REM   Filter.txt
REM
REM   Author: Steven R. Wheeler
REM
REM   Copyright 1998 Vesta Technology, Inc.
REM   All rights reserved.
REM
REM   This is a filter function which can be used to add a portion of a new reading
REM   to an "old" value. It works with integer parameters. A similar but simpler
REM   filter can be implemented on the SBC2000-074 using floating-point operations.
REM   The parameters are as follows:
REM
REM       old       This is the previous filtered value.
REM       new       This is the value to be added to the filtered value.
REM       retain    This is the portion of the old value which will be retained.
REM                 This can be numerically anywhere from 0 to scale.
REM       scale     This is the scaling value to be used in the filter. It can be
REM                 up to 181. Larger values will cause numeric overflow.
REM
REM   The calculation started with the equation:
REM
REM                        (old * retain) + new * (scale - retain)
REM       filtered_value = ---------------------------------------
REM                                        scale
REM
REM   This was simplified to:
REM
REM                        (old - new) * retain
REM       filtered_value = -------------------- + new
REM                                scale
REM
REM   The calculations are done with absolute values for simplicity. A persistent
REM   remainder value is kept for better accuracy. If more than one signal is to be
REM   filtered in an application, you will either need to have separate copies of
REM   the filter function with unique names for each signal, or you will have to
REM   make "remainder" a global variable, and save and restore the value each time
REM   you change to filtering a different signal.

FUNCTION Filter(old AS INTEGER, new AS INTEGER, retain AS INTEGER, scale AS INTEGER) AS INTEGER
STATIC remainder AS INTEGER
	Filter   = abs(old - new)
	remainder = (Filter \ scale) * retain + remainder
	Filter   = (Filter / scale) * retain
	Filter   = Filter + remainder / scale
	if (old - new) < 0
		Filter = -Filter
	endif
	Filter = Filter + new
	remainder = remainder \ scale
END



rem   This is the main body of the application.

rem GLOBAL z AS INTEGER

rem z = 0

rem DO WHILE 1
rem	z = Filter(z, 31416,  99, 100)
rem	PRINT "\013\010", z
rem LOOP