bwb_ops.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

static int
op_subtract( level, precision )
   int level;
   int precision;
#endif
   {

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be numbers for
            string addition; if not, report an error */

#if PROG_ERRORS
         sprintf( bwb_ebuf, "Strings cannot be subtracted." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif

         break;

      case NUMBER:
         CURTASK exps[ level - 1 ].nval
            = exp_getnval( &( CURTASK exps[ level - 1 ] ))
            - exp_getnval( &( CURTASK exps[ level + 1 ] ));
         break;

      }

   /* set variable to requested precision */

   CURTASK exps[ level - 1 ].type = (char) precision;
   CURTASK exps[ level - 1 ].operation = NUMBER;

   /* decrement the stack twice */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_multiply()

	DESCRIPTION:    This function multiplies the number on
			the left by the number on the right.

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

#if ANSI_C
static int
op_multiply( int level, int precision )
#else
static int
op_multiply( level, precision )
   int level;
   int precision;
#endif
   {

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be numbers for
            string addition; if not, report an error */

#if PROG_ERRORS
         sprintf( bwb_ebuf, "Strings cannot be multiplied." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif

         break;

      case NUMBER:
         CURTASK exps[ level - 1 ].nval
            = exp_getnval( &( CURTASK exps[ level - 1 ] ))
            * exp_getnval( &( CURTASK exps[ level + 1 ] ));
         break;

      }

   /* set variable to requested precision */

   CURTASK exps[ level - 1 ].type = (char) precision;
   CURTASK exps[ level - 1 ].operation = NUMBER;

   /* decrement the stack twice */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_divide()

	DESCRIPTION:    This function divides the number on
			the left by the number on the right.

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

#if ANSI_C
static int
op_divide( int level, int precision )
#else
static int
op_divide( level, precision )
   int level;
   int precision;
#endif
   {

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be numbers for
            division; if not, report an error */

#if PROG_ERRORS
         sprintf( bwb_ebuf, "Strings cannot be divided." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif

         break;

      case NUMBER:
         if ( exp_getnval( &( CURTASK exps[ level + 1 ] ))
            == (bnumber) 0 )
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) -1.0;
            op_pulldown( 2 );
#if PROG_ERRORS
            sprintf( bwb_ebuf, "Divide by 0." );
            bwb_error( bwb_ebuf );
#else
            bwb_error( err_dbz );
#endif
            return FALSE;
            }
         CURTASK exps[ level - 1 ].nval
            = exp_getnval( &( CURTASK exps[ level - 1 ] ))
            / exp_getnval( &( CURTASK exps[ level + 1 ] ));
         break;
      }

   /* set variable to requested precision */

   CURTASK exps[ level - 1 ].type = (char) precision;
   CURTASK exps[ level - 1 ].operation = NUMBER;

   /* decrement the stack twice */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_assign()

	DESCRIPTION:    This function assigns the value in the
			right hand side to the variable in the
			left hand side.

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

#if ANSI_C
static int
op_assign( int level, int precision )
#else
static int
op_assign( level, precision )
   int level;
   int precision;
#endif
   {

   /* Make sure the position one level below is a variable */

   if ( CURTASK exps[ level - 1 ].operation != VARIABLE )
      {
      op_pulldown( 2 );
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in op_assign(): Assignment must be to variable: level -1 <%d> op <%d>",
         level - 1, CURTASK exps[ level - 1 ].operation );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      return FALSE;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in op_assign(): entered function level <%d>",
      level );
   bwb_debug( bwb_ebuf );
#endif

  /* if the assignment is numerical, then the precision should be set
     to that of the variable on the left-hand side of the assignment */

   if ( precision != STRING )
      {
      precision = (int) CURTASK exps[ level - 1 ].type;
      }

   switch( precision )
      {
      case STRING:

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in op_assign(): try exp_getsval(), level <%d> op <%d> type <%c>:",
            level - 1, CURTASK exps[ level - 1 ].operation, CURTASK exps[ level - 1 ].type );
         bwb_debug( bwb_ebuf );
         exp_getsval( &( CURTASK exps[ level - 1 ] ));
         sprintf( bwb_ebuf, "in op_assign(): try exp_getsval(), level <%d> op <%d> type <%c>:",
            level + 1, CURTASK exps[ level + 1 ].operation, CURTASK exps[ level + 1 ].type );
         bwb_debug( bwb_ebuf );
         exp_getsval( &( CURTASK exps[ level + 1 ] ));
         sprintf( bwb_ebuf, "in op_assign(): string addition, exp_getsval()s completed" );
         bwb_debug( bwb_ebuf );
#endif

         str_btob( exp_getsval( &( CURTASK exps[ level - 1 ] )),
                   exp_getsval( &( CURTASK exps[ level + 1 ] )) );
         break;

      case NUMBER:
         * var_findnval( CURTASK exps[ level - 1 ].xvar, 
            CURTASK exps[ level - 1 ].array_pos ) =
            CURTASK exps[ level - 1 ].nval = 
            exp_getnval( &( CURTASK exps[ level + 1 ] ) );
         break;

      default:
#if PROG_ERRORS
         sprintf( bwb_ebuf, "in op_assign(): Variable before assignment operator has unidentified type." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif
         return FALSE;

      }

   /* set variable to requested precision */

   CURTASK exps[ level - 1 ].type = (char) precision;

   /* decrement the stack twice */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_equals()

	DESCRIPTION:    This function compares two values and
			returns an integer value: TRUE if they are
			the same and FALSE if they are not.

