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): ready to exit, position <%d>",
      l->position );
   bwb_debug( bwb_ebuf );
#endif

   /* proceed with processing */

   return bwb_zline( l );

   }

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

        FUNCTION:       bwb_next()

        DESCRIPTION:    This function handles the BASIC NEXT
                        statement.

	SYNTAX:		NEXT counter

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

#if ANSI_C
struct bwb_line *
bwb_next( struct bwb_line *l )
#else
struct bwb_line *
bwb_next( l )
   struct bwb_line *l;
#endif
   {
   char tbuf[ MAXSTRINGSIZE + 1 ];
   struct bwb_variable *v; /* Relocated from INTENSIVE_DEBUG (JBV) */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_next(): entered function, cmdnum <%d> exsc level <%d> code <%d>",
      l->cmdnum, CURTASK exsc, CURTASK excs[ CURTASK exsc ].code );
   bwb_debug( bwb_ebuf );
#endif

   /* Check the integrity of the FOR statement */

   if ( CURTASK excs[ CURTASK exsc ].code != EXEC_FOR )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_next(): NEXT without FOR; code is <%d> instead of <%d>",
	 CURTASK excs[ CURTASK exsc ].code, EXEC_FOR );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      }

   /* read the argument, if there is one */

   /* Relocated from MULTISEG_LINES (JBV) */
   exp_getvfname( &( l->buffer[ l->position ] ), tbuf );

   if (strlen(tbuf) != 0)
   {
   /* Relocated from INTENSIVE_DEBUG (JBV) */
   v = var_find( tbuf );

#if MULTISEG_LINES                   /* not currently needed otherwise */

   l->position += strlen( tbuf );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_next(): variable name detected <%s>.", v->name );
   bwb_debug( bwb_ebuf );
#endif
#endif

   /* decrement or increment the value */

   /*--------------------------------------------------------------*/
   /* Make sure we are in the right FOR-NEXT level!                */
   /* If we aren't (which could happen for legit reasons), fix the */
   /* exec stack.                                                  */
   /* JBV, 9/20/95                                                 */
   /*--------------------------------------------------------------*/
   while (v != CURTASK excs[ CURTASK exsc].local_variable) bwb_decexec();
   }

   var_setnval( CURTASK excs[ CURTASK exsc ].local_variable,
      var_getnval( CURTASK excs[ CURTASK exsc ].local_variable )
      + (bnumber) CURTASK excs[ CURTASK exsc ].for_step );

   /* check for completion of the loop */

   if ( CURTASK excs[ CURTASK exsc ].for_step > 0 )            /* if step is positive */
      {
      if ( (int) var_getnval( CURTASK excs[ CURTASK exsc ].local_variable )
         > CURTASK excs[ CURTASK exsc ].for_target )
         {
         bwb_decexec();
#if MULTISEG_LINES
	 bwb_setexec( l, l->position, CURTASK excs[ CURTASK exsc ].code );
#else
	 bwb_setexec( l->next, 0, CURTASK excs[ CURTASK exsc ].code );
#endif

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_next(): end of loop" );
	 bwb_debug( bwb_ebuf );
#endif

#ifdef OLD_WAY
	 l->next->position = 0;
	 return l->next;
#else
	 return bwb_zline( l );
#endif
         }
      }
   else                                         /* if step is negative */
      {
      if ( (int) var_getnval( CURTASK excs[ CURTASK exsc ].local_variable )
         < CURTASK excs[ CURTASK exsc ].for_target )
         {
         bwb_decexec();
	 bwb_setexec( l->next, 0, CURTASK excs[ CURTASK exsc ].code );

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_next(): end of loop" );
	 bwb_debug( bwb_ebuf );
#endif

#ifdef OLD_WAY
	 l->next->position = 0;
	 return l->next;
#else
	 return bwb_zline( l );
#endif
         }
      }

   /* Target not reached: return to the top of the FOR loop */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_next(): resetting code to EXEC_FOR",
      l->position );
   bwb_debug( bwb_ebuf );
#endif

#if MULTISEG_LINES
   CURTASK excs[ CURTASK exsc ].for_line->position
      = CURTASK excs[ CURTASK exsc ].for_position;
   bwb_setexec( CURTASK excs[ CURTASK exsc ].for_line,
      CURTASK excs[ CURTASK exsc ].for_position, EXEC_FOR );

   return CURTASK excs[ CURTASK exsc ].for_line; /* Added (JBV) */
#else
   bwb_setexec( CURTASK excs[ CURTASK exsc - 1 ].line,
      CURTASK excs[ CURTASK exsc - 1 ].position, EXEC_FOR );

   return CURTASK excs[ CURTASK exsc - 1 ].line; /* Relocated (JBV) */
#endif

   }

#if STRUCT_CMDS

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

	FUNCTION:       bwb_exitfor()

	DESCRIPTION:    This function handles the BASIC EXIT
			FOR statement.  This is a structured
			programming command compatible with ANSI
			BASIC. It is called from the bwb_exit()
			subroutine.

