ARRAY_TREND.EXP

(* @NESTEDCOMMENTS := 'Yes' *)
(* @PATH := '\/Mathematical\/Array' *)
(* @OBJECTFLAGS := '0, 8' *)
(* @SYMFILEFLAGS := '2048' *)
FUNCTION ARRAY_TREND : REAL
VAR_INPUT
	pt : POINTER TO ARRAY[0..32000] OF REAL;
	size : UINT;
END_VAR
VAR
	i: UINT;
	stop: UINT;
	x: REAL;
	stop2: UINT;
END_VAR

(*
version 1.3	10. mar. 2009
programmer 	hugo
tested by		tobias

this function will calculate the trend of a given array.
trend will calculate the avg of the first half of the array and then the avg of the second half, trend = avg2 - avg1.
for example:  [0,1,4,5,3,4,6,3] = 4 - 2.5 = 1.5
the function needs to be called:	array_trend(adr("array"),sizeof("array"));
because this function works with pointers its very time efficient and it needs no extra memory.

*)
(* @END_DECLARATION := '0' *)
stop := SHR(size,2)-1;
stop2 := SHR(stop,1);
FOR i := 0 TO stop2 DO x := x - pt^[i]; END_FOR;
IF EVEN(UINT_TO_INT(stop)) THEN
	FOR i := stop2 TO stop DO X := X + pt^[i]; END_FOR;
ELSE
	FOR i := stop2 + 1 TO stop DO X := X + pt^[i]; END_FOR;
END_IF;
ARRAY_TREND := x / UINT_TO_REAL(stop2 + 1);

(* revision history
hm	2 oct 2007	rev 1.0
	original version

hm	12 dec 2007	rev 1.1
	changed code for better performance

hm	16. mar. 2008	rev 1.2
	changed type of input size to uint

hm	10. mar. 2009	rev 1.3
	added type conversions for compatibility reasons
*)
END_FUNCTION