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.

struct bwb_line *
bwb_endif( l )
   struct bwb_line *l;
#endif
   {

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_endif(): entered function" );
   bwb_debug( bwb_ebuf );
#endif

   if (( CURTASK excs[ CURTASK exsc ].code != EXEC_IFTRUE )
      && ( CURTASK excs[ CURTASK exsc ].code != EXEC_IFFALSE ))
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_endif(): END IF without IF" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      }

   bwb_decexec();


#if MULTISEG_LINES
   adv_eos( l->buffer, &( l->position ));
#endif
   return bwb_zline( l );
   }

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

        FUNCTION:       find_endif()

        DESCRIPTION:    This C function attempts to find an
			END IF statement.

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

#if ANSI_C
static struct bwb_line *
find_endif( struct bwb_line *l, struct bwb_line **else_line )
#else
static struct bwb_line *
find_endif( l, else_line )
   struct bwb_line *l;
   struct bwb_line **else_line;
#endif
   {
   struct bwb_line *current;
   register int i_level;
   int position;

   *else_line = NULL;
   i_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_if )
            {
            ++i_level;

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

            }
         else if ( is_endif( current ) == TRUE )
            {
            --i_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in find_endif(): found END IF at line %d, level %d",
               current->number, i_level );
            bwb_debug( bwb_ebuf );
#endif

            if ( i_level == 0 )
               {
               return current;
               }
            }

         else if ( ( bwb_cmdtable[ current->cmdnum ].vector == bwb_else )
            || ( bwb_cmdtable[ current->cmdnum ].vector == bwb_elseif ))
            {

            /* we must only report the first ELSE or ELSE IF we encounter
               at level 1 */

            if ( ( i_level == 1 ) && ( *else_line == NULL ))
               {
               *else_line = current;
               }

            }
         }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "Multiline IF without END IF" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

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

	FUNCTION:       is_endif()

	DESCRIPTION:    This C function attempts to determine if
			a given line contains an END IF statement.

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

#if ANSI_C
static int
is_endif( struct bwb_line *l )
#else
static int
is_endif( l )
   struct bwb_line *l;
#endif
   {
   int position;
   char tbuf[ MAXVARNAMESIZE + 1];

   if ( bwb_cmdtable[ l->cmdnum ].vector != bwb_xend )
      {
      return FALSE;
      }

   position = l->startpos;
   adv_ws( l->buffer, &position );
   adv_element( l->buffer, &position, tbuf );
   bwb_strtoupper( tbuf );

   if ( strcmp( tbuf, "IF" ) == 0 )
      {
      return TRUE;
      }

   return FALSE;

   }

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

        FUNCTION:       bwb_select()

        DESCRIPTION:    This C function handles the BASIC SELECT
                        statement.

	SYNTAX:		SELECT CASE expression

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

#if ANSI_C
struct bwb_line *
bwb_select( struct bwb_line *l )
#else
struct bwb_line *
bwb_select( l )
   struct bwb_line *l;
#endif
   {
   char tbuf[ MAXSTRINGSIZE + 1 ];
   struct exp_ese *e;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_select(): entered function" );
   bwb_debug( bwb_ebuf );
#endif

   /* first element should be "CASE" */

   adv_element( l->buffer, &( l->position ), tbuf );
   bwb_strtoupper( tbuf );
   if ( strcmp( tbuf, "CASE" ) != 0 )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "SELECT without CASE" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );

      return bwb_zline( l );
#endif
      }

   /* increment the level and set to EXEC_SELFALSE */

   bwb_incexec();
   CURTASK excs[ CURTASK exsc ].code = EXEC_SELFALSE;

   /* evaluate the expression at this level */

   e = bwb_exp( l->buffer, FALSE, &( l->position ) );

#if OLDWAY
   memcpy( &( CURTASK excs[ CURTASK exsc ].expression ), e,
      sizeof( struct exp_ese ) );
#endif

   if ( e->type == STRING )
      {
      CURTASK excs[ CURTASK exsc ].expression.type = STRING;
      str_btob( &( CURTASK excs[ CURTASK exsc ].expression.sval ),
	 &( e->sval ) );
      }
   else
      {
      CURTASK excs[ CURTASK exsc ].expression.type = NUMBER;
      CURTASK excs[ CURTASK exsc ].expression.nval
	 = exp_getnval( e );
      }

   /* return */

#if MULTISEG_LINES
   adv_eos( l->buffer, &( l->position ));
#endif

   return bwb_zline( l );
   }

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

        FUNCTION:       bwb_case()

        DESCRIPTION:    This C function handles the BASIC CASE
                        statement.

