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.

               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_lteq()

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

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

#if ANSI_C
static int
op_lteq( int level, int precision )
#else
static int
op_lteq( 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_gteq()

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

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

#if ANSI_C
static int
op_gteq( int level, int precision )
#else
static int
op_gteq( 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_notequal()

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

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

#if ANSI_C
static int
op_notequal( int level, int precision )
#else
static int
op_notequal( 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_modulus()

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

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

#if ANSI_C
static int
op_modulus( int level, int precision )
#else
static int
op_modulus( level, precision )
   int level;
   int precision;
#endif
   {
   static double iportion;

   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 divided." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_syntax );
#endif

         break;

      case NUMBER:
         if ( exp_getnval( &( CURTASK exps[ level + 1 ] ))
            == (bnumber) 0 )
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) -1;
            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 ].nval
            = exp_getnval( &( CURTASK exps[ level - 1 ] ))
            / exp_getnval( &( CURTASK exps[ level + 1 ] ));
         modf( (double) CURTASK exps[ level ].nval, &iportion );
         CURTASK exps[ level - 1 ].nval
            = exp_getnval( &( CURTASK exps[ level - 1 ] ))
            - ( exp_getnval( &( CURTASK exps[ level + 1 ] ))
            * iportion );
         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_exponent()

	DESCRIPTION:    This function finds the exponential value
			of a number (on the left) to the power
			indicated on the right-hand side.

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

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

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in op_exponent(): entered function level <%d>.",
      level );
   bwb_debug ( bwb_ebuf );
#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 taken as exponents." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif

         break;

      case NUMBER:
         CURTASK exps[ level - 1 ].nval
           = (bnumber) pow( (double) exp_getnval( &( CURTASK exps[ level - 1 ] )),
                  (double) 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_intdiv()

	DESCRIPTION:    This function divides the number on
			the left by the number on the right,
			returning the result as an integer.

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

#if ANSI_C
static int
op_intdiv( int level, int precision )
#else
static int
op_intdiv( 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 divided." );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_mismatch );
#endif

         break;

      default:
         if ( exp_getnval( &( CURTASK exps[ level + 1 ] ))
            == (bnumber) 0 )
            {
            CURTASK exps[ level - 1 ].nval = (bnumber) -1;
            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 = NUMBER;
   CURTASK exps[ level - 1 ].operation = NUMBER;