> -----Original Message-----
> From: M. Adam Davis [SMTP:adampic@UBASICS.COM]
> Sent: Tuesday, June 10, 2003 3:59 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: brain teaser
>
> Does it beat all of the options here:
> http://www.piclist.com/techref/microchip/math/bit/revbits.htm
>
> The fastest one takes 4 instruction cycles (lookup table).
>
I make that 8 cycles (REG being the randomly chosen register):

        movf    REG,w           ; one cycle
        call            reverse         ; two cycles
        movwf   REG             ; one cycle

reverse:
        addwf   PCL,f           ; two cycles
        retlw   0x00            ; two cycles
        retlw   0x80
        retlw   0x40


Cross-wiring two ports gives a 4 cycle solution:

        movf    REG,w           ; one cycle
        movwf   PORTB           ; one cycle
        movf    PORTC,w ; one cycle
        movwf   REG             ; one cycle


Regards

Mike


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