	SYNTAX:		CASE constant | IF partial-expression | ELSE

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

#if ANSI_C
struct bwb_line *
bwb_case( struct bwb_line *l )
#else
struct bwb_line *
bwb_case( l )
   struct bwb_line *l;
#endif
   {
   char tbuf[ MAXSTRINGSIZE + 1 ];
   int oldpos;
   struct exp_ese minvalue;
   struct exp_ese *maxval, *minval;
   struct bwb_line *retline;
   char cbuf1[ MAXSTRINGSIZE + 1 ];
   char cbuf2[ MAXSTRINGSIZE + 1 ];

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_case(): entered function" );
   bwb_debug( bwb_ebuf );
#endif

   /* if code is EXEC_SELTRUE, then we should jump to the end */

   if ( CURTASK excs[ CURTASK exsc ].code == EXEC_SELTRUE )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_case(): exit EXEC_SELTRUE" );
      bwb_debug( bwb_ebuf );
#endif
      retline = find_endselect( l );
      retline->position = 0;
      return retline;
      }

   /* read first element */

   oldpos = l->position;
   adv_element( l->buffer, &( l->position ), tbuf );
   bwb_strtoupper( tbuf );

   /* check for CASE IF */

   if ( strcmp( tbuf, CMD_IF ) == 0 )
      {
      return bwb_caseif( l );
      }

   /* check for CASE ELSE: if true, simply proceed to the next line,
      because other options should have been detected by now */

   else if ( strcmp( tbuf, CMD_ELSE ) == 0 )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_case(): execute CASE ELSE" );
      bwb_debug( bwb_ebuf );
#endif

      return bwb_zline( l );
      }

   /* neither CASE ELSE nor CASE IF; presume constant here for min value */

   l->position = oldpos;
   minval = bwb_exp( l->buffer, FALSE, &( l->position ));
   memcpy( &minvalue, minval, sizeof( struct exp_ese ) );
   maxval = minval = &minvalue;

   /* check for string value */

   if ( minvalue.type == STRING )
      {

      str_btoc( cbuf1, &( CURTASK excs[ CURTASK exsc ].expression.sval ) );
      str_btoc( cbuf2, &( minvalue.sval ) );

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_case(): compare strings <%s> and <%s>",
	 cbuf1, cbuf2 );
      bwb_debug( bwb_ebuf );
#endif

      if ( strncmp( cbuf1, cbuf2, MAXSTRINGSIZE ) == 0 )
	 {
#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_case(): string comparison returns TRUE" );
	 bwb_debug( bwb_ebuf );
#endif
	 CURTASK excs[ CURTASK exsc ].code = EXEC_SELTRUE;

#if MULTISEG_LINES
         adv_eos( l->buffer, &( l->position ));
#endif
	 return bwb_zline( l );
	 }

      else
	 {
#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_case(): string comparison returns FALSE" );
	 bwb_debug( bwb_ebuf );
#endif
	 retline = find_case( l );
	 retline->position = 0;
	 return retline;
	 }

      }

   /* not a string; advance */

   adv_ws( l->buffer, &( l->position ));

   /* check for TO */

   if ( is_eol( l->buffer, &( l->position )) != TRUE )
      {

      /* find the TO statement */

      adv_element( l->buffer, &( l->position ), tbuf );
      bwb_strtoupper( tbuf );
      if ( strcmp( tbuf, CMD_TO ) != 0 )
         {
#if PROG_ERRORS
         sprintf( bwb_ebuf, "CASE has inexplicable code following expression" );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_syntax );

