Post by thread:[PIC]: NUmber crunching 48/24 equ 24 optimisations

Hi, an small suggestion for speeding up the 48/24 routine posted the other day. If result is known to be (or most often) within 24 bits then this alternative start snippet might save 24 loops to the expence of about 20 lines of code. Here goes: ( only the startbit ) DIVIDE_48by24 ; Test for zero division MOVF Divisor,W IORWF Divisor+1,W IORWF Divisor+2,W BTFSC STATUS,Z RETLW 0x00 ; divisor = zero, not possible to calculate return with zero in w ; prepare used variables CLRF Temp CLRF Temp+1 CLRF Temp+2 MOVLW D'48' ; initialize bit counter MOVWF BitCount CLRC ; clear carry at entry ; some test to shorten number of loops ; in division routine. ; Not required, but ; can save 24 loops when the result is known to ; fit into 24 bits ; if we have something in the top nibble ; of divisor we know that the result will ; always fit into 3 bytes and 24 loops can be skipped MOVF Divisor,W ; get msb of divisor ANDLW 0xF0 ; Mask out top four bits BZ DIVIDE_LOOP_48by24 ; ok result larger than 24 bits run full loop ; here carry MUST be cleared ( in this snippet performed above ) ; we know that result will fit into 24 bits ; first divide counter with 2 RRF BitCount,F ; i.e. bitcount = 24 ( note does not affect carry ) ; setup dividend and temp ; i.e move top three bytes of dividend into Temp MOVF Dividend,W MOVWF Temp MOVF Dividend+1,W MOVWF Temp+1 MOVF Dividend+2,W MOVWF Temp+2 ; move bottom three bytes in dividend into top three bytes MOVF Dividend+3,W MOVWF Dividend MOVF Dividend+4,W MOVWF Dividend+1 MOVF Dividend+5,W MOVWF Dividend+2 ; finally clear bottom three bytes ( which will be ; top three bytes in the result ) CLRF Dividend+3 CLRF Dividend+4 CLRF Dividend+5 DIVIDE_LOOP_48by24 . . . the same as before but with Nicolai's improvements. /Tony Tony Kübek, Flintab AB ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² E-mail: spam_OUTtony.kubekTakeThisOuTflintab.com ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.