PIC Microcontroller DSP Math Method

8bit 16 step Averageing filter by Dmitry Kiryashov [zews at AHA.RU]

Hi Andrew.

I got some time and tried to rewrite your filter code to optimize it a little bit.

The formula can be rewritten as: Ave' = Ave + ( New - Ave )/16 ;

Used the same names for variables. TEMP cell isn't used.

I having more and more believing that 12 is some magical number for small completed code fragments. ;)

;       Initially written by Andrew Warren (fastfwd at ix.netcom.com).
;       Optimized by Dmitry A. Kiryashov (zews at aha.ru) 06/18/2000
;       12 clocks/words

Filter:
        movfw   AVE
        subwf   NEW,F   ;NEW - AVE

        swapf   NEW,W
        andlw   0x0F    ;get /16 int part
        skpc            ;result is neg?
        iorlw   0xF0    ;yes
        addwf   AVE,F

        swapf   NEW,W
        andlw   0xF0    ;get /16 frac part
        addwf   AVFRAC,F
        skpnc
        incf    AVE,F
;
;       low nibble of AVFRAC isn't used
;       so we can utilize it for other purposes ;)