#if MULTISEG_LINES
         adv_eos( l->buffer, &( l->position ));
#endif
         return bwb_zline( l );
#endif
         }

      /* now evaluate the MAX expression */

      maxval = bwb_exp( l->buffer, FALSE, &( l->position ));

      }

   /* evaluate the expression */

   if ( case_eval( &( CURTASK excs[ CURTASK exsc ].expression ),
      minval, maxval ) == TRUE )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_case(): evaluation returns TRUE" );
      bwb_debug( bwb_ebuf );
#endif
      CURTASK excs[ CURTASK exsc ].code = EXEC_SELTRUE;

#if MULTISEG_LINES
      adv_eos( l->buffer, &( l->position ));
#endif
      return bwb_zline( l );
      }

   /* evaluation returns a FALSE value; find next CASE or END SELECT statement */

   else
      {
#if INTENSIVE_DEBUGb
      sprintf( bwb_ebuf, "in bwb_case(): evaluation returns FALSE" );
      bwb_debug( bwb_ebuf );
#endif
      retline = find_case( l );
      retline->position = 0;
      return retline;
      }

   }

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

        FUNCTION:       bwb_caseif()

        DESCRIPTION:    This C function handles the BASIC CASE IF
                        statement.

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

#if ANSI_C
static struct bwb_line *
bwb_caseif( struct bwb_line *l )
#else
static struct bwb_line *
bwb_caseif( l )
   struct bwb_line *l;
#endif
   {
   char tbuf[ MAXSTRINGSIZE + 1 ];
   int position;
   struct exp_ese *r;
   struct bwb_line *retline;

   if ( CURTASK excs[ CURTASK exsc ].expression.type == NUMBER )
      {
      sprintf( tbuf, "%f %s",
         (float) CURTASK excs[ CURTASK exsc ].expression.nval,
         &( l->buffer[ l->position ] ) );
      }
   else
      {
      bwb_error( err_mismatch );
#if MULTISEG_LINES
      adv_eos( l->buffer, &( l->position ));
#endif
      return bwb_zline( l );
      }

   position = 0;
   r = bwb_exp( tbuf, FALSE, &position );

   if ( r->nval == (bnumber) TRUE )
      {
      CURTASK excs[ CURTASK exsc ].code = EXEC_SELTRUE;

#if MULTISEG_LINES
      adv_eos( l->buffer, &( l->position ));
#endif
      return bwb_zline( l );
      }
   else
      {
      retline = find_case( l );
      retline->position = 0;
      return retline;
      }

   }

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

        FUNCTION:       case_eval()

        DESCRIPTION:    This function evaluates a case statement
			by comparing minimum and maximum values
			with a set expression. It returns either
			TRUE or FALSE

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

#if ANSI_C
static int
case_eval( struct exp_ese *expression, struct exp_ese *minval,
   struct exp_ese *maxval )
#else
static int
case_eval( expression, minval, maxval )
   struct exp_ese *expression;
   struct exp_ese *minval;
   struct exp_ese *maxval;
#endif
   {

   /* string value */

   if ( expression->type == STRING )
      {
      bwb_error( err_mismatch );
      return FALSE;
      }

   /* numerical value */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in case_eval(): n <%f> min <%f> max <%f>",
      (float) expression->nval,
      (float) minval->nval,
      (float) maxval->nval );
   bwb_debug( bwb_ebuf );
#endif

   if (  ( expression->nval >= minval->nval )
      && ( expression->nval <= maxval->nval ))
      {
      return TRUE;
      }

   return FALSE;

   }

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

        FUNCTION:       find_case()

        DESCRIPTION:    This function searches for a line containing
                        a CASE statement corresponding to a previous
                        SELECT CASE statement.

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

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

   c_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_select )
            {
            ++c_level;

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

            }
         else if ( is_endselect( current ) == TRUE )
            {
            --c_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in find_endif(): found END SELECT at line %d, level %d",
               current->number, c_level );
            bwb_debug( bwb_ebuf );
#endif

            if ( c_level == 0 )
               {
               return current;
               }
            }

         else if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_case )
            {
            --c_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in find_case(): found CASE at line %d, level %d",
               current->number, c_level );