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

#if ANSI_C
static int
op_equals( int level, int precision )
#else
static int
op_equals( level, precision )
   int level;
   int precision;
#endif
   {
   int error_condition;
   static bstring b;
   bstring *bp;

   error_condition = FALSE;
   b.rab = FALSE;

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be strings for
            string addition; if not, report an error */

         if (  ( op_islevelstr( level - 1 ) != TRUE )
            || ( op_islevelstr( level + 1 ) != TRUE ) )
            {
#if PROG_ERRORS
            sprintf( bwb_ebuf, "in op_equals(): Type mismatch in string comparison." );
            bwb_error( bwb_ebuf );
#else
            bwb_error( err_mismatch );
#endif
            error_condition = TRUE;
            }

         /* compare the two strings */

         if ( error_condition == FALSE )
            {
            bp = exp_getsval( &( CURTASK exps[ level - 1 ] ));
#if OLDWAY
	    b.length = bp->length;
	    b.sbuffer = bp->sbuffer;
#endif
	    str_btob( &b, bp );

            if ( str_cmp( &b,
               exp_getsval( &( CURTASK exps[ level + 1 ] )) ) == 0 )
               {
               CURTASK exps[ level - 1 ].nval = (bnumber) TRUE;
               }
            else
               {
               CURTASK exps[ level - 1 ].nval = (bnumber) FALSE;
               }
            }
         break;

      case NUMBER:
         if ( exp_getnval( &( CURTASK exps[ level - 1 ] ))
            == exp_getnval( &( CURTASK exps[ level + 1 ] )) )
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) TRUE;
            }
         else
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) FALSE;
            }
         break;

      }

   /* set variable to integer and operation to NUMBER:
      this must be done at the end, since at the beginning it
      might cause op_islevelstr() to return a false error */

   CURTASK exps[ level - 1 ].type = NUMBER;
   CURTASK exps[ level - 1 ].operation = NUMBER;

   /* decrement the stack */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_lessthan()

	DESCRIPTION:    This function compares two values and
			returns an integer value: TRUE if the
			left hand value is less than the right,
			and FALSE if it is not.

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

#if ANSI_C
static int
op_lessthan( int level, int precision )
#else
static int
op_lessthan( level, precision )
   int level;
   int precision;
#endif
   {
   int error_condition;

   error_condition = FALSE;

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be numbers for
            string addition; if not, report an error */

         if (  ( op_islevelstr( level - 1 ) != TRUE )
            || ( op_islevelstr( level + 1 ) != TRUE ) )
            {
#if PROG_ERRORS
            sprintf( bwb_ebuf, "Type mismatch in string comparison." );
            bwb_error( bwb_ebuf );
#else
            bwb_error( err_mismatch );
#endif
            error_condition = TRUE;
            }

         /* compare the two strings */

         if ( error_condition == FALSE )
            {
            if ( str_cmp( exp_getsval( &( CURTASK exps[ level - 1 ] )),
               exp_getsval( &( CURTASK exps[ level + 1 ] )) ) < 0 )
               {
               CURTASK exps[ level - 1 ].nval = (bnumber) TRUE;
               }
            else
               {
               CURTASK exps[ level - 1 ].nval = (bnumber) FALSE;
               }
            }
         break;

      case NUMBER:
         if ( exp_getnval( &( CURTASK exps[ level - 1 ] ))
            < exp_getnval( &( CURTASK exps[ level + 1 ] )) )
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) TRUE;
            }
         else
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) FALSE;
            }
         break;

      }

   /* set variable to integer and operation to NUMBER:
      this must be done at the end, since at the beginning it
      might cause op_islevelstr() to return a false error */

   CURTASK exps[ level - 1 ].type = NUMBER;
   CURTASK exps[ level - 1 ].operation = NUMBER;

   /* decrement the stack */

   op_pulldown( 2 );

   return TRUE;

   }

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

	FUNCTION:       op_greaterthan()

	DESCRIPTION:    This function compares two values and
			returns an integer value: TRUE if the
			left hand value is greater than the right,
			and FALSE if it is not.

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

#if ANSI_C
static int
op_greaterthan( int level, int precision )
#else
static int
op_greaterthan( level, precision )
   int level;
   int precision;
#endif
   {
   int error_condition;

   error_condition = FALSE;

   switch( precision )
      {
      case STRING:

         /* both sides of the operation should be numbers for
            string addition; if not, report an error */

         if (  ( op_islevelstr( level - 1 ) != TRUE )
            || ( op_islevelstr( level + 1 ) != TRUE ) )
            {
#if PROG_ERRORS
            sprintf( bwb_ebuf, "Type mismatch in string comparison." );
            bwb_error( bwb_ebuf );
#else
            bwb_error( err_mismatch );
#endif
            error_condition = TRUE;
            }

         /* compare the two strings */

         if ( error_condition == FALSE )
            {
            if ( str_cmp( exp_getsval( &( CURTASK exps[ level - 1 ] )),
               exp_getsval( &( CURTASK exps[ level + 1 ] )) ) > 0 )
               {