bwb_elx.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

                  else
                     {
                     build_loop = FALSE;
                     }
                  break;
               case '.':                        /* note at least single precision */
               case '0':                        /* or ordinary digit */
               case '1':
               case '2':
               case '3':
               case '4':
               case '5':
               case '6':
               case '7':
               case '8':
               case '9':
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
                  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                  ++s_pos;
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
                  break;

	       case '#':                        /* Microsoft-type precision indicator; ignored but terminates */
	       case '!':                        /* Microsoft-type precision indicator; ignored but terminates */
		  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
		  CURTASK exps[ CURTASK expsc ].type = NUMBER;
		  exponent = FALSE;
		  build_loop = FALSE;
		  break;

	       case 'E':                        /* exponential, single precision */
               case 'e':
                  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                  CURTASK exps[ CURTASK expsc ].type = NUMBER;
		  exponent = TRUE;
                  build_loop = FALSE;
		  break;

               case 'D':                        /* exponential, double precision */
               case 'd':
                  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                  CURTASK exps[ CURTASK expsc ].type = NUMBER;
		  exponent = TRUE;
                  build_loop = FALSE;
                  break;

               default:                         /* anything else, terminate */
                  build_loop = FALSE;
                  break;
               }

            }

         /* assign the value to the mantissa variable */
         
#if NUMBER_DOUBLE
         sscanf( CURTASK exps[ CURTASK expsc ].string, "%lf", 
           var_findnval( &mantissa, mantissa.array_pos ));
#else
         sscanf( CURTASK exps[ CURTASK expsc ].string, "%f", 
           var_findnval( &mantissa, mantissa.array_pos ));
#endif

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in exp_numconst(): read mantissa, string <%s> val <%lf>",
            CURTASK exps[ CURTASK expsc ].string, var_getnval( &mantissa ) );
         bwb_debug( bwb_ebuf );
#endif

         /* test if integer bounds have been exceeded */

         if ( CURTASK exps[ CURTASK expsc ].type == NUMBER )
            {
            i = (int) var_getnval( &mantissa );
            d = (bnumber) i;
            if ( d != var_getnval( &mantissa ))
               {
               CURTASK exps[ CURTASK expsc ].type = NUMBER;
#if INTENSIVE_DEBUG
               sprintf( bwb_ebuf, "in exp_numconst(): integer bounds violated, promote to NUMBER" );
               bwb_debug( bwb_ebuf );
#endif               
               }
            }

         /* read the exponent if there is one */

         if ( exponent == TRUE )
            {

	    /* allow a plus or minus once at the beginning */

	    need_pm = TRUE;

	    /* initialize counters */

            CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';
            s_pos = 0;
            build_loop = TRUE;

            /* loop to build the string */

            while ( build_loop == TRUE )
               {
               switch( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] )
                  {
		  case '-':                        /* prefixed plus or minus */
                  case '+':

		     if ( need_pm == TRUE )        /* only allow once */
			{
			CURTASK exps[ CURTASK expsc ].string[ s_pos ] = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
			++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
			++s_pos;
			CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
			}
		     else
			{
			build_loop = FALSE;
			}
		     break;

		  case '0':                        /* or ordinary digit */
                  case '1':
                  case '2':
                  case '3':
                  case '4':
                  case '5':
                  case '6':
                  case '7':
                  case '8':
                  case '9':

                     CURTASK exps[ CURTASK expsc ].string[ s_pos ] = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
                     ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                     ++s_pos;
		     CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
		     need_pm = FALSE;
                     break;

                  default:                         /* anything else, terminate */
                     build_loop = FALSE;
                     break;
                  }

               }                                /* end of build loop for exponent */

            /* assign the value to the user variable */

#if NUMBER_DOUBLE
            sscanf( CURTASK exps[ CURTASK expsc ].string, "%lf",
               &( CURTASK exps[ CURTASK expsc ].nval ) );
#else
            sscanf( CURTASK exps[ CURTASK expsc ].string, "%f",
               &( CURTASK exps[ CURTASK expsc ].nval ) );
#endif

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in exp_numconst(): exponent is <%d>",
               (int) CURTASK exps[ CURTASK expsc ].nval );
            bwb_debug( bwb_ebuf );
#endif

            }                           /* end of exponent search */

         if ( CURTASK exps[ CURTASK expsc ].nval == (bnumber) 0 )
            {
            CURTASK exps[ CURTASK expsc ].nval = var_getnval( &mantissa );
            }
         else
            {
            CURTASK exps[ CURTASK expsc ].nval = var_getnval( &mantissa )
               * pow( (bnumber) 10.0, (bnumber) CURTASK exps[ CURTASK expsc ].nval );
            }

         break;

      case 8:                           /* octal constant */

         /* initialize counters */

         CURTASK exps[ CURTASK expsc ].pos_adv = man_start;
         CURTASK exps[ CURTASK expsc ].type = NUMBER;
         CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';
         s_pos = 0;
         exponent = OP_NULL;
         build_loop = TRUE;

         /* loop to build the string */

         while ( build_loop == TRUE )
            {
            switch( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] )
               {
               case '0':                        /* or ordinary digit */
               case '1':
               case '2':
               case '3':
               case '4':
               case '5':
               case '6':
               case '7':
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
                  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                  ++s_pos;
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
                  break;

               default:                         /* anything else, terminate */
                  build_loop = FALSE;
                  break;
               }