	SYNTAX:		EXIT FOR
			
***************************************************************/

#if ANSI_C
struct bwb_line *
bwb_exitfor( struct bwb_line *l )
#else
struct bwb_line *
bwb_exitfor( l )
   struct bwb_line *l;
#endif
   {
   struct bwb_line *next_line;
   int found;
   register int level;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_exitfor(): entered subroutine" );
   bwb_debug( bwb_ebuf );
#endif

   /* Check the integrity of the FOR statement */

   found = FALSE;
   level = CURTASK exsc;
   do
      {
      if ( CURTASK excs[ level ].code == EXEC_FOR )
	 {
	 next_line = CURTASK excs[ CURTASK level ].wend_line;
	 found = TRUE;
	 }
      else
	 {
	 --level;
	 }
      }
   while ( ( level >= 0 ) && ( found == FALSE ) );

   if ( found != TRUE )
      {

#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_exitfor(): EXIT FOR without FOR" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif

      return bwb_zline( l );

      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_exitfor(): level found is <%d>, current <%d>",
      level, CURTASK exsc );
   bwb_debug( bwb_ebuf );
#endif

   /* decrement below the level of the NEXT statement */

   while( CURTASK exsc >= level )
      {
      bwb_decexec();
      }

   /* set the next line in the exec stack */

   next_line->position = 0;
   /* bwb_setexec( next_line, 0, EXEC_NORM ); */  /* WRONG (JBV) */
   bwb_setexec( next_line, 0, CURTASK excs[ CURTASK exsc ].code ); /* JBV */

   return next_line;

   }

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

	FUNCTION:       find_next()

	DESCRIPTION:    This function searches for a line containing
			a NEXT statement corresponding to a previous
			FOR statement.

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

#if ANSI_C
static struct bwb_line *
find_next( struct bwb_line *l )
#else
static struct bwb_line *
find_next( l )
   struct bwb_line *l;
#endif
   {
   struct bwb_line *current;
   register int w_level;
   int position;

   w_level = 1;
   for ( current = l->next; current != &CURTASK bwb_end; current = current->next )
      {
      position = 0;
      if ( current->marked != TRUE )
	 {
	 line_start( current->buffer, &position, &( current->lnpos ),
	    &( current->lnum ),
	    &( current->cmdpos ),
	    &( current->cmdnum ),
	    &( current->startpos ) );
	 }
      current->position = current->startpos;

      if ( current->cmdnum > -1 )
	 {

	 if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_for )
	    {
	    ++w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in find_next(): found FOR at line %d, level %d",
	       current->number, w_level );
	    bwb_debug( bwb_ebuf );
#endif

	    }
	 else if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_next )
	    {
	    --w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in find_next(): found NEXT at line %d, level %d",
	       current->number, w_level );
	    bwb_debug( bwb_ebuf );
#endif

	    if ( w_level == 0 )
	       {

#if INTENSIVE_DEBUG
	       sprintf( bwb_ebuf, "in find_next(): found returning line <%d>",
		  current->next->number );
	       bwb_debug( bwb_ebuf );
#endif

	       return current->next;
	       }
	    }
	 }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "FOR without NEXT" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

#endif				/* STRUCT_CMDS for EXIT FOR */

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

	FUNCTION:	cnd_tostep()

	DESCRIPTION:	This function searches through the
			<buffer> beginning at point <position>
			and attempts to find positions of TO
			and STEP statements.

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

#if ANSI_C
static int
cnd_tostep( char *buffer, int position, int *to, int *step )
#else
static int
cnd_tostep( buffer, position, to, step )
   char *buffer;
   int position;
   int *to;
   int *step;
#endif
   {
   int loop, t_pos, b_pos, p_word;
   char tbuf[ MAXSTRINGSIZE + 1 ];

   /* set then and els to FALSE initially */

   *to = *step = FALSE;

   /* loop to find words */

   p_word = b_pos = position;
   t_pos = 0;
   tbuf[ 0 ] = '\0';
   loop = TRUE;
   while ( loop == TRUE )
      {

      switch( buffer[ b_pos ] )
         {
         case '\0':                     /* end of string */
         case ':':			/* end of line segment */
            return TRUE;
         case ' ':                      /* whitespace = end of word */
         case '\t':

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

            if ( strncmp( tbuf, CMD_TO, (size_t) strlen( CMD_TO ) ) == 0 )
               {

#if INTENSIVE_DEBUG
               sprintf( bwb_ebuf, "in cnd_tostep(): TO found at position <%d>.",
                  p_word );
               bwb_debug( bwb_ebuf );
#endif

               *to = p_word;
               }
            else if ( strncmp( tbuf, CMD_STEP, (size_t) strlen( CMD_STEP ) ) == 0 )
               {

#if INTENSIVE_DEBUG
               sprintf( bwb_ebuf, "in cnd_tostep(): STEP found at position <%d>.",
                  p_word );
               bwb_debug( bwb_ebuf );
#endif

               *step = p_word;
               }
            ++b_pos;
            p_word = b_pos;
            t_pos = 0;
            tbuf[ 0 ] = '\0';
            break;

         default:
            if ( islower( buffer[ b_pos ] ) != FALSE )
               {
               tbuf[ t_pos ] = (char) toupper( buffer[ b_pos ] );
               }
            else
               {
               tbuf[ t_pos ] = buffer[ b_pos ];
               }
            ++b_pos;
            ++t_pos;
            tbuf[ t_pos ] = '\0';
            break;
         }

      }

   return TRUE;

   }

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

	FUNCTION:       var_setnval()

	DESCRIPTION:    This function sets the value of numerical
			variable v to the value of i.

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

#if ANSI_C
extern int
var_setnval( struct bwb_variable *v, bnumber i )
#else
int
var_setnval( v, i )
   struct bwb_variable *v;
   bnumber i;
#endif
   {

   switch( v->type )
      {
      case NUMBER:
         * var_findnval( v, v->array_pos ) = i;
         break;
      default:
#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in var_setnval(): variable <%s> is not a number",
            v->name );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif
      }

   /* successful assignment */

   return TRUE;

   }