PIC Microcontoller 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 ;)

See also:

• http://www.piclist.com/techref/microchip/dsp/av-256w-aw.htm 8bit 256 step Averageing filter by Andrew Warren

Comments:

• If |NEW-AVE|<.16 ,new AVE=old AVE; so the first method is good. Dollyshor+
• I am greatly impressed with this code! Very clever stuff. Many thanks, and Good Day from FLA!~
  
  kl+

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