            }

         /* now scan the string to determine the number */

         sscanf( CURTASK exps[ CURTASK expsc ].string, "%o", &i );
         CURTASK exps[ CURTASK expsc ].nval = (bnumber) i;

         break;

      case 16:                          /* hexadecimal constant */

         /* initialize counters */

         CURTASK exps[ CURTASK expsc ].pos_adv = man_start;
         CURTASK exps[ CURTASK expsc ].type = NUMBER;
         CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';
         s_pos = 0;
         exponent = OP_NULL;
         build_loop = TRUE;

         /* loop to build the string */

         while ( build_loop == TRUE )
            {
            switch( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] )
               {
               case '0':                        /* or ordinary digit */
               case '1':
               case '2':
               case '3':
               case '4':
               case '5':
               case '6':
               case '7':
               case '8':
               case '9':
               case 'A':
               case 'a':
               case 'B':
               case 'b':
               case 'C':
               case 'c':
               case 'D':
               case 'd':
               case 'E':
               case 'e':
               case 'F': /* Don't forget these! (JBV) */
               case 'f':
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];

                  ++CURTASK exps[ CURTASK expsc ].pos_adv;  /* advance to next character */
                  ++s_pos;
                  CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
                  break;

               default:                         /* anything else, terminate */
                  build_loop = FALSE;
                  break;
               }

            }

         /* now scan the string to determine the number */

         sscanf( CURTASK exps[ CURTASK expsc ].string, "%x", &i );
         CURTASK exps[ CURTASK expsc ].nval = (bnumber) i;
         break;
      }

   /* note that the operation at this level is now a determined NUMBER */

   CURTASK exps[ CURTASK expsc ].operation = NUMBER;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_numconst(): exit level <%d> precision <%c> value <%lf>",
      CURTASK expsc, CURTASK exps[ CURTASK expsc ].type, exp_getnval( &( CURTASK exps[ CURTASK expsc ] ) ) );
   bwb_debug( bwb_ebuf );
#endif

#if CHECK_RECURSION
   in_use = FALSE;
#endif

   return TRUE;

   }

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

	FUNCTION:       exp_function()

	DESCRIPTION:    This function interprets a function,
			calling bwb_exp() (recursively) to resolve any
			arguments to the function.

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

#if ANSI_C
int
exp_function( char *expression )
#else
int
exp_function( expression )
   char *expression;
#endif
   {
   struct exp_ese *e;
   int s_pos;                           /* position in build buffer */
   int loop;
   int paren_level;
   int n_args;
   struct bwb_variable *v;
   /* struct bwb_variable argv[ MAX_FARGS ]; */ /* Removed by JBV */
   struct bwb_variable *argv; /* Added by JBV */
   bstring *b;
#if INTENSIVE_DEBUG
   char tbuf[ MAXSTRINGSIZE + 1 ];

   sprintf( bwb_ebuf, "in exp_function(): entered function, expression <%s>",
      expression );
   bwb_debug( bwb_ebuf );
#endif

   /*-----------------------------------------------------------*/
   /* Added by JBV                                              */
   /* Required because adding a simple "static" modifier in the */
   /* argv declaration doesn't work for recursive calls!        */
   /*-----------------------------------------------------------*/
   if ( ( argv = (struct bwb_variable *) CALLOC( MAX_FARGS,
      sizeof( struct bwb_variable ), "exp_function" )) == NULL )
      {
      bwb_error( err_getmem );
      return NULL;
      }

   /* assign pointers to argument stack */

   /* get the function name */

   exp_getvfname( expression, CURTASK exps[ CURTASK expsc ].string );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_function(): name is <%s>.",
      CURTASK exps[ CURTASK expsc ].string );
   bwb_debug( bwb_ebuf );
#endif

   /* now find the function itself */

   CURTASK exps[ CURTASK expsc ].function = fnc_find( CURTASK exps[ CURTASK expsc ].string );

   /* check to see if it is valid */

   if ( CURTASK exps[ CURTASK expsc ].function == NULL )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "Failed to find function <%s>.",
         CURTASK exps[ CURTASK expsc ].string );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_uf  );
#endif
      return OP_ERROR;
      }

   /* note that this level is a function */

   CURTASK exps[ CURTASK expsc ].operation = FUNCTION;
   CURTASK exps[ CURTASK expsc ].pos_adv = strlen( CURTASK exps[ CURTASK expsc ].string );

   /* check for begin parenthesis */

   loop = TRUE;
   while( loop == TRUE )
      {
      switch( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] )
         {

         case ' ':                              /* whitespace */
         case '\t':
            ++CURTASK exps[ CURTASK expsc ].pos_adv;        /* advance */
            break;

         case '(':                              /* begin paren */

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in exp_function(): found begin parenthesis." );
            bwb_debug( bwb_ebuf );
#endif

            ++CURTASK exps[ CURTASK expsc ].pos_adv;        /* advance beyond it */
            paren_level = 1;                    /* set paren_level */
            loop = FALSE;                       /* and break out */
            break;